Commit Graph

1286 Commits

Author SHA1 Message Date
Al Viro
06422964c8 teach set_nameidata() to handle setting the root as well
That way we don't need the callers to mess with manually setting any fields
of nameidata instances.  Old set_nameidata() gets renamed (__set_nameidata()),
new becomes an inlined helper that takes a struct path pointer and deals
with setting nd->root and putting ND_ROOT_PRESET in nd->state when new
argument is non-NULL.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-04-07 13:57:16 -04:00
Al Viro
bcba1e7d0d take LOOKUP_{ROOT,ROOT_GRABBED,JUMPED} out of LOOKUP_... space
Separate field in nameidata (nd->state) holding the flags that
should be internal-only - that way we both get some spare bits
in LOOKUP_... and get simpler rules for nd->root lifetime rules,
since we can set the replacement of LOOKUP_ROOT (ND_ROOT_PRESET)
at the same time we set nd->root.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-04-07 13:57:13 -04:00
Al Viro
ffb37ca3bd switch file_open_root() to struct path
... and provide file_open_root_mnt(), using the root of given mount.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-04-07 13:56:43 -04:00
Al Viro
4f0ed93fb9 LOOKUP_MOUNTPOINT: we are cleaning "jumped" flag too late
That (and traversals in case of umount .) should be done before
complete_walk().  Either a braino or mismerge damage on queue
reorders - either way, I should've spotted that much earlier.

Fucked-up-by: Al Viro <viro@zeniv.linux.org.uk>
X-Paperbag: Brown
Fixes: 161aff1d93 "LOOKUP_MOUNTPOINT: fold path_mountpointat() into path_lookupat()"
Cc: stable@vger.kernel.org # v5.7+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-04-06 20:33:00 -04:00
Al Viro
7d01ef7585 Make sure nd->path.mnt and nd->path.dentry are always valid pointers
Initialize them in set_nameidata() and make sure that terminate_walk() clears them
once the pointers become potentially invalid (i.e. we leave RCU mode or drop them
in non-RCU one).  Currently we have "path_init() always initializes them and nobody
accesses them outside of path_init()/terminate_walk() segments", which is asking
for trouble.

With that change we would have nd->path.{mnt,dentry}
	1) always valid - NULL or pointing to currently allocated objects.
	2) non-NULL while we are successfully walking
	3) NULL when we are not walking at all
	4) contributing to refcounts whenever non-NULL outside of RCU mode.

Fixes: 6c6ec2b0a3 ("fs: add support for LOOKUP_CACHED")
Reported-by: syzbot+c88a7030da47945a3cc3@syzkaller.appspotmail.com
Tested-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-04-06 12:33:07 -04:00
Randy Dunlap
2111c3c012
namei: fix kernel-doc for struct renamedata and more
Fix kernel-doc warnings in namei.c:

../fs/namei.c:1149: warning: Excess function parameter 'dir_mode' description in 'may_create_in_sticky'
../fs/namei.c:1149: warning: Excess function parameter 'dir_uid' description in 'may_create_in_sticky'
../fs/namei.c:3396: warning: Function parameter or member 'open_flag' not described in 'vfs_tmpfile'
../fs/namei.c:3396: warning: Excess function parameter 'open_flags' description in 'vfs_tmpfile'
../fs/namei.c:4460: warning: Function parameter or member 'rd' not described in 'vfs_rename'
../fs/namei.c:4460: warning: Excess function parameter 'old_mnt_userns' description in 'vfs_rename'
../fs/namei.c:4460: warning: Excess function parameter 'old_dir' description in 'vfs_rename'
../fs/namei.c:4460: warning: Excess function parameter 'old_dentry' description in 'vfs_rename'
../fs/namei.c:4460: warning: Excess function parameter 'new_mnt_userns' description in 'vfs_rename'
../fs/namei.c:4460: warning: Excess function parameter 'new_dir' description in 'vfs_rename'
../fs/namei.c:4460: warning: Excess function parameter 'new_dentry' description in 'vfs_rename'
../fs/namei.c:4460: warning: Excess function parameter 'delegated_inode' description in 'vfs_rename'
../fs/namei.c:4460: warning: Excess function parameter 'flags' description in 'vfs_rename'

Link: https://lore.kernel.org/r/20210216042929.8931-3-rdunlap@infradead.org
Fixes: 9fe6145097 ("namei: introduce struct renamedata")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-03-23 11:20:25 +01:00
Christian Brauner
8e5389132a
fs: introduce fsuidgid_has_mapping() helper
Don't open-code the checks and instead move them into a clean little
helper we can call. This also reduces the risk that if we ever change
something we forget to change all locations.

Link: https://lore.kernel.org/r/20210320122623.599086-4-christian.brauner@ubuntu.com
Inspired-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-03-23 11:15:24 +01:00
Christian Brauner
a65e58e791
fs: document and rename fsid helpers
Vivek pointed out that the fs{g,u}id_into_mnt() naming scheme can be
misleading as it could be understood as implying they do the exact same
thing as i_{g,u}id_into_mnt(). The original motivation for this naming
scheme was to signal to callers that the helpers will always take care
to map the k{g,u}id such that the ownership is expressed in terms of the
mnt_users.
Get rid of the confusion by renaming those helpers to something more
sensible. Al suggested mapped_fs{g,u}id() which seems a really good fit.
Usually filesystems don't need to bother with these helpers directly
only in some cases where they allocate objects that carry {g,u}ids which
are either filesystem specific (e.g. xfs quota objects) or don't have a
clean set of helpers as inodes have.

Link: https://lore.kernel.org/r/20210320122623.599086-3-christian.brauner@ubuntu.com
Inspired-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-03-23 11:13:32 +01:00
Linus Torvalds
7d6beb71da idmapped-mounts-v5.12
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Merge tag 'idmapped-mounts-v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull idmapped mounts from Christian Brauner:
 "This introduces idmapped mounts which has been in the making for some
  time. Simply put, different mounts can expose the same file or
  directory with different ownership. This initial implementation comes
  with ports for fat, ext4 and with Christoph's port for xfs with more
  filesystems being actively worked on by independent people and
  maintainers.

  Idmapping mounts handle a wide range of long standing use-cases. Here
  are just a few:

   - Idmapped mounts make it possible to easily share files between
     multiple users or multiple machines especially in complex
     scenarios. For example, idmapped mounts will be used in the
     implementation of portable home directories in
     systemd-homed.service(8) where they allow users to move their home
     directory to an external storage device and use it on multiple
     computers where they are assigned different uids and gids. This
     effectively makes it possible to assign random uids and gids at
     login time.

   - It is possible to share files from the host with unprivileged
     containers without having to change ownership permanently through
     chown(2).

   - It is possible to idmap a container's rootfs and without having to
     mangle every file. For example, Chromebooks use it to share the
     user's Download folder with their unprivileged containers in their
     Linux subsystem.

   - It is possible to share files between containers with
     non-overlapping idmappings.

   - Filesystem that lack a proper concept of ownership such as fat can
     use idmapped mounts to implement discretionary access (DAC)
     permission checking.

   - They allow users to efficiently changing ownership on a per-mount
     basis without having to (recursively) chown(2) all files. In
     contrast to chown (2) changing ownership of large sets of files is
     instantenous with idmapped mounts. This is especially useful when
     ownership of a whole root filesystem of a virtual machine or
     container is changed. With idmapped mounts a single syscall
     mount_setattr syscall will be sufficient to change the ownership of
     all files.

   - Idmapped mounts always take the current ownership into account as
     idmappings specify what a given uid or gid is supposed to be mapped
     to. This contrasts with the chown(2) syscall which cannot by itself
     take the current ownership of the files it changes into account. It
     simply changes the ownership to the specified uid and gid. This is
     especially problematic when recursively chown(2)ing a large set of
     files which is commong with the aforementioned portable home
     directory and container and vm scenario.

   - Idmapped mounts allow to change ownership locally, restricting it
     to specific mounts, and temporarily as the ownership changes only
     apply as long as the mount exists.

  Several userspace projects have either already put up patches and
  pull-requests for this feature or will do so should you decide to pull
  this:

   - systemd: In a wide variety of scenarios but especially right away
     in their implementation of portable home directories.

         https://systemd.io/HOME_DIRECTORY/

   - container runtimes: containerd, runC, LXD:To share data between
     host and unprivileged containers, unprivileged and privileged
     containers, etc. The pull request for idmapped mounts support in
     containerd, the default Kubernetes runtime is already up for quite
     a while now: https://github.com/containerd/containerd/pull/4734

   - The virtio-fs developers and several users have expressed interest
     in using this feature with virtual machines once virtio-fs is
     ported.

   - ChromeOS: Sharing host-directories with unprivileged containers.

  I've tightly synced with all those projects and all of those listed
  here have also expressed their need/desire for this feature on the
  mailing list. For more info on how people use this there's a bunch of
  talks about this too. Here's just two recent ones:

      https://www.cncf.io/wp-content/uploads/2020/12/Rootless-Containers-in-Gitpod.pdf
      https://fosdem.org/2021/schedule/event/containers_idmap/

  This comes with an extensive xfstests suite covering both ext4 and
  xfs:

      https://git.kernel.org/brauner/xfstests-dev/h/idmapped_mounts

  It covers truncation, creation, opening, xattrs, vfscaps, setid
  execution, setgid inheritance and more both with idmapped and
  non-idmapped mounts. It already helped to discover an unrelated xfs
  setgid inheritance bug which has since been fixed in mainline. It will
  be sent for inclusion with the xfstests project should you decide to
  merge this.

  In order to support per-mount idmappings vfsmounts are marked with
  user namespaces. The idmapping of the user namespace will be used to
  map the ids of vfs objects when they are accessed through that mount.
  By default all vfsmounts are marked with the initial user namespace.
  The initial user namespace is used to indicate that a mount is not
  idmapped. All operations behave as before and this is verified in the
  testsuite.

  Based on prior discussions we want to attach the whole user namespace
  and not just a dedicated idmapping struct. This allows us to reuse all
  the helpers that already exist for dealing with idmappings instead of
  introducing a whole new range of helpers. In addition, if we decide in
  the future that we are confident enough to enable unprivileged users
  to setup idmapped mounts the permission checking can take into account
  whether the caller is privileged in the user namespace the mount is
  currently marked with.

  The user namespace the mount will be marked with can be specified by
  passing a file descriptor refering to the user namespace as an
  argument to the new mount_setattr() syscall together with the new
  MOUNT_ATTR_IDMAP flag. The system call follows the openat2() pattern
  of extensibility.

  The following conditions must be met in order to create an idmapped
  mount:

   - The caller must currently have the CAP_SYS_ADMIN capability in the
     user namespace the underlying filesystem has been mounted in.

   - The underlying filesystem must support idmapped mounts.

   - The mount must not already be idmapped. This also implies that the
     idmapping of a mount cannot be altered once it has been idmapped.

   - The mount must be a detached/anonymous mount, i.e. it must have
     been created by calling open_tree() with the OPEN_TREE_CLONE flag
     and it must not already have been visible in the filesystem.

  The last two points guarantee easier semantics for userspace and the
  kernel and make the implementation significantly simpler.

  By default vfsmounts are marked with the initial user namespace and no
  behavioral or performance changes are observed.

  The manpage with a detailed description can be found here:

      1d7b902e28

  In order to support idmapped mounts, filesystems need to be changed
  and mark themselves with the FS_ALLOW_IDMAP flag in fs_flags. The
  patches to convert individual filesystem are not very large or
  complicated overall as can be seen from the included fat, ext4, and
  xfs ports. Patches for other filesystems are actively worked on and
  will be sent out separately. The xfstestsuite can be used to verify
  that port has been done correctly.

  The mount_setattr() syscall is motivated independent of the idmapped
  mounts patches and it's been around since July 2019. One of the most
  valuable features of the new mount api is the ability to perform
  mounts based on file descriptors only.

  Together with the lookup restrictions available in the openat2()
  RESOLVE_* flag namespace which we added in v5.6 this is the first time
  we are close to hardened and race-free (e.g. symlinks) mounting and
  path resolution.

  While userspace has started porting to the new mount api to mount
  proper filesystems and create new bind-mounts it is currently not
  possible to change mount options of an already existing bind mount in
  the new mount api since the mount_setattr() syscall is missing.

  With the addition of the mount_setattr() syscall we remove this last
  restriction and userspace can now fully port to the new mount api,
  covering every use-case the old mount api could. We also add the
  crucial ability to recursively change mount options for a whole mount
  tree, both removing and adding mount options at the same time. This
  syscall has been requested multiple times by various people and
  projects.

  There is a simple tool available at

      https://github.com/brauner/mount-idmapped

  that allows to create idmapped mounts so people can play with this
  patch series. I'll add support for the regular mount binary should you
  decide to pull this in the following weeks:

  Here's an example to a simple idmapped mount of another user's home
  directory:

	u1001@f2-vm:/$ sudo ./mount --idmap both:1000:1001:1 /home/ubuntu/ /mnt

	u1001@f2-vm:/$ ls -al /home/ubuntu/
	total 28
	drwxr-xr-x 2 ubuntu ubuntu 4096 Oct 28 22:07 .
	drwxr-xr-x 4 root   root   4096 Oct 28 04:00 ..
	-rw------- 1 ubuntu ubuntu 3154 Oct 28 22:12 .bash_history
	-rw-r--r-- 1 ubuntu ubuntu  220 Feb 25  2020 .bash_logout
	-rw-r--r-- 1 ubuntu ubuntu 3771 Feb 25  2020 .bashrc
	-rw-r--r-- 1 ubuntu ubuntu  807 Feb 25  2020 .profile
	-rw-r--r-- 1 ubuntu ubuntu    0 Oct 16 16:11 .sudo_as_admin_successful
	-rw------- 1 ubuntu ubuntu 1144 Oct 28 00:43 .viminfo

	u1001@f2-vm:/$ ls -al /mnt/
	total 28
	drwxr-xr-x  2 u1001 u1001 4096 Oct 28 22:07 .
	drwxr-xr-x 29 root  root  4096 Oct 28 22:01 ..
	-rw-------  1 u1001 u1001 3154 Oct 28 22:12 .bash_history
	-rw-r--r--  1 u1001 u1001  220 Feb 25  2020 .bash_logout
	-rw-r--r--  1 u1001 u1001 3771 Feb 25  2020 .bashrc
	-rw-r--r--  1 u1001 u1001  807 Feb 25  2020 .profile
	-rw-r--r--  1 u1001 u1001    0 Oct 16 16:11 .sudo_as_admin_successful
	-rw-------  1 u1001 u1001 1144 Oct 28 00:43 .viminfo

	u1001@f2-vm:/$ touch /mnt/my-file

	u1001@f2-vm:/$ setfacl -m u:1001:rwx /mnt/my-file

	u1001@f2-vm:/$ sudo setcap -n 1001 cap_net_raw+ep /mnt/my-file

	u1001@f2-vm:/$ ls -al /mnt/my-file
	-rw-rwxr--+ 1 u1001 u1001 0 Oct 28 22:14 /mnt/my-file

	u1001@f2-vm:/$ ls -al /home/ubuntu/my-file
	-rw-rwxr--+ 1 ubuntu ubuntu 0 Oct 28 22:14 /home/ubuntu/my-file

	u1001@f2-vm:/$ getfacl /mnt/my-file
	getfacl: Removing leading '/' from absolute path names
	# file: mnt/my-file
	# owner: u1001
	# group: u1001
	user::rw-
	user:u1001:rwx
	group::rw-
	mask::rwx
	other::r--

	u1001@f2-vm:/$ getfacl /home/ubuntu/my-file
	getfacl: Removing leading '/' from absolute path names
	# file: home/ubuntu/my-file
	# owner: ubuntu
	# group: ubuntu
	user::rw-
	user:ubuntu:rwx
	group::rw-
	mask::rwx
	other::r--"

* tag 'idmapped-mounts-v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: (41 commits)
  xfs: remove the possibly unused mp variable in xfs_file_compat_ioctl
  xfs: support idmapped mounts
  ext4: support idmapped mounts
  fat: handle idmapped mounts
  tests: add mount_setattr() selftests
  fs: introduce MOUNT_ATTR_IDMAP
  fs: add mount_setattr()
  fs: add attr_flags_to_mnt_flags helper
  fs: split out functions to hold writers
  namespace: only take read lock in do_reconfigure_mnt()
  mount: make {lock,unlock}_mount_hash() static
  namespace: take lock_mount_hash() directly when changing flags
  nfs: do not export idmapped mounts
  overlayfs: do not mount on top of idmapped mounts
  ecryptfs: do not mount on top of idmapped mounts
  ima: handle idmapped mounts
  apparmor: handle idmapped mounts
  fs: make helpers idmap mount aware
  exec: handle idmapped mounts
  would_dump: handle idmapped mounts
  ...
2021-02-23 13:39:45 -08:00
Al Viro
eacd9aa8ce fix handling of nd->depth on LOOKUP_CACHED failures in try_to_unlazy*
After switching to non-RCU mode, we want nd->depth to match the number
of entries in nd->stack[] that need eventual path_put().
legitimize_links() takes care of that on failures; unfortunately,
failure exits added for LOOKUP_CACHED do not.

We could add the logics for that into those failure exits, both in
try_to_unlazy() and in try_to_unlazy_next(), but since both checks
are immediately followed by legitimize_links() and there's no calls
of legitimize_links() other than those two...  It's easier to
move the check (and required handling of nd->depth on failure) into
legitimize_links() itself.

[caught by Jens: ... and since we are zeroing ->depth here, we need
to do drop_links() first]

Fixes: 6c6ec2b0a3 "fs: add support for LOOKUP_CACHED"
Tested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-02-20 12:33:12 -05:00
Christian Brauner
a2d2329e30
ima: handle idmapped mounts
IMA does sometimes access the inode's i_uid and compares it against the
rules' fowner. Enable IMA to handle idmapped mounts by passing down the
mount's user namespace. We simply make use of the helpers we introduced
before. If the initial user namespace is passed nothing changes so
non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-27-christian.brauner@ubuntu.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:20 +01:00
Christian Brauner
549c729771
fs: make helpers idmap mount aware
Extend some inode methods with an additional user namespace argument. A
filesystem that is aware of idmapped mounts will receive the user
namespace the mount has been marked with. This can be used for
additional permission checking and also to enable filesystems to
translate between uids and gids if they need to. We have implemented all
relevant helpers in earlier patches.

As requested we simply extend the exisiting inode method instead of
introducing new ones. This is a little more code churn but it's mostly
mechanical and doesnt't leave us with additional inode methods.

Link: https://lore.kernel.org/r/20210121131959.646623-25-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:20 +01:00
Christian Brauner
643fe55a06
open: handle idmapped mounts in do_truncate()
When truncating files the vfs will verify that the caller is privileged
over the inode. Extend it to handle idmapped mounts. If the inode is
accessed through an idmapped mount it is mapped according to the mount's
user namespace. Afterwards the permissions checks are identical to
non-idmapped mounts. If the initial user namespace is passed nothing
changes so non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-16-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:18 +01:00
Christian Brauner
6521f89170
namei: prepare for idmapped mounts
The various vfs_*() helpers are called by filesystems or by the vfs
itself to perform core operations such as create, link, mkdir, mknod, rename,
rmdir, tmpfile and unlink. Enable them to handle idmapped mounts. If the
inode is accessed through an idmapped mount map it into the
mount's user namespace and pass it down. Afterwards the checks and
operations are identical to non-idmapped mounts. If the initial user
namespace is passed nothing changes so non-idmapped mounts will see
identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-15-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:18 +01:00
Christian Brauner
9fe6145097
namei: introduce struct renamedata
In order to handle idmapped mounts we will extend the vfs rename helper
to take two new arguments in follow up patches. Since this operations
already takes a bunch of arguments add a simple struct renamedata and
make the current helper use it before we extend it.

Link: https://lore.kernel.org/r/20210121131959.646623-14-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:18 +01:00
Christian Brauner
ba73d98745
namei: handle idmapped mounts in may_*() helpers
The may_follow_link(), may_linkat(), may_lookup(), may_open(),
may_o_create(), may_create_in_sticky(), may_delete(), and may_create()
helpers determine whether the caller is privileged enough to perform the
associated operations. Let them handle idmapped mounts by mapping the
inode or fsids according to the mount's user namespace. Afterwards the
checks are identical to non-idmapped inodes. The patch takes care to
retrieve the mount's user namespace right before performing permission
checks and passing it down into the fileystem so the user namespace
can't change in between by someone idmapping a mount that is currently
not idmapped. If the initial user namespace is passed nothing changes so
non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-13-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:17 +01:00
Christian Brauner
21cb47be6f
inode: make init and permission helpers idmapped mount aware
The inode_owner_or_capable() helper determines whether the caller is the
owner of the inode or is capable with respect to that inode. Allow it to
handle idmapped mounts. If the inode is accessed through an idmapped
mount it according to the mount's user namespace. Afterwards the checks
are identical to non-idmapped mounts. If the initial user namespace is
passed nothing changes so non-idmapped mounts will see identical
behavior as before.

Similarly, allow the inode_init_owner() helper to handle idmapped
mounts. It initializes a new inode on idmapped mounts by mapping the
fsuid and fsgid of the caller from the mount's user namespace. If the
initial user namespace is passed nothing changes so non-idmapped mounts
will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-7-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:16 +01:00
Christian Brauner
47291baa8d
namei: make permission helpers idmapped mount aware
The two helpers inode_permission() and generic_permission() are used by
the vfs to perform basic permission checking by verifying that the
caller is privileged over an inode. In order to handle idmapped mounts
we extend the two helpers with an additional user namespace argument.
On idmapped mounts the two helpers will make sure to map the inode
according to the mount's user namespace and then peform identical
permission checks to inode_permission() and generic_permission(). If the
initial user namespace is passed nothing changes so non-idmapped mounts
will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-6-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:16 +01:00
Christian Brauner
0558c1bf5a
capability: handle idmapped mounts
In order to determine whether a caller holds privilege over a given
inode the capability framework exposes the two helpers
privileged_wrt_inode_uidgid() and capable_wrt_inode_uidgid(). The former
verifies that the inode has a mapping in the caller's user namespace and
the latter additionally verifies that the caller has the requested
capability in their current user namespace.
If the inode is accessed through an idmapped mount map it into the
mount's user namespace. Afterwards the checks are identical to
non-idmapped inodes. If the initial user namespace is passed all
operations are a nop so non-idmapped mounts will not see a change in
behavior.

Link: https://lore.kernel.org/r/20210121131959.646623-5-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:27:16 +01:00
Jens Axboe
6c6ec2b0a3 fs: add support for LOOKUP_CACHED
io_uring always punts opens to async context, since there's no control
over whether the lookup blocks or not. Add LOOKUP_CACHED to support
just doing the fast RCU based lookups, which we know will not block. If
we can do a cached path resolution of the filename, then we don't have
to always punt lookups for a worker.

During path resolution, we always do LOOKUP_RCU first. If that fails and
we terminate LOOKUP_RCU, then fail a LOOKUP_CACHED attempt as well.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-01-04 11:42:21 -05:00
Al Viro
ae66db45fd saner calling conventions for unlazy_child()
same as for the previous commit - instead of 0/-ECHILD make
it return true/false, rename to try_to_unlazy_child().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-01-04 11:41:40 -05:00
Jens Axboe
e36cffed20 fs: make unlazy_walk() error handling consistent
Most callers check for non-zero return, and assume it's -ECHILD (which
it always will be). One caller uses the actual error return. Clean this
up and make it fully consistent, by having unlazy_walk() return a bool
instead. Rename it to try_to_unlazy() and return true on success, and
failure on error. That's easier to read.

No functional changes in this patch.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-01-04 11:10:49 -05:00
Steven Rostedt (VMware)
26ddb45e13 fs/namei.c: Remove unlikely of status being -ECHILD in lookup_fast()
Running my yearly branch profiling code, it detected a 100% wrong branch
condition in name.c for lookup_fast(). The code in question has:

		status = d_revalidate(dentry, nd->flags);
		if (likely(status > 0))
			return dentry;
		if (unlazy_child(nd, dentry, seq))
			return ERR_PTR(-ECHILD);
		if (unlikely(status == -ECHILD))
			/* we'd been told to redo it in non-rcu mode */
			status = d_revalidate(dentry, nd->flags);

If the status of the d_revalidate() is greater than zero, then the function
finishes. Otherwise, if it is an "unlazy_child" it returns with -ECHILD.
After the above two checks, the status is compared to -ECHILD, as that is
what is returned if the original d_revalidate() needed to be done in a
non-rcu mode.

Especially this path is called in a condition of:

	if (nd->flags & LOOKUP_RCU) {

And most of the d_revalidate() functions have:

	if (flags & LOOKUP_RCU)
		return -ECHILD;

It appears that that is the only case that this if statement is triggered
on two of my machines, running in production.

As it is dependent on what filesystem mix is configured in the running
kernel, simply remove the unlikely() from the if statement.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-01-04 00:12:33 -05:00
Al Viro
1e8f44f159 do_tmpfile(): don't mess with finish_open()
use vfs_open() instead

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2021-01-03 21:06:02 -05:00
Linus Torvalds
7bb5226c8a Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull misc vfs updates from Al Viro:
 "Assorted patches from previous cycle(s)..."

* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  fix hostfs_open() use of ->f_path.dentry
  Make sure that make_create_in_sticky() never sees uninitialized value of dir_mode
  fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set
  fs: Handle I_DONTCACHE in iput_final() instead of generic_drop_inode()
  fs/namespace.c: WARN if mnt_count has become negative
2020-12-25 10:54:29 -08:00
Al Viro
1a97d899ec Make sure that make_create_in_sticky() never sees uninitialized value of dir_mode
make sure nd->dir_mode is always initialized after success exit from
link_path_walk(); in case of empty path it did not happen.

Reported-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Tested-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-12-10 17:33:17 -05:00
Jens Axboe
e886663cfd fs: make do_renameat2() take struct filename
Pass in the struct filename pointers instead of the user string, and
update the three callers to do the same.

This behaves like do_unlinkat(), which also takes a filename struct and
puts it when it is done. Converting callers is then trivial.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-12-09 12:03:59 -07:00
Linus Torvalds
0eac1102e9 Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull misc vfs updates from Al Viro:
 "Assorted stuff all over the place (the largest group here is
  Christoph's stat cleanups)"

* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  fs: remove KSTAT_QUERY_FLAGS
  fs: remove vfs_stat_set_lookup_flags
  fs: move vfs_fstatat out of line
  fs: implement vfs_stat and vfs_lstat in terms of vfs_fstatat
  fs: remove vfs_statx_fd
  fs: omfs: use kmemdup() rather than kmalloc+memcpy
  [PATCH] reduce boilerplate in fsid handling
  fs: Remove duplicated flag O_NDELAY occurring twice in VALID_OPEN_FLAGS
  selftests: mount: add nosymfollow tests
  Add a "nosymfollow" mount option.
2020-10-24 12:26:05 -07:00
Christoph Hellwig
402dd2cf46 fs: remove the unused SB_I_MULTIROOT flag
The last user of SB_I_MULTIROOT is disappeared with commit f2aedb713c
("NFS: Add fs_context support.")

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-24 13:43:38 -06:00
Mattias Nissler
dab741e0e0 Add a "nosymfollow" mount option.
For mounts that have the new "nosymfollow" option, don't follow symlinks
when resolving paths. The new option is similar in spirit to the
existing "nodev", "noexec", and "nosuid" options, as well as to the
LOOKUP_NO_SYMLINKS resolve flag in the openat2(2) syscall. Various BSD
variants have been supporting the "nosymfollow" mount option for a long
time with equivalent implementations.

Note that symlinks may still be created on file systems mounted with
the "nosymfollow" option present. readlink() remains functional, so
user space code that is aware of symlinks can still choose to follow
them explicitly.

Setting the "nosymfollow" mount option helps prevent privileged
writers from modifying files unintentionally in case there is an
unexpected link along the accessed path. The "nosymfollow" option is
thus useful as a defensive measure for systems that need to deal with
untrusted file systems in privileged contexts.

More information on the history and motivation for this patch can be
found here:

https://sites.google.com/a/chromium.org/dev/chromium-os/chromiumos-design-docs/hardening-against-malicious-stateful-data#TOC-Restricting-symlink-traversal

Signed-off-by: Mattias Nissler <mnissler@chromium.org>
Signed-off-by: Ross Zwisler <zwisler@google.com>
Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-08-27 16:06:47 -04:00
Kees Cook
fc4177be96 exec: restore EACCES of S_ISDIR execve()
Patch series "Fix S_ISDIR execve() errno".

Fix an errno change for execve() of directories, noticed by Marc Zyngier.
Along with the fix, include a regression test to avoid seeing this return
in the future.

This patch (of 2):

The return code for attempting to execute a directory has always been
EACCES.  Adjust the S_ISDIR exec test to reflect the old errno instead of
the general EISDIR for other kinds of "open" attempts on directories.

Fixes: 633fb6ac39 ("exec: move S_ISREG() check earlier")
Reported-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Greg Kroah-Hartman <gregkh@android.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@google.com>
Link: http://lkml.kernel.org/r/20200813231723.2725102-2-keescook@chromium.org
Link: https://lore.kernel.org/lkml/20200813151305.6191993b@why
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-08-14 19:56:56 -07:00
Linus Torvalds
9ad57f6dfc Merge branch 'akpm' (patches from Andrew)
Merge more updates from Andrew Morton:

 - most of the rest of MM (memcg, hugetlb, vmscan, proc, compaction,
   mempolicy, oom-kill, hugetlbfs, migration, thp, cma, util,
   memory-hotplug, cleanups, uaccess, migration, gup, pagemap),

 - various other subsystems (alpha, misc, sparse, bitmap, lib, bitops,
   checkpatch, autofs, minix, nilfs, ufs, fat, signals, kmod, coredump,
   exec, kdump, rapidio, panic, kcov, kgdb, ipc).

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (164 commits)
  mm/gup: remove task_struct pointer for all gup code
  mm: clean up the last pieces of page fault accountings
  mm/xtensa: use general page fault accounting
  mm/x86: use general page fault accounting
  mm/sparc64: use general page fault accounting
  mm/sparc32: use general page fault accounting
  mm/sh: use general page fault accounting
  mm/s390: use general page fault accounting
  mm/riscv: use general page fault accounting
  mm/powerpc: use general page fault accounting
  mm/parisc: use general page fault accounting
  mm/openrisc: use general page fault accounting
  mm/nios2: use general page fault accounting
  mm/nds32: use general page fault accounting
  mm/mips: use general page fault accounting
  mm/microblaze: use general page fault accounting
  mm/m68k: use general page fault accounting
  mm/ia64: use general page fault accounting
  mm/hexagon: use general page fault accounting
  mm/csky: use general page fault accounting
  ...
2020-08-12 11:24:12 -07:00
Kees Cook
0fd338b2d2 exec: move path_noexec() check earlier
The path_noexec() check, like the regular file check, was happening too
late, letting LSMs see impossible execve()s.  Check it earlier as well in
may_open() and collect the redundant fs/exec.c path_noexec() test under
the same robustness comment as the S_ISREG() check.

My notes on the call path, and related arguments, checks, etc:

do_open_execat()
    struct open_flags open_exec_flags = {
        .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
        .acc_mode = MAY_EXEC,
        ...
    do_filp_open(dfd, filename, open_flags)
        path_openat(nameidata, open_flags, flags)
            file = alloc_empty_file(open_flags, current_cred());
            do_open(nameidata, file, open_flags)
                may_open(path, acc_mode, open_flag)
                    /* new location of MAY_EXEC vs path_noexec() test */
                    inode_permission(inode, MAY_OPEN | acc_mode)
                        security_inode_permission(inode, acc_mode)
                vfs_open(path, file)
                    do_dentry_open(file, path->dentry->d_inode, open)
                        security_file_open(f)
                        open()
    /* old location of path_noexec() test */

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: http://lkml.kernel.org/r/20200605160013.3954297-4-keescook@chromium.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-08-12 10:58:01 -07:00
Kees Cook
633fb6ac39 exec: move S_ISREG() check earlier
The execve(2)/uselib(2) syscalls have always rejected non-regular files.
Recently, it was noticed that a deadlock was introduced when trying to
execute pipes, as the S_ISREG() test was happening too late.  This was
fixed in commit 73601ea5b7 ("fs/open.c: allow opening only regular files
during execve()"), but it was added after inode_permission() had already
run, which meant LSMs could see bogus attempts to execute non-regular
files.

Move the test into the other inode type checks (which already look for
other pathological conditions[1]).  Since there is no need to use
FMODE_EXEC while we still have access to "acc_mode", also switch the test
to MAY_EXEC.

Also include a comment with the redundant S_ISREG() checks at the end of
execve(2)/uselib(2) to note that they are present to avoid any mistakes.

My notes on the call path, and related arguments, checks, etc:

do_open_execat()
    struct open_flags open_exec_flags = {
        .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
        .acc_mode = MAY_EXEC,
        ...
    do_filp_open(dfd, filename, open_flags)
        path_openat(nameidata, open_flags, flags)
            file = alloc_empty_file(open_flags, current_cred());
            do_open(nameidata, file, open_flags)
                may_open(path, acc_mode, open_flag)
		    /* new location of MAY_EXEC vs S_ISREG() test */
                    inode_permission(inode, MAY_OPEN | acc_mode)
                        security_inode_permission(inode, acc_mode)
                vfs_open(path, file)
                    do_dentry_open(file, path->dentry->d_inode, open)
                        /* old location of FMODE_EXEC vs S_ISREG() test */
                        security_file_open(f)
                        open()

[1] https://lore.kernel.org/lkml/202006041910.9EF0C602@keescook/

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: http://lkml.kernel.org/r/20200605160013.3954297-3-keescook@chromium.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-08-12 10:58:01 -07:00
Al Viro
24fb33d40d fix breakage in do_rmdir()
syzbot reported and bisected a use-after-free due to the recent init
cleanups.

The putname() should happen only after we'd *not* branched to retry,
same as it's done in do_unlinkat().

Reported-by: syzbot+bbeb1c88016c7db4aa24@syzkaller.appspotmail.com
Fixes: e24ab0ef68 "fs: push the getname from do_rmdir into the callers"
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-08-12 10:22:39 -07:00
Christoph Hellwig
5fee64fcde init: add an init_mknod helper
Add a simple helper to mknod with a kernel space file name and switch
the early init code over to it.  Remove the now unused ksys_mknod.

Signed-off-by: Christoph Hellwig <hch@lst.de>
2020-07-31 08:17:54 +02:00
Christoph Hellwig
83ff98c3e9 init: add an init_mkdir helper
Add a simple helper to mkdir with a kernel space file name and switch
the early init code over to it.  Remove the now unused ksys_mkdir.

Signed-off-by: Christoph Hellwig <hch@lst.de>
2020-07-31 08:17:53 +02:00
Christoph Hellwig
cd3acb6a79 init: add an init_symlink helper
Add a simple helper to symlink with a kernel space file name and switch
the early init code over to it.  Remove the now unused ksys_symlink.

Signed-off-by: Christoph Hellwig <hch@lst.de>
2020-07-31 08:17:53 +02:00
Christoph Hellwig
812931d693 init: add an init_link helper
Add a simple helper to link with a kernel space file name and switch
the early init code over to it.  Remove the now unused ksys_link.

Signed-off-by: Christoph Hellwig <hch@lst.de>
2020-07-31 08:17:53 +02:00
Christoph Hellwig
e24ab0ef68 fs: push the getname from do_rmdir into the callers
This mirrors do_unlinkat and will make life a little easier for
the init code to reuse the whole function with a kernel filename.

Signed-off-by: Christoph Hellwig <hch@lst.de>
2020-07-31 08:17:50 +02:00
Linus Torvalds
63d72b93f2 vfs: clean up posix_acl_permission() logic aroudn MAY_NOT_BLOCK
posix_acl_permission() does not care about MAY_NOT_BLOCK, and in fact
the permission logic internally must not check that bit (it's only for
upper layers to decide whether they can block to do IO to look up the
acl information or not).

But the way the code was written, it _looked_ like it cared, since the
function explicitly did not mask that bit off.

But it has exactly two callers: one for when that bit is set, which
first clears the bit before calling posix_acl_permission(), and the
other call site when that bit was clear.

So stop the silly games "saving" the MAY_NOT_BLOCK bit that must not be
used for the actual permission test, and that currently is pointlessly
cleared by the callers when the function itself should just not care.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-08 11:04:19 -07:00
Linus Torvalds
5fc475b749 vfs: do not do group lookup when not necessary
Rasmus Villemoes points out that the 'in_group_p()' tests can be a
noticeable expense, and often completely unnecessary.  A common
situation is that the 'group' bits are the same as the 'other' bits
wrt the permissions we want to test.

So rewrite 'acl_permission_check()' to not bother checking for group
ownership when the permission check doesn't care.

For example, if we're asking for read permissions, and both 'group' and
'other' allow reading, there's really no reason to check if we're part
of the group or not: either way, we'll allow it.

Rasmus says:
 "On a bog-standard Ubuntu 20.04 install, a workload consisting of
  compiling lots of userspace programs (i.e., calling lots of
  short-lived programs that all need to get their shared libs mapped in,
  and the compilers poking around looking for system headers - lots of
  /usr/lib, /usr/bin, /usr/include/ accesses) puts in_group_p around
  0.1% according to perf top.

  System-installed files are almost always 0755 (directories and
  binaries) or 0644, so in most cases, we can avoid the binary search
  and the cost of pulling the cred->groups array and in_group_p() .text
  into the cpu cache"

Reported-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-08 11:04:19 -07:00
Miklos Szeredi
a3c751a50f vfs: allow unprivileged whiteout creation
Whiteouts, unlike real device node should not require privileges to create.

The general concern with device nodes is that opening them can have side
effects.  The kernel already avoids zero major (see
Documentation/admin-guide/devices.txt).  To be on the safe side the patch
explicitly forbids registering a char device with 0/0 number (see
cdev_add()).

This guarantees that a non-O_PATH open on a whiteout will fail with ENODEV;
i.e. it won't have any side effect.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2020-05-14 16:44:23 +02:00
Al Viro
5bd73286d5 fix a braino in legitimize_path()
brown paperbag time... wrong order of arguments ended up confusing
the values to check dentry and mount_lock seqcounts against.

Reported-by: kernel test robot <rong.a.chen@intel.com>
Fixes: 2aa3847085 ("non-RCU analogue of the previous commit")
Tested-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-06 10:38:59 -04:00
Al Viro
99a4a90c8e lookup_open(): don't bother with fallbacks to lookup+create
We fall back to lookup+create (instead of atomic_open) in several cases:
	1) we don't have write access to filesystem and O_TRUNC is
present in the flags.  It's not something we want ->atomic_open() to
see - it just might go ahead and truncate the file.  However, we can
pass it the flags sans O_TRUNC - eventually do_open() will call
handle_truncate() anyway.
	2) we have O_CREAT | O_EXCL and we can't write to parent.
That's going to be an error, of course, but we want to know _which_
error should that be - might be EEXIST (if file exists), might be
EACCES or EROFS.  Simply stripping O_CREAT (and checking if we see
ENOENT) would suffice, if not for O_EXCL.  However, we used to have
->atomic_open() fully responsible for rejecting O_CREAT | O_EXCL
on existing file and just stripping O_CREAT would've disarmed
those checks.  With nothing downstream to catch the problem -
FMODE_OPENED used to be "don't bother with EEXIST checks,
->atomic_open() has done those".  Now EEXIST checks downstream
are skipped only if FMODE_CREATED is set - FMODE_OPENED alone
is not enough.  That has eliminated the need to fall back onto
lookup+create path in this case.
	3) O_WRONLY or O_RDWR when we have no write access to
filesystem, with nothing else objectionable.  Fallback is
(and had always been) pointless.

IOW, we don't really need that fallback; all we need in such
cases is to trim O_TRUNC and O_CREAT properly.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:31 -04:00
Al Viro
d489cf9a3e atomic_open(): no need to pass struct open_flags anymore
argument had been unused since 1643b43fbd (lookup_open(): lift the
"fallback to !O_CREAT" logics from atomic_open()) back in 2016

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:31 -04:00
Al Viro
ff326a3299 open_last_lookups(): move complete_walk() into do_open()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:30 -04:00
Al Viro
b94e0b32c8 open_last_lookups(): lift O_EXCL|O_CREAT handling into do_open()
Currently path_openat() has "EEXIST on O_EXCL|O_CREAT" checks done on one
of the ways out of open_last_lookups().  There are 4 cases:
	1) the last component is . or ..; check is not done.
	2) we had FMODE_OPENED or FMODE_CREATED set while in lookup_open();
check is not done.
	3) symlink to be traversed is found; check is not done (nor
should it be)
	4) everything else: check done (before complete_walk(), even).

In case (1) O_EXCL|O_CREAT ends up failing with -EISDIR - that's
	open("/tmp/.", O_CREAT|O_EXCL, 0600)
Note that in the same conditions
	open("/tmp", O_CREAT|O_EXCL, 0600)
would have yielded EEXIST.  Either error is allowed, switching to -EEXIST
in these cases would've been more consistent.

Case (2) is more subtle; first of all, if we have FMODE_CREATED set, the
object hadn't existed prior to the call.  The check should not be done in
such a case.  The rest is problematic, though - we have
	FMODE_OPENED set (i.e. it went through ->atomic_open() and got
successfully opened there)
	FMODE_CREATED is *NOT* set
	O_CREAT and O_EXCL are both set.
Any such case is a bug - either we failed to set FMODE_CREATED when we
had, in fact, created an object (no such instances in the tree) or
we have opened a pre-existing file despite having had both O_CREAT and
O_EXCL passed.  One of those was, in fact caught (and fixed) while
sorting out this mess (gfs2 on cold dcache).  And in such situations
we should fail with EEXIST.

Note that for (1) and (4) FMODE_CREATED is not set - for (1) there's nothing
in handle_dots() to set it, for (4) we'd explicitly checked that.

And (1), (2) and (4) are exactly the cases when we leave the loop in
the caller, with do_open() called immediately after that loop.  IOW, we
can move the check over there, and make it

	If we have O_CREAT|O_EXCL and after successful pathname resolution
FMODE_CREATED is *not* set, we must have run into a preexisting file and
should fail with EEXIST.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:30 -04:00
Al Viro
72287417ab open_last_lookups(): don't abuse complete_walk() when all we want is unlazy
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:29 -04:00
Al Viro
f7bb959d96 open_last_lookups(): consolidate fsnotify_create() calls
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:28 -04:00
Al Viro
c5971b8c63 take post-lookup part of do_last() out of loop
now we can have open_last_lookups() directly from the loop in
path_openat() - the rest of do_last() never returns a symlink
to follow, so we can bloody well leave the loop first.

Rename the rest of that thing from do_last() to do_open() and
make it return an int.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:28 -04:00
Al Viro
0f70595301 link_path_walk(): sample parent's i_uid and i_mode for the last component
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:27 -04:00
Al Viro
60ef60c7d7 __nd_alloc_stack(): make it return bool
... and adjust the caller (reserve_stack()).  Rename to nd_alloc_stack(),
while we are at it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:26 -04:00
Al Viro
4542576b79 reserve_stack(): switch to __nd_alloc_stack()
expand the call of nd_alloc_stack() into it (and don't
recheck the depth on the second call)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:26 -04:00
Al Viro
49055906af pick_link(): take reserving space on stack into a new helper
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:25 -04:00
Al Viro
aef9404d8c pick_link(): more straightforward handling of allocation failures
pick_link() needs to push onto stack; we start with using two-element
array embedded into struct nameidata and the first time we need
more than that we switch to separately allocated array.

Allocation can fail, of course, and handling of that would be simple
enough - we need to drop 'link' and bugger off.  However, the things
get more complicated in RCU mode.  There we must do GFP_ATOMIC
allocation.  If that fails, we try to switch to non-RCU mode and
repeat the allocation.

To switch to non-RCU mode we need to grab references to 'link' and
to everything in nameidata.  The latter done by unlazy_walk();
the former - legitimize_path().  'link' must go first - after
unlazy_walk() we are out of RCU-critical period and it's too
late to call legitimize_path() since the references in link->mnt
and link->dentry might be pointing to freed and reused memory.

So we do legitimize_path(), then unlazy_walk().  And that's where
it gets too subtle: what to do if the former fails?  We MUST
do path_put(link) to avoid leaks.  And we can't do that under
rcu_read_lock().  Solution in mainline was to empty then nameidata
manually, drop out of RCU mode and then do put_path().

In effect, we open-code the things eventual terminate_walk()
would've done on error in RCU mode.  That looks badly out of place
and confusing.  We could add a comment along the lines of the
explanation above, but... there's a simpler solution.  Call
unlazy_walk() even if legitimaze_path() fails.  It will take
us out of RCU mode, so we'll be able to do path_put(link).

Yes, it will do unnecessary work - attempt to grab references
on the stuff in nameidata, only to have them dropped as soon
as we return the error to upper layer and get terminate_walk()
called there.  So what?  We are thoroughly off the fast path
by that point - we had GFP_ATOMIC allocation fail, we had
->d_seq or mount_lock mismatch and we are about to try walking
the same path from scratch in non-RCU mode.  Which will need
to do the same allocation, this time with GFP_KERNEL, so it will
be able to apply memory pressure for blocking stuff.

Compared to that the cost of several lockref_get_not_dead()
is noise.  And the logics become much easier to understand
that way.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:25 -04:00
Al Viro
c99687a03a fold path_to_nameidata() into its only remaining caller
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:24 -04:00
Al Viro
84f0cd9e83 pick_link(): pass it struct path already with normal refcounting rules
step_into() tries to avoid grabbing and dropping mount references
on the steps that do not involve crossing mountpoints (which is
obviously the majority of cases).  So it uses a local struct path
with unusual refcounting rules - path.mnt is pinned if and only if
it's not equal to nd->path.mnt.

We used to have similar beasts all over the place and we had quite
a few bugs crop up in their handling - it's easy to get confused
when changing e.g. cleanup on failure exits (or adding a new check,
etc.)

Now that's mostly gone - the step_into() instance (which is what
we need them for) is the only one left.  It is exposed to mount
traversal and it's (shortly) seen by pick_link().  Since pick_link()
needs to store it in link stack, where the normal rules apply,
it has to make sure that mount is pinned regardless of nd->path.mnt
value.  That's done on all calls of pick_link() and very early
in those.  Let's do that in the caller (step_into()) instead -
that way the fewer places need to be aware of such struct path
instances.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:23 -04:00
Al Viro
19f6028a01 fs/namei.c: kill follow_mount()
The only remaining caller (path_pts()) should be using follow_down()
anyway.  And clean path_pts() a bit.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:23 -04:00
Al Viro
2aa3847085 non-RCU analogue of the previous commit
new helper: choose_mountpoint().  Wrapper around choose_mountpoint_rcu(),
similar to lookup_mnt() vs. __lookup_mnt().  follow_dotdot() switched to
it.  Now we don't grab mount_lock exclusive anymore; note that the
primitive used non-RCU mount traversals in other direction (lookup_mnt())
doesn't bother with that either - it uses mount_lock seqcount instead.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:22 -04:00
Al Viro
7ef482fa65 helper for mount rootwards traversal
The loops in follow_dotdot{_rcu()} are doing the same thing:
we have a mount and we want to find out how far up the chain
of mounts do we need to go.

We follow the chain of mount until we find one that is not
directly overmounting the root of another mount.  If such
a mount is found, we want the location it's mounted upon.
If we run out of chain (i.e. get to a mount that is not
mounted on anything else) or run into process' root, we
report failure.

On success, we want (in RCU case) d_seq of resulting location
sampled or (in non-RCU case) references to that location
acquired.

This commit introduces such primitive for RCU case and
switches follow_dotdot_rcu() to it; non-RCU case will be
go in the next commit.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:21 -04:00
Al Viro
165200d6cb follow_dotdot(): be lazy about changing nd->path
Change nd->path only after the loop is done and only in case we hadn't
ended up finding ourselves in root.  Same for NO_XDEV check.

That separates the "check how far back do we need to go through the
mount stack" logics from the rest of .. traversal.

NOTE: path_get/path_put introduced here are temporary.  They will
go away later in the series.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:21 -04:00
Al Viro
efe772d628 follow_dotdot_rcu(): be lazy about changing nd->path
Change nd->path only after the loop is done and only in case we hadn't
ended up finding ourselves in root.  Same for NO_XDEV check.  Don't
recheck mount_lock on each step either.

That separates the "check how far back do we need to go through the
mount stack" logics from the rest of .. traversal.

Note that the sequence for d_seq/d_inode here is
	* sample mount_lock seqcount
...
	* sample d_seq
	* fetch d_inode
	* verify mount_lock seqcount
The last step makes sure that d_inode value we'd got matches d_seq -
it dentry is guaranteed to have been a mountpoint through the
entire thing, so its d_inode must have been stable.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:20 -04:00
Al Viro
12487f3067 follow_dotdot{,_rcu}(): massage loops
The logics in both of them is the same:
	while true
		if in process' root	// uncommon
			break
		if *not* in mount root	// normal case
			find the parent
			return
		if at absolute root	// very uncommon
			break
		move to underlying mountpoint
	report that we are in root

Pull the common path out of the loop:
	if in process' root		// uncommon
		goto in_root
	if unlikely(in mount root)
		while true
			if at absolute root
				goto in_root
			move to underlying mountpoint
			if in process' root
				goto in_root
			if in mount root
				break;
	find the parent	// we are not in mount root
	return
in_root:
	report that we are in root

The reason for that transformation is that we get to keep the
common path straight *and* get a separate block for "move
through underlying mountpoints", which will allow to sanitize
NO_XDEV handling there.  What's more, the pared-down loops
will be easier to deal with - in particular, non-RCU case
has no need to grab mount_lock and rewriting it to the
form that wouldn't do that is a non-trivial change.  Better
do that with less stuff getting in the way...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:09:19 -04:00
Al Viro
c2df196876 lift all calls of step_into() out of follow_dotdot/follow_dotdot_rcu
lift step_into() into handle_dots() (where they merge with each other);
have follow_... return dentry and pass inode/seq to the caller.

[braino fix folded; kudos to Qian Cai <cai@lca.pw> for reporting it]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-04-02 01:07:30 -04:00
Al Viro
6dfd9fe54d follow_dotdot{,_rcu}(): switch to use of step_into()
gets the regular mount crossing on result of ..

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
7521f22b3c handle_dots(), follow_dotdot{,_rcu}(): preparation to switch to step_into()
Right now the tail ends of follow_dotdot{,_rcu}() are pretty
much the open-coded analogues of step_into().  The differences:
	* the lack of proper LOOKUP_NO_XDEV handling in non-RCU case
(arguably a bug)
	* the lack of ->d_manage() handling (again, arguably a bug)

Adjust the calling conventions so that on the next step with could
just switch those functions to returning step_into().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
957dd41d88 move handle_dots(), follow_dotdot() and follow_dotdot_rcu() past step_into()
pure move; we are going to have step_into() called by that bunch.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
c9a0f75d81 follow_dotdot{,_rcu}(): lift LOOKUP_BENEATH checks out of loop
Behaviour change: LOOKUP_BENEATH lookup of .. in absolute root
yields an error even if it's not the process' root.  That's
possible only if you'd managed to escape chroot jail by way of
procfs symlinks, but IMO the resulting behaviour is not worse -
more consistent and easier to describe:
	".." in root is "stay where you are", uness LOOKUP_BENEATH
	has been given, in which case it's "fail with EXDEV".

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
abc2c632e0 follow_dotdot{,_rcu}(): lift switching nd->path to parent out of loop
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
a6a7eb7628 expand path_parent_directory() in its callers
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
63b27720a4 path_parent_directory(): leave changing path->dentry to callers
Instead of returning 0, return new dentry; instead of returning
-ENOENT, return NULL.  Adjust the callers accordingly.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
6b03f7edf4 path_connected(): pass mount and dentry separately
eventually we'll want to do that check *before* mangling
nd->path.dentry...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
c981a48281 split the lookup-related parts of do_last() into a separate helper
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
973d4b73fb do_last(): rejoin the common path even earlier in FMODE_{OPENED,CREATED} case
... getting may_create_in_sticky() checks in FMODE_OPENED case as well.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
8795e7d482 do_last(): simplify the liveness analysis past finish_open_created
Don't mess with got_write there - it is guaranteed to be false on
entry and it will be set true if and only if we decide to go for
truncation and manage to get write access for that.

Don't carry acc_mode through the entire thing - it's only used
in that part.  And don't bother with gotos in there - compiler is
quite capable of optimizing that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:13 -04:00
Al Viro
5a2d3edd8d do_last(): rejoing the common path earlier in FMODE_{OPENED,CREATED} case
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
59e96e6583 do_last(): don't bother with keeping got_write in FMODE_OPENED case
it's easier to drop it right after lookup_open() and regain if
needed (i.e. if we will need to truncate).  On the non-FMODE_OPENED
path we do that anyway.  In case of FMODE_CREATED we won't be
needing it.  And it's easier to prove correctness that way,
especially since the initial failure to get write access is not
always fatal; proving that we'll never end up truncating in that
case is rather convoluted.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
3ad5615a07 do_last(): merge the may_open() calls
have FMODE_OPENED case rejoin the main path at earlier point

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
7be219b4dc atomic_open(): lift the call of may_open() into do_last()
there we'll be able to merge it with its counterparts in other
cases, and there's no reason to do it before the parent has
been unlocked

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
6fb968cdf9 atomic_open(): return the right dentry in FMODE_OPENED case
->atomic_open() might have used a different alias than the one we'd
passed to it; in "not opened" case we take care of that, in "opened"
one we don't.  Currently we don't care downstream of "opened" case
which alias to return; however, that will change shortly when we
get to unifying may_open() calls.

It's not hard to get right in all cases, anyway.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
9deed3ebca new helper: traverse_mounts()
common guts of follow_down() and follow_managed() taken to a new
helper - traverse_mounts().  The remnants of follow_managed()
are folded into its sole remaining caller (handle_mounts()).
Calling conventions of handle_mounts() slightly sanitized -
instead of the weird "1 for success, -E... for failure" that used
to be imposed by the calling conventions of walk_component() et.al.
we can use the normal "0 for success, -E... for failure".

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
ea936aeb3e massage __follow_mount_rcu() a bit
make the loop more similar to that in follow_managed(), with
explicit tracking of flags, etc.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
c108837e06 namei: have link_path_walk() maintain LOOKUP_PARENT
set on entry, clear when we get to the last component.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
d8d4611a4f link_path_walk(): simplify stack handling
We use nd->stack to store two things: pinning down the symlinks
we are resolving and resuming the name traversal when a nested
symlink is finished.

Currently, nd->depth is used to keep track of both.  It's 0 when
we call link_path_walk() for the first time (for the pathname
itself) and 1 on all subsequent calls (for trailing symlinks,
if any).  That's fine, as far as pinning symlinks goes - when
handling a trailing symlink, the string we are interpreting
is the body of symlink pinned down in nd->stack[0].  It's
rather inconvenient with respect to handling nested symlinks,
though - when we run out of a string we are currently interpreting,
we need to decide whether it's a nested symlink (in which case
we need to pick the string saved back when we started to interpret
that nested symlink and resume its traversal) or not (in which
case we are done with link_path_walk()).

Current solution is a bit of a kludge - in handling of trailing symlink
(in lookup_last() and open_last_lookups() we clear nd->stack[0].name.
That allows link_path_walk() to use the following rules when
running out of a string to interpret:
	* if nd->depth is zero, we are at the end of pathname itself.
	* if nd->depth is positive, check the saved string; for
nested symlink it will be non-NULL, for trailing symlink - NULL.

It works, but it's rather non-obvious.  Note that we have two sets:
the set of symlinks currently being traversed and the set of postponed
pathname tails.  The former is stored in nd->stack[0..nd->depth-1].link
and it's valid throught the pathname resolution; the latter is valid only
during an individual call of link_path_walk() and it occupies
nd->stack[0..nd->depth-1].name for the first call of link_path_walk() and
nd->stack[1..nd->depth-1].name for subsequent ones.  The kludge is basically
a way to recognize the second set becoming empty.

The things get simpler if we keep track of the second set's size
explicitly and always store it in nd->stack[0..depth-1].name.
We access the second set only inside link_path_walk(), so its
size can live in a local variable; that way the check becomes
trivial without the need of that kludge.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
b1a8197240 pick_link(): check for WALK_TRAILING, not LOOKUP_PARENT
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:12 -04:00
Al Viro
8c4efe22e7 namei: invert the meaning of WALK_FOLLOW
old flags & WALK_FOLLOW <=> new !(flags & WALK_TRAILING)
That's what that flag had really been used for.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:09:09 -04:00
Al Viro
b4c0353693 sanitize handling of nd->last_type, kill LAST_BIND
->last_type values are set in 3 places: path_init() (sets to LAST_ROOT),
link_path_walk (LAST_NORM/DOT/DOTDOT) and pick_link (LAST_BIND).

The are checked in walk_component(), lookup_last() and do_last().
They also get copied to the caller by filename_parentat().  In the last
3 cases the value is what we had at the return from link_path_walk().
In case of walk_component() it's either directly downstream from
assignment in link_path_walk() or, when called by lookup_last(), the
value we have at the return from link_path_walk().

The value at the entry into link_path_walk() can survive to return only
if the pathname contains nothing but slashes.  Note that pick_link()
never returns such - pure jumps are handled directly.  So for the calls
of link_path_walk() for trailing symlinks it does not matter what value
had been there at the entry; the value at the return won't depend upon it.

There are 3 call chains that might have pick_link() storing LAST_BIND:

1) pick_link() from step_into() from walk_component() from
link_path_walk().  In that case we will either be parsing the next
component immediately after return into link_path_walk(), which will
overwrite the ->last_type before anyone has a chance to look at it,
or we'll fail, in which case nobody will be looking at ->last_type at all.

2) pick_link() from step_into() from walk_component() from lookup_last().
The value is never looked at due to the above; it won't affect the value
seen at return from any link_path_walk().

3) pick_link() from step_into() from do_last().  Ditto.

In other words, assignemnt in pick_link() is pointless, and so is
LAST_BIND itself; nothing ever looks at that value.  Kill it off.
And make link_path_walk() _always_ assign ->last_type - in the only
case when the value at the entry might survive to the return that value
is always LAST_ROOT, inherited from path_init().  Move that assignment
from path_init() into the beginning of link_path_walk(), to consolidate
the things.

Historical note: LAST_BIND used to be used for the kludge with trailing
pure jump symlinks (extra iteration through the top-level loop).
No point keeping it anymore...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:19 -04:00
Al Viro
ad6cc4c338 finally fold get_link() into pick_link()
kill nd->link_inode, while we are at it

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:19 -04:00
Al Viro
06708adb99 merging pick_link() with get_link(), part 6
move the only remaining call of get_link() into pick_link()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:18 -04:00
Al Viro
b0417d2c72 merging pick_link() with get_link(), part 5
move get_link() call into step_into().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:18 -04:00
Al Viro
92d270165c merging pick_link() with get_link(), part 4
Move the call of get_link() into walk_component().  Change the
calling conventions for walk_component() to returning the link
body to follow (if any).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:18 -04:00
Al Viro
40fcf5a931 merging pick_link() with get_link(), part 3
After a pure jump ("/" or procfs-style symlink) we don't need to
hold the link anymore.  link_path_walk() dropped it if such case
had been detected, lookup_last/do_last() (i.e. old trailing_symlink())
left it on the stack - it ended up calling terminate_walk() shortly
anyway, which would've purged the entire stack.

Do it in get_link() itself instead.  Simpler logics that way...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:18 -04:00
Al Viro
1ccac622f9 merging pick_link() with get_link(), part 2
Fold trailing_symlink() into lookup_last() and do_last(), change
the calling conventions of those two.  Rules change:
	success, we are done => NULL instead of 0
	error	=> ERR_PTR(-E...) instead of -E...
	got a symlink to follow => return the path to be followed instead of 1

The loops calling those (in path_lookupat() and path_openat()) adjusted.

A subtle change of control flow here: originally a pure-jump trailing
symlink ("/" or procfs one) would've passed through the upper level
loop once more, with "" for path to traverse.  That would've brought
us back to the lookup_last/do_last entry and we would've hit LAST_BIND
case (LAST_BIND left from get_link() called by trailing_symlink())
and pretty much skip to the point right after where we'd left the
sucker back when we picked that trailing symlink.

Now we don't bother with that extra pass through the upper level
loop - if get_link() says "I've just done a pure jump, nothing
else to do", we just treat that as non-symlink case.

Boilerplate added on that step will go away shortly - it'll migrate
into walk_component() and then to step_into(), collapsing into the
change of calling conventions for those.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:18 -04:00
Al Viro
43679723d2 merging pick_link() with get_link(), part 1
Move restoring LOOKUP_PARENT and zeroing nd->stack.name[0] past
the call of get_link() (nothing _currently_ uses them in there).
That allows to moved the call of may_follow_link() into get_link()
as well, since now the presence of LOOKUP_PARENT distinguishes
the callers from each other (link_path_walk() has it, trailing_symlink()
doesn't).

Preparations for folding trailing_symlink() into callers (lookup_last()
and do_last()) and changing the calling conventions of those.  Next
stage after that will have get_link() call migrate into walk_component(),
then - into step_into().  It's tricky enough to warrant doing that
in stages, unfortunately...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:17 -04:00
Al Viro
a9dc1494a7 expand the only remaining call of path_lookup_conditional()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:17 -04:00
Al Viro
161aff1d93 LOOKUP_MOUNTPOINT: fold path_mountpointat() into path_lookupat()
New LOOKUP flag, telling path_lookupat() to act as path_mountpointat().
IOW, traverse mounts at the final point and skip revalidation of the
location where it ends up.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:17 -04:00
Al Viro
cbae4d12ee fold handle_mounts() into step_into()
The following is true:
	* calls of handle_mounts() and step_into() are always
paired in sequences like
	err = handle_mounts(nd, dentry, &path, &inode, &seq);
	if (unlikely(err < 0))
		return err;
	err = step_into(nd, &path, flags, inode, seq);
	* in all such sequences path is uninitialized before and
unused after this pair of calls
	* in all such sequences inode and seq are unused afterwards.

So the call of handle_mounts() can be shifted inside step_into(),
turning 'path' into a local variable in the combined function.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:08:15 -04:00
Al Viro
aca2903eef new step_into() flag: WALK_NOFOLLOW
Tells step_into() not to follow symlinks, regardless of LOOKUP_FOLLOW.
Allows to switch handle_lookup_down() to of step_into(), getting
all follow_managed() and step_into() calls paired.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:06:13 -04:00
Al Viro
56676ec390 step_into() callers: dismiss the symlink earlier
We need to dismiss a symlink when we are done traversing it;
currently that's done when we call step_into() for its last
component.  For the cases when we do not call step_into()
for that component (i.e. when it's . or ..) we do the same
symlink dismissal after the call of handle_dots().

What we need to guarantee is that the symlink won't be dismissed
while we are still using nd->last.name - it's pointing into the
body of said symlink.  step_into() is sufficiently late - by
the time it's called we'd already obtained the dentry, so the
name we'd been looking up is no longer needed.  However, it
turns out to be cleaner to have that ("we are done with that
component now, can dismiss the link") done explicitly - in the
callers of step_into().

In handle_dots() case we won't be using the component string
at all, so for . and .. the corresponding point is actually
_before_ the call of handle_dots(), not after it.

Fix a minor irregularity in do_last(), while we are at it -
if trailing symlink ended with . or .. we forgot to dismiss
it.  Not a problem, since nameidata is about to be done with
(neither . nor .. can be a trailing symlink, so this is the
last iteration through the loop) and terminate_walk() will
clean the stack anyway, but let's keep it more regular.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:00:32 -04:00
Al Viro
20e343571c lookup_fast(): take mount traversal into callers
Current calling conventions: -E... on error, 0 on cache miss,
result of handle_mounts(nd, dentry, path, inode, seqp) on
success.  Turn that into returning ERR_PTR(-E...), NULL and dentry
resp.; deal with handle_mounts() in the callers.  The thing
is, they already do that in cache miss handling case, so we
just need to supply dentry to them and unify the mount traversal
in those cases.  Fewer arguments that way, and we get closer
to merging handle_mounts() and step_into().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:00:32 -04:00
Al Viro
c153007b7b teach handle_mounts() to handle RCU mode
... and make the callers of __follow_mount_rcu() use handle_mounts().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 21:00:30 -04:00
Al Viro
b023e1728b lookup_fast(): consolidate the RCU success case
1) in case of __follow_mount_rcu() failure, lookup_fast() proceeds
to call unlazy_child() and, should it succeed, handle_mounts().
Note that we have status > 0 (or we wouldn't be calling
__follow_mount_rcu() at all), so all stuff conditional upon
non-positive status won't be even touched.

Consolidate just that sequence after the call of __follow_mount_rcu().

2) calling d_is_negative() and keeping its result is pointless -
we either don't get past checking ->d_seq (and don't use the results of
d_is_negative() at all), or we are guaranteed that ->d_inode and
type bits of ->d_flags had been consistent at the time of d_is_negative()
call.  IOW, we could only get to the use of its result if it's
equal to !inode.  The same ->d_seq check guarantees that after that point
this CPU won't observe ->d_flags values older than ->d_inode update.
So 'negative' variable is completely pointless these days.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-13 20:59:49 -04:00
Al Viro
db3c9ade50 handle_mounts(): pass dentry in, turn path into a pure out argument
All callers are equivalent to
	path->dentry = dentry;
	path->mnt = nd->path.mnt;
	err = handle_mounts(path, ...)
Pass dentry as an explicit argument, fill *path in handle_mounts()
itself.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-12 18:15:42 -04:00
Al Viro
e73cabff59 do_last(): collapse the call of path_to_nameidata()
... and shift filling struct path to just before the call of
handle_mounts().  All callers of handle_mounts() are
immediately preceded by path->mnt = nd->path.mnt now.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-12 18:15:42 -04:00
Al Viro
da5ebf5aa6 lookup_open(): saner calling conventions (return dentry on success)
same story as for atomic_open() in the previous commit.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-03-12 18:09:20 -04:00
Al Viro
239eb98338 atomic_open(): saner calling conventions (return dentry on success)
Currently it either returns -E... or puts (nd->path.mnt,dentry)
into *path and returns 0.  Make it return ERR_PTR(-E...) or
dentry; adjust the caller.  Fewer arguments and it's easier
to keep track of *path contents that way.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-02-27 14:43:56 -05:00
Al Viro
bd7c4b5083 handle_mounts(): start building a sane wrapper for follow_managed()
All callers of follow_managed() follow it on success with the same steps -
d_backing_inode(path->dentry) is calculated and stored into some struct inode *
variable and, in all but one case, an unsigned variable (nd->seq to be) is
zeroed.  The single exception is lookup_fast() and there zeroing is correct
thing to do - not doing it is a pointless microoptimization.

	Add a wrapper for follow_managed() that would do that combination.
It's mostly a vehicle for code massage - it will be changing quite a bit,
and the current calling conventions are by no means final.  Right now it
takes path, nameidata and (as out params) inode and seq, similar to
__follow_mount_rcu().  Which will soon get folded into it...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-02-27 14:43:56 -05:00
Al Viro
31d1726d72 make build_open_flags() treat O_CREAT | O_EXCL as implying O_NOFOLLOW
O_CREAT | O_EXCL means "-EEXIST if we run into a trailing symlink".
As it is, we might or might not have LOOKUP_FOLLOW in op->intent
in that case - that depends upon having O_NOFOLLOW in open flags.
It doesn't matter, since we won't be checking it in that case -
do_last() bails out earlier.

However, making sure it's not set (i.e. acting as if we had an explicit
O_NOFOLLOW) makes the behaviour more explicit and allows to reorder the
check for O_CREAT | O_EXCL in do_last() with the call of step_into()
immediately following it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-02-27 14:43:56 -05:00
Al Viro
1c9f5e06a6 follow_automount() doesn't need the entire nameidata
Only the address of ->total_link_count and the flags.
And fix an off-by-one is ELOOP detection - make it
consistent with symlink following, where we check if
the pre-increment value has reached 40, rather than
check the post-increment one.

[kudos to Christian Brauner for spotted braino]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-02-27 14:43:55 -05:00
Al Viro
25e195aa1e follow_automount(): get rid of dead^Wstillborn code
1) no instances of ->d_automount() have ever made use of the "return
ERR_PTR(-EISDIR) if you don't feel like mounting anything" - that's
a rudiment of plans that got superseded before the thing went into
the tree.  Despite the comment in follow_automount(), autofs has
never done that.

2) if there's no ->d_automount() in dentry_operations, filesystems
should not set DCACHE_NEED_AUTOMOUNT in the first place.  None have
ever done so...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-02-27 14:43:55 -05:00
Al Viro
26df6034fd fix automount/automount race properly
Protection against automount/automount races (two threads hitting the same
referral point at the same time) is based upon do_add_mount() prevention of
identical overmounts - trying to overmount the root of mounted tree with
the same tree fails with -EBUSY.  It's unreliable (the other thread might've
mounted something on top of the automount it has triggered) *and* causes
no end of headache for follow_automount() and its caller, since
finish_automount() behaves like do_new_mount() - if the mountpoint to be is
overmounted, it mounts on top what's overmounting it.  It's not only wrong
(we want to go into what's overmounting the automount point and quietly
discard what we planned to mount there), it introduces the possibility of
original parent mount getting dropped.  That's what 8aef188452 (VFS: Fix
vfsmount overput on simultaneous automount) deals with, but it can't do
anything about the reliability of conflict detection - if something had
been overmounted the other thread's automount (e.g. that other thread
having stepped into automount in mount(2)), we don't get that -EBUSY and
the result is
	 referral point under automounted NFS under explicit overmount
under another copy of automounted NFS

What we need is finish_automount() *NOT* digging into overmounts - if it
finds one, it should just quietly discard the thing it was asked to mount.
And don't bother with actually crossing into the results of finish_automount() -
the same loop that calls follow_automount() will do that just fine on the
next iteration.

IOW, instead of calling lock_mount() have finish_automount() do it manually,
_without_ the "move into overmount and retry" part.  And leave crossing into
the results to the caller of follow_automount(), which simplifies it a lot.

Moral: if you end up with a lot of glue working around the calling conventions
of something, perhaps these calling conventions are simply wrong...

Fixes: 8aef188452 (VFS: Fix vfsmount overput on simultaneous automount)
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-02-27 14:40:43 -05:00
Al Viro
6404674acd vfs: fix do_last() regression
Brown paperbag time: fetching ->i_uid/->i_mode really should've been
done from nd->inode.  I even suggested that, but the reason for that has
slipped through the cracks and I went for dir->d_inode instead - made
for more "obvious" patch.

Analysis:

 - at the entry into do_last() and all the way to step_into(): dir (aka
   nd->path.dentry) is known not to have been freed; so's nd->inode and
   it's equal to dir->d_inode unless we are already doomed to -ECHILD.
   inode of the file to get opened is not known.

 - after step_into(): inode of the file to get opened is known; dir
   might be pointing to freed memory/be negative/etc.

 - at the call of may_create_in_sticky(): guaranteed to be out of RCU
   mode; inode of the file to get opened is known and pinned; dir might
   be garbage.

The last was the reason for the original patch.  Except that at the
do_last() entry we can be in RCU mode and it is possible that
nd->path.dentry->d_inode has already changed under us.

In that case we are going to fail with -ECHILD, but we need to be
careful; nd->inode is pointing to valid struct inode and it's the same
as nd->path.dentry->d_inode in "won't fail with -ECHILD" case, so we
should use that.

Reported-by: "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@nokia.com>
Reported-by: syzbot+190005201ced78a74ad6@syzkaller.appspotmail.com
Wearing-brown-paperbag: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@kernel.org
Fixes: d0cb50185a ("do_last(): fetch directory ->i_mode and ->i_uid before it's too late")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-02-01 10:36:49 -08:00
Linus Torvalds
6aee4badd8 Merge branch 'work.openat2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull openat2 support from Al Viro:
 "This is the openat2() series from Aleksa Sarai.

  I'm afraid that the rest of namei stuff will have to wait - it got
  zero review the last time I'd posted #work.namei, and there had been a
  leak in the posted series I'd caught only last weekend. I was going to
  repost it on Monday, but the window opened and the odds of getting any
  review during that... Oh, well.

  Anyway, openat2 part should be ready; that _did_ get sane amount of
  review and public testing, so here it comes"

From Aleksa's description of the series:
 "For a very long time, extending openat(2) with new features has been
  incredibly frustrating. This stems from the fact that openat(2) is
  possibly the most famous counter-example to the mantra "don't silently
  accept garbage from userspace" -- it doesn't check whether unknown
  flags are present[1].

  This means that (generally) the addition of new flags to openat(2) has
  been fraught with backwards-compatibility issues (O_TMPFILE has to be
  defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old
  kernels gave errors, since it's insecure to silently ignore the
  flag[2]). All new security-related flags therefore have a tough road
  to being added to openat(2).

  Furthermore, the need for some sort of control over VFS's path
  resolution (to avoid malicious paths resulting in inadvertent
  breakouts) has been a very long-standing desire of many userspace
  applications.

  This patchset is a revival of Al Viro's old AT_NO_JUMPS[3] patchset
  (which was a variant of David Drysdale's O_BENEATH patchset[4] which
  was a spin-off of the Capsicum project[5]) with a few additions and
  changes made based on the previous discussion within [6] as well as
  others I felt were useful.

  In line with the conclusions of the original discussion of
  AT_NO_JUMPS, the flag has been split up into separate flags. However,
  instead of being an openat(2) flag it is provided through a new
  syscall openat2(2) which provides several other improvements to the
  openat(2) interface (see the patch description for more details). The
  following new LOOKUP_* flags are added:

  LOOKUP_NO_XDEV:

     Blocks all mountpoint crossings (upwards, downwards, or through
     absolute links). Absolute pathnames alone in openat(2) do not
     trigger this. Magic-link traversal which implies a vfsmount jump is
     also blocked (though magic-link jumps on the same vfsmount are
     permitted).

  LOOKUP_NO_MAGICLINKS:

     Blocks resolution through /proc/$pid/fd-style links. This is done
     by blocking the usage of nd_jump_link() during resolution in a
     filesystem. The term "magic-links" is used to match with the only
     reference to these links in Documentation/, but I'm happy to change
     the name.

     It should be noted that this is different to the scope of
     ~LOOKUP_FOLLOW in that it applies to all path components. However,
     you can do openat2(NO_FOLLOW|NO_MAGICLINKS) on a magic-link and it
     will *not* fail (assuming that no parent component was a
     magic-link), and you will have an fd for the magic-link.

     In order to correctly detect magic-links, the introduction of a new
     LOOKUP_MAGICLINK_JUMPED state flag was required.

  LOOKUP_BENEATH:

     Disallows escapes to outside the starting dirfd's
     tree, using techniques such as ".." or absolute links. Absolute
     paths in openat(2) are also disallowed.

     Conceptually this flag is to ensure you "stay below" a certain
     point in the filesystem tree -- but this requires some additional
     to protect against various races that would allow escape using
     "..".

     Currently LOOKUP_BENEATH implies LOOKUP_NO_MAGICLINKS, because it
     can trivially beam you around the filesystem (breaking the
     protection). In future, there might be similar safety checks done
     as in LOOKUP_IN_ROOT, but that requires more discussion.

  In addition, two new flags are added that expand on the above ideas:

  LOOKUP_NO_SYMLINKS:

     Does what it says on the tin. No symlink resolution is allowed at
     all, including magic-links. Just as with LOOKUP_NO_MAGICLINKS this
     can still be used with NOFOLLOW to open an fd for the symlink as
     long as no parent path had a symlink component.

  LOOKUP_IN_ROOT:

     This is an extension of LOOKUP_BENEATH that, rather than blocking
     attempts to move past the root, forces all such movements to be
     scoped to the starting point. This provides chroot(2)-like
     protection but without the cost of a chroot(2) for each filesystem
     operation, as well as being safe against race attacks that
     chroot(2) is not.

     If a race is detected (as with LOOKUP_BENEATH) then an error is
     generated, and similar to LOOKUP_BENEATH it is not permitted to
     cross magic-links with LOOKUP_IN_ROOT.

     The primary need for this is from container runtimes, which
     currently need to do symlink scoping in userspace[7] when opening
     paths in a potentially malicious container.

     There is a long list of CVEs that could have bene mitigated by
     having RESOLVE_THIS_ROOT (such as CVE-2017-1002101,
     CVE-2017-1002102, CVE-2018-15664, and CVE-2019-5736, just to name a
     few).

  In order to make all of the above more usable, I'm working on
  libpathrs[8] which is a C-friendly library for safe path resolution.
  It features a userspace-emulated backend if the kernel doesn't support
  openat2(2). Hopefully we can get userspace to switch to using it, and
  thus get openat2(2) support for free once it's ready.

  Future work would include implementing things like
  RESOLVE_NO_AUTOMOUNT and possibly a RESOLVE_NO_REMOTE (to allow
  programs to be sure they don't hit DoSes though stale NFS handles)"

* 'work.openat2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  Documentation: path-lookup: include new LOOKUP flags
  selftests: add openat2(2) selftests
  open: introduce openat2(2) syscall
  namei: LOOKUP_{IN_ROOT,BENEATH}: permit limited ".." resolution
  namei: LOOKUP_IN_ROOT: chroot-like scoped resolution
  namei: LOOKUP_BENEATH: O_BENEATH-like scoped resolution
  namei: LOOKUP_NO_XDEV: block mountpoint crossing
  namei: LOOKUP_NO_MAGICLINKS: block magic-link resolution
  namei: LOOKUP_NO_SYMLINKS: block symlink resolution
  namei: allow set_root() to produce errors
  namei: allow nd_jump_link() to produce errors
  nsfs: clean-up ns_get_path() signature to return int
  namei: only return -ECHILD from follow_dotdot_rcu()
2020-01-29 11:20:24 -08:00
Al Viro
d0cb50185a do_last(): fetch directory ->i_mode and ->i_uid before it's too late
may_create_in_sticky() call is done when we already have dropped the
reference to dir.

Fixes: 30aba6656f (namei: allow restricted O_CREAT of FIFOs and regular files)
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-26 09:31:07 -05:00
Al Viro
508c877276 fix autofs regression caused by follow_managed() changes
we need to reload ->d_flags after the call of ->d_manage() - the thing
might've been called with dentry still negative and have the damn thing
turned positive while we'd waited.

Fixes: d41efb522e "fs/namei.c: pull positivity check into follow_managed()"
Reported-by: Ian Kent <raven@themaw.net>
Tested-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-15 01:36:46 -05:00
Al Viro
c64cd6e34e reimplement path_mountpoint() with less magic
... and get rid of a bunch of bugs in it.  Background:
the reason for path_mountpoint() is that umount() really doesn't
want attempts to revalidate the root of what it's trying to umount.
The thing we want to avoid actually happen from complete_walk();
solution was to do something parallel to normal path_lookupat()
and it both went overboard and got the boilerplate subtly
(and not so subtly) wrong.

A better solution is to do pretty much what the normal path_lookupat()
does, but instead of complete_walk() do unlazy_walk().  All it takes
to avoid that ->d_weak_revalidate() call...  mountpoint_last() goes
away, along with everything it got wrong, and so does the magic around
LOOKUP_NO_REVAL.

Another source of bugs is that when we traverse mounts at the final
location (and we need to do that - umount . expects to get whatever's
overmounting ., if any, out of the lookup) we really ought to take
care of ->d_manage() - as it is, manual umount of autofs automount
in progress can lead to unpleasant surprises for the daemon.  Easily
solved by using handle_lookup_down() instead of follow_mount().

Tested-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-01-15 01:36:06 -05:00
Aleksa Sarai
ab87f9a56c namei: LOOKUP_{IN_ROOT,BENEATH}: permit limited ".." resolution
Allow LOOKUP_BENEATH and LOOKUP_IN_ROOT to safely permit ".." resolution
(in the case of LOOKUP_BENEATH the resolution will still fail if ".."
resolution would resolve a path outside of the root -- while
LOOKUP_IN_ROOT will chroot(2)-style scope it). Magic-link jumps are
still disallowed entirely[*].

As Jann explains[1,2], the need for this patch (and the original no-".."
restriction) is explained by observing there is a fairly easy-to-exploit
race condition with chroot(2) (and thus by extension LOOKUP_IN_ROOT and
LOOKUP_BENEATH if ".." is allowed) where a rename(2) of a path can be
used to "skip over" nd->root and thus escape to the filesystem above
nd->root.

  thread1 [attacker]:
    for (;;)
      renameat2(AT_FDCWD, "/a/b/c", AT_FDCWD, "/a/d", RENAME_EXCHANGE);
  thread2 [victim]:
    for (;;)
      openat2(dirb, "b/c/../../etc/shadow",
              { .flags = O_PATH, .resolve = RESOLVE_IN_ROOT } );

With fairly significant regularity, thread2 will resolve to
"/etc/shadow" rather than "/a/b/etc/shadow". There is also a similar
(though somewhat more privileged) attack using MS_MOVE.

With this patch, such cases will be detected *during* ".." resolution
and will return -EAGAIN for userspace to decide to either retry or abort
the lookup. It should be noted that ".." is the weak point of chroot(2)
-- walking *into* a subdirectory tautologically cannot result in you
walking *outside* nd->root (except through a bind-mount or magic-link).
There is also no other way for a directory's parent to change (which is
the primary worry with ".." resolution here) other than a rename or
MS_MOVE.

The primary reason for deferring to userspace with -EAGAIN is that an
in-kernel retry loop (or doing a path_is_under() check after re-taking
the relevant seqlocks) can become unreasonably expensive on machines
with lots of VFS activity (nfsd can cause lots of rename_lock updates).
Thus it should be up to userspace how many times they wish to retry the
lookup -- the selftests for this attack indicate that there is a ~35%
chance of the lookup succeeding on the first try even with an attacker
thrashing rename_lock.

A variant of the above attack is included in the selftests for
openat2(2) later in this patch series. I've run this test on several
machines for several days and no instances of a breakout were detected.
While this is not concrete proof that this is safe, when combined with
the above argument it should lend some trustworthiness to this
construction.

[*] It may be acceptable in the future to do a path_is_under() check for
    magic-links after they are resolved. However this seems unlikely to
    be a feature that people *really* need -- it can be added later if
    it turns out a lot of people want it.

[1]: https://lore.kernel.org/lkml/CAG48ez1jzNvxB+bfOBnERFGp=oMM0vHWuLD6EULmne3R6xa53w@mail.gmail.com/
[2]: https://lore.kernel.org/lkml/CAG48ez30WJhbsro2HOc_DR7V91M+hNFzBP5ogRMZaxbAORvqzg@mail.gmail.com/

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Suggested-by: Jann Horn <jannh@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-12-08 19:09:44 -05:00
Aleksa Sarai
8db52c7e7e namei: LOOKUP_IN_ROOT: chroot-like scoped resolution
/* Background. */
Container runtimes or other administrative management processes will
often interact with root filesystems while in the host mount namespace,
because the cost of doing a chroot(2) on every operation is too
prohibitive (especially in Go, which cannot safely use vfork). However,
a malicious program can trick the management process into doing
operations on files outside of the root filesystem through careful
crafting of symlinks.

Most programs that need this feature have attempted to make this process
safe, by doing all of the path resolution in userspace (with symlinks
being scoped to the root of the malicious root filesystem).
Unfortunately, this method is prone to foot-guns and usually such
implementations have subtle security bugs.

Thus, what userspace needs is a way to resolve a path as though it were
in a chroot(2) -- with all absolute symlinks being resolved relative to
the dirfd root (and ".." components being stuck under the dirfd root).
It is much simpler and more straight-forward to provide this
functionality in-kernel (because it can be done far more cheaply and
correctly).

More classical applications that also have this problem (which have
their own potentially buggy userspace path sanitisation code) include
web servers, archive extraction tools, network file servers, and so on.

/* Userspace API. */
LOOKUP_IN_ROOT will be exposed to userspace through openat2(2).

/* Semantics. */
Unlike most other LOOKUP flags (most notably LOOKUP_FOLLOW),
LOOKUP_IN_ROOT applies to all components of the path.

With LOOKUP_IN_ROOT, any path component which attempts to cross the
starting point of the pathname lookup (the dirfd passed to openat) will
remain at the starting point. Thus, all absolute paths and symlinks will
be scoped within the starting point.

There is a slight change in behaviour regarding pathnames -- if the
pathname is absolute then the dirfd is still used as the root of
resolution of LOOKUP_IN_ROOT is specified (this is to avoid obvious
foot-guns, at the cost of a minor API inconsistency).

As with LOOKUP_BENEATH, Jann's security concern about ".."[1] applies to
LOOKUP_IN_ROOT -- therefore ".." resolution is blocked. This restriction
will be lifted in a future patch, but requires more work to ensure that
permitting ".." is done safely.

Magic-link jumps are also blocked, because they can beam the path lookup
across the starting point. It would be possible to detect and block
only the "bad" crossings with path_is_under() checks, but it's unclear
whether it makes sense to permit magic-links at all. However, userspace
is recommended to pass LOOKUP_NO_MAGICLINKS if they want to ensure that
magic-link crossing is entirely disabled.

/* Testing. */
LOOKUP_IN_ROOT is tested as part of the openat2(2) selftests.

[1]: https://lore.kernel.org/lkml/CAG48ez1jzNvxB+bfOBnERFGp=oMM0vHWuLD6EULmne3R6xa53w@mail.gmail.com/

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-12-08 19:09:43 -05:00
Aleksa Sarai
adb21d2b52 namei: LOOKUP_BENEATH: O_BENEATH-like scoped resolution
/* Background. */
There are many circumstances when userspace wants to resolve a path and
ensure that it doesn't go outside of a particular root directory during
resolution. Obvious examples include archive extraction tools, as well as
other security-conscious userspace programs. FreeBSD spun out O_BENEATH
from their Capsicum project[1,2], so it also seems reasonable to
implement similar functionality for Linux.

This is part of a refresh of Al's AT_NO_JUMPS patchset[3] (which was a
variation on David Drysdale's O_BENEATH patchset[4], which in turn was
based on the Capsicum project[5]).

/* Userspace API. */
LOOKUP_BENEATH will be exposed to userspace through openat2(2).

/* Semantics. */
Unlike most other LOOKUP flags (most notably LOOKUP_FOLLOW),
LOOKUP_BENEATH applies to all components of the path.

With LOOKUP_BENEATH, any path component which attempts to "escape" the
starting point of the filesystem lookup (the dirfd passed to openat)
will yield -EXDEV. Thus, all absolute paths and symlinks are disallowed.

Due to a security concern brought up by Jann[6], any ".." path
components are also blocked. This restriction will be lifted in a future
patch, but requires more work to ensure that permitting ".." is done
safely.

Magic-link jumps are also blocked, because they can beam the path lookup
across the starting point. It would be possible to detect and block
only the "bad" crossings with path_is_under() checks, but it's unclear
whether it makes sense to permit magic-links at all. However, userspace
is recommended to pass LOOKUP_NO_MAGICLINKS if they want to ensure that
magic-link crossing is entirely disabled.

/* Testing. */
LOOKUP_BENEATH is tested as part of the openat2(2) selftests.

[1]: https://reviews.freebsd.org/D2808
[2]: https://reviews.freebsd.org/D17547
[3]: https://lore.kernel.org/lkml/20170429220414.GT29622@ZenIV.linux.org.uk/
[4]: https://lore.kernel.org/lkml/1415094884-18349-1-git-send-email-drysdale@google.com/
[5]: https://lore.kernel.org/lkml/1404124096-21445-1-git-send-email-drysdale@google.com/
[6]: https://lore.kernel.org/lkml/CAG48ez1jzNvxB+bfOBnERFGp=oMM0vHWuLD6EULmne3R6xa53w@mail.gmail.com/

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Suggested-by: David Drysdale <drysdale@google.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-12-08 19:09:42 -05:00
Aleksa Sarai
72ba29297e namei: LOOKUP_NO_XDEV: block mountpoint crossing
/* Background. */
The need to contain path operations within a mountpoint has been a
long-standing usecase that userspace has historically implemented
manually with liberal usage of stat(). find, rsync, tar and
many other programs implement these semantics -- but it'd be much
simpler to have a fool-proof way of refusing to open a path if it
crosses a mountpoint.

This is part of a refresh of Al's AT_NO_JUMPS patchset[1] (which was a
variation on David Drysdale's O_BENEATH patchset[2], which in turn was
based on the Capsicum project[3]).

/* Userspace API. */
LOOKUP_NO_XDEV will be exposed to userspace through openat2(2).

/* Semantics. */
Unlike most other LOOKUP flags (most notably LOOKUP_FOLLOW),
LOOKUP_NO_XDEV applies to all components of the path.

With LOOKUP_NO_XDEV, any path component which crosses a mount-point
during path resolution (including "..") will yield an -EXDEV. Absolute
paths, absolute symlinks, and magic-links will only yield an -EXDEV if
the jump involved changing mount-points.

/* Testing. */
LOOKUP_NO_XDEV is tested as part of the openat2(2) selftests.

[1]: https://lore.kernel.org/lkml/20170429220414.GT29622@ZenIV.linux.org.uk/
[2]: https://lore.kernel.org/lkml/1415094884-18349-1-git-send-email-drysdale@google.com/
[3]: https://lore.kernel.org/lkml/1404124096-21445-1-git-send-email-drysdale@google.com/

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Suggested-by: David Drysdale <drysdale@google.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-12-08 19:09:41 -05:00
Aleksa Sarai
4b99d49969 namei: LOOKUP_NO_MAGICLINKS: block magic-link resolution
/* Background. */
There has always been a special class of symlink-like objects in procfs
(and a few other pseudo-filesystems) which allow for non-lexical
resolution of paths using nd_jump_link(). These "magic-links" do not
follow traditional mount namespace boundaries, and have been used
consistently in container escape attacks because they can be used to
trick unsuspecting privileged processes into resolving unexpected paths.

It is also non-trivial for userspace to unambiguously avoid resolving
magic-links, because they do not have a reliable indication that they
are a magic-link (in order to verify them you'd have to manually open
the path given by readlink(2) and then verify that the two file
descriptors reference the same underlying file, which is plagued with
possible race conditions or supplementary attack scenarios).

It would therefore be very helpful for userspace to be able to avoid
these symlinks easily, thus hopefully removing a tool from attackers'
toolboxes.

This is part of a refresh of Al's AT_NO_JUMPS patchset[1] (which was a
variation on David Drysdale's O_BENEATH patchset[2], which in turn was
based on the Capsicum project[3]).

/* Userspace API. */
LOOKUP_NO_MAGICLINKS will be exposed to userspace through openat2(2).

/* Semantics. */
Unlike most other LOOKUP flags (most notably LOOKUP_FOLLOW),
LOOKUP_NO_MAGICLINKS applies to all components of the path.

With LOOKUP_NO_MAGICLINKS, any magic-link path component encountered
during path resolution will yield -ELOOP. The handling of ~LOOKUP_FOLLOW
for a trailing magic-link is identical to LOOKUP_NO_SYMLINKS.

LOOKUP_NO_SYMLINKS implies LOOKUP_NO_MAGICLINKS.

/* Testing. */
LOOKUP_NO_MAGICLINKS is tested as part of the openat2(2) selftests.

[1]: https://lore.kernel.org/lkml/20170429220414.GT29622@ZenIV.linux.org.uk/
[2]: https://lore.kernel.org/lkml/1415094884-18349-1-git-send-email-drysdale@google.com/
[3]: https://lore.kernel.org/lkml/1404124096-21445-1-git-send-email-drysdale@google.com/

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Suggested-by: David Drysdale <drysdale@google.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-12-08 19:09:40 -05:00
Aleksa Sarai
278121417a namei: LOOKUP_NO_SYMLINKS: block symlink resolution
/* Background. */
Userspace cannot easily resolve a path without resolving symlinks, and
would have to manually resolve each path component with O_PATH and
O_NOFOLLOW. This is clearly inefficient, and can be fairly easy to screw
up (resulting in possible security bugs). Linus has mentioned that Git
has a particular need for this kind of flag[1]. It also resolves a
fairly long-standing perceived deficiency in O_NOFOLLOw -- that it only
blocks the opening of trailing symlinks.

This is part of a refresh of Al's AT_NO_JUMPS patchset[2] (which was a
variation on David Drysdale's O_BENEATH patchset[3], which in turn was
based on the Capsicum project[4]).

/* Userspace API. */
LOOKUP_NO_SYMLINKS will be exposed to userspace through openat2(2).

/* Semantics. */
Unlike most other LOOKUP flags (most notably LOOKUP_FOLLOW),
LOOKUP_NO_SYMLINKS applies to all components of the path.

With LOOKUP_NO_SYMLINKS, any symlink path component encountered during
path resolution will yield -ELOOP. If the trailing component is a
symlink (and no other components were symlinks), then O_PATH|O_NOFOLLOW
will not error out and will instead provide a handle to the trailing
symlink -- without resolving it.

/* Testing. */
LOOKUP_NO_SYMLINKS is tested as part of the openat2(2) selftests.

[1]: https://lore.kernel.org/lkml/CA+55aFyOKM7DW7+0sdDFKdZFXgptb5r1id9=Wvhd8AgSP7qjwQ@mail.gmail.com/
[2]: https://lore.kernel.org/lkml/20170429220414.GT29622@ZenIV.linux.org.uk/
[3]: https://lore.kernel.org/lkml/1415094884-18349-1-git-send-email-drysdale@google.com/
[4]: https://lore.kernel.org/lkml/1404124096-21445-1-git-send-email-drysdale@google.com/

Cc: Christian Brauner <christian.brauner@ubuntu.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-12-08 19:09:40 -05:00
Aleksa Sarai
740a167827 namei: allow set_root() to produce errors
For LOOKUP_BENEATH and LOOKUP_IN_ROOT it is necessary to ensure that
set_root() is never called, and thus (for hardening purposes) it should
return an error rather than permit a breakout from the root. In
addition, move all of the repetitive set_root() calls to nd_jump_root().

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-12-08 19:09:39 -05:00
Aleksa Sarai
1bc82070fa namei: allow nd_jump_link() to produce errors
In preparation for LOOKUP_NO_MAGICLINKS, it's necessary to add the
ability for nd_jump_link() to return an error which the corresponding
get_link() caller must propogate back up to the VFS.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-12-08 19:09:38 -05:00
Aleksa Sarai
2b98149c23 namei: only return -ECHILD from follow_dotdot_rcu()
It's over-zealous to return hard errors under RCU-walk here, given that
a REF-walk will be triggered for all other cases handling ".." under
RCU.

The original purpose of this check was to ensure that if a rename occurs
such that a directory is moved outside of the bind-mount which the
resolution started in, it would be detected and blocked to avoid being
able to mess with paths outside of the bind-mount. However, triggering a
new REF-walk is just as effective a solution.

Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Fixes: 397d425dc2 ("vfs: Test for and handle paths that are unreachable from their mnt_root")
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-12-08 19:09:36 -05:00
Linus Torvalds
0aecba6173 Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull vfs d_inode/d_flags memory ordering fixes from Al Viro:
 "Fallout from tree-wide audit for ->d_inode/->d_flags barriers use.
  Basically, the problem is that negative pinned dentries require
  careful treatment - unless ->d_lock is locked or parent is held at
  least shared, another thread can make them positive right under us.

  Most of the uses turned out to be safe - the main surprises as far as
  filesystems are concerned were

   - race in dget_parent() fastpath, that might end up with the caller
     observing the returned dentry _negative_, due to insufficient
     barriers. It is positive in memory, but we could end up seeing the
     wrong value of ->d_inode in CPU cache. Fixed.

   - manual checks that result of lookup_one_len_unlocked() is positive
     (and rejection of negatives). Again, insufficient barriers (we
     might end up with inconsistent observed values of ->d_inode and
     ->d_flags). Fixed by switching to a new primitive that does the
     checks itself and returns ERR_PTR(-ENOENT) instead of a negative
     dentry. That way we get rid of boilerplate converting negatives
     into ERR_PTR(-ENOENT) in the callers and have a single place to
     deal with the barrier-related mess - inside fs/namei.c rather than
     in every caller out there.

  The guts of pathname resolution *do* need to be careful - the race
  found by Ritesh is real, as well as several similar races.
  Fortunately, it turns out that we can take care of that with fairly
  local changes in there.

  The tree-wide audit had not been fun, and I hate the idea of repeating
  it. I think the right approach would be to annotate the places where
  we are _not_ guaranteed ->d_inode/->d_flags stability and have sparse
  catch regressions. But I'm still not sure what would be the least
  invasive way of doing that and it's clearly the next cycle fodder"

* 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  fs/namei.c: fix missing barriers when checking positivity
  fix dget_parent() fastpath race
  new helper: lookup_positive_unlocked()
  fs/namei.c: pull positivity check into follow_managed()
2019-12-06 09:06:58 -08:00
Al Viro
2fa6b1e01a fs/namei.c: fix missing barriers when checking positivity
Pinned negative dentries can, generally, be made positive
by another thread.  Conditions that prevent that are
	* ->d_lock on dentry in question
	* parent directory held at least shared
	* nobody else could have observed the address of dentry
Most of the places working with those fall into one of those
categories; however, d_lookup() and friends need to be used
with some care.  Fortunately, there's not a lot of call sites,
and with few exceptions all of those fall under one of the
cases above.

Exceptions are all in fs/namei.c - in lookup_fast(), lookup_dcache()
and mountpoint_last().  Another one is lookup_slow() - there
dcache lookup is done with parent held shared, but the result
is used after we'd drop the lock.  The same happens in do_last() -
the lookup (in lookup_one()) is done with parent locked, but
result is used after unlocking.

lookup_fast(), do_last() and mountpoint_last() flat-out reject
negatives.

Most of lookup_dcache() calls are made with parent locked at least
shared; the only exception is lookup_one_len_unlocked().  It might
return pinned negative, needs serious care from callers.  Fortunately,
almost nobody calls it directly anymore; all but two callers have
converted to lookup_positive_unlocked(), which rejects negatives.

lookup_slow() is called by the same lookup_one_len_unlocked() (see
above), mountpoint_last() and walk_component().  In those two negatives
are rejected.

In other words, there is a small set of places where we need to
check carefully if a pinned potentially negative dentry is, in
fact, positive.  After that check we want to be sure that both
->d_inode and type bits in ->d_flags are stable and observed.
The set consists of follow_managed() (where the rejection happens
for lookup_fast(), walk_component() and do_last()), last_mountpoint()
and lookup_positive_unlocked().

Solution:
	1) transition from negative to positive (in __d_set_inode_and_type())
stores ->d_inode, then uses smp_store_release() to set ->d_flags type bits.
	2) aforementioned 3 places in fs/namei.c fetch ->d_flags with
smp_load_acquire() and bugger off if it type bits say "negative".
That way anyone downstream of those checks has dentry know positive pinned,
with ->d_inode and type bits of ->d_flags stable and observed.

I considered splitting off d_lookup_positive(), so that the checks could
be done right there, under ->d_lock.  However, that leads to massive
duplication of rather subtle code in fs/namei.c and fs/dcache.c.  It's
worse than it might seem, thanks to autofs ->d_manage() getting involved ;-/
No matter what, autofs_d_manage()/autofs_d_automount() must live with
the possibility of pinned negative dentry passed their way, becoming
positive under them - that's the intended behaviour when lookup comes
in the middle of automount in progress, so we can't keep them out of
the area that has to deal with those, more's the pity...

Reported-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-11-15 13:49:04 -05:00
Al Viro
6c2d4798a8 new helper: lookup_positive_unlocked()
Most of the callers of lookup_one_len_unlocked() treat negatives are
ERR_PTR(-ENOENT).  Provide a helper that would do just that.  Note
that a pinned positive dentry remains positive - it's ->d_inode is
stable, etc.; a pinned _negative_ dentry can become positive at any
point as long as you are not holding its parent at least shared.
So using lookup_one_len_unlocked() needs to be careful;
lookup_positive_unlocked() is safer and that's what the callers
end up open-coding anyway.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-11-15 13:49:04 -05:00
Al Viro
d41efb522e fs/namei.c: pull positivity check into follow_managed()
There are 4 callers; two proceed to check if result is positive and
fail with ENOENT if it isn't; one (in handle_lookup_down()) is
guaranteed to yield positive and one (in lookup_fast()) is _preceded_
by positivity check.

However, follow_managed() on a negative dentry is a (fairly cheap)
no-op on anything other than autofs.  And negative autofs dentries
are never hashed, so lookup_fast() is not going to run into one
of those.  Moreover, successful follow_managed() on a _positive_
dentry never yields a negative one (and we significantly rely upon
that in callers of lookup_fast()).

In other words, we can easily transpose the positivity check and
the call of follow_managed() in lookup_fast().  And that allows
to fold the positivity check *into* follow_managed(), simplifying
life for the code downstream of its calls.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-11-15 13:49:04 -05:00
Kees Cook
245d73698e audit: Report suspicious O_CREAT usage
This renames the very specific audit_log_link_denied() to
audit_log_path_denied() and adds the AUDIT_* type as an argument. This
allows for the creation of the new AUDIT_ANOM_CREAT that can be used to
report the fifo/regular file creation restrictions that were introduced
in commit 30aba6656f ("namei: allow restricted O_CREAT of FIFOs and
regular files").

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>
2019-10-03 13:59:29 -04:00
Al Viro
84a2bd3940 fs/namei.c: keep track of nd->root refcount status
The rules for nd->root are messy:
	* if we have LOOKUP_ROOT, it doesn't contribute to refcounts
	* if we have LOOKUP_RCU, it doesn't contribute to refcounts
	* if nd->root.mnt is NULL, it doesn't contribute to refcounts
	* otherwise it does contribute

terminate_walk() needs to drop the references if they are contributing.
So everything else should be careful not to confuse it, leading to
rather convoluted code.

It's easier to keep track of whether we'd grabbed the reference(s)
explicitly.  Use a new flag for that.  Don't bother with zeroing
nd->root.mnt on unlazy failures and in terminate_walk - it's not
needed anymore (terminate_walk() won't care and the next path_init()
will zero nd->root in !LOOKUP_ROOT case anyway).

Resulting rules for nd->root refcounts are much simpler: they are
contributing iff LOOKUP_ROOT_GRABBED is set in nd->flags.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-09-03 09:30:45 -04:00
Al Viro
ee594bfff3 fs/namei.c: new helper - legitimize_root()
identical logics in unlazy_walk() and unlazy_child()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-08-30 21:30:13 -04:00
Al Viro
c9b07eab0c audit_inode(): switch to passing AUDIT_INODE_...
don't bother with remapping LOOKUP_... values - all callers pass
constants and we can just as well pass the right ones from the
very beginning.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-07-21 18:24:46 -04:00
Al Viro
39145f5f0c filename_mountpoint(): make LOOKUP_NO_EVAL unconditional there
user_path_mountpoint_at() always gets it and the reasons to have it
there (i.e. in umount(2)) apply to kern_path_mountpoint() callers
as well.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-07-21 18:24:45 -04:00
Al Viro
ff0ebee239 filename_lookup(): audit_inode() argument is always 0
We hadn't been passing LOOKUP_PARENT in flags to that thing
since filename_parentat() had been split off back in 2015.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-07-21 18:24:44 -04:00
Amir Goldstein
116b9731ad fsnotify: add empty fsnotify_{unlink,rmdir}() hooks
We would like to move fsnotify_nameremove() calls from d_delete()
into a higher layer where the hook makes more sense and so we can
consider every d_delete() call site individually.

Start by creating empty hook fsnotify_{unlink,rmdir}() and place
them in the proper VFS call sites.  After all d_delete() call sites
will be converted to use the new hook, the new hook will generate the
delete events and fsnotify_nameremove() hook will be removed.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
2019-06-20 14:44:55 +02:00
Linus Torvalds
a9fbcd6728 Clean up fscrypt's dcache revalidation support, and other
miscellaneous cleanups.
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Merge tag 'fscrypt_for_linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt

Pull fscrypt updates from Ted Ts'o:
 "Clean up fscrypt's dcache revalidation support, and other
  miscellaneous cleanups"

* tag 'fscrypt_for_linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt:
  fscrypt: cache decrypted symlink target in ->i_link
  vfs: use READ_ONCE() to access ->i_link
  fscrypt: fix race where ->lookup() marks plaintext dentry as ciphertext
  fscrypt: only set dentry_operations on ciphertext dentries
  fs, fscrypt: clear DCACHE_ENCRYPTED_NAME when unaliasing directory
  fscrypt: fix race allowing rename() and link() of ciphertext dentries
  fscrypt: clean up and improve dentry revalidation
  fscrypt: use READ_ONCE() to access ->i_crypt_info
  fscrypt: remove WARN_ON_ONCE() when decryption fails
  fscrypt: drop inode argument from fscrypt_get_ctx()
2019-05-07 21:28:04 -07:00
Al Viro
f4ec3a3d43 switch fsnotify_move() to passing const struct qstr * for old_name
note that in the second (RENAME_EXCHANGE) call of fsnotify_move() in
vfs_rename() the old_dentry->d_name is guaranteed to be unchanged
throughout the evaluation of fsnotify_move() (by the fact that the
parent directory is locked exclusive), so we don't need to fetch
old_dentry->d_name.name in the caller.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-04-26 13:22:05 -04:00
Al Viro
230c6402b1 ovl_lookup_real_one(): don't bother with strlen()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-04-26 13:13:33 -04:00
Eric Biggers
4c4f7c19b3 vfs: use READ_ONCE() to access ->i_link
Use 'READ_ONCE(inode->i_link)' to explicitly support filesystems caching
the symlink target in ->i_link later if it was unavailable at iget()
time, or wasn't easily available.  I'll be doing this in fscrypt, to
improve the performance of encrypted symlinks on ext4, f2fs, and ubifs.

->i_link will start NULL and may later be set to a non-NULL value by a
smp_store_release() or cmpxchg_release().  READ_ONCE() is needed on the
read side.  smp_load_acquire() is unnecessary because only a data
dependency barrier is required.  (Thanks to Al for pointing this out.)

Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2019-04-17 12:43:14 -04:00
Linus Torvalds
7b47a9e7c8 Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull vfs mount infrastructure updates from Al Viro:
 "The rest of core infrastructure; no new syscalls in that pile, but the
  old parts are switched to new infrastructure. At that point
  conversions of individual filesystems can happen independently; some
  are done here (afs, cgroup, procfs, etc.), there's also a large series
  outside of that pile dealing with NFS (quite a bit of option-parsing
  stuff is getting used there - it's one of the most convoluted
  filesystems in terms of mount-related logics), but NFS bits are the
  next cycle fodder.

  It got seriously simplified since the last cycle; documentation is
  probably the weakest bit at the moment - I considered dropping the
  commit introducing Documentation/filesystems/mount_api.txt (cutting
  the size increase by quarter ;-), but decided that it would be better
  to fix it up after -rc1 instead.

  That pile allows to do followup work in independent branches, which
  should make life much easier for the next cycle. fs/super.c size
  increase is unpleasant; there's a followup series that allows to
  shrink it considerably, but I decided to leave that until the next
  cycle"

* 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (41 commits)
  afs: Use fs_context to pass parameters over automount
  afs: Add fs_context support
  vfs: Add some logging to the core users of the fs_context log
  vfs: Implement logging through fs_context
  vfs: Provide documentation for new mount API
  vfs: Remove kern_mount_data()
  hugetlbfs: Convert to fs_context
  cpuset: Use fs_context
  kernfs, sysfs, cgroup, intel_rdt: Support fs_context
  cgroup: store a reference to cgroup_ns into cgroup_fs_context
  cgroup1_get_tree(): separate "get cgroup_root to use" into a separate helper
  cgroup_do_mount(): massage calling conventions
  cgroup: stash cgroup_root reference into cgroup_fs_context
  cgroup2: switch to option-by-option parsing
  cgroup1: switch to option-by-option parsing
  cgroup: take options parsing into ->parse_monolithic()
  cgroup: fold cgroup1_mount() into cgroup1_get_tree()
  cgroup: start switching to fs_context
  ipc: Convert mqueue fs to fs_context
  proc: Add fs_context support to procfs
  ...
2019-03-12 14:08:19 -07:00
Linus Torvalds
c3665a6be5 Merge branch 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security
Pull integrity updates from James Morris:
 "Mimi Zohar says:

   'Linux 5.0 introduced the platform keyring to allow verifying the IMA
    kexec kernel image signature using the pre-boot keys. This pull
    request similarly makes keys on the platform keyring accessible for
    verifying the PE kernel image signature.

    Also included in this pull request is a new IMA hook that tags tmp
    files, in policy, indicating the file hash needs to be calculated.
    The remaining patches are cleanup'"

* 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security:
  evm: Use defined constant for UUID representation
  ima: define ima_post_create_tmpfile() hook and add missing call
  evm: remove set but not used variable 'xattr'
  encrypted-keys: fix Opt_err/Opt_error = -1
  kexec, KEYS: Make use of platform keyring for signature verify
  integrity, KEYS: add a reference to platform keyring
2019-03-10 17:32:04 -07:00
Linus Torvalds
b5dd0c658c Merge branch 'akpm' (patches from Andrew)
Merge more updates from Andrew Morton:

 - some of the rest of MM

 - various misc things

 - dynamic-debug updates

 - checkpatch

 - some epoll speedups

 - autofs

 - rapidio

 - lib/, lib/lzo/ updates

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (83 commits)
  samples/mic/mpssd/mpssd.h: remove duplicate header
  kernel/fork.c: remove duplicated include
  include/linux/relay.h: fix percpu annotation in struct rchan
  arch/nios2/mm/fault.c: remove duplicate include
  unicore32: stop printing the virtual memory layout
  MAINTAINERS: fix GTA02 entry and mark as orphan
  mm: create the new vm_fault_t type
  arm, s390, unicore32: remove oneliner wrappers for memblock_alloc()
  arch: simplify several early memory allocations
  openrisc: simplify pte_alloc_one_kernel()
  sh: prefer memblock APIs returning virtual address
  microblaze: prefer memblock API returning virtual address
  powerpc: prefer memblock APIs returning virtual address
  lib/lzo: separate lzo-rle from lzo
  lib/lzo: implement run-length encoding
  lib/lzo: fast 8-byte copy on arm64
  lib/lzo: 64-bit CTZ on arm64
  lib/lzo: tidy-up ifdefs
  ipc/sem.c: replace kvmalloc/memset with kvzalloc and use struct_size
  ipc: annotate implicit fall through
  ...
2019-03-07 19:25:37 -08:00
Rasmus Villemoes
f1fffbd447 linux/fs.h: move member alignment check next to definition of struct filename
Instead of doing this compile-time check in some slightly arbitrary user
of struct filename, put it next to the definition.

Link: http://lkml.kernel.org/r/20190208203015.29702-3-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-03-07 18:31:59 -08:00
David Howells
31d921c7fb vfs: Add configuration parser helpers
Because the new API passes in key,value parameters, match_token() cannot be
used with it.  Instead, provide three new helpers to aid with parsing:

 (1) fs_parse().  This takes a parameter and a simple static description of
     all the parameters and maps the key name to an ID.  It returns 1 on a
     match, 0 on no match if unknowns should be ignored and some other
     negative error code on a parse error.

     The parameter description includes a list of key names to IDs, desired
     parameter types and a list of enumeration name -> ID mappings.

     [!] Note that for the moment I've required that the key->ID mapping
     array is expected to be sorted and unterminated.  The size of the
     array is noted in the fsconfig_parser struct.  This allows me to use
     bsearch(), but I'm not sure any performance gain is worth the hassle
     of requiring people to keep the array sorted.

     The parameter type array is sized according to the number of parameter
     IDs and is indexed directly.  The optional enum mapping array is an
     unterminated, unsorted list and the size goes into the fsconfig_parser
     struct.

     The function can do some additional things:

	(a) If it's not ambiguous and no value is given, the prefix "no" on
	    a key name is permitted to indicate that the parameter should
	    be considered negatory.

	(b) If the desired type is a single simple integer, it will perform
	    an appropriate conversion and store the result in a union in
	    the parse result.

	(c) If the desired type is an enumeration, {key ID, name} will be
	    looked up in the enumeration list and the matching value will
	    be stored in the parse result union.

	(d) Optionally generate an error if the key is unrecognised.

     This is called something like:

	enum rdt_param {
		Opt_cdp,
		Opt_cdpl2,
		Opt_mba_mpbs,
		nr__rdt_params
	};

	const struct fs_parameter_spec rdt_param_specs[nr__rdt_params] = {
		[Opt_cdp]	= { fs_param_is_bool },
		[Opt_cdpl2]	= { fs_param_is_bool },
		[Opt_mba_mpbs]	= { fs_param_is_bool },
	};

	const const char *const rdt_param_keys[nr__rdt_params] = {
		[Opt_cdp]	= "cdp",
		[Opt_cdpl2]	= "cdpl2",
		[Opt_mba_mpbs]	= "mba_mbps",
	};

	const struct fs_parameter_description rdt_parser = {
		.name		= "rdt",
		.nr_params	= nr__rdt_params,
		.keys		= rdt_param_keys,
		.specs		= rdt_param_specs,
		.no_source	= true,
	};

	int rdt_parse_param(struct fs_context *fc,
			    struct fs_parameter *param)
	{
		struct fs_parse_result parse;
		struct rdt_fs_context *ctx = rdt_fc2context(fc);
		int ret;

		ret = fs_parse(fc, &rdt_parser, param, &parse);
		if (ret < 0)
			return ret;

		switch (parse.key) {
		case Opt_cdp:
			ctx->enable_cdpl3 = true;
			return 0;
		case Opt_cdpl2:
			ctx->enable_cdpl2 = true;
			return 0;
		case Opt_mba_mpbs:
			ctx->enable_mba_mbps = true;
			return 0;
		}

		return -EINVAL;
	}

 (2) fs_lookup_param().  This takes a { dirfd, path, LOOKUP_EMPTY? } or
     string value and performs an appropriate path lookup to convert it
     into a path object, which it will then return.

     If the desired type was a blockdev, the type of the looked up inode
     will be checked to make sure it is one.

     This can be used like:

	enum foo_param {
		Opt_source,
		nr__foo_params
	};

	const struct fs_parameter_spec foo_param_specs[nr__foo_params] = {
		[Opt_source]	= { fs_param_is_blockdev },
	};

	const char *char foo_param_keys[nr__foo_params] = {
		[Opt_source]	= "source",
	};

	const struct constant_table foo_param_alt_keys[] = {
		{ "device",	Opt_source },
	};

	const struct fs_parameter_description foo_parser = {
		.name		= "foo",
		.nr_params	= nr__foo_params,
		.nr_alt_keys	= ARRAY_SIZE(foo_param_alt_keys),
		.keys		= foo_param_keys,
		.alt_keys	= foo_param_alt_keys,
		.specs		= foo_param_specs,
	};

	int foo_parse_param(struct fs_context *fc,
			    struct fs_parameter *param)
	{
		struct fs_parse_result parse;
		struct foo_fs_context *ctx = foo_fc2context(fc);
		int ret;

		ret = fs_parse(fc, &foo_parser, param, &parse);
		if (ret < 0)
			return ret;

		switch (parse.key) {
		case Opt_source:
			return fs_lookup_param(fc, &foo_parser, param,
					       &parse, &ctx->source);
		default:
			return -EINVAL;
		}
	}

 (3) lookup_constant().  This takes a table of named constants and looks up
     the given name within it.  The table is expected to be sorted such
     that bsearch() be used upon it.

     Possibly I should require the table be terminated and just use a
     for-loop to scan it instead of using bsearch() to reduce hassle.

     Tables look something like:

	static const struct constant_table bool_names[] = {
		{ "0",		false },
		{ "1",		true },
		{ "false",	false },
		{ "no",		false },
		{ "true",	true },
		{ "yes",	true },
	};

     and a lookup is done with something like:

	b = lookup_constant(bool_names, param->string, -1);

Additionally, optional validation routines for the parameter description
are provided that can be enabled at compile time.  A later patch will
invoke these when a filesystem is registered.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2019-02-28 03:28:53 -05:00
Mimi Zohar
fdb2410f77 ima: define ima_post_create_tmpfile() hook and add missing call
If tmpfiles can be made persistent, then newly created tmpfiles need to
be treated like any other new files in policy.

This patch indicates which newly created tmpfiles are in policy, causing
the file hash to be calculated on __fput().

Reported-by: Ignaz Forster <ignaz.forster@gmx.de>
[rgoldwyn@suse.com: Call ima_post_create_tmpfile() in vfs_tmpfile() as
opposed to do_tmpfile(). This will help the case for overlayfs where
copy_up is denied while overwriting a file.]
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
2019-02-04 17:36:01 -05:00
Richard Guy Briggs
57d4657716 audit: ignore fcaps on umount
Don't fetch fcaps when umount2 is called to avoid a process hang while
it waits for the missing resource to (possibly never) re-appear.

Note the comment above user_path_mountpoint_at():
 * A umount is a special case for path walking. We're not actually interested
 * in the inode in this situation, and ESTALE errors can be a problem.  We
 * simply want track down the dentry and vfsmount attached at the mountpoint
 * and avoid revalidating the last component.

This can happen on ceph, cifs, 9p, lustre, fuse (gluster) or NFS.

Please see the github issue tracker
https://github.com/linux-audit/audit-kernel/issues/100

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
[PM: merge fuzz in audit_log_fcaps()]
Signed-off-by: Paul Moore <paul@paul-moore.com>
2019-01-30 20:51:47 -05:00
Christian Brauner
94f82008ce Revert "vfs: Allow userns root to call mknod on owned filesystems."
This reverts commit 55956b59df.

commit 55956b59df ("vfs: Allow userns root to call mknod on owned filesystems.")
enabled mknod() in user namespaces for userns root if CAP_MKNOD is
available. However, these device nodes are useless since any filesystem
mounted from a non-initial user namespace will set the SB_I_NODEV flag on
the filesystem. Now, when a device node s created in a non-initial user
namespace a call to open() on said device node will fail due to:

bool may_open_dev(const struct path *path)
{
        return !(path->mnt->mnt_flags & MNT_NODEV) &&
                !(path->mnt->mnt_sb->s_iflags & SB_I_NODEV);
}

The problem with this is that as of the aforementioned commit mknod()
creates partially functional device nodes in non-initial user namespaces.
In particular, it has the consequence that as of the aforementioned commit
open() will be more privileged with respect to device nodes than mknod().
Before it was the other way around. Specifically, if mknod() succeeded
then it was transparent for any userspace application that a fatal error
must have occured when open() failed.

All of this breaks multiple userspace workloads and a widespread assumption
about how to handle mknod(). Basically, all container runtimes and systemd
live by the slogan "ask for forgiveness not permission" when running user
namespace workloads. For mknod() the assumption is that if the syscall
succeeds the device nodes are useable irrespective of whether it succeeds
in a non-initial user namespace or not. This logic was chosen explicitly
to allow for the glorious day when mknod() will actually be able to create
fully functional device nodes in user namespaces.
A specific problem people are already running into when running 4.18 rc
kernels are failing systemd services. For any distro that is run in a
container systemd services started with the PrivateDevices= property set
will fail to start since the device nodes in question cannot be
opened (cf. the arguments in [1]).

Full disclosure, Seth made the very sound argument that it is already
possible to end up with partially functional device nodes. Any filesystem
mounted with MS_NODEV set will allow mknod() to succeed but will not allow
open() to succeed. The difference to the case here is that the MS_NODEV
case is transparent to userspace since it is an explicitly set mount option
while the SB_I_NODEV case is an implicit property enforced by the kernel
and hence opaque to userspace.

[1]: https://github.com/systemd/systemd/pull/9483

Signed-off-by: Christian Brauner <christian@brauner.io>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Seth Forshee <seth.forshee@canonical.com>
Cc: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-12-22 14:18:34 -08:00
Salvatore Mesoraca
30aba6656f namei: allow restricted O_CREAT of FIFOs and regular files
Disallows open of FIFOs or regular files not owned by the user in world
writable sticky directories, unless the owner is the same as that of the
directory or the file is opened without the O_CREAT flag.  The purpose
is to make data spoofing attacks harder.  This protection can be turned
on and off separately for FIFOs and regular files via sysctl, just like
the symlinks/hardlinks protection.  This patch is based on Openwall's
"HARDEN_FIFO" feature by Solar Designer.

This is a brief list of old vulnerabilities that could have been prevented
by this feature, some of them even allow for privilege escalation:

CVE-2000-1134
CVE-2007-3852
CVE-2008-0525
CVE-2009-0416
CVE-2011-4834
CVE-2015-1838
CVE-2015-7442
CVE-2016-7489

This list is not meant to be complete.  It's difficult to track down all
vulnerabilities of this kind because they were often reported without any
mention of this particular attack vector.  In fact, before
hardlinks/symlinks restrictions, fifos/regular files weren't the favorite
vehicle to exploit them.

[s.mesoraca16@gmail.com: fix bug reported by Dan Carpenter]
  Link: https://lkml.kernel.org/r/20180426081456.GA7060@mwanda
  Link: http://lkml.kernel.org/r/1524829819-11275-1-git-send-email-s.mesoraca16@gmail.com
[keescook@chromium.org: drop pr_warn_ratelimited() in favor of audit changes in the future]
[keescook@chromium.org: adjust commit subjet]
Link: http://lkml.kernel.org/r/20180416175918.GA13494@beast
Signed-off-by: Salvatore Mesoraca <s.mesoraca16@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Suggested-by: Solar Designer <solar@openwall.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-08-23 18:48:43 -07:00