Many file systems that implement the show_options hook fail to correctly
escape their output which could lead to unescaped characters (e.g. new
lines) leaking into /proc/mounts and /proc/[pid]/mountinfo files. This
could lead to confusion, spoofed entries (resulting in things like
systemd issuing false d-bus "mount" notifications), and who knows what
else. This looks like it would only be the root user stepping on
themselves, but it's possible weird things could happen in containers or
in other situations with delegated mount privileges.
Here's an example using overlay with setuid fusermount trusting the
contents of /proc/mounts (via the /etc/mtab symlink). Imagine the use
of "sudo" is something more sneaky:
$ BASE="ovl"
$ MNT="$BASE/mnt"
$ LOW="$BASE/lower"
$ UP="$BASE/upper"
$ WORK="$BASE/work/ 0 0
none /proc fuse.pwn user_id=1000"
$ mkdir -p "$LOW" "$UP" "$WORK"
$ sudo mount -t overlay -o "lowerdir=$LOW,upperdir=$UP,workdir=$WORK" none /mnt
$ cat /proc/mounts
none /root/ovl/mnt overlay rw,relatime,lowerdir=ovl/lower,upperdir=ovl/upper,workdir=ovl/work/ 0 0
none /proc fuse.pwn user_id=1000 0 0
$ fusermount -u /proc
$ cat /proc/mounts
cat: /proc/mounts: No such file or directory
This fixes the problem by adding new seq_show_option and
seq_show_option_n helpers, and updating the vulnerable show_option
handlers to use them as needed. Some, like SELinux, need to be open
coded due to unusual existing escape mechanisms.
[akpm@linux-foundation.org: add lost chunk, per Kees]
[keescook@chromium.org: seq_show_option should be using const parameters]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Jan Kara <jack@suse.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Cc: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull more vfs updates from Al Viro:
"Assorted VFS fixes and related cleanups (IMO the most interesting in
that part are f_path-related things and Eric's descriptor-related
stuff). UFS regression fixes (it got broken last cycle). 9P fixes.
fs-cache series, DAX patches, Jan's file_remove_suid() work"
[ I'd say this is much more than "fixes and related cleanups". The
file_table locking rule change by Eric Dumazet is a rather big and
fundamental update even if the patch isn't huge. - Linus ]
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (49 commits)
9p: cope with bogus responses from server in p9_client_{read,write}
p9_client_write(): avoid double p9_free_req()
9p: forgetting to cancel request on interrupted zero-copy RPC
dax: bdev_direct_access() may sleep
block: Add support for DAX reads/writes to block devices
dax: Use copy_from_iter_nocache
dax: Add block size note to documentation
fs/file.c: __fget() and dup2() atomicity rules
fs/file.c: don't acquire files->file_lock in fd_install()
fs:super:get_anon_bdev: fix race condition could cause dev exceed its upper limitation
vfs: avoid creation of inode number 0 in get_next_ino
namei: make set_root_rcu() return void
make simple_positive() public
ufs: use dir_pages instead of ufs_dir_pages()
pagemap.h: move dir_pages() over there
remove the pointless include of lglock.h
fs: cleanup slight list_entry abuse
xfs: Correctly lock inode when removing suid and file capabilities
fs: Call security_ops->inode_killpriv on truncate
fs: Provide function telling whether file_remove_privs() will do anything
...
Allow filesystems with .d_revalidate as lower layer(s), but not as upper
layer.
For local filesystems the rule was that modifications on the layers
directly while being part of the overlay results in undefined behavior.
This can easily be extended to distributed filesystems: we assume the tree
used as lower layer is static, which means ->d_revalidate() should always
return "1". If that is not the case, return -ESTALE, don't try to work
around the modification.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
NFS and other distributed filesystems may place automount points in the
tree. Previoulsy overlayfs refused to mount such filesystems types (based
on the existence of the .d_automount callback), even if the actual export
didn't have any automount points.
It cannot be determined in advance whether the filesystem has automount
points or not. The solution is to allow fs with .d_automount but refuse to
traverse any automount points encountered.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Make file->f_path always point to the overlay dentry so that the path in
/proc/pid/fd is correct and to ensure that label-based LSMs have access to the
overlay as well as the underlay (path-based LSMs probably don't need it).
Using my union testsuite to set things up, before the patch I see:
[root@andromeda union-testsuite]# bash 5</mnt/a/foo107
[root@andromeda union-testsuite]# ls -l /proc/$$/fd/
...
lr-x------. 1 root root 64 Jun 5 14:38 5 -> /a/foo107
[root@andromeda union-testsuite]# stat /mnt/a/foo107
...
Device: 23h/35d Inode: 13381 Links: 1
...
[root@andromeda union-testsuite]# stat -L /proc/$$/fd/5
...
Device: 23h/35d Inode: 13381 Links: 1
...
After the patch:
[root@andromeda union-testsuite]# bash 5</mnt/a/foo107
[root@andromeda union-testsuite]# ls -l /proc/$$/fd/
...
lr-x------. 1 root root 64 Jun 5 14:22 5 -> /mnt/a/foo107
[root@andromeda union-testsuite]# stat /mnt/a/foo107
...
Device: 23h/35d Inode: 40346 Links: 1
...
[root@andromeda union-testsuite]# stat -L /proc/$$/fd/5
...
Device: 23h/35d Inode: 40346 Links: 1
...
Note the change in where /proc/$$/fd/5 points to in the ls command. It was
pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107
(which is correct).
The inode accessed, however, is the lower layer. The union layer is on device
25h/37d and the upper layer on 24h/36d.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
OpenWRT folks reported that overlayfs fails to mount if upper fs is full,
because workdir can't be created. Wordir creation can fail for various
other reasons too.
There's no reason that the mount itself should fail, overlayfs can work
fine without a workdir, as long as the overlay isn't modified.
So mount it read-only and don't allow remounting read-write.
Add a couple of WARN_ON()s for the impossible case of workdir being used
despite being read-only.
Reported-by: Bastian Bittorf <bittorf@bluebottle.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: <stable@vger.kernel.org> # v3.18+
After importing multi-lower layer support, users could mount a r/o
partition as the left most lowerdir instead of using it as upperdir.
And a r/o upperdir may cause an error like
overlayfs: failed to create directory ./workdir/work
during mount.
This patch check the *s_flags* of upper fs and return an error if
it is a r/o partition. The checking of *upper_mnt->mnt_sb->s_flags*
can be removed now.
This patch also remove
/* FIXME: workdir is not needed for a R/O mount */
from ovl_fill_super() because:
1) for upper fs r/o case
Setting a r/o partition as upper is prevented, no need to care about
workdir in this case.
2) for "mount overlay -o ro" with a r/w upper fs case
Users could remount overlayfs to r/w in this case, so workdir should
not be omitted.
Signed-off-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Recently multi-lower layer mount support allow upperdir and workdir
to be omitted, then cause overlayfs can be mount with only one
lowerdir directory. This action make no sense and have potential risk.
This patch check the total number of lower directories to prevent
mounting overlayfs with only one directory.
Also, an error message is added to indicate lower directories exceed
OVL_MAX_STACK limit.
Signed-off-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Overlayfs should print an error message if an incorrect mount option
is caught like other filesystems.
After this patch, improper option input could be clearly known.
Reported-by: Fabian Sturm <fabian.sturm@aduu.de>
Signed-off-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Overlayfs should be mounted read-only when upper-fs is read-only or nonexistent.
But now it can be remounted read-write and this can cause kernel panic.
So we should prevent read-write remount when the above situation happens.
Signed-off-by: Seunghun Lee <waydi1@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Current multi-layer support overlayfs has a regression in
.lookup(). If there is a directory in upperdir and a regular
file has same name in lowerdir in a merged directory, lower
file is hidden and upper directory is set to opaque in former
case. But it is changed in present code.
In lowerdir lookup path, if a found inode is not directory,
the type checking of previous inode is missing. This inode
will be copied to the lowerstack of ovl_entry directly.
That will lead to several wrong conditions, for example,
the reading of the directory in upperdir may return an error
like:
ls: reading directory .: Not a directory
This patch makes the lowerdir lookup path check the opaque
for non-directory file too.
Signed-off-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
The function ovl_fill_super() in recently multi-layer support
version will incorrectly return 0 at error handling path and
then cause kernel panic.
This failure can be reproduced by mounting a overlayfs with
upperdir and workdir in different mounts.
And also, If the memory allocation of *lower_mnt* fail, this
function may return an zero either.
This patch fix this problem by setting *err* to proper error
number before jumping to error handling path.
Signed-off-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
This patch adds two macros:
OVL_XATTR_PRE_NAME and OVL_XATTR_PRE_LEN
to present ovl_xattr name prefix and its length. Also, a
new macro OVL_XATTR_OPAQUE is introduced to replace old
*ovl_opaque_xattr*.
Fix the length of "trusted.overlay." to *16*.
Signed-off-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Allow "lowerdir=" option to contain multiple lower directories separated by
a colon (e.g. "lowerdir=/bin:/usr/bin"). Colon characters in filenames can
be escaped with a backslash.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Make "upperdir=" mount option optional. If "upperdir=" is not given, then
the "workdir=" option is also optional (and ignored if given).
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Move allocation of root entry above to where it's needed.
Move initializations related to upperdir and workdir near each other.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
"Suppose you have in one of the lower layers a filesystem with
->lookup()-enforced upper limit on name length. Pretty much every local fs
has one, but... they are not all equal. 255 characters is the common upper
limit, but e.g. jffs2 stops at 254, minixfs upper limit is somewhere from
14 to 60, depending upon version, etc. You are doing a lookup for
something that is present in upper layer, but happens to be too long for
one of the lower layers. Too bad - ENAMETOOLONG for you..."
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Not checking whiteouts on lowest layer was an optimization (there's nothing
to white out there), but it could result in inconsitent behavior when a
layer previously used as upper/middle is later used as lowest.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
If multiple lower layers exist, merge them as well in readdir according to
the same rules as merging upper with lower. I.e. take whiteouts and opaque
directories into account on all but the lowers layer.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Add helper to iterate through all the layers, starting from the upper layer
(if exists) and continuing down through the lower layers.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Add multiple lower layers to 'struct ovl_fs' and 'struct ovl_entry'.
ovl_entry will have an array of paths, instead of just the dentry. This
allows a compact array containing just the layers which exist at current
point in the tree (which is expected to be a small number for the majority
of dentries).
The number of layers is not limited by this infrastructure.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Some distributions carry an "old" format of overlayfs while mainline has a
"new" format.
The distros will possibly want to keep the old overlayfs alongside the new
for compatibility reasons.
To make it possible to differentiate the two versions change the name of
the new one from "overlayfs" to "overlay".
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reported-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: Andy Whitcroft <apw@canonical.com>
Add a simple read-only counter to super_block that indicates how deep this
is in the stack of filesystems. Previously ecryptfs was the only stackable
filesystem and it explicitly disallowed multiple layers of itself.
Overlayfs, however, can be stacked recursively and also may be stacked
on top of ecryptfs or vice versa.
To limit the kernel stack usage we must limit the depth of the
filesystem stack. Initially the limit is set to 2.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
This is useful because of the stacking nature of overlayfs. Users like to
find out (via /proc/mounts) which lower/upper directory were used at mount
time.
AV: even failing ovl_parse_opt() could've done some kstrdup()
AV: failure of ovl_alloc_entry() should end up with ENOMEM, not EINVAL
Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Add support for statfs to the overlayfs filesystem. As the upper layer
is the target of all write operations assume that the space in that
filesystem is the space in the overlayfs. There will be some inaccuracy as
overwriting a file will copy it up and consume space we were not expecting,
but it is better than nothing.
Use the upper layer dentry and mount from the overlayfs root inode,
passing the statfs call to that filesystem.
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Overlayfs allows one, usually read-write, directory tree to be
overlaid onto another, read-only directory tree. All modifications
go to the upper, writable layer.
This type of mechanism is most often used for live CDs but there's a
wide variety of other uses.
The implementation differs from other "union filesystem"
implementations in that after a file is opened all operations go
directly to the underlying, lower or upper, filesystems. This
simplifies the implementation and allows native performance in these
cases.
The dentry tree is duplicated from the underlying filesystems, this
enables fast cached lookups without adding special support into the
VFS. This uses slightly more memory than union mounts, but dentries
are relatively small.
Currently inodes are duplicated as well, but it is a possible
optimization to share inodes for non-directories.
Opening non directories results in the open forwarded to the
underlying filesystem. This makes the behavior very similar to union
mounts (with the same limitations vs. fchmod/fchown on O_RDONLY file
descriptors).
Usage:
mount -t overlayfs overlayfs -olowerdir=/lower,upperdir=/upper/upper,workdir=/upper/work /overlay
The following cotributions have been folded into this patch:
Neil Brown <neilb@suse.de>:
- minimal remount support
- use correct seek function for directories
- initialise is_real before use
- rename ovl_fill_cache to ovl_dir_read
Felix Fietkau <nbd@openwrt.org>:
- fix a deadlock in ovl_dir_read_merged
- fix a deadlock in ovl_remove_whiteouts
Erez Zadok <ezk@fsl.cs.sunysb.edu>
- fix cleanup after WARN_ON
Sedat Dilek <sedat.dilek@googlemail.com>
- fix up permission to confirm to new API
Robin Dong <hao.bigrat@gmail.com>
- fix possible leak in ovl_new_inode
- create new inode in ovl_link
Andy Whitcroft <apw@canonical.com>
- switch to __inode_permission()
- copy up i_uid/i_gid from the underlying inode
AV:
- ovl_copy_up_locked() - dput(ERR_PTR(...)) on two failure exits
- ovl_clear_empty() - one failure exit forgetting to do unlock_rename(),
lack of check for udir being the parent of upper, dropping and regaining
the lock on udir (which would require _another_ check for parent being
right).
- bogus d_drop() in copyup and rename [fix from your mail]
- copyup/remove and copyup/rename races [fix from your mail]
- ovl_dir_fsync() leaving ERR_PTR() in ->realfile
- ovl_entry_free() is pointless - it's just a kfree_rcu()
- fold ovl_do_lookup() into ovl_lookup()
- manually assigning ->d_op is wrong. Just use ->s_d_op.
[patches picked from Miklos]:
* copyup/remove and copyup/rename races
* bogus d_drop() in copyup and rename
Also thanks to the following people for testing and reporting bugs:
Jordi Pujol <jordipujolp@gmail.com>
Andy Whitcroft <apw@canonical.com>
Michal Suchanek <hramrach@centrum.cz>
Felix Fietkau <nbd@openwrt.org>
Erez Zadok <ezk@fsl.cs.sunysb.edu>
Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
