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3a6bdda0b5
linux/fs
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Axel Rasmussen 2d5de004e0 userfaultfd: add /dev/userfaultfd for fine grained access control 
Historically, it has been shown that intercepting kernel faults with
userfaultfd (thereby forcing the kernel to wait for an arbitrary amount of
time) can be exploited, or at least can make some kinds of exploits
easier.  So, in 37cd0575b8 "userfaultfd: add UFFD_USER_MODE_ONLY" we
changed things so, in order for kernel faults to be handled by
userfaultfd, either the process needs CAP_SYS_PTRACE, or this sysctl must
be configured so that any unprivileged user can do it.

In a typical implementation of a hypervisor with live migration (take
QEMU/KVM as one such example), we do indeed need to be able to handle
kernel faults.  But, both options above are less than ideal:

- Toggling the sysctl increases attack surface by allowing any
  unprivileged user to do it.

- Granting the live migration process CAP_SYS_PTRACE gives it this
  ability, but *also* the ability to "observe and control the
  execution of another process [...], and examine and change [its]
  memory and registers" (from ptrace(2)). This isn't something we need
  or want to be able to do, so granting this permission violates the
  "principle of least privilege".

This is all a long winded way to say: we want a more fine-grained way to
grant access to userfaultfd, without granting other additional permissions
at the same time.

To achieve this, add a /dev/userfaultfd misc device.  This device provides
an alternative to the userfaultfd(2) syscall for the creation of new
userfaultfds.  The idea is, any userfaultfds created this way will be able
to handle kernel faults, without the caller having any special
capabilities.  Access to this mechanism is instead restricted using e.g. 
standard filesystem permissions.

[axelrasmussen@google.com: Handle misc_register() failure properly]
  Link: https://lkml.kernel.org/r/20220819205201.658693-3-axelrasmussen@google.com
Link: https://lkml.kernel.org/r/20220808175614.3885028-3-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Nadav Amit <namit@vmware.com>
Acked-by: Peter Xu <peterx@redhat.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dmitry V. Levin <ldv@altlinux.org>
Cc: Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zhang Yi <yi.zhang@huawei.com>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-09-11 20:25:48 -07:00
..
9p 9p: Fix some kernel-doc comments 2022-07-02 18:52:21 +09:00
adfs fs: Convert block_read_full_page() to block_read_full_folio() 2022-05-09 16:21:44 -04:00
affs affs: use memcpy_to_page and remove replace kmap_atomic() 2022-08-01 19:53:31 +02:00
afs afs: Enable multipage folio support 2022-08-13 17:20:51 -07:00
autofs autofs: remove unused ino field inode 2022-07-17 17:31:42 -07:00
befs befs: Convert befs_symlink_read_folio() to use a folio 2022-08-02 12:34:03 -04:00
bfs fs: Convert block_read_full_page() to block_read_full_folio() 2022-05-09 16:21:44 -04:00
btrfs for-6.0-rc3-tag 2022-08-28 10:44:04 -07:00
cachefiles cachefiles: narrow the scope of flushed requests when releasing fd 2022-07-05 16:12:21 +01:00
ceph We have a good pile of various fixes and cleanups from Xiubo, Jeff, 2022-08-11 12:41:07 -07:00
cifs cifs: Add helper function to check smb1+ server 2022-08-24 22:30:09 -05:00
coda coda: Convert coda_symlink_filler() to use a folio 2022-08-02 12:34:03 -04:00
configfs configfs: fix a race in configfs_{,un}register_subsystem() 2022-02-22 18:30:28 +01:00
cramfs cramfs: read_mapping_page() is synchronous 2022-08-02 12:34:02 -04:00
crypto We have a good pile of various fixes and cleanups from Xiubo, Jeff, 2022-08-11 12:41:07 -07:00
debugfs debugfs: Document that debugfs_create functions need not be error checked 2022-02-25 11:56:13 +01:00
devpts fsnotify: fix fsnotify hooks in pseudo filesystems 2022-01-24 14:17:02 +01:00
dlm fs: dlm: move kref_put assert for lkb structs 2022-08-01 09:31:46 -05:00
ecryptfs ecryptfs: Convert ecryptfs to read_folio 2022-05-09 16:21:45 -04:00
efivarfs efi: vars: Move efivar caching layer into efivarfs 2022-06-24 20:40:19 +02:00
efs efs: Convert efs symlinks to read_folio 2022-05-09 16:21:45 -04:00
erofs - The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe 2022-08-05 16:32:45 -07:00
exfat exfat: Drop superfluous new line for error messages 2022-08-01 10:14:07 +09:00
exportfs exportfs: support idmapped mounts 2022-04-28 16:31:10 +02:00
ext2 - The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe 2022-08-05 16:32:45 -07:00
ext4 - The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe 2022-08-05 16:32:45 -07:00
f2fs f2fs-for-6.0 2022-08-08 11:18:31 -07:00
fat Updates to various subsystems which I help look after. lib, ocfs2, 2022-08-07 10:03:24 -07:00
freevxfs freevxfs: Convert vxfs_immed_read_folio() to use a folio 2022-08-02 12:34:03 -04:00
fscache fscache: add tracepoint when failing cookie 2022-08-09 14:13:59 +01:00
fuse iov_iter stuff, part 2, rebased 2022-08-08 20:04:35 -07:00
gfs2 New code for 6.0: 2022-08-11 13:11:49 -07:00
hfs hfs: Remove check for PageError 2022-06-29 08:51:06 -04:00
hfsplus Folio changes for 6.0 2022-08-03 10:35:43 -07:00
hostfs hostfs: Handle page write errors correctly 2022-08-02 12:34:02 -04:00
hpfs hpfs: Convert symlinks to read_folio 2022-05-09 16:21:45 -04:00
hugetlbfs iov_iter stuff, part 2, rebased 2022-08-08 20:04:35 -07:00
iomap New code for 6.0: 2022-08-11 13:11:49 -07:00
isofs fs/buffer: Combine two submit_bh() and ll_rw_block() arguments 2022-07-14 12:14:32 -06:00
jbd2 - The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe 2022-08-05 16:32:45 -07:00
jffs2 This pull request contains fixes for JFFS2, UBI and UBIFS 2022-06-03 14:42:24 -07:00
jfs Folio changes for 6.0 2022-08-03 10:35:43 -07:00
kernfs kernfs: Fix typo 'the the' in comment 2022-07-28 10:57:25 +02:00
ksmbd ksmbd: don't remove dos attribute xattr on O_TRUNC open 2022-08-15 21:07:01 -05:00
lockd lockd: detect and reject lock arguments that overflow 2022-08-04 10:28:48 -04:00
minix fs: Convert block_read_full_page() to block_read_full_folio() 2022-05-09 16:21:44 -04:00
netfs netfs: do not unlock and put the folio twice 2022-07-14 10:10:12 +02:00
nfs NFS client bugfixes for Linux 6.0 2022-08-22 11:40:01 -07:00
nfs_common
nfsd NFSD 6.0 Release Notes 2022-08-09 14:56:49 -07:00
nilfs2 Folio changes for 6.0 2022-08-03 10:35:43 -07:00
nls
notify fsnotify: Fix comment typo 2022-07-26 13:38:47 +02:00
ntfs Folio changes for 6.0 2022-08-03 10:35:43 -07:00
ntfs3 fs.idmapped.fixes.v6.0-rc3 2022-08-22 11:33:02 -07:00
ocfs2 ocfs2: fix freeing uninitialized resource on ocfs2_dlm_shutdown 2022-08-28 14:02:45 -07:00
omfs fs: Convert block_read_full_page() to block_read_full_folio() 2022-05-09 16:21:44 -04:00
openpromfs fs: allocate inode by using alloc_inode_sb() 2022-03-22 15:57:03 -07:00
orangefs orangefs: Remove test for folio error 2022-06-29 08:51:07 -04:00
overlayfs acl: handle idmapped mounts for idmapped filesystems 2022-08-17 11:23:31 +02:00
proc mm/thp: add flag to enforce sysfs THP in hugepage_vma_check() 2022-09-11 20:25:45 -07:00
pstore EFI updates for v5.20 2022-08-03 14:38:02 -07:00
qnx4 fs: Convert block_read_full_page() to block_read_full_folio() 2022-05-09 16:21:44 -04:00
qnx6 fs: Convert mpage_readpage to mpage_read_folio 2022-05-09 16:21:44 -04:00
quota - The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe 2022-08-05 16:32:45 -07:00
ramfs
reiserfs Folio changes for 6.0 2022-08-03 10:35:43 -07:00
romfs romfs: Convert romfs to read_folio 2022-05-09 16:21:46 -04:00
smbfs_common Add various fsctl structs 2022-05-23 20:24:12 -05:00
squashfs squashfs: don't call kmalloc in decompressors 2022-08-28 14:02:45 -07:00
sysfs kobject: kobj_type: remove default_attrs 2022-04-05 15:39:19 +02:00
sysv Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
tracefs tracefs: Fix syntax errors in comments 2022-06-17 19:01:28 -04:00
ubifs - The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe 2022-08-05 16:32:45 -07:00
udf fs/buffer: Combine two submit_bh() and ll_rw_block() arguments 2022-07-14 12:14:32 -06:00
ufs Folio changes for 6.0 2022-08-03 10:35:43 -07:00
unicode kbuild: unify cmd_copy and cmd_shipped 2022-02-14 10:37:32 +09:00
vboxsf vboxsf: Convert vboxsf to read_folio 2022-05-09 16:21:46 -04:00
verity fs-verity: mention btrfs support 2022-07-15 23:42:30 -07:00
xfs New code for 6.0: 2022-08-13 13:50:11 -07:00
zonefs New code for 6.0: 2022-08-11 13:11:49 -07:00
aio.c iov_iter work, part 1 - isolated cleanups and optimizations. 2022-08-03 13:50:22 -07:00
anon_inodes.c
attr.c vfs: Check the truncate maximum size in inode_newsize_ok() 2022-08-08 10:39:29 -07:00
bad_inode.c
binfmt_aout.c
binfmt_elf_fdpic.c coredump: Snapshot the vmas in do_coredump 2022-03-08 12:55:29 -06:00
binfmt_elf_test.c binfmt_elf: Introduce KUnit test 2022-03-03 20:38:56 -08:00
binfmt_elf.c revert "fs/binfmt_elf: use PT_LOAD p_align values for static PIE" 2022-04-15 14:49:56 -07:00
binfmt_flat.c binfmt_flat: Remove shared library support 2022-04-22 10:57:18 -07:00
binfmt_misc.c Fix regression due to "fs: move binfmt_misc sysctl to its own file" 2022-02-09 09:50:02 -08:00
binfmt_script.c
buffer.c Folio changes for 6.0 2022-08-03 10:35:43 -07:00
char_dev.c
compat_binfmt_elf.c binfmt_elf: Introduce KUnit test 2022-03-03 20:38:56 -08:00
coredump.c fs: do not compare against ->llseek 2022-07-16 09:19:15 -04:00
d_path.c
dax.c - The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe 2022-08-05 16:32:45 -07:00
dcache.c dcache: move the DCACHE_OP_COMPARE case out of the __d_lookup_rcu loop 2022-08-17 14:33:03 -07:00
direct-io.c iov_iter: advancing variants of iov_iter_get_pages{,_alloc}() 2022-08-08 22:37:22 -04:00
drop_caches.c
eventfd.c
eventpoll.c epoll: autoremove wakers even more aggressively 2022-07-17 17:31:40 -07:00
exec.c execve fix for v6.0-rc2 2022-08-19 14:02:24 -07:00
fcntl.c keep iocb_flags() result cached in struct file 2022-06-10 16:10:23 -04:00
fhandle.c
file_table.c iov_iter work, part 1 - isolated cleanups and optimizations. 2022-08-03 13:50:22 -07:00
file.c fix the breakage in close_fd_get_file() calling conventions change 2022-06-05 15:03:03 -04:00
filesystems.c
fs_context.c vfs: fs_context: fix up param length parsing in legacy_parse_param 2022-01-18 09:23:19 +02:00
fs_parser.c fs_parse: allow parameter value to be empty 2021-12-09 14:09:36 -05:00
fs_pin.c
fs_struct.c
fs_types.c
fs-writeback.c writeback: avoid use-after-free after removing device 2022-08-28 14:02:43 -07:00
fsopen.c uninline may_mount() and don't opencode it in fspick(2)/fsopen(2) 2022-05-19 23:25:10 -04:00
init.c
inode.c fs: __file_remove_privs(): restore call to inode_has_no_xattr() 2022-08-18 09:39:33 +02:00
internal.h Cleanups (and one fix) around struct mount handling. 2022-06-04 19:00:05 -07:00
ioctl.c Fixes for 5.18-rc1: 2022-04-01 19:35:56 -07:00
Kconfig mm: hugetlb_vmemmap: introduce the name HVO 2022-08-08 18:06:42 -07:00
Kconfig.binfmt m68knommu: changes for linux 5.19 2022-05-30 10:56:18 -07:00
kernel_read_file.c fs/kernel_read_file: allow to read files up-to ssize_t 2022-06-16 19:58:21 -07:00
libfs.c fs: Convert simple_readpage to simple_read_folio 2022-05-09 16:21:44 -04:00
locks.c locks: Fix dropped call to ->fl_release_private() 2022-08-17 15:08:58 -04:00
Makefile io_uring: move to separate directory 2022-07-24 18:39:10 -06:00
mbcache.c - The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe 2022-08-05 16:32:45 -07:00
mount.h switch try_to_unlazy_next() to __legitimize_mnt() 2022-07-05 16:18:21 -04:00
mpage.c Folio changes for 6.0 2022-08-03 10:35:43 -07:00
namei.c fs.setgid.v6.0 2022-08-09 09:52:28 -07:00
namespace.c fs: require CAP_SYS_ADMIN in target namespace for idmapped mounts 2022-08-17 11:27:11 +02:00
no-block.c
nsfs.c
open.c iov_iter work, part 1 - isolated cleanups and optimizations. 2022-08-03 13:50:22 -07:00
pipe.c Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
pnode.c
pnode.h
posix_acl.c acl: handle idmapped mounts for idmapped filesystems 2022-08-17 11:23:31 +02:00
proc_namespace.c vfs: escape hash as well 2022-06-28 13:58:05 -04:00
read_write.c switch new_sync_{read,write}() to ITER_UBUF 2022-08-08 22:37:15 -04:00
readdir.c
remap_range.c - The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe 2022-08-05 16:32:45 -07:00
select.c select: Fix indefinitely sleeping task in poll_schedule_timeout() 2022-01-11 09:03:05 -08:00
seq_file.c rxrpc: Fix locking issue 2022-05-22 21:03:01 +01:00
signalfd.c Merge branch 'signal-for-v5.17' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2022-01-17 05:49:30 +02:00
splice.c iter_to_pipe(): switch to advancing variant of iov_iter_get_pages() 2022-08-08 22:37:23 -04:00
stack.c
stat.c RISC-V Patches for the 5.19 Merge Window, Part 1 2022-05-31 14:10:54 -07:00
statfs.c
super.c fuse update for 6.0 2022-08-08 11:10:02 -07:00
sync.c riscv: compat: syscall: Add compat_sys_call_table implementation 2022-04-26 13:36:25 -07:00
sysctls.c fs: move namespace sysctls and declare fs base directory 2022-01-22 08:33:36 +02:00
timerfd.c
userfaultfd.c userfaultfd: add /dev/userfaultfd for fine grained access control 2022-09-11 20:25:48 -07:00
utimes.c
xattr.c acl: move idmapped mount fixup into vfs_{g,s}etxattr() 2022-07-15 22:08:59 +02:00