linux-stable.git/fs/file_table.c, branch linux-6.6.y

lsm: add backing_file LSM hooks

2026-07-04T11:42:23+00:00

[ Upstream commit 6af36aeb147a06dea47c49859cd6ca5659aeb987 ]

Stacked filesystems such as overlayfs do not currently provide the
necessary mechanisms for LSMs to properly enforce access controls on the
mmap() and mprotect() operations.  In order to resolve this gap, a LSM
security blob is being added to the backing_file struct and the following
new LSM hooks are being created:

 security_backing_file_alloc()
 security_backing_file_free()
 security_mmap_backing_file()

The first two hooks are to manage the lifecycle of the LSM security blob
in the backing_file struct, while the third provides a new mmap() access
control point for the underlying backing file.  It is also expected that
LSMs will likely want to update their security_file_mprotect() callback
to address issues with their mprotect() controls, but that does not
require a change to the security_file_mprotect() LSM hook.

There are a three other small changes to support these new LSM hooks:
* Pass the user file associated with a backing file down to
alloc_empty_backing_file() so it can be included in the
security_backing_file_alloc() hook.
* Add getter and setter functions for the backing_file struct LSM blob
as the backing_file struct remains private to fs/file_table.c.
* Constify the file struct field in the LSM common_audit_data struct to
better support LSMs that need to pass a const file struct pointer into
the common LSM audit code.

Thanks to Arnd Bergmann for identifying the missing EXPORT_SYMBOL_GPL()
and supplying a fixup.

Cc: stable@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-unionfs@vger.kernel.org
Cc: linux-erofs@lists.ozlabs.org
Reviewed-by: Amir Goldstein 
Reviewed-by: Serge Hallyn 
Reviewed-by: Christian Brauner 
Signed-off-by: Paul Moore 
[1. Mainline uses call_int_hook(FUNC, ...) with the default IRC baked
into the macro. Linux 6.6.y uses call_int_hook(FUNC, IRC, ...) requiring
an explicit default return value.

2. fs/backing-file.c does not exist in LTS
Linux 6.6.y places backing_file_open() in fs/open.c and lacks a
dedicated fs/backing-file.c.  The backing_file_mmap() function and
scoped_with_creds() do not exist in 6.6.y.  Therefore the LTS patch calls
security_mmap_backing_file() directly in ovl_mmap() in
fs/overlayfs/file.c rather than modifying backing_file_mmap().

3. Missing filesystems/modules
Linux 6.6.y does not have backing_tmpfile_open(), fs/fuse/passthrough.c,
or the erofs ishare mmap path that the mainline patch touches.  These hunks
are dropped in the 6.6 LTS backport.

4. Use macro backing_file to replace inline function to eliminate the
const warning.]
Signed-off-by: Cai Xinchen 
Signed-off-by: Sasha Levin

fs: prepare for adding LSM blob to backing_file

2026-07-04T11:42:23+00:00

[ Upstream commit 880bd496ec72a6dcb00cb70c430ef752ba242ae7 ]

In preparation to adding LSM blob to backing_file struct, factor out
helpers init_backing_file() and backing_file_free().

Cc: stable@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-unionfs@vger.kernel.org
Cc: linux-erofs@lists.ozlabs.org
Signed-off-by: Amir Goldstein 
Reviewed-by: Serge Hallyn 
[PM: use the term "LSM blob", fix comment style to match file]
Signed-off-by: Paul Moore 
[1. The commit def3ae83da02
("fs: store real path instead of fake path in backing file f_path")
is not merged, The 6.6 LTS version accordingly operates on
&ff->real_path instead of &ff->user_path.

2. Mainline's file_free() does both the backing_file cleanup and the
kmem_cache_free() synchronously.  Linux 6.6.y defers the actual kfree()
to file_free_rcu() via call_rcu(), so only path_put() is done
synchronously in file_free().]
Signed-off-by: Cai Xinchen 

Signed-off-by: Sasha Levin

fs: fix proc_handler for sysctl_nr_open

2025-02-08T08:51:42+00:00

[ Upstream commit d727935cad9f6f52c8d184968f9720fdc966c669 ]

Use proc_douintvec_minmax() instead of proc_dointvec_minmax() to handle
sysctl_nr_open, because its data type is unsigned int, not int.

Fixes: 9b80a184eaad ("fs/file: more unsigned file descriptors")
Signed-off-by: Jinliang Zheng 
Link: https://lore.kernel.org/r/20241124034636.325337-1-alexjlzheng@tencent.com
Signed-off-by: Christian Brauner 
Signed-off-by: Sasha Levin

fs: use __fput_sync in close(2)

2023-08-08T17:36:51+00:00

close(2) is a special case which guarantees a shallow kernel stack,
making delegation to task_work machinery unnecessary. Said delegation is
problematic as it involves atomic ops and interrupt masking trips, none
of which are cheap on x86-64. Forcing close(2) to do it looks like an
oversight in the original work.

Moreover presence of CONFIG_RSEQ adds an additional overhead as fput()
-> task_work_add(..., TWA_RESUME) -> set_notify_resume() makes the
thread returning to userspace land in resume_user_mode_work(), where
rseq_handle_notify_resume takes a SMAP round-trip if rseq is enabled for
the thread (and it is by default with contemporary glibc).

Sample result when benchmarking open1_processes -t 1 from will-it-scale
(that's an open + close loop) + tmpfs on /tmp, running on the Sapphire
Rapid CPU (ops/s):
stock+RSEQ:     1329857
stock-RSEQ:     1421667 (+7%)
patched:        1523521 (+14.5% / +7%) (with / without rseq)

Patched result is the same regardless of rseq as the codepath is avoided.

Signed-off-by: Linus Torvalds 
Signed-off-by: Christian Brauner

fs: move cleanup from init_file() into its callers

2023-07-02T11:15:49+00:00

The use of file_free_rcu() in init_file() to free the struct that was
allocated by the caller was hacky and we got what we deserved.

Let init_file() and its callers take care of cleaning up each after
their own allocated resources on error.

Fixes: 62d53c4a1dfe ("fs: use backing_file container for internal files with "fake" f_path") # mainline only
Reported-and-tested-by: syzbot+ada42aab05cf51b00e98@syzkaller.appspotmail.com
Signed-off-by: Amir Goldstein 
Message-Id: <20230701171134.239409-1-amir73il@gmail.com>
Signed-off-by: Christian Brauner

fs: use backing_file container for internal files with "fake" f_path

2023-06-19T16:16:38+00:00

Overlayfs uses open_with_fake_path() to allocate internal kernel files,
with a "fake" path - whose f_path is not on the same fs as f_inode.

Allocate a container struct backing_file for those internal files, that
is used to hold the "fake" ovl path along with the real path.

backing_file_real_path() can be used to access the stored real path.

Signed-off-by: Amir Goldstein 
Message-Id: <20230615112229.2143178-5-amir73il@gmail.com>
Signed-off-by: Christian Brauner

fs: move kmem_cache_zalloc() into alloc_empty_file*() helpers

2023-06-19T16:12:04+00:00

Use a common helper init_file() instead of __alloc_file() for
alloc_empty_file*() helpers and improrve the documentation.

This is needed for a follow up patch that allocates a backing_file
container.

Suggested-by: Christoph Hellwig 
Signed-off-by: Amir Goldstein 
Reviewed-by: Christoph Hellwig 
Message-Id: <20230615112229.2143178-4-amir73il@gmail.com>
Signed-off-by: Christian Brauner

filelock: move file locking definitions to separate header file

2023-01-11T11:52:32+00:00

The file locking definitions have lived in fs.h since the dawn of time,
but they are only used by a small subset of the source files that
include it.

Move the file locking definitions to a new header file, and add the
appropriate #include directives to the source files that need them. By
doing this we trim down fs.h a bit and limit the amount of rebuilding
that has to be done when we make changes to the file locking APIs.

Reviewed-by: Xiubo Li 
Reviewed-by: Christian Brauner (Microsoft) 
Reviewed-by: Christoph Hellwig 
Reviewed-by: David Howells 
Reviewed-by: Russell King (Oracle) 
Acked-by: Chuck Lever 
Acked-by: Joseph Qi 
Acked-by: Steve French 
Acked-by: Al Viro 
Acked-by: Darrick J. Wong 
Signed-off-by: Jeff Layton

locks: fix TOCTOU race when granting write lease

2022-08-16T14:59:54+00:00

Thread A trying to acquire a write lease checks the value of i_readcount
and i_writecount in check_conflicting_open() to verify that its own fd
is the only fd referencing the file.

Thread B trying to open the file for read will call break_lease() in
do_dentry_open() before incrementing i_readcount, which leaves a small
window where thread A can acquire the write lease and then thread B
completes the open of the file for read without breaking the write lease
that was acquired by thread A.

Fix this race by incrementing i_readcount before checking for existing
leases, same as the case with i_writecount.

Use a helper put_file_access() to decrement i_readcount or i_writecount
in do_dentry_open() and __fput().

Fixes: 387e3746d01c ("locks: eliminate false positive conflicts for write lease")
Reviewed-by: Jeff Layton 
Signed-off-by: Amir Goldstein 
Signed-off-by: Al Viro

Merge tag 'pull-work.iov_iter-base' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2022-08-03T20:50:22+00:00

Pull vfs iov_iter updates from Al Viro:
 "Part 1 - isolated cleanups and optimizations.

  One of the goals is to reduce the overhead of using ->read_iter() and
  ->write_iter() instead of ->read()/->write().

  new_sync_{read,write}() has a surprising amount of overhead, in
  particular inside iocb_flags(). That's the explanation for the
  beginning of the series is in this pile; it's not directly
  iov_iter-related, but it's a part of the same work..."

* tag 'pull-work.iov_iter-base' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  first_iovec_segment(): just return address
  iov_iter: massage calling conventions for first_{iovec,bvec}_segment()
  iov_iter: first_{iovec,bvec}_segment() - simplify a bit
  iov_iter: lift dealing with maxpages out of first_{iovec,bvec}_segment()
  iov_iter_get_pages{,_alloc}(): cap the maxsize with MAX_RW_COUNT
  iov_iter_bvec_advance(): don't bother with bvec_iter
  copy_page_{to,from}_iter(): switch iovec variants to generic
  keep iocb_flags() result cached in struct file
  iocb: delay evaluation of IS_SYNC(...) until we want to check IOCB_DSYNC
  struct file: use anonymous union member for rcuhead and llist
  btrfs: use IOMAP_DIO_NOSYNC
  teach iomap_dio_rw() to suppress dsync
  No need of likely/unlikely on calls of check_copy_size()