linux-stable.git/fs/fuse, branch linux-6.12.y

lsm: add backing_file LSM hooks

2026-07-04T11:43:31+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 
[ Mainline declares lsm_backing_file_cache in security/lsm.h.  Linux 6.12.y
does not have security/lsm_init.c or security/lsm.h; the cache variable
is defined locally as static struct kmem_cache *lsm_backing_file_cache in
security/security.c. ]
Signed-off-by: Cai Xinchen 
Signed-off-by: Sasha Levin

virtiofs: fix UAF on submount umount

2026-07-04T11:43:29+00:00

commit 06b41351779e9289e8785694ade9042ae85e41ea upstream.

iput() called from fuse_release_end() can Oops if the super block has
already been destroyed.  Normally this is prevented by waiting for
num_waiting to go down to zero before commencing with super block shutdown.

This only works, however, for the last submount instance, as the wait
counter is per connection, not per superblock.

Revert to using synchronous release requests for the auto_submounts case,
which is virtiofs only at this time.

Reported-by: Aurélien Bombo 
Reported-by: Zhihao Cheng 
Cc: Greg Kurz 
Closes: https://github.com/kata-containers/kata-containers/issues/12589
Fixes: 26e5c67deb2e ("fuse: fix livelock in synchronous file put from fuseblk workers")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kurz 
Signed-off-by: Miklos Szeredi 
Signed-off-by: Greg Kroah-Hartman

fuse: re-lock request before replacing page cache folio

2026-07-04T11:43:27+00:00

[ Upstream commit a078484921052d0badd827fcc2770b5cfc1d4120 ]

fuse_try_move_folio() unlocks the request on entry but does not
re-lock it on the success path. This means fuse_chan_abort() can end the
request and free the fuse_io_args (eg fuse_readpages_end()) while the
subsequent copy chain logic after fuse_try_move_folio() accesses the
fuse_io_args, leading to use-after-free issues.

Fix this by calling lock_request() before replace_page_cache_folio().
This ensures the request is locked on the success path which will
prevent the fuse_io_args from being freed while the later copying logic
runs, and also ensures that the ap->folios[i]->mapping is never null
since ap->folios[i] will always point to the newfolio after
replace_page_cache_folio().

Fixes: ce534fb05292 ("fuse: allow splice to move pages")
Cc: stable@vger.kernel.org
Reported-by: Lei Lu 
Signed-off-by: Joanne Koong 
Signed-off-by: Miklos Szeredi 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

fuse: limit FUSE_NOTIFY_RETRIEVE to uptodate folios

2026-07-04T11:43:23+00:00

[ Upstream commit 4e3d1b2c48ca6c55f1e9ca7f8dccc76f120f276c ]

FUSE_NOTIFY_RETRIEVE must be limited to uptodate folios; !uptodate folios
can contain uninitialized data.
Since FUSE_NOTIFY_RETRIEVE is intended to only return data that is already
in the page cache and not wait for data from the FUSE daemon, treat
!uptodate folios as if they weren't present.

This only has security impact on systems that don't enable automatic
zero-initialization of all page allocations via
CONFIG_INIT_ON_ALLOC_DEFAULT_ON or init_on_alloc=1.

Cc: stable@kernel.org
Fixes: 2d45ba381a74 ("fuse: add retrieve request")
Signed-off-by: Jann Horn 
Link: https://patch.msgid.link/20260519-fuse-retrieve-uptodate-v1-1-a7a1912a37f9@google.com
Acked-by: Miklos Szeredi 
Signed-off-by: Christian Brauner (Amutable) 
[adjusted for stable: page instead of folio]
Signed-off-by: Jann Horn 
Signed-off-by: Sasha Levin

fuse: reject fuse_notify() pagecache ops on directories

2026-06-19T11:42:31+00:00

commit 9c954499d43aefac01c5dfb57a82b13d2dcf4b94 upstream.

The operations FUSE_NOTIFY_STORE and FUSE_NOTIFY_RETRIEVE allow the
FUSE daemon to actively write/read pagecache contents.

For directories with FOPEN_CACHE_DIR, the pagecache is used as
kernel-internal cache storage, and userspace is not supposed to have
direct access to this cache - in particular, fuse_parse_cache() will hit
WARN_ON() if the cache contains bogus data.

Reject FUSE_NOTIFY_STORE and FUSE_NOTIFY_RETRIEVE on anything other than
regular files with -EINVAL.

Fixes: 5d7bc7e8680c ("fuse: allow using readdir cache")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn 
Link: https://patch.msgid.link/20260519-fuse-dir-pagecache-v2-1-5428fa48e175@google.com
Acked-by: Miklos Szeredi 
Signed-off-by: Christian Brauner (Amutable) 
Signed-off-by: Greg Kroah-Hartman

fuse: quiet down complaints in fuse_conn_limit_write

2026-04-27T13:24:25+00:00

commit 129a45f9755a89f573c6a513a6b9e3d234ce89b0 upstream.

gcc 15 complains about an uninitialized variable val that is passed by
reference into fuse_conn_limit_write:

 control.c: In function ‘fuse_conn_congestion_threshold_write’:
 include/asm-generic/rwonce.h:55:37: warning: ‘val’ may be used uninitialized [-Wmaybe-uninitialized]
    55 |         *(volatile typeof(x) *)&(x) = (val);                            \
       |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
 include/asm-generic/rwonce.h:61:9: note: in expansion of macro ‘__WRITE_ONCE’
    61 |         __WRITE_ONCE(x, val);                                           \
       |         ^~~~~~~~~~~~
 control.c:178:9: note: in expansion of macro ‘WRITE_ONCE’
   178 |         WRITE_ONCE(fc->congestion_threshold, val);
       |         ^~~~~~~~~~
 control.c:166:18: note: ‘val’ was declared here
   166 |         unsigned val;
       |                  ^~~

Unfortunately there's enough macro spew involved in kstrtoul_from_user
that I think gcc gives up on its analysis and sprays the above warning.
AFAICT it's not actually a bug, but we could just zero-initialize the
variable to enable using -Wmaybe-uninitialized to find real problems.

Previously we would use some weird uninitialized_var annotation to quiet
down the warnings, so clearly this code has been like this for quite
some time.

Cc: stable@vger.kernel.org # v5.9
Fixes: 3f649ab728cda8 ("treewide: Remove uninitialized_var() usage")
Signed-off-by: Darrick J. Wong 
Signed-off-by: Miklos Szeredi 
Signed-off-by: Greg Kroah-Hartman

fuse: Check for large folio with SPLICE_F_MOVE

2026-04-27T13:24:25+00:00

commit 59ba47b6be9cd0146ef9a55c6e32e337e11e7625 upstream.

xfstest generic/074 and generic/075 complain result in kernel
warning messages / page dumps.
This is easily reproducible (on 6.19) with
CONFIG_TRANSPARENT_HUGEPAGE_SHMEM_HUGE_ALWAYS=y
CONFIG_TRANSPARENT_HUGEPAGE_TMPFS_HUGE_ALWAYS=y

This just adds a test for large folios fuse_try_move_folio
with the same page copy fallback, but to avoid the warnings
from fuse_check_folio().

Cc: stable@vger.kernel.org
Signed-off-by: Bernd Schubert 
Signed-off-by: Horst Birthelmer 
Signed-off-by: Miklos Szeredi 
Signed-off-by: Greg Kroah-Hartman

fuse: reject oversized dirents in page cache

2026-04-27T13:24:25+00:00

commit 51a8de6c50bf947c8f534cd73da4c8f0a13e7bed upstream.

fuse_add_dirent_to_cache() computes a serialized dirent size from the
server-controlled namelen field and copies the dirent into a single
page-cache page. The existing logic only checks whether the dirent fits
in the remaining space of the current page and advances to a fresh page
if not. It never checks whether the dirent itself exceeds PAGE_SIZE.

As a result, a malicious FUSE server can return a dirent with
namelen=4095, producing a serialized record size of 4120 bytes. On 4 KiB
page systems this causes memcpy() to overflow the cache page by 24 bytes
into the following kernel page.

Reject dirents that cannot fit in a single page before copying them into
the readdir cache.

Fixes: 69e34551152a ("fuse: allow caching readdir")
Cc: stable@vger.kernel.org # v6.16+
Assisted-by: Bynario AI
Signed-off-by: Samuel Page 
Reported-by: Qi Tang 
Reported-by: Zijun Hu 
Signed-off-by: Miklos Szeredi 
Link: https://patch.msgid.link/20260420090139.662772-1-mszeredi@redhat.com
Signed-off-by: Christian Brauner 
Signed-off-by: Greg Kroah-Hartman

fuse: fix readahead reclaim deadlock

2026-01-08T09:14:31+00:00

commit bd5603eaae0aabf527bfb3ce1bb07e979ce5bd50 upstream.

Commit e26ee4efbc79 ("fuse: allocate ff->release_args only if release is
needed") skips allocating ff->release_args if the server does not
implement open. However in doing so, fuse_prepare_release() now skips
grabbing the reference on the inode, which makes it possible for an
inode to be evicted from the dcache while there are inflight readahead
requests. This causes a deadlock if the server triggers reclaim while
servicing the readahead request and reclaim attempts to evict the inode
of the file being read ahead. Since the folio is locked during
readahead, when reclaim evicts the fuse inode and fuse_evict_inode()
attempts to remove all folios associated with the inode from the page
cache (truncate_inode_pages_range()), reclaim will block forever waiting
for the lock since readahead cannot relinquish the lock because it is
itself blocked in reclaim:

>>> stack_trace(1504735)
 folio_wait_bit_common (mm/filemap.c:1308:4)
 folio_lock (./include/linux/pagemap.h:1052:3)
 truncate_inode_pages_range (mm/truncate.c:336:10)
 fuse_evict_inode (fs/fuse/inode.c:161:2)
 evict (fs/inode.c:704:3)
 dentry_unlink_inode (fs/dcache.c:412:3)
 __dentry_kill (fs/dcache.c:615:3)
 shrink_kill (fs/dcache.c:1060:12)
 shrink_dentry_list (fs/dcache.c:1087:3)
 prune_dcache_sb (fs/dcache.c:1168:2)
 super_cache_scan (fs/super.c:221:10)
 do_shrink_slab (mm/shrinker.c:435:9)
 shrink_slab (mm/shrinker.c:626:10)
 shrink_node (mm/vmscan.c:5951:2)
 shrink_zones (mm/vmscan.c:6195:3)
 do_try_to_free_pages (mm/vmscan.c:6257:3)
 do_swap_page (mm/memory.c:4136:11)
 handle_pte_fault (mm/memory.c:5562:10)
 handle_mm_fault (mm/memory.c:5870:9)
 do_user_addr_fault (arch/x86/mm/fault.c:1338:10)
 handle_page_fault (arch/x86/mm/fault.c:1481:3)
 exc_page_fault (arch/x86/mm/fault.c:1539:2)
 asm_exc_page_fault+0x22/0x27

Fix this deadlock by allocating ff->release_args and grabbing the
reference on the inode when preparing the file for release even if the
server does not implement open. The inode reference will be dropped when
the last reference on the fuse file is dropped (see fuse_file_put() ->
fuse_release_end()).

Fixes: e26ee4efbc79 ("fuse: allocate ff->release_args only if release is needed")
Cc: stable@vger.kernel.org
Signed-off-by: Joanne Koong 
Reported-by: Omar Sandoval 
Signed-off-by: Miklos Szeredi 
Signed-off-by: Greg Kroah-Hartman

fuse: Invalidate the page cache after FOPEN_DIRECT_IO write

2026-01-08T09:14:10+00:00

[ Upstream commit b359af8275a982a458e8df6c6beab1415be1f795 ]

generic_file_direct_write() also does this and has a large
comment about.

Reproducer here is xfstest's generic/209, which is exactly to
have competing DIO write and cached IO read.

Signed-off-by: Bernd Schubert 
Signed-off-by: Miklos Szeredi 
Signed-off-by: Sasha Levin