kernel/linux.git/fs/notify, branch v6.6.132

fsnotify: do not generate ACCESS/MODIFY events on child for special files

2026-01-11T14:22:02+00:00

commit 635bc4def026a24e071436f4f356ea08c0eed6ff upstream. inotify/fanotify do not allow users with no read access to a file to subscribe to events (e.g. IN_ACCESS/IN_MODIFY), but they do allow the same user to subscribe for watching events on children when the user has access to the parent directory (e.g. /dev). Users with no read access to a file but with read access to its parent directory can still stat the file and see if it was accessed/modified via atime/mtime change. The same is not true for special files (e.g. /dev/null). Users will not generally observe atime/mtime changes when other users read/write to special files, only when someone sets atime/mtime via utimensat(). Align fsnotify events with this stat behavior and do not generate ACCESS/MODIFY events to parent watchers on read/write of special files. The events are still generated to parent watchers on utimensat(). This closes some side-channels that could be possibly used for information exfiltration [1]. [1] https://snee.la/pdf/pubs/file-notification-attacks.pdf Reported-by: Sudheendra Raghav Neela CC: stable@vger.kernel.org Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Signed-off-by: Greg Kroah-Hartman

fs/notify: call exportfs_encode_fid with s_umount

2025-10-29T13:07:06+00:00

[ Upstream commit a7c4bb43bfdc2b9f06ee9d036028ed13a83df42a ] Calling intotify_show_fdinfo() on fd watching an overlayfs inode, while the overlayfs is being unmounted, can lead to dereferencing NULL ptr. This issue was found by syzkaller. Race Condition Diagram: Thread 1 Thread 2 -------- -------- generic_shutdown_super() shrink_dcache_for_umount sb->s_root = NULL | | vfs_read() | inotify_fdinfo() | * inode get from mark * | show_mark_fhandle(m, inode) | exportfs_encode_fid(inode, ..) | ovl_encode_fh(inode, ..) | ovl_check_encode_origin(inode) | * deref i_sb->s_root * | | v fsnotify_sb_delete(sb) Which then leads to: [ 32.133461] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI [ 32.134438] KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037] [ 32.135032] CPU: 1 UID: 0 PID: 4468 Comm: systemd-coredum Not tainted 6.17.0-rc6 #22 PREEMPT(none) [ 32.143353] Call Trace: [ 32.143732] ovl_encode_fh+0xd5/0x170 [ 32.144031] exportfs_encode_inode_fh+0x12f/0x300 [ 32.144425] show_mark_fhandle+0xbe/0x1f0 [ 32.145805] inotify_fdinfo+0x226/0x2d0 [ 32.146442] inotify_show_fdinfo+0x1c5/0x350 [ 32.147168] seq_show+0x530/0x6f0 [ 32.147449] seq_read_iter+0x503/0x12a0 [ 32.148419] seq_read+0x31f/0x410 [ 32.150714] vfs_read+0x1f0/0x9e0 [ 32.152297] ksys_read+0x125/0x240 IOW ovl_check_encode_origin derefs inode->i_sb->s_root, after it was set to NULL in the unmount path. Fix it by protecting calling exportfs_encode_fid() from show_mark_fhandle() with s_umount lock. This form of fix was suggested by Amir in [1]. [1]: https://lore.kernel.org/all/CAOQ4uxhbDwhb+2Brs1UdkoF0a3NSdBAOQPNfEHjahrgoKJpLEw@mail.gmail.com/ Fixes: c45beebfde34 ("ovl: support encoding fid from inode with no alias") Signed-off-by: Jakub Acs Cc: Jan Kara Cc: Amir Goldstein Cc: Miklos Szeredi Cc: Christian Brauner Cc: linux-unionfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Jan Kara [ Adjust context ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

fanotify: sanitize handle_type values when reporting fid

2025-08-15T10:08:52+00:00

[ Upstream commit 8631e01c2c5d1fe6705bcc0d733a0b7a17d3daac ] Unlike file_handle, type and len of struct fanotify_fh are u8. Traditionally, filesystem return handle_type < 0xff, but there is no enforecement for that in vfs. Add a sanity check in fanotify to avoid truncating handle_type if its value is > 0xff. Fixes: 7cdafe6cc4a6 ("exportfs: check for error return value from exportfs_encode_*()") Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/20250627104835.184495-1-amir73il@gmail.com Signed-off-by: Sasha Levin

fs: relax assertions on failure to encode file handles

2025-01-23T16:21:19+00:00

commit 974e3fe0ac61de85015bbe5a4990cf4127b304b2 upstream. Encoding file handles is usually performed by a filesystem >encode_fh() method that may fail for various reasons. The legacy users of exportfs_encode_fh(), namely, nfsd and name_to_handle_at(2) syscall are ready to cope with the possibility of failure to encode a file handle. There are a few other users of exportfs_encode_{fh,fid}() that currently have a WARN_ON() assertion when ->encode_fh() fails. Relax those assertions because they are wrong. The second linked bug report states commit 16aac5ad1fa9 ("ovl: support encoding non-decodable file handles") in v6.6 as the regressing commit, but this is not accurate. The aforementioned commit only increases the chances of the assertion and allows triggering the assertion with the reproducer using overlayfs, inotify and drop_caches. Triggering this assertion was always possible with other filesystems and other reasons of ->encode_fh() failures and more particularly, it was also possible with the exact same reproducer using overlayfs that is mounted with options index=on,nfs_export=on also on kernels < v6.6. Therefore, I am not listing the aforementioned commit as a Fixes commit. Backport hint: this patch will have a trivial conflict applying to v6.6.y, and other trivial conflicts applying to stable kernels < v6.6. Reported-by: syzbot+ec07f6f5ce62b858579f@syzkaller.appspotmail.com Tested-by: syzbot+ec07f6f5ce62b858579f@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-unionfs/671fd40c.050a0220.4735a.024f.GAE@google.com/ Reported-by: Dmitry Safonov Closes: https://lore.kernel.org/linux-fsdevel/CAGrbwDTLt6drB9eaUagnQVgdPBmhLfqqxAf3F+Juqy_o6oP8uw@mail.gmail.com/ Cc: stable@vger.kernel.org Signed-off-by: Amir Goldstein Link: https://lore.kernel.org/r/20241219115301.465396-1-amir73il@gmail.com Signed-off-by: Christian Brauner Signed-off-by: Amir Goldstein Signed-off-by: Greg Kroah-Hartman

fanotify: allow reporting errors on failure to open fd

2024-12-14T19:00:05+00:00

[ Upstream commit 522249f05c5551aec9ec0ba9b6438f1ec19c138d ] When working in "fd mode", fanotify_read() needs to open an fd from a dentry to report event->fd to userspace. Opening an fd from dentry can fail for several reasons. For example, when tasks are gone and we try to open their /proc files or we try to open a WRONLY file like in sysfs or when trying to open a file that was deleted on the remote network server. Add a new flag FAN_REPORT_FD_ERROR for fanotify_init(). For a group with FAN_REPORT_FD_ERROR, we will send the event with the error instead of the open fd, otherwise userspace may not get the error at all. For an overflow event, we report -EBADF to avoid confusing FAN_NOFD with -EPERM. Similarly for pidfd open errors we report either -ESRCH or the open error instead of FAN_NOPIDFD and FAN_EPIDFD. In any case, userspace will not know which file failed to open, so add a debug print for further investigation. Reported-by: Krishna Vivek Vitta Link: https://lore.kernel.org/linux-fsdevel/SI2P153MB07182F3424619EDDD1F393EED46D2@SI2P153MB0718.APCP153.PROD.OUTLOOK.COM/ Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/20241003142922.111539-1-amir73il@gmail.com Signed-off-by: Sasha Levin

fsnotify: fix sending inotify event with unexpected filename

2024-12-09T09:32:44+00:00

commit aa52c54da40d9eee3ba87c05cdcb0cd07c04fa13 upstream. We got a report that adding a fanotify filsystem watch prevents tail -f from receiving events. Reproducer: 1. Create 3 windows / login sessions. Become root in each session. 2. Choose a mounted filesystem that is pretty quiet; I picked /boot. 3. In the first window, run: fsnotifywait -S -m /boot 4. In the second window, run: echo data >> /boot/foo 5. In the third window, run: tail -f /boot/foo 6. Go back to the second window and run: echo more data >> /boot/foo 7. Observe that the tail command doesn't show the new data. 8. In the first window, hit control-C to interrupt fsnotifywait. 9. In the second window, run: echo still more data >> /boot/foo 10. Observe that the tail command in the third window has now printed the missing data. When stracing tail, we observed that when fanotify filesystem mark is set, tail does get the inotify event, but the event is receieved with the filename: read(4, "\1\0\0\0\2\0\0\0\0\0\0\0\20\0\0\0foo\0\0\0\0\0\0\0\0\0\0\0\0\0", 50) = 32 This is unexpected, because tail is watching the file itself and not its parent and is inconsistent with the inotify event received by tail when fanotify filesystem mark is not set: read(4, "\1\0\0\0\2\0\0\0\0\0\0\0\0\0\0\0", 50) = 16 The inteference between different fsnotify groups was caused by the fact that the mark on the sb requires the filename, so the filename is passed to fsnotify(). Later on, fsnotify_handle_event() tries to take care of not passing the filename to groups (such as inotify) that are interested in the filename only when the parent is watching. But the logic was incorrect for the case that no group is watching the parent, some groups are watching the sb and some watching the inode. Reported-by: Miklos Szeredi Fixes: 7372e79c9eb9 ("fanotify: fix logic of reporting name info with watched parent") Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Signed-off-by: Greg Kroah-Hartman

fsnotify: clear PARENT_WATCHED flags lazily

2024-09-08T05:54:44+00:00

[ Upstream commit 172e422ffea20a89bfdc672741c1aad6fbb5044e ] In some setups directories can have many (usually negative) dentries. Hence __fsnotify_update_child_dentry_flags() function can take a significant amount of time. Since the bulk of this function happens under inode->i_lock this causes a significant contention on the lock when we remove the watch from the directory as the __fsnotify_update_child_dentry_flags() call from fsnotify_recalc_mask() races with __fsnotify_update_child_dentry_flags() calls from __fsnotify_parent() happening on children. This can lead upto softlockup reports reported by users. Fix the problem by calling fsnotify_update_children_dentry_flags() to set PARENT_WATCHED flags only when parent starts watching children. When parent stops watching children, clear false positive PARENT_WATCHED flags lazily in __fsnotify_parent() for each accessed child. Suggested-by: Jan Kara Signed-off-by: Amir Goldstein Signed-off-by: Stephen Brennan Signed-off-by: Jan Kara Signed-off-by: Sasha Levin

fanotify: limit reporting of event with non-decodeable file handles

2023-10-19T14:19:20+00:00

Commit a95aef69a740 ("fanotify: support reporting non-decodeable file handles") merged in v6.5-rc1, added the ability to use an fanotify group with FAN_REPORT_FID mode to watch filesystems that do not support nfs export, but do know how to encode non-decodeable file handles, with the newly introduced AT_HANDLE_FID flag. At the time that this commit was merged, there were no filesystems in-tree with those traits. Commit 16aac5ad1fa9 ("ovl: support encoding non-decodable file handles"), merged in v6.6-rc1, added this trait to overlayfs, thus allowing fanotify watching of overlayfs with FAN_REPORT_FID mode. In retrospect, allowing an fanotify filesystem/mount mark on such filesystem in FAN_REPORT_FID mode will result in getting events with file handles, without the ability to resolve the filesystem objects from those file handles (i.e. no open_by_handle_at() support). For v6.6, the safer option would be to allow this mode for inode marks only, where the caller has the opportunity to use name_to_handle_at() at the time of setting the mark. In the future we can revise this decision. Fixes: a95aef69a740 ("fanotify: support reporting non-decodeable file handles") Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Message-Id: <20231018100000.2453965-2-amir73il@gmail.com>

dnotify: Pass argument of fcntl_dirnotify as int

2023-07-10T12:36:12+00:00

The interface for fcntl expects the argument passed for the command F_DIRNOTIFY to be of type int. The current code wrongly treats it as a long. In order to avoid access to undefined bits, we should explicitly cast the argument to int. Cc: Jan Kara Cc: Amir Goldstein Cc: Alexander Viro Cc: Christian Brauner Cc: Jeff Layton Cc: Chuck Lever Cc: Kevin Brodsky Cc: Vincenzo Frascino Cc: Szabolcs Nagy Cc: "Theodore Ts'o" Cc: David Laight Cc: Mark Rutland Cc: linux-fsdevel@vger.kernel.org Cc: linux-morello@op-lists.linaro.org Acked-by: Jan Kara Signed-off-by: Luca Vizzarro Message-Id: <20230414152459.816046-6-Luca.Vizzarro@arm.com> Signed-off-by: Christian Brauner

fanotify: disallow mount/sb marks on kernel internal pseudo fs

2023-07-04T11:29:29+00:00

Hopefully, nobody is trying to abuse mount/sb marks for watching all anonymous pipes/inodes. I cannot think of a good reason to allow this - it looks like an oversight that dated back to the original fanotify API. Link: https://lore.kernel.org/linux-fsdevel/20230628101132.kvchg544mczxv2pm@quack3/ Fixes: 0ff21db9fcc3 ("fanotify: hooks the fanotify_mark syscall to the vfsmount code") Signed-off-by: Amir Goldstein Reviewed-by: Christian Brauner Signed-off-by: Jan Kara Message-Id: <20230629042044.25723-1-amir73il@gmail.com>