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linux/fs/notify
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Amir Goldstein 82f7416bcb fsnotify: do not generate ACCESS/MODIFY events on child for special files 
commit 635bc4def0 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 <sneela@tugraz.at>
CC: stable@vger.kernel.org
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-01-08 10:14:24 +01:00
..
dnotify fix a leak in fcntl_dirnotify() 2025-07-24 08:56:30 +02:00
fanotify fanotify: sanitize handle_type values when reporting fid 2025-08-15 12:13:51 +02:00
inotify fsnotify: Avoid data race between fsnotify_recalc_mask() and fsnotify_object_watched() 2024-10-02 15:11:40 +02:00
fdinfo.c fs/notify: call exportfs_encode_fid with s_umount 2025-10-29 14:08:55 +01:00
fdinfo.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fsnotify.c fsnotify: do not generate ACCESS/MODIFY events on child for special files 2026-01-08 10:14:24 +01:00
fsnotify.h fsnotify: clear PARENT_WATCHED flags lazily 2024-06-05 09:52:38 +02:00
group.c inotify: Fix possible deadlock in fsnotify_destroy_mark 2024-10-02 15:14:29 +02:00
Kconfig fs/notify: Remove "select SRCU" 2023-02-02 16:26:06 -08:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mark.c fsnotify: Fix ordering of iput() and watched_objects decrement 2024-12-05 14:02:46 +01:00
notification.c fsnotify: Pass group argument to free_event 2021-10-27 12:34:18 +02:00