diff options
| author | Amir Goldstein <amir73il@gmail.com> | 2025-12-07 11:44:55 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2026-01-11 15:22:02 +0100 |
| commit | e0643d46759db8b84c0504a676043e5e341b6c81 (patch) | |
| tree | 9a05893f8b178a4c96270eb0d7ae979b3d2d28fd /fs/notify | |
| parent | 19d4c57ae91b07d55691f16542ae82cf6e11a00e (diff) | |
fsnotify: do not generate ACCESS/MODIFY events on child for special files
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 <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>
Diffstat (limited to 'fs/notify')
| -rw-r--r-- | fs/notify/fsnotify.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c index 9cc4ebb53504..82602157bcc0 100644 --- a/fs/notify/fsnotify.c +++ b/fs/notify/fsnotify.c @@ -224,8 +224,15 @@ int __fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data, /* * Include parent/name in notification either if some notification * groups require parent info or the parent is interested in this event. + * The parent interest in ACCESS/MODIFY events does not apply to special + * files, where read/write are not on the filesystem of the parent and + * events can provide an undesirable side-channel for information + * exfiltration. */ - parent_interested = mask & p_mask & ALL_FSNOTIFY_EVENTS; + parent_interested = mask & p_mask & ALL_FSNOTIFY_EVENTS && + !(data_type == FSNOTIFY_EVENT_PATH && + d_is_special(dentry) && + (mask & (FS_ACCESS | FS_MODIFY))); if (parent_needed || parent_interested) { /* When notifying parent, child should be passed as data */ WARN_ON_ONCE(inode != fsnotify_data_inode(data, data_type)); |