kernel/linux.git/include/linux/fsnotify.h, branch v6.12.107

fsnotify: opt-in for permission events at file open time

2026-08-23T12:22:46+00:00

[ Upstream commit a94204f4d48e28a711b7ed10399f749286c433e3 ] Legacy inotify/fanotify listeners can add watches for events on inode, parent or mount and expect to get events (e.g. FS_MODIFY) on files that were already open at the time of setting up the watches. fanotify permission events are typically used by Anti-malware sofware, that is watching the entire mount and it is not common to have more that one Anti-malware engine installed on a system. To reduce the overhead of the fsnotify_file_perm() hooks on every file access, relax the semantics of the legacy FAN_ACCESS_PERM event to generate events only if there were *any* permission event listeners on the filesystem at the time that the file was opened. The new semantic is implemented by extending the FMODE_NONOTIFY bit into two FMODE_NONOTIFY_* bits, that are used to store a mode for which of the events types to report. This is going to apply to the new fanotify pre-content events in order to reduce the cost of the new pre-content event vfs hooks. [Thanks to Bert Karwatzki for reporting a bug in this code with CONFIG_FANOTIFY_ACCESS_PERMISSIONS disabled] Suggested-by: Linus Torvalds Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wj8L=mtcRTi=NECHMGfZQgXOp_uix1YVh04fEmrKaMnXA@mail.gmail.com/ Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/5ea5f8e283d1edb55aa79c35187bfe344056af14.1731684329.git.josef@toxicpanda.com Stable-dep-of: db1856ea9196 ("binfmt_misc: restore write access when removing an entry") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

fsnotify: Do not generate events for O_PATH file descriptors

2024-06-18T14:25:50+00:00

Currently we will not generate FS_OPEN events for O_PATH file descriptors but we will generate FS_CLOSE events for them. This is asymmetry is confusing. Arguably no fsnotify events should be generated for O_PATH file descriptors as they cannot be used to access or modify file content, they are just convenient handles to file objects like paths. So fix the asymmetry by stopping to generate FS_CLOSE for O_PATH file descriptors. Cc: Signed-off-by: Jan Kara Link: https://lore.kernel.org/r/20240617162303.1596-1-jack@suse.cz Reviewed-by: Amir Goldstein Signed-off-by: Christian Brauner

fsnotify: optimize the case of no permission event watchers

2024-04-04T14:24:16+00:00

Commit e43de7f0862b ("fsnotify: optimize the case of no marks of any type") optimized the case where there are no fsnotify watchers on any of the filesystem's objects. It is quite common for a system to have a single local filesystem and it is quite common for the system to have some inotify watches on some config files or directories, so the optimization of no marks at all is often not in effect. Permission event watchers, which require high priority group are more rare, so optimizing the case of no marks og high priority groups can improve performance for more systems, especially for performance sensitive io workloads. Count per-sb watched objects by high priority groups and use that the optimize out the call to __fsnotify_parent() and fsnotify() in fsnotify permission hooks. Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Message-Id: <20240317184154.1200192-11-amir73il@gmail.com>

fsnotify: move s_fsnotify_connectors into fsnotify_sb_info

2024-04-04T14:24:16+00:00

Move the s_fsnotify_connectors counter into the per-sb fsnotify state. Suggested-by: Christian Brauner Signed-off-by: Amir Goldstein Reviewed-by: Christian Brauner Signed-off-by: Jan Kara Message-Id: <20240317184154.1200192-9-amir73il@gmail.com>

fsnotify: rename fsnotify_{get,put}_sb_connectors()

2024-04-04T14:21:12+00:00

Instead of counting the number of connectors in an sb, we would like to count the number of watched objects per priority group. As a start, create an accessor fsnotify_sb_watched_objects() to s_fsnotify_connectors and rename the fsnotify_{get,put}_sb_connectors() helpers to fsnotify_{get,put}_sb_watchers() to better describes the counter. Increment the counter at the end of fsnotify_attach_connector_to_object() if connector was attached instead of decrementing it on race to connect. This is fine, because fsnotify_delete_sb() cannot be running in parallel to fsnotify_attach_connector_to_object() which requires a reference to a filesystem object. Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Message-Id: <20240317184154.1200192-2-amir73il@gmail.com>

fsnotify: Add fsnotify_sb_has_watchers() helper

2024-01-24T15:29:33+00:00

Instead of opencoded checks for number of fsnotify connectors add a helper fsnotify_sb_has_watchers(). Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara

fsnotify: compile out fsnotify permission hooks if !FANOTIFY_ACCESS_PERMISSIONS

2024-01-12T14:34:50+00:00

The depency of FANOTIFY_ACCESS_PERMISSIONS on SECURITY made sure that the fsnotify permission hooks were never called when SECURITY was disabled. Moving the fsnotify permission hook out of the secutiy hook broke that optimisation. Reported-and-tested-by: Jens Axboe Closes: https://lore.kernel.org/linux-fsdevel/53682ece-f0e7-48de-9a1c-879ee34b0449@kernel.dk/ Fixes: d9e5d31084b0 ("fsnotify: optionally pass access range in file permission hooks") Signed-off-by: Amir Goldstein Link: https://lore.kernel.org/r/20240109182245.38884-1-amir73il@gmail.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

fsnotify: optionally pass access range in file permission hooks

2023-12-12T15:20:02+00:00

In preparation for pre-content permission events with file access range, move fsnotify_file_perm() hook out of security_file_permission() and into the callers. Callers that have the access range information call the new hook fsnotify_file_area_perm() with the access range. Reviewed-by: Jan Kara Signed-off-by: Amir Goldstein Link: https://lore.kernel.org/r/20231212094440.250945-6-amir73il@gmail.com Signed-off-by: Christian Brauner

fsnotify: assert that file_start_write() is not held in permission hooks

2023-12-12T15:20:02+00:00

filesystem may be modified in the context of fanotify permission events (e.g. by HSM service), so assert that sb freeze protection is not held. If the assertion fails, then the following deadlock would be possible: CPU0 CPU1 CPU2 ------------------------------------------------------------------------- file_start_write()#0 ... fsnotify_perm() fanotify_get_response() => (read event and fill file) ... ... freeze_super() ... sb_wait_write() ... vfs_write() file_start_write()#1 This example demonstrates a use case of an hierarchical storage management (HSM) service that uses fanotify permission events to fill the content of a file before access, while a 3rd process starts fsfreeze. This creates a circular dependeny: file_start_write()#0 => fanotify_get_response => file_start_write()#1 => sb_wait_write() => file_end_write()#0 Where file_end_write()#0 can never be called and none of the threads can make progress. The assertion is checked for both MAY_READ and MAY_WRITE permission hooks in preparation for a pre-modify permission event. The assertion is not checked for an open permission event, because do_open() takes mnt_want_write() in O_TRUNC case, meaning that it is not safe to write to filesystem in the content of an open permission event. Reviewed-by: Josef Bacik Reviewed-by: Jan Kara Signed-off-by: Amir Goldstein Link: https://lore.kernel.org/r/20231212094440.250945-5-amir73il@gmail.com Signed-off-by: Christian Brauner

fsnotify: split fsnotify_perm() into two hooks

2023-12-12T15:20:02+00:00

We would like to make changes to the fsnotify access permission hook - add file range arguments and add the pre modify event. In preparation for these changes, split the fsnotify_perm() hook into fsnotify_open_perm() and fsnotify_file_perm(). This is needed for fanotify "pre content" events. Reviewed-by: Josef Bacik Reviewed-by: Jan Kara Signed-off-by: Amir Goldstein Link: https://lore.kernel.org/r/20231212094440.250945-4-amir73il@gmail.com Signed-off-by: Christian Brauner