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fsnotify: add a way to stop queueing events on group shutdown

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Implement a function that can be called when a group is being shutdown
to stop queueing new events to the group.  Fanotify will use this.

Fixes: 5838d4442b ("fanotify: fix double free of pending permission events")
Link: http://lkml.kernel.org/r/1473797711-14111-2-git-send-email-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jan Kara 2016-09-19 14:44:27 -07:00 committed by Linus Torvalds
parent d5bf141893
commit 12703dbfeb
3 changed files with 29 additions and 1 deletions
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19
fs/notify/group.c
View file

@ -39,6 +39,17 @@ static void fsnotify_final_destroy_group(struct fsnotify_group *group)
kfree(group);
}
/*
* Stop queueing new events for this group. Once this function returns
* fsnotify_add_event() will not add any new events to the group's queue.
*/
void fsnotify_group_stop_queueing(struct fsnotify_group *group)
{
mutex_lock(&group->notification_mutex);
group->shutdown = true;
mutex_unlock(&group->notification_mutex);
}
/*
* Trying to get rid of a group. Remove all marks, flush all events and release
* the group reference.
@ -47,6 +58,14 @@ static void fsnotify_final_destroy_group(struct fsnotify_group *group)
*/
void fsnotify_destroy_group(struct fsnotify_group *group)
{
/*
* Stop queueing new events. The code below is careful enough to not
* require this but fanotify needs to stop queuing events even before
* fsnotify_destroy_group() is called and this makes the other callers
* of fsnotify_destroy_group() to see the same behavior.
*/
fsnotify_group_stop_queueing(group);
/* clear all inode marks for this group, attach them to destroy_list */
fsnotify_detach_group_marks(group);

8
fs/notify/notification.c
View file

@ -82,7 +82,8 @@ void fsnotify_destroy_event(struct fsnotify_group *group,
* Add an event to the group notification queue. The group can later pull this
* event off the queue to deal with. The function returns 0 if the event was
* added to the queue, 1 if the event was merged with some other queued event,
* 2 if the queue of events has overflown.
* 2 if the event was not queued - either the queue of events has overflown
* or the group is shutting down.
*/
int fsnotify_add_event(struct fsnotify_group *group,
struct fsnotify_event *event,
@ -96,6 +97,11 @@ int fsnotify_add_event(struct fsnotify_group *group,
mutex_lock(&group->notification_mutex);
if (group->shutdown) {
mutex_unlock(&group->notification_mutex);
return 2;
}
if (group->q_len >= group->max_events) {
ret = 2;
/* Queue overflow event only if it isn't already queued */

3
include/linux/fsnotify_backend.h
View file

@ -148,6 +148,7 @@ struct fsnotify_group {
#define FS_PRIO_1 1 /* fanotify content based access control */
#define FS_PRIO_2 2 /* fanotify pre-content access */
unsigned int priority;
bool shutdown; /* group is being shut down, don't queue more events */
/* stores all fastpath marks assoc with this group so they can be cleaned on unregister */
struct mutex mark_mutex; /* protect marks_list */
@ -292,6 +293,8 @@ extern struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *op
extern void fsnotify_get_group(struct fsnotify_group *group);
/* drop reference on a group from fsnotify_alloc_group */
extern void fsnotify_put_group(struct fsnotify_group *group);
/* group destruction begins, stop queuing new events */
extern void fsnotify_group_stop_queueing(struct fsnotify_group *group);
/* destroy group */
extern void fsnotify_destroy_group(struct fsnotify_group *group);
/* fasync handler function */