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Commit 5838d444 authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
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fanotify: fix double free of pending permission events 



Commit 85816794 ("fanotify: Fix use after free for permission
events") introduced a double free issue for permission events which are
pending in group's notification queue while group is being destroyed.
These events are freed from fanotify_handle_event() but they are not
removed from groups notification queue and thus they get freed again
from fsnotify_flush_notify().

Fix the problem by removing permission events from notification queue
before freeing them if we skip processing access response.  Also expand
comments in fanotify_release() to explain group shutdown in detail.

Fixes: 85816794
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Reported-by: default avatarDouglas Leeder <douglas.leeder@sophos.com>
Tested-by: default avatarDouglas Leeder <douglas.leeder@sophos.com>
Reported-by: default avatarHeinrich Schuchard <xypron.glpk@gmx.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8ba8fa91

fs/notify/fanotify/fanotify.c

+8 −1
Original line number Diff line number Diff line
@@ -70,8 +70,15 @@ static int fanotify_get_response(struct fsnotify_group *group, 
	wait_event(group->fanotify_data.access_waitq, event->response ||

				atomic_read(&group->fanotify_data.bypass_perm));



	if (!event->response) /* bypass_perm set */

	if (!event->response) {	/* bypass_perm set */

		/*

		 * Event was canceled because group is being destroyed. Remove

		 * it from group's event list because we are responsible for

		 * freeing the permission event.

		 */

		fsnotify_remove_event(group, &event->fae.fse);

		return 0;

	}



	/* userspace responded, convert to something usable */

	switch (event->response) {

fs/notify/fanotify/fanotify_user.c

+12 −0
Original line number Diff line number Diff line
@@ -359,6 +359,11 @@ static int fanotify_release(struct inode *ignored, struct file *file) 
#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS

	struct fanotify_perm_event_info *event, *next;



	/*

	 * There may be still new events arriving in the notification queue

	 * but since userspace cannot use fanotify fd anymore, no event can

	 * enter or leave access_list by now.

	 */

	spin_lock(&group->fanotify_data.access_lock);



	atomic_inc(&group->fanotify_data.bypass_perm);
@@ -373,6 +378,13 @@ static int fanotify_release(struct inode *ignored, struct file *file) 
	}

	spin_unlock(&group->fanotify_data.access_lock);



	/*

	 * Since bypass_perm is set, newly queued events will not wait for

	 * access response. Wake up the already sleeping ones now.

	 * synchronize_srcu() in fsnotify_destroy_group() will wait for all

	 * processes sleeping in fanotify_handle_event() waiting for access

	 * response and thus also for all permission events to be freed.

	 */

	wake_up(&group->fanotify_data.access_waitq);

#endif

fs/notify/notification.c

+17 −1
Original line number Diff line number Diff line
@@ -73,7 +73,8 @@ void fsnotify_destroy_event(struct fsnotify_group *group, 
	/* Overflow events are per-group and we don't want to free them */

	if (!event || event->mask == FS_Q_OVERFLOW)

		return;



	/* If the event is still queued, we have a problem... */

	WARN_ON(!list_empty(&event->list));

	group->ops->free_event(event);

}
@@ -124,6 +125,21 @@ int fsnotify_add_event(struct fsnotify_group *group, 
	return ret;

}



/*

 * Remove @event from group's notification queue. It is the responsibility of

 * the caller to destroy the event.

 */

void fsnotify_remove_event(struct fsnotify_group *group,

			   struct fsnotify_event *event)

{

	mutex_lock(&group->notification_mutex);

	if (!list_empty(&event->list)) {

		list_del_init(&event->list);

		group->q_len--;

	}

	mutex_unlock(&group->notification_mutex);

}



/*

 * Remove and return the first event from the notification list.  It is the

 * responsibility of the caller to destroy the obtained event

include/linux/fsnotify_backend.h

+2 −0
Original line number Diff line number Diff line
@@ -326,6 +326,8 @@ extern int fsnotify_add_event(struct fsnotify_group *group, 
			      struct fsnotify_event *event,

			      int (*merge)(struct list_head *,

					   struct fsnotify_event *));

/* Remove passed event from groups notification queue */

extern void fsnotify_remove_event(struct fsnotify_group *group, struct fsnotify_event *event);

/* true if the group notification queue is empty */

extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);

/* return, but do not dequeue the first event on the notification queue */