Commit 1404ff3c authored Oct 07, 2016 by Jan Kara Committed by Linus Torvalds Oct 07, 2016

fsnotify: drop notification_mutex before destroying event

fsnotify_flush_notify() and fanotify_release() destroy notification
event while holding notification_mutex.

The destruction of fanotify event includes a path_put() call which may
end up calling into a filesystem to delete an inode if we happen to be
the last holders of dentry reference which happens to be the last holder
of inode reference.

That in turn may violate lock ordering for some filesystems since
notification_mutex is also acquired e. g. during write when generating
fanotify event.

Also this is the only thing that forces notification_mutex to be a
sleeping lock.  So drop notification_mutex before destroying a
notification event.

Link: http://lkml.kernel.org/r/1473797711-14111-4-git-send-email-jack@suse.cz


Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Cc: Eric Paris <eparis@redhat.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 87840a2b

fs/notify/fanotify/fanotify_user.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -390,9 +390,11 @@ static int fanotify_release(struct inode ignored, struct file file)
		mutex_lock(&group->notification_mutex);
		while (!fsnotify_notify_queue_is_empty(group)) {
		fsn_event = fsnotify_remove_first_event(group);
		if (!(fsn_event->mask & FAN_ALL_PERM_EVENTS))
		if (!(fsn_event->mask & FAN_ALL_PERM_EVENTS)) {
		mutex_unlock(&group->notification_mutex);
		fsnotify_destroy_event(group, fsn_event);
		else
		mutex_lock(&group->notification_mutex);
		} else
		FANOTIFY_PE(fsn_event)->response = FAN_ALLOW;
		}
		mutex_unlock(&group->notification_mutex);

fs/notify/notification.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -178,7 +178,9 @@ void fsnotify_flush_notify(struct fsnotify_group *group)
		mutex_lock(&group->notification_mutex);
		while (!fsnotify_notify_queue_is_empty(group)) {
		event = fsnotify_remove_first_event(group);
		mutex_unlock(&group->notification_mutex);
		fsnotify_destroy_event(group, event);
		mutex_lock(&group->notification_mutex);
		}
		mutex_unlock(&group->notification_mutex);
		}

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