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

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: 5838d4442bd5 ("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>

diff --git a/fs/notify/group.c b/fs/notify/group.c
index 3e2dd85..b47f7cf 100644 (file)
--- a/fs/notify/group.c
+++ b/fs/notify/group.c
@@ -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);
 

diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index a95d8e0..3d76e65 100644 (file)
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -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 */

diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 58205f3..40a9e99 100644 (file)
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -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 */