notify: unused event private race

inotify decides if private data it passed to get added to an event was
used by checking list_empty().  But it's possible that the event may
have been dequeued and the private event removed so it would look empty.

The fix is to use the return code from fsnotify_add_notify_event rather
than looking at the list.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 4 deletions

diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 521368574e97..74b3cf30bc6b 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -171,9 +171,7 @@ int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_even
         struct list_head *list = &group->notification_list;
         struct fsnotify_event_holder *last_holder;
         struct fsnotify_event *last_event;
-
-        /* easy to tell if priv was attached to the event */
-        INIT_LIST_HEAD(&priv->event_list);
+        int ret = 0;
 
         /*
          * There is one fsnotify_event_holder embedded inside each fsnotify_event.
@@ -194,6 +192,7 @@ alloc_holder:
 
         if (group->q_len >= group->max_events) {
                 event = &q_overflow_event;
+                ret = -EOVERFLOW;
                 /* sorry, no private data on the overflow event */
                 priv = NULL;
         }
@@ -235,7 +234,7 @@ alloc_holder:
         mutex_unlock(&group->notification_mutex);
 
         wake_up(&group->notification_waitq);
-        return 0;
+        return ret;
 }
 
 /*