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, 7 insertions, 6 deletions

diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
index 47cd258fd24d..5dcbafe72d71 100644
--- a/fs/notify/inotify/inotify_fsnotify.c
+++ b/fs/notify/inotify/inotify_fsnotify.c
@@ -62,13 +62,14 @@ static int inotify_handle_event(struct fsnotify_group *group, struct fsnotify_ev
         event_priv->wd = wd;
 
         ret = fsnotify_add_notify_event(group, event, fsn_event_priv);
-        /* EEXIST is not an error */
-        if (ret == -EEXIST)
-                ret = 0;
-
-        /* did event_priv get attached? */
-        if (list_empty(&fsn_event_priv->event_list))
+        if (ret) {
                 inotify_free_event_priv(fsn_event_priv);
+                /* EEXIST says we tail matched, EOVERFLOW isn't something
+                 * to report up the stack. */
+                if ((ret == -EEXIST) ||
+                    (ret == -EOVERFLOW))
+                        ret = 0;
+        }
 
         /*
          * If we hold the entry until after the event is on the queue