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>

3 files changed, 13 insertions, 14 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
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index f30d9bbc2e1b..c172a7a17b17 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -386,6 +386,7 @@ void inotify_ignored_and_remove_idr(struct fsnotify_mark_entry *entry,
         struct fsnotify_event *ignored_event;
         struct inotify_event_private_data *event_priv;
         struct fsnotify_event_private_data *fsn_event_priv;
+        int ret;
 
         ignored_event = fsnotify_create_event(NULL, FS_IN_IGNORED, NULL,
                                               FSNOTIFY_EVENT_NONE, NULL, 0,
@@ -404,10 +405,8 @@ void inotify_ignored_and_remove_idr(struct fsnotify_mark_entry *entry,
         fsn_event_priv->group = group;
         event_priv->wd = ientry->wd;
 
-        fsnotify_add_notify_event(group, ignored_event, fsn_event_priv);
-
-        /* did the private data get added? */
-        if (list_empty(&fsn_event_priv->event_list))
+        ret = fsnotify_add_notify_event(group, ignored_event, fsn_event_priv);
+        if (ret)
                 inotify_free_event_priv(fsn_event_priv);
 
 skip_send_ignore:
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;
 }
 
 /*