fsnotify: Do not return merged event from fsnotify_add_notify_event()

The event returned from fsnotify_add_notify_event() cannot ever be used
safely as the event may be freed by the time the function returns (after
dropping notification_mutex). So change the prototype to just return
whether the event was added or merged into some existing event.

Reported-and-tested-by: Jiri Kosina <jkosina@suse.cz>
Reported-and-tested-by: Dave Jones <davej@fedoraproject.org>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 7 insertions, 11 deletions

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index cc78e2fbc8e4..c7e5e8f54748 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -28,8 +28,7 @@ static bool should_merge(struct fsnotify_event *old_fsn,
 }
 
 /* and the list better be locked by something too! */
-static struct fsnotify_event *fanotify_merge(struct list_head *list,
-                                             struct fsnotify_event *event)
+static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
 {
         struct fsnotify_event *test_event;
         bool do_merge = false;
@@ -43,7 +42,7 @@ static struct fsnotify_event *fanotify_merge(struct list_head *list,
          * one we should check for permission response.
          */
         if (event->mask & FAN_ALL_PERM_EVENTS)
-                return NULL;
+                return 0;
 #endif
 
         list_for_each_entry_reverse(test_event, list, list) {
@@ -54,10 +53,10 @@ static struct fsnotify_event *fanotify_merge(struct list_head *list,
         }
 
         if (!do_merge)
-                return NULL;
+                return 0;
 
         test_event->mask |= event->mask;
-        return test_event;
+        return 1;
 }
 
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
@@ -153,7 +152,6 @@ static int fanotify_handle_event(struct fsnotify_group *group,
         int ret = 0;
         struct fanotify_event_info *event;
         struct fsnotify_event *fsn_event;
-        struct fsnotify_event *notify_fsn_event;
 
         BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
         BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
@@ -192,13 +190,11 @@ static int fanotify_handle_event(struct fsnotify_group *group,
         event->response = 0;
 #endif
 
-        notify_fsn_event = fsnotify_add_notify_event(group, fsn_event,
-                                                     fanotify_merge);
-        if (notify_fsn_event) {
+        ret = fsnotify_add_notify_event(group, fsn_event, fanotify_merge);
+        if (ret) {
                 /* Our event wasn't used in the end. Free it. */
                 fsnotify_destroy_event(group, fsn_event);
-                if (IS_ERR(notify_fsn_event))
-                        return PTR_ERR(notify_fsn_event);
+                ret = 0;
         }
 
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS