fanotify: limit number of listeners per user

fanotify currently has no limit on the number of listeners a given user can
have open.  This patch limits the total number of listeners per user to
128.  This is the same as the inotify default limit.

Signed-off-by: Eric Paris <eparis@redhat.com>

include/linux/fsnotify_backend.h

@@ -170,6 +170,7 @@ struct fsnotify_group {
 #endif /* CONFIG_FANOTIFY_ACCESS_PERMISSIONS */
 			int f_flags;
 			unsigned int max_marks;
+			struct user_struct *user;
 		} fanotify_data;
 #endif /* CONFIG_FANOTIFY */
 	};