fsnotify: Allocate overflow events with proper type

Commit 7053aee26a35 "fsnotify: do not share events between notification
groups" used overflow event statically allocated in a group with the
size of the generic notification event. This causes problems because
some code looks at type specific parts of event structure and gets
confused by a random data it sees there and causes crashes.

Fix the problem by allocating overflow event with type corresponding to
the group type so code cannot get confused.

Signed-off-by: Jan Kara <jack@suse.cz>

4 files changed, 34 insertions, 3 deletions

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index b6175fa11bf8..287a22c04149 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -698,6 +698,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
         struct fsnotify_group *group;
         int f_flags, fd;
         struct user_struct *user;
+        struct fanotify_event_info *oevent;
 
         pr_debug("%s: flags=%d event_f_flags=%d\n",
                 __func__, flags, event_f_flags);
@@ -730,8 +731,20 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
         group->fanotify_data.user = user;
         atomic_inc(&user->fanotify_listeners);
 
+        oevent = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
+        if (unlikely(!oevent)) {
+                fd = -ENOMEM;
+                goto out_destroy_group;
+        }
+        group->overflow_event = &oevent->fse;
+        fsnotify_init_event(group->overflow_event, NULL, FS_Q_OVERFLOW);
+        oevent->tgid = get_pid(task_tgid(current));
+        oevent->path.mnt = NULL;
+        oevent->path.dentry = NULL;
+
         group->fanotify_data.f_flags = event_f_flags;
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+        oevent->response = 0;
         mutex_init(&group->fanotify_data.access_mutex);
         init_waitqueue_head(&group->fanotify_data.access_waitq);
         INIT_LIST_HEAD(&group->fanotify_data.access_list);
diff --git a/fs/notify/group.c b/fs/notify/group.c
index ee674fe2cec7..ad1995980456 100644
--- a/fs/notify/group.c
+++ b/fs/notify/group.c
@@ -55,6 +55,13 @@ void fsnotify_destroy_group(struct fsnotify_group *group)
         /* clear the notification queue of all events */
         fsnotify_flush_notify(group);
 
+        /*
+         * Destroy overflow event (we cannot use fsnotify_destroy_event() as
+         * that deliberately ignores overflow events.
+         */
+        if (group->overflow_event)
+                group->ops->free_event(group->overflow_event);
+
         fsnotify_put_group(group);
 }
 
@@ -99,7 +106,6 @@ struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
         INIT_LIST_HEAD(&group->marks_list);
 
         group->ops = ops;
-        fsnotify_init_event(&group->overflow_event, NULL, FS_Q_OVERFLOW);
 
         return group;
 }
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index 6528b5a54ca0..78a2ca3966c3 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -633,11 +633,23 @@ static int inotify_update_watch(struct fsnotify_group *group, struct inode *inod
 static struct fsnotify_group *inotify_new_group(unsigned int max_events)
 {
         struct fsnotify_group *group;
+        struct inotify_event_info *oevent;
 
         group = fsnotify_alloc_group(&inotify_fsnotify_ops);
         if (IS_ERR(group))
                 return group;
 
+        oevent = kmalloc(sizeof(struct inotify_event_info), GFP_KERNEL);
+        if (unlikely(!oevent)) {
+                fsnotify_destroy_group(group);
+                return ERR_PTR(-ENOMEM);
+        }
+        group->overflow_event = &oevent->fse;
+        fsnotify_init_event(group->overflow_event, NULL, FS_Q_OVERFLOW);
+        oevent->wd = -1;
+        oevent->sync_cookie = 0;
+        oevent->name_len = 0;
+
         group->max_events = max_events;
 
         spin_lock_init(&group->inotify_data.idr_lock);
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 6a4ba17c0395..1e58402171a5 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -98,11 +98,11 @@ int fsnotify_add_notify_event(struct fsnotify_group *group,
         if (group->q_len >= group->max_events) {
                 ret = 2;
                 /* Queue overflow event only if it isn't already queued */
-                if (!list_empty(&group->overflow_event.list)) {
+                if (!list_empty(&group->overflow_event->list)) {
                         mutex_unlock(&group->notification_mutex);
                         return ret;
                 }
-                event = &group->overflow_event;
+                event = group->overflow_event;
                 goto queue;
         }