inotify: Avoid reporting event with invalid wd

When inotify_freeing_mark() races with inotify_handle_inode_event() it
can happen that inotify_handle_inode_event() sees that i_mark->wd got
already reset to -1 and reports this value to userspace which can
confuse the inotify listener. Avoid the problem by validating that wd is
sensible (and pretend the mark got removed before the event got
generated otherwise).

CC: stable@vger.kernel.org
Fixes: 7e790dd5fc93 ("inotify: fix error paths in inotify_update_watch")
Message-Id: <20230424163219.9250-1-jack@suse.cz>
Reported-by: syzbot+4a06d4373fd52f0b2f9c@syzkaller.appspotmail.com
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
index 49cfe2ae6d23dff0e593d2faabb5b44b549b1404..993375f0db673112808bab6fe787bfbcc2a4a238 100644 (file)
--- a/fs/notify/inotify/inotify_fsnotify.c
+++ b/fs/notify/inotify/inotify_fsnotify.c
@@ -65,7 +65,7 @@ int inotify_handle_inode_event(struct fsnotify_mark *inode_mark, u32 mask,
        struct fsnotify_event *fsn_event;
        struct fsnotify_group *group = inode_mark->group;
        int ret;
-       int len = 0;
+       int len = 0, wd;
        int alloc_len = sizeof(struct inotify_event_info);
        struct mem_cgroup *old_memcg;
 
@@ -80,6 +80,13 @@ int inotify_handle_inode_event(struct fsnotify_mark *inode_mark, u32 mask,
        i_mark = container_of(inode_mark, struct inotify_inode_mark,
                              fsn_mark);
 
+       /*
+        * We can be racing with mark being detached. Don't report event with
+        * invalid wd.
+        */
+       wd = READ_ONCE(i_mark->wd);
+       if (wd == -1)
+               return 0;
        /*
         * Whoever is interested in the event, pays for the allocation. Do not
         * trigger OOM killer in the target monitoring memcg as it may have
@@ -110,7 +117,7 @@ int inotify_handle_inode_event(struct fsnotify_mark *inode_mark, u32 mask,
        fsn_event = &event->fse;
        fsnotify_init_event(fsn_event);
        event->mask = mask;
-       event->wd = i_mark->wd;
+       event->wd = wd;
        event->sync_cookie = cookie;
        event->name_len = len;
        if (len)