inotify: Avoid reporting event with invalid wd

commit c915d8f5918bea7c3962b09b8884ca128bfd9b0c upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
index d1a64daa0171ec851903be87cd7357bf4ecba556..b0530f75b274acc9788f091e205bd00a84b8ff40 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)