The following commit has been merged in the linux branch: commit 9f0d793b52eb2266359661369ef6303838904855 Author: Eric Paris eparis@redhat.com Date: Fri Sep 11 13:03:19 2009 -0400

fsnotify: do not set group for a mark before it is on the i_list

fsnotify_add_mark is supposed to add a mark to the g_list and i_list and to set the group and inode for the mark. fsnotify_destroy_mark_by_entry uses the fact that ->group != NULL to know if this group should be destroyed or if it's already been done.

But fsnotify_add_mark sets the group and inode before it actually adds the mark to the i_list and g_list. This can result in a race in inotify, it requires 3 threads.

sys_inotify_add_watch("file") sys_inotify_add_watch("file") sys_inotify_rm_watch([a]) inotify_update_watch() inotify_new_watch() inotify_add_to_idr() ^--- returns wd = [a] inotfiy_update_watch() inotify_new_watch() inotify_add_to_idr() fsnotify_add_mark() ^--- returns wd = [b] returns to userspace; inotify_idr_find([a]) ^--- gives us the pointer from task 1 fsnotify_add_mark() ^--- this is going to set the mark->group and mark->inode fields, but will return -EEXIST because of the race with [b]. fsnotify_destroy_mark() ^--- since ->group != NULL we call back into inotify_freeing_mark() which calls inotify_remove_from_idr([a])

since fsnotify_add_mark() failed we call: inotify_remove_from_idr([a]) <------WHOOPS it's not in the idr, this could have been any entry added later!

The fix is to make sure we don't set mark->group until we are sure the mark is on the inode and fsnotify_add_mark will return success.

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

diff --git a/fs/notify/inode_mark.c b/fs/notify/inode_mark.c index c8a07c6..3165d85 100644 --- a/fs/notify/inode_mark.c +++ b/fs/notify/inode_mark.c @@ -324,11 +324,11 @@ int fsnotify_add_mark(struct fsnotify_mark_entry *entry, spin_lock(&group->mark_lock); spin_lock(&inode->i_lock);

- entry->group = group; - entry->inode = inode; - lentry = fsnotify_find_mark_entry(group, inode); if (!lentry) { + entry->group = group; + entry->inode = inode; + hlist_add_head(&entry->i_list, &inode->i_fsnotify_mark_entries); list_add(&entry->g_list, &group->mark_entries);