Hello,

On Fri, 1 Jul 2022 19:41:55 -0700 Jakub Kicinski wrote:

On Wed, 29 Jun 2022 18:49:41 +0800 Duoming Zhou wrote:

quoted

When the link layer connection is broken, the rose->neighbour is
set to null. But rose->neighbour could be used by rose_connection()
and rose_release() later, because there is no synchronization among
them. As a result, the null-ptr-deref bugs will happen.

One of the null-ptr-deref bugs is shown below:

    (thread 1)                  |        (thread 2)
                                |  rose_connect
rose_kill_by_neigh              |    lock_sock(sk)
  spin_lock_bh(&rose_list_lock) |    if (!rose->neighbour)
  rose->neighbour = NULL;//(1)  |
                                |    rose->neighbour->use++;//(2)

quoted

 		if (rose->neighbour == neigh) {

Why is it okay to perform this comparison without the socket lock,
if we need a socket lock to clear it? Looks like rose_kill_by_neigh()
is not guaranteed to clear all the uses of a neighbor.

I am sorry, the comparision should also be protected with socket lock.
The rose_kill_by_neigh() only clear the neighbor that is passed as
parameter of rose_kill_by_neigh(). 

quoted

+			sock_hold(s);
+			spin_unlock_bh(&rose_list_lock);
+			lock_sock(s);
 			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
 			rose->neighbour->use--;

What protects the use counter?

The use coounter is protected by socket lock.

quoted

 			rose->neighbour = NULL;
+			release_sock(s);
+			spin_lock_bh(&rose_list_lock);

Don't take the lock here just dump one line further back.

Ok, I will dump one line further back.

Best regards,
Duoming Zhou