On Sat, 2 Jul 2022 15:23:57 +0800 (GMT+08:00) duoming@zju.edu.cn wrote:

quoted

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(). 

Don't think that's possible, you'd have to drop the neigh lock every
time.

quoted

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.

Which one, the neigh object can be shared by multiple sockets, no?