On Wed, Nov 22, 2023 at 11:24:51AM -0800, John Fastabend wrote: > AF_UNIX stream sockets are a paired socket. So sending on one of the pairs > will lookup the paired socket as part of the send operation. It is possible > however to put just one of the pairs in a BPF map. This currently > increments the refcnt on the sock in the sockmap to ensure it is not > free'd by the stack before sockmap cleans up its state and stops any > skbs being sent/recv'd to that socket. > > But we missed a case. If the peer socket is closed it will be > free'd by the stack. However, the paired socket can still be > referenced from BPF sockmap side because we hold a reference > there. Then if we are sending traffic through BPF sockmap to > that socket it will try to dereference the free'd pair in its > send logic creating a use after free. And following splat, Hmm, how could it pass the SOCK_DEAD test in unix_stream_sendmsg()? 2285 unix_state_lock(other); 2286 2287 if (sock_flag(other, SOCK_DEAD) || 2288 (other->sk_shutdown & RCV_SHUTDOWN)) 2289 goto pipe_err_free; Thanks.
