Re: [PATCH bpf-next v3 2/3] bpf, sockmap: avoid using sk_socket after free when reading

[Cong Wang]

On Mon, Mar 17, 2025 at 05:22:55PM +0800, Jiayuan Chen wrote:
> There are potential concurrency issues, as shown below.
> '''
> CPU0                               CPU1
> sk_psock_verdict_data_ready:
>   socket *sock = sk->sk_socket
>   if (!sock) return
>                                    close(fd):
>                                      ...
>                                      ops->release()
>   if (!sock->ops) return
>                                      sock->ops = NULL
>                                      rcu_call(sock)
>                                      free(sock)
>   READ_ONCE(sock->ops)
>   ^
>   use 'sock' after free
> '''
> 
> RCU is not applicable to Unix sockets read path, because the Unix socket
> implementation itself assumes it's always in process context and heavily
> uses mutex_lock, so, we can't call read_skb within rcu lock.

Hm, I guess the RCU work in sk_psock_drop() does not work for Unix
domain sockets either?

Thanks.