bpf: sockmap: Fix use-after-free of sk->sk_socket in sk_psock_verdict_data_ready().
In the Linux kernel, the following vulnerability has been resolved: bpf: sockmap: Fix use-after-free of sk->sk_socket in sk_psock_verdict_data_ready(). syzbot reported use-after-free of AF_UNIX socket's sk->sk_socket in sk_psock_verdict_data_ready(). [0] In unix_stream_sendmsg(), the peer socket's ->sk_data_ready() is called after dropping its unix_state_lock(). Although the sender socket holds the peer's refcount, it does not prevent the peer's sock_orphan(), and the peer's sk_socket might be freed after one RCU grace period. Let's fetch the peer's sk->sk_socket and sk->sk_socket->ops under RCU in sk_psock_verdict_data_ready(). [0]: BU