Poison

RST

发表于

接收到 RST 包后的处理逻辑位于 tcp_input.c at v4.15：

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/* When we get a reset we do this. */
void tcp_reset(struct sock *sk)
{
    trace_tcp_receive_reset(sk);

    /* We want the right error as BSD sees it (and indeed as we do). */
    switch (sk->sk_state) {
    case TCP_SYN_SENT:
        sk->sk_err = ECONNREFUSED;
        break;
    case TCP_CLOSE_WAIT:
        sk->sk_err = EPIPE;
        break;
    case TCP_CLOSE:
        return;
    default:
        sk->sk_err = ECONNRESET;
    }
    /* This barrier is coupled with smp_rmb() in tcp_poll() */
    smp_wmb();

    tcp_done(sk);

    if (!sock_flag(sk, SOCK_DEAD))
        sk->sk_error_report(sk);
}

即根据当前 Socket 所处的状态设置不同的 sk->sk_err，随即调用了 tcp_done 函数，源码位于 tcp.c at v4.15:

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void tcp_done(struct sock *sk)
{
    struct request_sock *req = tcp_sk(sk)->fastopen_rsk;

    if (sk->sk_state == TCP_SYN_SENT || sk->sk_state == TCP_SYN_RECV)
        TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS);

    tcp_set_state(sk, TCP_CLOSE);
    tcp_clear_xmit_timers(sk);
    if (req)
        reqsk_fastopen_remove(sk, req, false);

    sk->sk_shutdown = SHUTDOWN_MASK;

    if (!sock_flag(sk, SOCK_DEAD))
        sk->sk_state_change(sk);
    else
        inet_csk_destroy_sock(sk);
}

即设置 Socket 状态为 CLOSE 并执行相关清理操作。其中 ECONNREFUSED 的注释为 Connection refused，EPIPE 的注释为 Broken pipe，ECONNRESET 的注释为 Connection reset by peer。