netdev - Question about timewait timer

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:	Wed, 28 Mar 2012 22:21:59 +0800
From:	Chao Pei <peichao85@...il.com>
To:	netdev@...r.kernel.org
Subject: Question about timewait timer

Hi,
    I have a qestion about timewait timer in tcp_keepalive_timer. In
the following code:

int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
			  const struct tcphdr *th, unsigned int len)
{
    .....
    case FIN_WAIT_1:
    ......
            tmo = tcp_fin_time(sk);
            if (tmo > TCP_TIMEWAIT_LEN) {
                inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
            } else if (.....)
    ......
}

    If tmo is larger than TCP_TIMEWAIT_LEN and the FIN flag is not
set, schedule keepalive timer. But in tcp_keepalive_timer, the timer
is set to tcp_fin_time(sk) -TCP_TIMEWAIT_LEN again. See the source
code below:
	if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
		if (tp->linger2 >= 0) {
			const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;

			if (tmo > 0) {
				tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
				goto out;
			}
		}
		.....
	}

    I think the first piece of code set keepalive timer to
tmo-TCP_TIMEWAIT_LEN is because TCP_TIMEWAIT_LEN is the longest timer
that tcp_death_row can handle. So the extra time should be taken care
of by the keepalive timer first. If this is correct, then the timer
should be set to TCP_TIMEWAIT_LEN in tcp_keepalive_timer, instead of
tcp_fin_time(sk) - TCP_TIMEWAIT_LEN.

Thanks.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html