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net: tcp: fix unexcepted socket die when snd_wnd is 0

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In tcp_retransmit_timer(), a window shrunk connection will be regarded
as timeout if 'tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX'. This is not
right all the time.

The retransmits will become zero-window probes in tcp_retransmit_timer()
if the 'snd_wnd==0'. Therefore, the icsk->icsk_rto will come up to
TCP_RTO_MAX sooner or later.

However, the timer can be delayed and be triggered after 122877ms, not
TCP_RTO_MAX, as I tested.

Therefore, 'tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX' is always true
once the RTO come up to TCP_RTO_MAX, and the socket will die.

Fix this by replacing the 'tcp_jiffies32' with '(u32)icsk->icsk_timeout',
which is exact the timestamp of the timeout.

However, "tp->rcv_tstamp" can restart from idle, then tp->rcv_tstamp
could already be a long time (minutes or hours) in the past even on the
first RTO. So we double check the timeout with the duration of the
retransmission.

Meanwhile, making "2 * TCP_RTO_MAX" as the timeout to avoid the socket
dying too soon.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Link: https://lore.kernel.org/netdev/CADxym3YyMiO+zMD4zj03YPM3FBi-1LHi6gSD2XT8pyAMM096pg@mail.gmail.com/
Signed-off-by: Menglong Dong <imagedong@tencent.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Menglong Dong 2023-08-11 10:55:29 +08:00 committed by David S. Miller
parent 800a666141
commit e89688e3e9
1 changed files with 17 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

18
net/ipv4/tcp_timer.c
View file

@ -454,6 +454,22 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
req->timeout << req->num_timeout, TCP_RTO_MAX);
}
static bool tcp_rtx_probe0_timed_out(const struct sock *sk,
const struct sk_buff *skb)
{
const struct tcp_sock *tp = tcp_sk(sk);
const int timeout = TCP_RTO_MAX * 2;
u32 rcv_delta, rtx_delta;
rcv_delta = inet_csk(sk)->icsk_timeout - tp->rcv_tstamp;
if (rcv_delta <= timeout)
return false;
rtx_delta = (u32)msecs_to_jiffies(tcp_time_stamp(tp) -
(tp->retrans_stamp ?: tcp_skb_timestamp(skb)));
return rtx_delta > timeout;
}
/**
* tcp_retransmit_timer() - The TCP retransmit timeout handler
@ -519,7 +535,7 @@ void tcp_retransmit_timer(struct sock *sk)
tp->snd_una, tp->snd_nxt);
}
#endif
if (tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX) {
if (tcp_rtx_probe0_timed_out(sk, skb)) {
tcp_write_err(sk);
goto out;
}