This is a note to let you know that I've just added the patch titled
net: tcp: fix unexcepted socket die when snd_wnd is 0
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-tcp-fix-unexcepted-socket-die-when-snd_wnd-is-0.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 186695735c368f0738d7a3e5aef210b720f9577c
Author: Menglong Dong <imagedong@xxxxxxxxxxx>
Date: Fri Aug 11 10:55:29 2023 +0800
net: tcp: fix unexcepted socket die when snd_wnd is 0
[ Upstream commit e89688e3e97868451a5d05b38a9d2633d6785cd4 ]
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: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Link: https://lore.kernel.org/netdev/CADxym3YyMiO+zMD4zj03YPM3FBi-1LHi6gSD2XT8pyAMM096pg@xxxxxxxxxxxxxx/
Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 366c3c25ebe20..db90bd2d4ed66 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -441,6 +441,22 @@ 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
@@ -506,7 +522,7 @@ 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;
}
