From 36534d3c54537bf098224a32dc31397793d4594d Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 7 Jun 2024 12:56:52 +0000 Subject: [PATCH] tcp: use signed arithmetic in tcp_rtx_probe0_timed_out() Due to timer wheel implementation, a timer will usually fire after its schedule. For instance, for HZ=1000, a timeout between 512ms and 4s has a granularity of 64ms. For this range of values, the extra delay could be up to 63ms. For TCP, this means that tp->rcv_tstamp may be after inet_csk(sk)->icsk_timeout whenever the timer interrupt finally triggers, if one packet came during the extra delay. We need to make sure tcp_rtx_probe0_timed_out() handles this case. Fixes: e89688e3e978 ("net: tcp: fix unexcepted socket die when snd_wnd is 0") Signed-off-by: Eric Dumazet Cc: Menglong Dong Acked-by: Neal Cardwell Reviewed-by: Jason Xing Link: https://lore.kernel.org/r/20240607125652.1472540-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- net/ipv4/tcp_timer.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 83fe7f62f7f1..5bfd76a31af6 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -485,8 +485,12 @@ static bool tcp_rtx_probe0_timed_out(const struct sock *sk, { const struct tcp_sock *tp = tcp_sk(sk); const int timeout = TCP_RTO_MAX * 2; - u32 rcv_delta; + s32 rcv_delta; + /* Note: timer interrupt might have been delayed by at least one jiffy, + * and tp->rcv_tstamp might very well have been written recently. + * rcv_delta can thus be negative. + */ rcv_delta = inet_csk(sk)->icsk_timeout - tp->rcv_tstamp; if (rcv_delta <= timeout) return false;