git: e8d1cee43741 - stable/15 - tcp: improve handling of stopped timers

The branch stable/15 has been updated by tuexen:

URL: https://cgit.FreeBSD.org/src/commit/?id=e8d1cee437414dd9bb3c779ff0a0c234fb7d411e

commit e8d1cee437414dd9bb3c779ff0a0c234fb7d411e
Author:     Michael Tuexen <tuexen@FreeBSD.org>
AuthorDate: 2026-07-28 20:15:22 +0000
Commit:     Michael Tuexen <tuexen@FreeBSD.org>
CommitDate: 2026-08-06 09:07:02 +0000

    tcp: improve handling of stopped timers
    
    When a TCP timer is stopped, t_timers[] is set to SBT_MAX. Adding the
    corresponding t_precisions[], if it is not zero, would result in
    overflows in tcp_timer_next(). To avoid this, skip stopped timers.
    
    The problem was identified while debugging uperf by Lukas Book and
    an initial patch was provided by him. The committed patch was
    suggested by glebius.
    
    The problem can be observed by running netstat -nxptcp and looking for
    negative timer values and by observing very long running timers in
    some cases.
    
    Reported by:            Lukas Book <lkbook@outlook.de>
    Reviewed by:            glebius
    Differential Revision:  https://reviews.freebsd.org/D58484
    
    (cherry picked from commit 52b7cbcb78c14e89f6faec8da5acc2caa3d37208)
---
 sys/netinet/tcp_timer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sys/netinet/tcp_timer.c b/sys/netinet/tcp_timer.c
index 57c57666fa3a..56c50faaf4d1 100644
--- a/sys/netinet/tcp_timer.c
+++ b/sys/netinet/tcp_timer.c
@@ -859,6 +859,8 @@ tcp_timer_next(struct tcpcb *tp, sbintime_t *precision)
 	sbintime_t after, before;
 
 	for (i = 0, rv = TT_N, after = before = SBT_MAX; i < TT_N; i++) {
+		if (tp->t_timers[i] == SBT_MAX)
+			continue;
 		if (tp->t_timers[i] < after) {
 			after = tp->t_timers[i];
 			rv = i;