From 2b9f6f7065d4cfb65ba19126e0b35ac4544c3f3a Mon Sep 17 00:00:00 2001 From: Altan Hacigumus Date: Thu, 23 Apr 2026 18:46:38 -0700 Subject: [PATCH] tcp: make probe0 timer handle expired user timeout tcp_clamp_probe0_to_user_timeout() computes remaining time in jiffies using subtraction with an unsigned lvalue. If elapsed probing time exceeds the configured TCP_USER_TIMEOUT, the underflow yields a large value. This ends up re-arming the probe timer for a full backoff interval instead of expiring immediately, delaying connection teardown beyond the configured timeout. Fix this by preventing underflow so user-set timeout expiration is handled correctly without extending the probe timer. Fixes: 344db93ae3ee ("tcp: make TCP_USER_TIMEOUT accurate for zero window probes") Link: https://lore.kernel.org/r/20260414013634.43997-1-ahacigu.linux@gmail.com Signed-off-by: Altan Hacigumus Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260424014639.54110-1-ahacigu.linux@gmail.com Signed-off-by: Jakub Kicinski --- net/ipv4/tcp_timer.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 8d791a954cd6..322db13333c7 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -50,7 +50,8 @@ static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk) u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when) { const struct inet_connection_sock *icsk = inet_csk(sk); - u32 remaining, user_timeout; + u32 user_timeout; + s32 remaining; s32 elapsed; user_timeout = READ_ONCE(icsk->icsk_user_timeout); @@ -61,7 +62,7 @@ u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when) if (unlikely(elapsed < 0)) elapsed = 0; remaining = msecs_to_jiffies(user_timeout) - elapsed; - remaining = max_t(u32, remaining, TCP_TIMEOUT_MIN); + remaining = max_t(int, remaining, TCP_TIMEOUT_MIN); return min_t(u32, remaining, when); }