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tcp: make probe0 timer handle expired user timeout

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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: 344db93ae3 ("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 <ahacigu.linux@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260424014639.54110-1-ahacigu.linux@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Altan Hacigumus
2026-04-23 18:46:38 -07:00
committed by Jakub Kicinski
parent cc427d24ac
commit 2b9f6f7065
1 changed files with 3 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
net/ipv4/tcp_timer.c
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@@ -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);
}