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mptcp: pm: add WARN_ON_ONCE guards on extra_subflows underflow

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extra_subflows is a u8 counter that can underflow if a decrement races
with or precedes an increment. While the recently fixed userspace PM
subflow creation path eliminated the primary cause, add defensive
WARN_ON_ONCE guards at both decrement sites to catch any remaining edge
cases rather than silently wrapping to 255.

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260812-net-next-mptcp-misc-feat-7-3-v1-1-1905a818f6cb@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Tao Cui 2026-08-12 16:55:36 +02:00 committed by Jakub Kicinski
parent ff31c9a708
commit e99c1ca890
2 changed files with 4 additions and 2 deletions
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3
net/mptcp/pm.c
View File

@ -670,7 +670,8 @@ void mptcp_pm_subflow_check_next(struct mptcp_sock *msk,
if (mptcp_pm_is_userspace(msk)) {
if (update_subflows) {
spin_lock_bh(&pm->lock);
pm->extra_subflows--;
if (!WARN_ON_ONCE(pm->extra_subflows == 0))
pm->extra_subflows--;
spin_unlock_bh(&pm->lock);
}
return;

3
net/mptcp/protocol.h
View File

@ -1254,7 +1254,8 @@ u8 mptcp_pm_get_limit_extra_subflows(const struct mptcp_sock *msk);
/* called under PM lock */
static inline void __mptcp_pm_close_subflow(struct mptcp_sock *msk)
{
if (--msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk))
if (!WARN_ON_ONCE(msk->pm.extra_subflows == 0) &&
--msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk))
WRITE_ONCE(msk->pm.accept_subflow, true);
}