FAILED: patch "[PATCH] mptcp: pm: fix data race in add_addr timer callback" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] mptcp: pm: fix data race in add_addr timer callback" failed to apply to 5.15-stable tree

[gregkh]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x a7aad5b69d3bdaec20a3ed9284e184502450c0cd
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026082026-treble-stylized-d851@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a7aad5b69d3bdaec20a3ed9284e184502450c0cd Mon Sep 17 00:00:00 2001
From: Qing Luo <luoqing@kylinos.cn>
Date: Mon, 3 Aug 2026 18:16:36 +0200
Subject: [PATCH] mptcp: pm: fix data race in add_addr timer callback

The timer callback reads entry->retrans_times outside pm.lock to decide
whether to call mptcp_pm_subflow_established(). Since
mptcp_pm_announced_del_timer() can concurrently set retrans_times =
ADD_ADDR_RETRANS_MAX under pm.lock, a race condition exists.

I discovered this issue while studying the code. AI tools helped me to
verify the issue can potentially happen under race conditions.

Use a local 'retransmit' flag set inside pm.lock to capture whether
retransmission is still possible when the lock is taken. This allows to
call mptcp_pm_subflow_established() accordingly, and not depending on
the situation that can be different when checked outside the pm.lock.

Fixes: 348d5c1dec60 ("mptcp: move to next addr when timeout")
Cc: stable@vger.kernel.org
Signed-off-by: Qing Luo <luoqing@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-4-b8f496d71664@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index 6afd39aea110..c71dcf887683 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -380,6 +380,7 @@ static void mptcp_pm_add_addr_timer(struct timer_list *timer)
 	struct mptcp_sock *msk = entry->sock;
 	struct sock *sk = (struct sock *)msk;
 	unsigned int timeout = 0;
+	bool retransmit;
 
 	pr_debug("msk=%p\n", msk);
 
@@ -412,14 +413,15 @@ static void mptcp_pm_add_addr_timer(struct timer_list *timer)
 		entry->retrans_times++;
 	}
 
-	if (entry->retrans_times < ADD_ADDR_RETRANS_MAX)
+	retransmit = entry->retrans_times < ADD_ADDR_RETRANS_MAX;
+	if (retransmit)
 		timeout <<= entry->retrans_times;
 	else
 		timeout = 0;
 
 	spin_unlock_bh(&msk->pm.lock);
 
-	if (entry->retrans_times == ADD_ADDR_RETRANS_MAX)
+	if (!retransmit)
 		mptcp_pm_subflow_established(msk);
 
 out: