[SRU][Q][PATCH 1/1] mptcp: pm: ADD_ADDR rtx: fix potential data-race

[Cengiz Can]

From: "Matthieu Baerts (NGI0)" <matttbe at kernel.org>

This mptcp_pm_add_timer() helper is executed as a timer callback in
softirq context. To avoid any data races, the socket lock needs to be
held with bh_lock_sock().

If the socket is in use, retry again soon after, similar to what is done
with the keepalive timer.

Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
Cc: stable at vger.kernel.org
Reviewed-by: Mat Martineau <martineau at kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe at kernel.org>
Link: https://patch.msgid.link/20260505-net-mptcp-pm-fixes-7-1-rc3-v1-3-fca8091060a4@kernel.org
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(backported from commit 5cd6e0ad79d2615264f63929f8b457ad97ae550d)
[bot_kybele: Kept this tree's extra "if (!entry->addr.id) return;" guard before
 the new bh_lock_sock() block, since that bare return must stay outside the lock
 to avoid returning while holding it.]
CVE-2026-46137
Assisted-by: kybele:claude-opus-4.8
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 net/mptcp/pm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index c27035e1c046..f41f4bad8993 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -288,6 +288,13 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 	if (!entry->addr.id)
 		return;
 
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		/* Try again later. */
+		sk_reset_timer(sk, timer, jiffies + HZ / 20);
+		goto out;
+	}
+
 	if (mptcp_pm_should_add_signal_addr(msk)) {
 		sk_reset_timer(sk, timer, jiffies + TCP_RTO_MAX / 8);
 		goto out;
@@ -316,6 +323,7 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 		mptcp_pm_subflow_established(msk);
 
 out:
+	bh_unlock_sock(sk);
 	__sock_put(sk);
 }
 
-- 
2.43.0