[PATCH 6.12.y] mptcp: pm: fix data race in add_addr timer callback

From: Qing Luo <[email protected]>

[ Upstream commit a7aad5b69d3bdaec20a3ed9284e184502450c0cd ]

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: [email protected]
Signed-off-by: Qing Luo <[email protected]>
Reviewed-by: Matthieu Baerts (NGI0) <[email protected]>
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Link: https://patch.msgid.link/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-4-b8f496d71664@kernel.org
Signed-off-by: Jakub Kicinski <[email protected]>
[ applied to mptcp_pm_add_timer() in pm_netlink.c instead of pm.c and collapsed the adaptive backoff branch to `if (!retransmit) timeout = 0;` since the tree lacks exponential ADD_ADDR retransmission timeouts ]
Signed-off-by: Sasha Levin <[email protected]>
---
 net/mptcp/pm_netlink.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 550c4c1b963d8..2762b3f1a25ac 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -296,6 +296,7 @@ static void mptcp_pm_add_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);
 
@@ -333,12 +334,13 @@ static void mptcp_pm_add_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 = 0;
 
 	spin_unlock_bh(&msk->pm.lock);
 
-	if (entry->retrans_times == ADD_ADDR_RETRANS_MAX)
+	if (!retransmit)
 		mptcp_pm_subflow_established(msk);
 
 out:
-- 
2.53.0