[PATCH 5.10.y 1/2] mptcp: pm: ADD_ADDR rtx: always decrease sk refcount

[Karl Mehltretter]

From: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>

[ Upstream commit 9634cb35af17019baec21ca648516ce376fa10e6 ]

When an ADD_ADDR is retransmitted, the sk is held in sk_reset_timer().
It should then be released in all cases at the end.

Some (unlikely) checks were returning directly instead of calling
sock_put() to decrease the refcount. Jump to a new 'exit' label to call
__sock_put() (which will become sock_put() in the next commit) to fix
this potential leak.

While at it, drop the '!msk' check which cannot happen because it is
never reset, and explicitly mark the remaining one as "unlikely".

Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Mat Martineau <martineau@xxxxxxxxxx>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
Link: https://patch.msgid.link/20260505-net-mptcp-pm-fixes-7-1-rc3-v1-4-fca8091060a4@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
[ Karl Mehltretter: applied to pm_netlink.c; retained v5.10's ID 0 guard
  and routed it through the common refcount drop. ]
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>
---
 net/mptcp/pm_netlink.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index d4d56f0af3e0a..aee3a8dd9287a 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -217,14 +217,11 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 
 	pr_debug("msk=%p\n", msk);
 
-	if (!msk)
-		return;
-
-	if (inet_sk_state_load(sk) == TCP_CLOSE)
-		return;
+	if (unlikely(inet_sk_state_load(sk) == TCP_CLOSE))
+		goto exit;
 
 	if (!entry->addr.id)
-		return;
+		goto exit;
 
 	bh_lock_sock(sk);
 	if (sock_owned_by_user(sk)) {
@@ -253,6 +250,7 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 
 out:
 	bh_unlock_sock(sk);
+exit:
 	__sock_put(sk);
 }
 
-- 
2.53.0