[PATCH 6.12.y 7/8] mptcp: Use __sk_dst_get() and dst_dev_rcu() in mptcp_active_enable().

[Sasha Levin <sashal@kernel.org>]

From: Kuniyuki Iwashima <kuniyu@google.com>

[ Upstream commit 893c49a78d9f85e4b8081b908fb7c407d018106a ]

mptcp_active_enable() is called from subflow_finish_connect(),
which is icsk->icsk_af_ops->sk_rx_dst_set() and it's not always
under RCU.

Using sk_dst_get(sk)->dev could trigger UAF.

Let's use __sk_dst_get() and dst_dev_rcu().

Fixes: 27069e7cb3d1 ("mptcp: disable active MPTCP in case of blackhole")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250916214758.650211-8-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 833d4313bc1e ("mptcp: reset blackhole on success with non-loopback ifaces")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/mptcp/ctrl.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 6a97d11bda7e2..9e1f61b02a66e 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -381,12 +381,15 @@ void mptcp_active_enable(struct sock *sk)
 	struct mptcp_pernet *pernet = mptcp_get_pernet(sock_net(sk));
 
 	if (atomic_read(&pernet->active_disable_times)) {
-		struct dst_entry *dst = sk_dst_get(sk);
+		struct net_device *dev;
+		struct dst_entry *dst;
 
-		if (dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK))
+		rcu_read_lock();
+		dst = __sk_dst_get(sk);
+		dev = dst ? dst_dev_rcu(dst) : NULL;
+		if (dev && (dev->flags & IFF_LOOPBACK))
 			atomic_set(&pernet->active_disable_times, 0);
-
-		dst_release(dst);
+		rcu_read_unlock();
 	}
 }
 
-- 
2.51.0