mptcp: Use __sk_dst_get() and dst_dev_rcu() in mptcp_active_enable().

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>

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index c0e516872b4b5943d57f6f3f4122f66e65f98a28..e8ffa62ec183f3cd8156e3969ac4a7d0213a990b 100644 (file)
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -501,12 +501,15 @@ 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();
        }
 }