netdev - [PATCH v1 net 8/8] mptcp: Use sk_dst_dev_rcu() in mptcp_active

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Message-ID: <20250911030620.1284754-9-kuniyu@google.com>
Date: Thu, 11 Sep 2025 03:05:36 +0000
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	Matthieu Baerts <matttbe@...nel.org>, Mat Martineau <martineau@...nel.org>, 
	Geliang Tang <geliang@...nel.org>
Subject: [PATCH v1 net 8/8] mptcp: Use sk_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.

Also, mptcp_active_enable() forgot dst_release().

Let's use sk_dst_dev_rcu().

Fixes: 27069e7cb3d1 ("mptcp: disable active MPTCP in case of blackhole")
Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
---
Cc: Matthieu Baerts <matttbe@...nel.org>
Cc: Mat Martineau <martineau@...nel.org>
Cc: Geliang Tang <geliang@...nel.org>
---
 net/mptcp/ctrl.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index fed40dae5583..f227415e8568 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -501,10 +501,13 @@ 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;
 
-		if (dst && dst->dev && (dst->dev->flags & IFF_LOOPBACK))
+		rcu_read_lock();
+		dev = sk_dst_dev_rcu(sk);
+		if (dev && (dev->flags & IFF_LOOPBACK))
 			atomic_set(&pernet->active_disable_times, 0);
+		rcu_read_unlock();
 	}
 }
 
-- 
2.51.0.384.g4c02a37b29-goog