netdev - [PATCH v1 net 6/8] tcp: Use sk_dst_dev_rcu() in tcp_fastopen_active_disable_ofo

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Message-ID: <20250911030620.1284754-7-kuniyu@google.com>
Date: Thu, 11 Sep 2025 03:05:34 +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, 
	Neal Cardwell <ncardwell@...gle.com>
Subject: [PATCH v1 net 6/8] tcp: Use sk_dst_dev_rcu() in tcp_fastopen_active_disable_ofo_check().

tcp_fastopen_active_disable_ofo_check() is called from tcp_disconnect()
or tcp_v4_destroy_sock(), so not under RCU nor RTNL.

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

Let's use sk_dst_dev_rcu().

Fixes: 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()")
Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
---
Cc: Neal Cardwell <ncardwell@...gle.com>
---
 net/ipv4/tcp_fastopen.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index f1884f0c9e52..de849b8c87ef 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -560,7 +560,6 @@ void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct net_device *dev;
-	struct dst_entry *dst;
 	struct sk_buff *skb;
 
 	if (!tp->syn_fastopen)
@@ -576,11 +575,11 @@ void tcp_fastopen_active_disable_ofo_check(struct sock *sk)
 		}
 	} else if (tp->syn_fastopen_ch &&
 		   atomic_read(&sock_net(sk)->ipv4.tfo_active_disable_times)) {
-		dst = sk_dst_get(sk);
-		dev = dst ? dst_dev(dst) : NULL;
+		rcu_read_lock();
+		dev = sk_dst_dev_rcu(sk);
 		if (!(dev && (dev->flags & IFF_LOOPBACK)))
 			atomic_set(&sock_net(sk)->ipv4.tfo_active_disable_times, 0);
-		dst_release(dst);
+		rcu_read_unlock();
 	}
 }
 
-- 
2.51.0.384.g4c02a37b29-goog