From: Eric Dumazet <edumazet@google.com>
Date: Thu, 28 Aug 2025 19:58:22 +0000 (+0000)
Subject: tcp: use dst_dev_rcu() in tcp_fastopen_active_disable_ofo_check()
X-Git-Tag: v6.18-rc1~132^2~295^2~1
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=b62a59c18b692f892dcb8109c1c2e653b2abc95c;p=thirdparty%2Fkernel%2Fstable.git

tcp: use dst_dev_rcu() in tcp_fastopen_active_disable_ofo_check()

Use RCU to avoid a pair of atomic operations and a potential
UAF on dst_dev()->flags.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250828195823.3958522-8-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---

diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index f1884f0c9e523..7d945a527daf0 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -576,11 +576,12 @@ 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();
+		dst = __sk_dst_get(sk);
+		dev = dst ? dst_dev_rcu(dst) : NULL;
 		if (!(dev && (dev->flags & IFF_LOOPBACK)))
 			atomic_set(&sock_net(sk)->ipv4.tfo_active_disable_times, 0);
-		dst_release(dst);
+		rcu_read_unlock();
 	}
 }