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 f1884f0c9e523d50b2d120175cc94bc40b489dfb..7d945a527daf093f87882c7949e21058ed6df1cc 100644 (file)
--- 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();
        }
 }