tcp: Fix data-races around sysctl_tcp_fastopen_blackhole_timeout.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2149949
Upstream Status: linux.git

commit 021266e
Author: Kuniyuki Iwashima <kuniyu@amazon.com>
Date:   Fri Jul 15 10:17:55 2022 -0700

    tcp: Fix data-races around sysctl_tcp_fastopen_blackhole_timeout.

    While reading sysctl_tcp_fastopen_blackhole_timeout, it can be changed
    concurrently.  Thus, we need to add READ_ONCE() to its readers.

    Fixes: cf1ef3f ("net/tcp_fastopen: Disable active side TFO in certain scenarios")
    Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Guillaume Nault <gnault@redhat.com>

Author: Guillaume Nault

net/ipv4/tcp_fastopen.c

@@ -507,7 +507,7 @@ void tcp_fastopen_active_disable(struct sock *sk)
 {
 	struct net *net = sock_net(sk);
 
-	if (!sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout)
+	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout))
 		return;
 
 	/* Paired with READ_ONCE() in tcp_fastopen_active_should_disable() */
@@ -528,7 +528,8 @@ void tcp_fastopen_active_disable(struct sock *sk)
  */
 bool tcp_fastopen_active_should_disable(struct sock *sk)
 {
-	unsigned int tfo_bh_timeout = sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout;
+	unsigned int tfo_bh_timeout =
+		READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_fastopen_blackhole_timeout);
 	unsigned long timeout;
 	int tfo_da_times;
 	int multiplier;