tcp: Fix a data-race around sysctl_tcp_abort_on_overflow.

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

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_minisocks.c

@@ -781,7 +781,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 	if (sk != req->rsk_listener)
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
 
-	if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) {
+	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) {
 		inet_rsk(req)->acked = 1;
 		return NULL;
 	}