tcp: Fix data-races around sysctl_tcp_reflect_tos.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2160073
Upstream Status: linux.git

commit 870e3a6
Author: Kuniyuki Iwashima <kuniyu@amazon.com>
Date:   Fri Jul 22 11:22:04 2022 -0700

    tcp: Fix data-races around sysctl_tcp_reflect_tos.

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

    Fixes: ac8f171 ("tcp: reflect tos value received in SYN to the socket")
    Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
    Acked-by: Wei Wang <weiwan@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

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

Author: Guillaume Nault

net/ipv4/tcp_ipv4.c

@@ -1000,7 +1000,7 @@ static int tcp_v4_send_synack(const struct sock *sk, struct dst_entry *dst,
 	if (skb) {
 		__tcp_v4_send_check(skb, ireq->ir_loc_addr, ireq->ir_rmt_addr);
 
-		tos = sock_net(sk)->ipv4.sysctl_tcp_reflect_tos ?
+		tos = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reflect_tos) ?
 				(tcp_rsk(req)->syn_tos & ~INET_ECN_MASK) |
 				(inet_sk(sk)->tos & INET_ECN_MASK) :
 				inet_sk(sk)->tos;
@@ -1514,7 +1514,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
 	/* Set ToS of the new socket based upon the value of incoming SYN.
 	 * ECT bits are set later in tcp_init_transfer().
 	 */
-	if (sock_net(sk)->ipv4.sysctl_tcp_reflect_tos)
+	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reflect_tos))
 		newinet->tos = tcp_rsk(req)->syn_tos & ~INET_ECN_MASK;
 
 	if (!dst) {

net/ipv6/tcp_ipv6.c

@@ -546,7 +546,7 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst,
 		if (np->repflow && ireq->pktopts)
 			fl6->flowlabel = ip6_flowlabel(ipv6_hdr(ireq->pktopts));
 
-		tclass = sock_net(sk)->ipv4.sysctl_tcp_reflect_tos ?
+		tclass = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reflect_tos) ?
 				(tcp_rsk(req)->syn_tos & ~INET_ECN_MASK) |
 				(np->tclass & INET_ECN_MASK) :
 				np->tclass;
@@ -1313,7 +1313,7 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 	/* Set ToS of the new socket based upon the value of incoming SYN.
 	 * ECT bits are set later in tcp_init_transfer().
 	 */
-	if (sock_net(sk)->ipv4.sysctl_tcp_reflect_tos)
+	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reflect_tos))
 		newnp->tclass = tcp_rsk(req)->syn_tos & ~INET_ECN_MASK;
 
 	/* Clone native IPv6 options from listening socket (if any)