inet: implement lockless IP_TOS

Some reads of inet->tos are racy.

Add needed READ_ONCE() annotations and convert IP_TOS option lockless.

v2: missing changes in include/net/route.h (David Ahern)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 20 insertions, 24 deletions

diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 9f0bd518901a..f01aee832aab 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -134,7 +134,7 @@ int inet_diag_msg_attrs_fill(struct sock *sk, struct sk_buff *skb,
 	 * hence this needs to be included regardless of socket family.
 	 */
 	if (ext & (1 << (INET_DIAG_TOS - 1)))
-		if (nla_put_u8(skb, INET_DIAG_TOS, inet->tos) < 0)
+		if (nla_put_u8(skb, INET_DIAG_TOS, READ_ONCE(inet->tos)) < 0)
 			goto errout;
 
 #if IS_ENABLED(CONFIG_IPV6)
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 9fc7be2c2033..89e62ed08dad 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -544,7 +544,7 @@ EXPORT_SYMBOL(__ip_queue_xmit);
 
 int ip_queue_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl)
 {
-	return __ip_queue_xmit(sk, skb, fl, inet_sk(sk)->tos);
+	return __ip_queue_xmit(sk, skb, fl, READ_ONCE(inet_sk(sk)->tos));
 }
 EXPORT_SYMBOL(ip_queue_xmit);
 
@@ -1438,7 +1438,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
 	iph = ip_hdr(skb);
 	iph->version = 4;
 	iph->ihl = 5;
-	iph->tos = (cork->tos != -1) ? cork->tos : inet->tos;
+	iph->tos = (cork->tos != -1) ? cork->tos : READ_ONCE(inet->tos);
 	iph->frag_off = df;
 	iph->ttl = ttl;
 	iph->protocol = sk->sk_protocol;
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 6d874cc03c8b..50c008efbb6d 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -585,25 +585,20 @@ out:
 	return err;
 }
 
-void __ip_sock_set_tos(struct sock *sk, int val)
+void ip_sock_set_tos(struct sock *sk, int val)
 {
+	u8 old_tos = READ_ONCE(inet_sk(sk)->tos);
+
 	if (sk->sk_type == SOCK_STREAM) {
 		val &= ~INET_ECN_MASK;
-		val |= inet_sk(sk)->tos & INET_ECN_MASK;
+		val |= old_tos & INET_ECN_MASK;
 	}
-	if (inet_sk(sk)->tos != val) {
-		inet_sk(sk)->tos = val;
+	if (old_tos != val) {
+		WRITE_ONCE(inet_sk(sk)->tos, val);
 		WRITE_ONCE(sk->sk_priority, rt_tos2priority(val));
 		sk_dst_reset(sk);
 	}
 }
-
-void ip_sock_set_tos(struct sock *sk, int val)
-{
-	lock_sock(sk);
-	__ip_sock_set_tos(sk, val);
-	release_sock(sk);
-}
 EXPORT_SYMBOL(ip_sock_set_tos);
 
 void ip_sock_set_freebind(struct sock *sk)
@@ -1050,6 +1045,9 @@ int do_ip_setsockopt(struct sock *sk, int level, int optname,
 		return 0;
 	case IP_MTU_DISCOVER:
 		return ip_sock_set_mtu_discover(sk, val);
+	case IP_TOS:	/* This sets both TOS and Precedence */
+		ip_sock_set_tos(sk, val);
+		return 0;
 	}
 
 	err = 0;
@@ -1104,9 +1102,6 @@ int do_ip_setsockopt(struct sock *sk, int level, int optname,
 			}
 		}
 		break;
-	case IP_TOS:	/* This sets both TOS and Precedence */
-		__ip_sock_set_tos(sk, val);
-		break;
 	case IP_UNICAST_IF:
 	{
 		struct net_device *dev = NULL;
@@ -1593,6 +1588,9 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
 	case IP_MTU_DISCOVER:
 		val = READ_ONCE(inet->pmtudisc);
 		goto copyval;
+	case IP_TOS:
+		val = READ_ONCE(inet->tos);
+		goto copyval;
 	}
 
 	if (needs_rtnl)
@@ -1629,9 +1627,6 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
 			return -EFAULT;
 		return 0;
 	}
-	case IP_TOS:
-		val = inet->tos;
-		break;
 	case IP_MTU:
 	{
 		struct dst_entry *dst;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 95e972be0c05..a441740616d7 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1024,10 +1024,11 @@ 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 = 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;
+		tos = READ_ONCE(inet_sk(sk)->tos);
+
+		if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reflect_tos))
+			tos = (tcp_rsk(req)->syn_tos & ~INET_ECN_MASK) |
+			      (tos & INET_ECN_MASK);
 
 		if (!INET_ECN_is_capable(tos) &&
 		    tcp_bpf_ca_needs_ecn((struct sock *)req))