net-timestamp: make tcp_recvmsg call ipv6_recv_error for AF_INET6 socks

TCP timestamping introduced MSG_ERRQUEUE handling for TCP sockets.
If the socket is of family AF_INET6, call ipv6_recv_error instead
of ip_recv_error.

This change is more complex than a single branch due to the loadable
ipv6 module. It reuses a pre-existing indirect function call from
ping. The ping code is safe to call, because it is part of the core
ipv6 module and always present when AF_INET6 sockets are active.

Fixes: 4ed2d76 (net-timestamp: TCP timestamping)
Signed-off-by: Willem de Bruijn <willemb@google.com>

----

It may also be worthwhile to add WARN_ON_ONCE(sk->family == AF_INET6)
to ip_recv_error.
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_common.h

@@ -37,6 +37,8 @@ int inet_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg);
 int inet_ctl_sock_create(struct sock **sk, unsigned short family,
 			 unsigned short type, unsigned char protocol,
 			 struct net *net);
+int inet_recv_error(struct sock *sk, struct msghdr *msg, int len,
+		    int *addr_len);
 
 static inline void inet_ctl_sock_destroy(struct sock *sk)
 {

net/ipv4/af_inet.c

@@ -1386,6 +1386,17 @@ static struct sk_buff **inet_gro_receive(struct sk_buff **head,
 	return pp;
 }
 
+int inet_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
+{
+	if (sk->sk_family == AF_INET)
+		return ip_recv_error(sk, msg, len, addr_len);
+#if IS_ENABLED(CONFIG_IPV6)
+	if (sk->sk_family == AF_INET6)
+		return pingv6_ops.ipv6_recv_error(sk, msg, len, addr_len);
+#endif
+	return -EINVAL;
+}
+
 static int inet_gro_complete(struct sk_buff *skb, int nhoff)
 {
 	__be16 newlen = htons(skb->len - nhoff);

net/ipv4/ping.c

@@ -855,16 +855,8 @@ int ping_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	if (flags & MSG_OOB)
 		goto out;
 
-	if (flags & MSG_ERRQUEUE) {
-		if (family == AF_INET) {
-			return ip_recv_error(sk, msg, len, addr_len);
-#if IS_ENABLED(CONFIG_IPV6)
-		} else if (family == AF_INET6) {
-			return pingv6_ops.ipv6_recv_error(sk, msg, len,
-							  addr_len);
-#endif
-		}
-	}
+	if (flags & MSG_ERRQUEUE)
+		return inet_recv_error(sk, msg, len, addr_len);
 
 	skb = skb_recv_datagram(sk, flags, noblock, &err);
 	if (!skb)

net/ipv4/tcp.c

@@ -1598,7 +1598,7 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	u32 urg_hole = 0;
 
 	if (unlikely(flags & MSG_ERRQUEUE))
-		return ip_recv_error(sk, msg, len, addr_len);
+		return inet_recv_error(sk, msg, len, addr_len);
 
 	if (sk_can_busy_loop(sk) && skb_queue_empty(&sk->sk_receive_queue) &&
 	    (sk->sk_state == TCP_ESTABLISHED))