ipv6: lockless IPV6_RECVERR_RFC4884 implementation

Move np->recverr_rfc4884 to an atomic flag to fix data-races.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/ipv6.h

@@ -256,7 +256,6 @@ struct ipv6_pinfo {
 				autoflowlabel:1,
 				autoflowlabel_set:1,
 				mc_all:1,
-				recverr_rfc4884:1,
 				rtalert_isolate:1;
 	__u8			min_hopcount;
 	__u8			tclass;

include/net/inet_sock.h

@@ -269,6 +269,7 @@ enum {
 	INET_FLAGS_BIND_ADDRESS_NO_PORT = 18,
 	INET_FLAGS_DEFER_CONNECT = 19,
 	INET_FLAGS_MC6_LOOP	= 20,
+	INET_FLAGS_RECVERR6_RFC4884 = 21,
 };
 
 /* cmsg flags for inet */

net/ipv6/datagram.c

@@ -332,7 +332,7 @@ void ipv6_icmp_error(struct sock *sk, struct sk_buff *skb, int err,
 
 	__skb_pull(skb, payload - skb->data);
 
-	if (inet6_sk(sk)->recverr_rfc4884)
+	if (inet6_test_bit(RECVERR6_RFC4884, sk))
 		ipv6_icmp_error_rfc4884(skb, &serr->ee.ee_rfc4884);
 
 	skb_reset_transport_header(skb);

net/ipv6/ipv6_sockglue.c

@@ -462,6 +462,13 @@ int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 		 */
 		WRITE_ONCE(np->min_hopcount, val);
 		return 0;
+	case IPV6_RECVERR_RFC4884:
+		if (optlen < sizeof(int))
+			return -EINVAL;
+		if (val < 0 || val > 1)
+			return -EINVAL;
+		inet6_assign_bit(RECVERR6_RFC4884, sk, valbool);
+		return 0;
 	}
 	if (needs_rtnl)
 		rtnl_lock();
@@ -974,14 +981,6 @@ int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 		np->rxopt.bits.recvfragsize = valbool;
 		retv = 0;
 		break;
-	case IPV6_RECVERR_RFC4884:
-		if (optlen < sizeof(int))
-			goto e_inval;
-		if (val < 0 || val > 1)
-			goto e_inval;
-		np->recverr_rfc4884 = valbool;
-		retv = 0;
-		break;
 	}
 
 unlock:
@@ -1462,7 +1461,7 @@ int do_ipv6_getsockopt(struct sock *sk, int level, int optname,
 		break;
 
 	case IPV6_RECVERR_RFC4884:
-		val = np->recverr_rfc4884;
+		val = inet6_test_bit(RECVERR6_RFC4884, sk);
 		break;
 
 	default: