ipv6: Add sockopt IPV6_MULTICAST_ALL analogue to IP_MULTICAST_ALL

The socket option will be enabled by default to ensure current behaviour
is not changed. This is the same for the IPv4 version.

A socket bound to in6addr_any and a specific port will receive all traffic
on that port. Analogue to IP_MULTICAST_ALL, disable this behaviour, if
one or more multicast groups were joined (using said socket) and only
pass on multicast traffic from groups, which were explicitly joined via
this socket.

Without this option disabled a socket (system even) joined to multiple
multicast groups is very hard to get right. Filtering by destination
address has to take place in user space to avoid receiving multicast
traffic from other multicast groups, which might have traffic on the same
port.

The extension of the IP_MULTICAST_ALL socketoption to just apply to ipv6,
too, is not done to avoid changing the behaviour of current applications.

Signed-off-by: Andre Naujoks <[e-mail]>
Acked-By: YOSHIFUJI Hideaki <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/ipv6.h

···
 						 */
 				dontfrag:1,
 				autoflowlabel:1,
-				autoflowlabel_set:1;
+				autoflowlabel_set:1,
+				mc_all:1;
 	__u8			min_hopcount;
 	__u8			tclass;
 	__be32			rcv_flowinfo;

include/uapi/linux/in6.h

···
 #define IPV6_V6ONLY		26
 #define IPV6_JOIN_ANYCAST	27
 #define IPV6_LEAVE_ANYCAST	28
+#define IPV6_MULTICAST_ALL	29
 
 /* IPV6_MTU_DISCOVER values */
 #define IPV6_PMTUDISC_DONT		0

net/ipv6/af_inet6.c

···
 	np->hop_limit	= -1;
 	np->mcast_hops	= IPV6_DEFAULT_MCASTHOPS;
 	np->mc_loop	= 1;
+	np->mc_all	= 1;
 	np->pmtudisc	= IPV6_PMTUDISC_WANT;
 	np->repflow	= net->ipv6.sysctl.flowlabel_reflect;
 	sk->sk_ipv6only	= net->ipv6.sysctl.bindv6only;

net/ipv6/ipv6_sockglue.c

···
 			retv = ipv6_sock_ac_drop(sk, mreq.ipv6mr_ifindex, &mreq.ipv6mr_acaddr);
 		break;
 	}
+	case IPV6_MULTICAST_ALL:
+		if (optlen < sizeof(int))
+			goto e_inval;
+		np->mc_all = valbool;
+		retv = 0;
+		break;
+
 	case MCAST_JOIN_GROUP:
 	case MCAST_LEAVE_GROUP:
 	{
···
 
 	case IPV6_MULTICAST_IF:
 		val = np->mcast_oif;
+		break;
+
+	case IPV6_MULTICAST_ALL:
+		val = np->mc_all;
 		break;
 
 	case IPV6_UNICAST_IF:

net/ipv6/mcast.c

···
 	}
 	if (!mc) {
 		rcu_read_unlock();
-		return true;
+		return np->mc_all;
 	}
 	read_lock(&mc->sflock);
 	psl = mc->sflist;