bridge: Snoop Multicast Router Advertisements

When multiple multicast routers are present in a broadcast domain then
only one of them will be detectable via IGMP/MLD query snooping. The
multicast router with the lowest IP address will become the selected and
active querier while all other multicast routers will then refrain from
sending queries.

To detect such rather silent multicast routers, too, RFC4286
("Multicast Router Discovery") provides a standardized protocol to
detect multicast routers for multicast snooping switches.

This patch implements the necessary MRD Advertisement message parsing
and after successful processing adds such routers to the internal
multicast router list.

Signed-off-by: Linus Lüssing <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/in.h

···
 	return addr == htonl(INADDR_BROADCAST);
 }
 
+static inline bool ipv4_is_all_snoopers(__be32 addr)
+{
+	return addr == htonl(INADDR_ALLSNOOPERS_GROUP);
+}
+
 static inline bool ipv4_is_zeronet(__be32 addr)
 {
 	return (addr & htonl(0xff000000)) == htonl(0x00000000);

include/net/addrconf.h

···
 void ipv6_mc_remap(struct inet6_dev *idev);
 void ipv6_mc_init_dev(struct inet6_dev *idev);
 void ipv6_mc_destroy_dev(struct inet6_dev *idev);
+int ipv6_mc_check_icmpv6(struct sk_buff *skb);
 int ipv6_mc_check_mld(struct sk_buff *skb);
 void addrconf_dad_failure(struct sk_buff *skb, struct inet6_ifaddr *ifp);
 
···
 		addr->s6_addr32[1] |
 		(addr->s6_addr32[2] ^ htonl(0x00000001)) |
 		(addr->s6_addr[12] ^ 0xff)) == 0;
+#endif
+}
+
+static inline bool ipv6_addr_is_all_snoopers(const struct in6_addr *addr)
+{
+#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && BITS_PER_LONG == 64
+	__be64 *p = (__be64 *)addr;
+
+	return ((p[0] ^ cpu_to_be64(0xff02000000000000UL)) |
+		(p[1] ^ cpu_to_be64(0x6a))) == 0UL;
+#else
+	return ((addr->s6_addr32[0] ^ htonl(0xff020000)) |
+		addr->s6_addr32[1] | addr->s6_addr32[2] |
+		(addr->s6_addr32[3] ^ htonl(0x0000006a))) == 0;
 #endif
 }
 

include/uapi/linux/icmpv6.h

···
 #define ICMPV6_MOBILE_PREFIX_SOL	146
 #define ICMPV6_MOBILE_PREFIX_ADV	147
 
+#define ICMPV6_MRDISC_ADV		151
+
 /*
  *	Codes for Destination Unreachable
  */

include/uapi/linux/igmp.h

···
 #define IGMP_MTRACE_RESP		0x1e
 #define IGMP_MTRACE			0x1f
 
+#define IGMP_MRDISC_ADV			0x30	/* From RFC4286 */
 
 /*
  *	Use the BSD names for these for compatibility

net/bridge/br_multicast.c

···
 #include <linux/export.h>
 #include <linux/if_ether.h>
 #include <linux/igmp.h>
+#include <linux/in.h>
 #include <linux/jhash.h>
 #include <linux/kernel.h>
 #include <linux/log2.h>
···
 #include <net/ip.h>
 #include <net/switchdev.h>
 #if IS_ENABLED(CONFIG_IPV6)
+#include <linux/icmpv6.h>
 #include <net/ipv6.h>
 #include <net/mld.h>
 #include <net/ip6_checksum.h>
 #include <net/addrconf.h>
+#include <net/ipv6.h>
 #endif
 
 #include "br_private.h"
···
 	br_multicast_mark_router(br, port);
 }
 
+static int br_ip4_multicast_mrd_rcv(struct net_bridge *br,
+				    struct net_bridge_port *port,
+				    struct sk_buff *skb)
+{
+	if (ip_hdr(skb)->protocol != IPPROTO_IGMP ||
+	    igmp_hdr(skb)->type != IGMP_MRDISC_ADV)
+		return -ENOMSG;
+
+	br_multicast_mark_router(br, port);
+
+	return 0;
+}
+
 static int br_multicast_ipv4_rcv(struct net_bridge *br,
 				 struct net_bridge_port *port,
 				 struct sk_buff *skb,
···
 		} else if (pim_ipv4_all_pim_routers(ip_hdr(skb)->daddr)) {
 			if (ip_hdr(skb)->protocol == IPPROTO_PIM)
 				br_multicast_pim(br, port, skb);
+		} else if (ipv4_is_all_snoopers(ip_hdr(skb)->daddr)) {
+			err = br_ip4_multicast_mrd_rcv(br, port, skb);
+
+			if (err < 0 && err != -ENOMSG) {
+				br_multicast_err_count(br, port, skb->protocol);
+				return err;
+			}
 		}
+
 		return 0;
 	} else if (err < 0) {
 		br_multicast_err_count(br, port, skb->protocol);
···
 }
 
 #if IS_ENABLED(CONFIG_IPV6)
+static int br_ip6_multicast_mrd_rcv(struct net_bridge *br,
+				    struct net_bridge_port *port,
+				    struct sk_buff *skb)
+{
+	int ret;
+
+	if (ipv6_hdr(skb)->nexthdr != IPPROTO_ICMPV6)
+		return -ENOMSG;
+
+	ret = ipv6_mc_check_icmpv6(skb);
+	if (ret < 0)
+		return ret;
+
+	if (icmp6_hdr(skb)->icmp6_type != ICMPV6_MRDISC_ADV)
+		return -ENOMSG;
+
+	br_multicast_mark_router(br, port);
+
+	return 0;
+}
+
 static int br_multicast_ipv6_rcv(struct net_bridge *br,
 				 struct net_bridge_port *port,
 				 struct sk_buff *skb,
···
 	if (err == -ENOMSG) {
 		if (!ipv6_addr_is_ll_all_nodes(&ipv6_hdr(skb)->daddr))
 			BR_INPUT_SKB_CB(skb)->mrouters_only = 1;
+
+		if (ipv6_addr_is_all_snoopers(&ipv6_hdr(skb)->daddr)) {
+			err = br_ip6_multicast_mrd_rcv(br, port, skb);
+
+			if (err < 0 && err != -ENOMSG) {
+				br_multicast_err_count(br, port, skb->protocol);
+				return err;
+			}
+		}
+
 		return 0;
 	} else if (err < 0) {
 		br_multicast_err_count(br, port, skb->protocol);

net/ipv6/mcast_snoop.c

···
 	if (skb->len < len || len <= offset)
 		return -EINVAL;
 
+	skb_set_transport_header(skb, offset);
+
 	return 0;
 }
 
···
 	return skb_checksum_validate(skb, IPPROTO_ICMPV6, ip6_compute_pseudo);
 }
 
-static int ipv6_mc_check_icmpv6(struct sk_buff *skb)
+int ipv6_mc_check_icmpv6(struct sk_buff *skb)
 {
 	unsigned int len = skb_transport_offset(skb) + sizeof(struct icmp6hdr);
 	unsigned int transport_len = ipv6_transport_len(skb);
···
 
 	return 0;
 }
+EXPORT_SYMBOL(ipv6_mc_check_icmpv6);
 
 /**
  * ipv6_mc_check_mld - checks whether this is a sane MLD packet