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 <linus.luessing@c0d3.blue>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 59 insertions, 1 deletions

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 2366f4a2780e..2c46c7aca571 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -14,6 +14,7 @@
 #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>
@@ -29,10 +30,12 @@
 #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"
@@ -1583,6 +1586,19 @@ static void br_multicast_pim(struct net_bridge *br,
 	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,
@@ -1600,7 +1616,15 @@ static int br_multicast_ipv4_rcv(struct net_bridge *br,
 		} 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);
@@ -1635,6 +1659,27 @@ static int br_multicast_ipv4_rcv(struct net_bridge *br,
 }
 
 #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,
@@ -1649,6 +1694,16 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
 	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);
diff --git a/net/ipv6/mcast_snoop.c b/net/ipv6/mcast_snoop.c
index a72ddfc40eb3..55e2ac179f28 100644
--- a/net/ipv6/mcast_snoop.c
+++ b/net/ipv6/mcast_snoop.c
@@ -41,6 +41,8 @@ static int ipv6_mc_check_ip6hdr(struct sk_buff *skb)
 	if (skb->len < len || len <= offset)
 		return -EINVAL;
 
+	skb_set_transport_header(skb, offset);
+
 	return 0;
 }
 
@@ -142,7 +144,7 @@ static inline __sum16 ipv6_mc_validate_checksum(struct sk_buff *skb)
 	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);
@@ -161,6 +163,7 @@ static int ipv6_mc_check_icmpv6(struct sk_buff *skb)
 
 	return 0;
 }
+EXPORT_SYMBOL(ipv6_mc_check_icmpv6);
 
 /**
  * ipv6_mc_check_mld - checks whether this is a sane MLD packet