net: Allow all multicast packets to be received on a interface.

To receive IGMP or MLD packets on a IP socket on any interface the
multicast group needs to be explicitly joined. This works well for when
the multicast group the user is interested in is known, but does not
provide an easy way to snoop all packets in the 224.0.0.0/8 or the
FF00::/8 range.

Define a new sysctl to allow a given interface to become a IGMP or MLD
snooper. When set the interface will allow any IGMP or MLD packet to be
received on sockets bound to these devices.

Documentation/networking/ip-sysctl.rst

@@ -1328,6 +1328,14 @@ mc_forwarding - BOOLEAN
 	conf/all/mc_forwarding must also be set to TRUE to enable multicast
 	routing	for the interface
 
+mc_snooping - BOOLEAN
+	Enable multicast snooping on the interface. This allows any given
+	multicast group to be received without explicitly being joined.
+	The kernel needs to be compiled with CONFIG_MROUTE and/or
+	CONFIG_IPV6_MROUTE.
+	conf/all/mc_snooping must also be set to TRUE to enable multicast
+	snooping for the interface.
+
 medium_id - INTEGER
 	Integer value used to differentiate the devices by the medium they
 	are attached to. Two devices can have different id values when

include/linux/inetdevice.h

@@ -95,6 +95,7 @@ static inline void ipv4_devconf_setall(struct in_device *in_dev)
 
 #define IN_DEV_FORWARD(in_dev)		IN_DEV_CONF_GET((in_dev), FORWARDING)
 #define IN_DEV_MFORWARD(in_dev)		IN_DEV_ANDCONF((in_dev), MC_FORWARDING)
+#define IN_DEV_MSNOOPING(in_dev)	IN_DEV_ANDCONF((in_dev), MC_SNOOPING)
 #define IN_DEV_BFORWARD(in_dev)		IN_DEV_ANDCONF((in_dev), BC_FORWARDING)
 #define IN_DEV_RPFILTER(in_dev)		IN_DEV_MAXCONF((in_dev), RP_FILTER)
 #define IN_DEV_SRC_VMARK(in_dev)    	IN_DEV_ORCONF((in_dev), SRC_VMARK)

include/linux/ipv6.h

@@ -52,6 +52,7 @@ struct ipv6_devconf {
 #endif
 #ifdef CONFIG_IPV6_MROUTE
 	__s32		mc_forwarding;
+	__s32		mc_snooping;
 #endif
 	__s32		disable_ipv6;
 	__s32		drop_unicast_in_l2_multicast;

include/uapi/linux/ip.h

@@ -169,6 +169,7 @@ enum
 	IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST,
 	IPV4_DEVCONF_DROP_GRATUITOUS_ARP,
 	IPV4_DEVCONF_BC_FORWARDING,
+	IPV4_DEVCONF_MC_SNOOPING,
 	__IPV4_DEVCONF_MAX
 };
 

include/uapi/linux/ipv6.h

@@ -190,6 +190,7 @@ enum {
 	DEVCONF_NDISC_TCLASS,
 	DEVCONF_RPL_SEG_ENABLED,
 	DEVCONF_RA_DEFRTR_METRIC,
+	DEVCONF_MC_SNOOPING,
 	DEVCONF_MAX
 };
 

include/uapi/linux/netconf.h

@@ -19,6 +19,7 @@ enum {
 	NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN,
 	NETCONFA_INPUT,
 	NETCONFA_BC_FORWARDING,
+	NETCONFA_MC_SNOOPING,
 	__NETCONFA_MAX
 };
 #define NETCONFA_MAX	(__NETCONFA_MAX - 1)

include/uapi/linux/sysctl.h

@@ -482,6 +482,7 @@ enum
 	NET_IPV4_CONF_PROMOTE_SECONDARIES=20,
 	NET_IPV4_CONF_ARP_ACCEPT=21,
 	NET_IPV4_CONF_ARP_NOTIFY=22,
+	NET_IPV4_CONF_MC_SNOOPING=23,
 };
 
 /* /proc/sys/net/ipv4/netfilter */

net/ipv4/devinet.c

@@ -2014,6 +2014,8 @@ static int inet_netconf_msgsize_devconf(int type)
 		size += nla_total_size(4);
 	if (all || type == NETCONFA_MC_FORWARDING)
 		size += nla_total_size(4);
+	if (all || type == NETCONFA_MC_SNOOPING)
+		size += nla_total_size(4);
 	if (all || type == NETCONFA_BC_FORWARDING)
 		size += nla_total_size(4);
 	if (all || type == NETCONFA_PROXY_NEIGH)
@@ -2062,6 +2064,10 @@ static int inet_netconf_fill_devconf(struct sk_buff *skb, int ifindex,
 	    nla_put_s32(skb, NETCONFA_MC_FORWARDING,
 			IPV4_DEVCONF(*devconf, MC_FORWARDING)) < 0)
 		goto nla_put_failure;
+	if ((all || type == NETCONFA_MC_SNOOPING) &&
+	    nla_put_s32(skb, NETCONFA_MC_SNOOPING,
+			IPV4_DEVCONF(*devconf, NETCONFA_MC_SNOOPING)) < 0)
+		goto nla_put_failure;
 	if ((all || type == NETCONFA_BC_FORWARDING) &&
 	    nla_put_s32(skb, NETCONFA_BC_FORWARDING,
 			IPV4_DEVCONF(*devconf, BC_FORWARDING)) < 0)
@@ -2506,6 +2512,7 @@ static struct devinet_sysctl_table {
 		DEVINET_SYSCTL_COMPLEX_ENTRY(FORWARDING, "forwarding",
 					     devinet_sysctl_forward),
 		DEVINET_SYSCTL_RO_ENTRY(MC_FORWARDING, "mc_forwarding"),
+		DEVINET_SYSCTL_RW_ENTRY(MC_SNOOPING, "mc_snooping"),
 		DEVINET_SYSCTL_RW_ENTRY(BC_FORWARDING, "bc_forwarding"),
 
 		DEVINET_SYSCTL_RW_ENTRY(ACCEPT_REDIRECTS, "accept_redirects"),

net/ipv4/igmp.c

@@ -2692,6 +2692,11 @@ int ip_check_mc_rcu(struct in_device *in_dev, __be32 mc_addr, __be32 src_addr, u
 	struct ip_sf_list *psf;
 	int rv = 0;
 
+#ifdef CONFIG_IP_MROUTE
+	if (IN_DEV_MSNOOPING(in_dev))
+		return 1;
+#endif /* CONFIG_IP_MROUTE */
+
 	mc_hash = rcu_dereference(in_dev->mc_hash);
 	if (mc_hash) {
 		u32 hash = hash_32((__force u32)mc_addr, MC_HASH_SZ_LOG);

net/ipv6/addrconf.c

@@ -502,6 +502,8 @@ static int inet6_netconf_msgsize_devconf(int type)
 #ifdef CONFIG_IPV6_MROUTE
 	if (all || type == NETCONFA_MC_FORWARDING)
 		size += nla_total_size(4);
+	if (all || type == NETCONFA_MC_SNOOPING)
+		size += nla_total_size(4);
 #endif
 	if (all || type == NETCONFA_PROXY_NEIGH)
 		size += nla_total_size(4);
@@ -546,6 +548,10 @@ static int inet6_netconf_fill_devconf(struct sk_buff *skb, int ifindex,
 	    nla_put_s32(skb, NETCONFA_MC_FORWARDING,
 			devconf->mc_forwarding) < 0)
 		goto nla_put_failure;
+	if ((all || type == NETCONFA_MC_SNOOPING) &&
+	    nla_put_s32(skb, NETCONFA_MC_SNOOPING,
+			devconf->mc_snooping) < 0)
+		goto nla_put_failure;
 #endif
 	if ((all || type == NETCONFA_PROXY_NEIGH) &&
 	    nla_put_s32(skb, NETCONFA_PROXY_NEIGH, devconf->proxy_ndp) < 0)
@@ -5503,6 +5509,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
 #endif
 #ifdef CONFIG_IPV6_MROUTE
 	array[DEVCONF_MC_FORWARDING] = cnf->mc_forwarding;
+	array[DEVCONF_MC_SNOOPING] = cnf->mc_snooping;
 #endif
 	array[DEVCONF_DISABLE_IPV6] = cnf->disable_ipv6;
 	array[DEVCONF_ACCEPT_DAD] = cnf->accept_dad;
@@ -6786,6 +6793,13 @@ static const struct ctl_table addrconf_sysctl[] = {
 		.mode		= 0444,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname	= "mc_snooping",
+		.data		= &ipv6_devconf.mc_snooping,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 #endif
 	{
 		.procname	= "disable_ipv6",

net/ipv6/mcast.c

@@ -1013,6 +1013,11 @@ bool ipv6_chk_mcast_addr(struct net_device *dev, const struct in6_addr *group,
 	struct ifmcaddr6 *mc;
 	bool rv = false;
 
+#ifdef CONFIG_IPV6_MROUTE
+	if (dev_net(dev)->ipv6.devconf_all->mc_snooping)
+		return true;
+#endif
+
 	rcu_read_lock();
 	idev = __in6_dev_get(dev);
 	if (idev) {