netlink: add IGMP/MLD join/leave notifications

This change introduces netlink notifications for multicast address
changes. The following features are included:
* Addition and deletion of multicast addresses are reported using
  RTM_NEWMULTICAST and RTM_DELMULTICAST messages with AF_INET and
  AF_INET6.
* Two new notification groups: RTNLGRP_IPV4_MCADDR and
  RTNLGRP_IPV6_MCADDR are introduced for receiving these events.

This change allows user space applications (e.g., ip monitor) to
efficiently track multicast group memberships by listening for netlink
events. Previously, applications relied on inefficient polling of
procfs, introducing delays. With netlink notifications, applications
receive realtime updates on multicast group membership changes,
enabling more precise metrics collection and system monitoring. 

This change also unlocks the potential for implementing a wide range
of sophisticated multicast related features in user space by allowing
applications to combine kernel provided multicast address information
with user space data and communicate decisions back to the kernel for
more fine grained control. This mechanism can be used for various
purposes, including multicast filtering, IGMP/MLD offload, and
IGMP/MLD snooping.

Cc: Maciej Żenczykowski <maze@google.com>
Cc: Lorenzo Colitti <lorenzo@google.com>
Co-developed-by: Patrick Ruddy <pruddy@vyatta.att-mail.com>
Signed-off-by: Patrick Ruddy <pruddy@vyatta.att-mail.com>
Link: https://lore.kernel.org/r/20180906091056.21109-1-pruddy@vyatta.att-mail.com
Signed-off-by: Yuyang Huang <yuyanghuang@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 48 insertions, 20 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 0e765466d7f7..2e2684886953 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5127,22 +5127,6 @@ static inline int inet6_ifaddr_msgsize(void)
 	       + nla_total_size(4)  /* IFA_RT_PRIORITY */;
 }
 
-enum addr_type_t {
-	UNICAST_ADDR,
-	MULTICAST_ADDR,
-	ANYCAST_ADDR,
-};
-
-struct inet6_fill_args {
-	u32 portid;
-	u32 seq;
-	int event;
-	unsigned int flags;
-	int netnsid;
-	int ifindex;
-	enum addr_type_t type;
-};
-
 static int inet6_fill_ifaddr(struct sk_buff *skb,
 			     const struct inet6_ifaddr *ifa,
 			     struct inet6_fill_args *args)
@@ -5221,15 +5205,16 @@ error:
 	return -EMSGSIZE;
 }
 
-static int inet6_fill_ifmcaddr(struct sk_buff *skb,
-			       const struct ifmcaddr6 *ifmca,
-			       struct inet6_fill_args *args)
+int inet6_fill_ifmcaddr(struct sk_buff *skb,
+			const struct ifmcaddr6 *ifmca,
+			struct inet6_fill_args *args)
 {
 	int ifindex = ifmca->idev->dev->ifindex;
 	u8 scope = RT_SCOPE_UNIVERSE;
 	struct nlmsghdr *nlh;
 
-	if (ipv6_addr_scope(&ifmca->mca_addr) & IFA_SITE)
+	if (!args->force_rt_scope_universe &&
+	    ipv6_addr_scope(&ifmca->mca_addr) & IFA_SITE)
 		scope = RT_SCOPE_SITE;
 
 	nlh = nlmsg_put(skb, args->portid, args->seq, args->event,
@@ -5254,6 +5239,7 @@ static int inet6_fill_ifmcaddr(struct sk_buff *skb,
 	nlmsg_end(skb, nlh);
 	return 0;
 }
+EXPORT_SYMBOL(inet6_fill_ifmcaddr);
 
 static int inet6_fill_ifacaddr(struct sk_buff *skb,
 			       const struct ifacaddr6 *ifaca,
@@ -5418,6 +5404,7 @@ static int inet6_dump_addr(struct sk_buff *skb, struct netlink_callback *cb,
 		.flags = NLM_F_MULTI,
 		.netnsid = -1,
 		.type = type,
+		.force_rt_scope_universe = false,
 	};
 	struct {
 		unsigned long ifindex;
@@ -5546,6 +5533,7 @@ static int inet6_rtm_getaddr(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 		.event = RTM_NEWADDR,
 		.flags = 0,
 		.netnsid = -1,
+		.force_rt_scope_universe = false,
 	};
 	struct ifaddrmsg *ifm;
 	struct nlattr *tb[IFA_MAX+1];
@@ -5617,6 +5605,7 @@ static void inet6_ifa_notify(int event, struct inet6_ifaddr *ifa)
 		.event = event,
 		.flags = 0,
 		.netnsid = -1,
+		.force_rt_scope_universe = false,
 	};
 	int err = -ENOBUFS;
 
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 5ca8692d565d..587831c148de 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -33,8 +33,10 @@
 #include <linux/in.h>
 #include <linux/in6.h>
 #include <linux/netdevice.h>
+#include <linux/if_addr.h>
 #include <linux/if_arp.h>
 #include <linux/route.h>
+#include <linux/rtnetlink.h>
 #include <linux/init.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
@@ -47,6 +49,7 @@
 #include <linux/netfilter_ipv6.h>
 
 #include <net/net_namespace.h>
+#include <net/netlink.h>
 #include <net/sock.h>
 #include <net/snmp.h>
 
@@ -901,6 +904,39 @@ static struct ifmcaddr6 *mca_alloc(struct inet6_dev *idev,
 	return mc;
 }
 
+static void inet6_ifmcaddr_notify(struct net_device *dev,
+				  const struct ifmcaddr6 *ifmca, int event)
+{
+	struct inet6_fill_args fillargs = {
+		.portid = 0,
+		.seq = 0,
+		.event = event,
+		.flags = 0,
+		.netnsid = -1,
+		.force_rt_scope_universe = true,
+	};
+	struct net *net = dev_net(dev);
+	struct sk_buff *skb;
+	int err = -ENOMEM;
+
+	skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) +
+			nla_total_size(16), GFP_ATOMIC);
+	if (!skb)
+		goto error;
+
+	err = inet6_fill_ifmcaddr(skb, ifmca, &fillargs);
+	if (err < 0) {
+		WARN_ON_ONCE(err == -EMSGSIZE);
+		nlmsg_free(skb);
+		goto error;
+	}
+
+	rtnl_notify(skb, net, 0, RTNLGRP_IPV6_MCADDR, NULL, GFP_ATOMIC);
+	return;
+error:
+	rtnl_set_sk_err(net, RTNLGRP_IPV6_MCADDR, err);
+}
+
 /*
  *	device multicast group inc (add if not found)
  */
@@ -948,6 +984,7 @@ static int __ipv6_dev_mc_inc(struct net_device *dev,
 
 	mld_del_delrec(idev, mc);
 	igmp6_group_added(mc);
+	inet6_ifmcaddr_notify(dev, mc, RTM_NEWMULTICAST);
 	mutex_unlock(&idev->mc_lock);
 	ma_put(mc);
 	return 0;
@@ -977,6 +1014,8 @@ int __ipv6_dev_mc_dec(struct inet6_dev *idev, const struct in6_addr *addr)
 				*map = ma->next;
 
 				igmp6_group_dropped(ma);
+				inet6_ifmcaddr_notify(idev->dev, ma,
+						      RTM_DELMULTICAST);
 				ip6_mc_clear_src(ma);
 				mutex_unlock(&idev->mc_lock);