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>

1 files changed, 64 insertions, 0 deletions

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 6a238398acc9..8a370ef37d3f 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -88,6 +88,8 @@
 #include <linux/byteorder/generic.h>
 
 #include <net/net_namespace.h>
+#include <net/netlink.h>
+#include <net/addrconf.h>
 #include <net/arp.h>
 #include <net/ip.h>
 #include <net/protocol.h>
@@ -1430,6 +1432,63 @@ static void ip_mc_hash_remove(struct in_device *in_dev,
 	*mc_hash = im->next_hash;
 }
 
+static int inet_fill_ifmcaddr(struct sk_buff *skb, struct net_device *dev,
+			      const struct ip_mc_list *im, int event)
+{
+	struct ifa_cacheinfo ci;
+	struct ifaddrmsg *ifm;
+	struct nlmsghdr *nlh;
+
+	nlh = nlmsg_put(skb, 0, 0, event, sizeof(struct ifaddrmsg), 0);
+	if (!nlh)
+		return -EMSGSIZE;
+
+	ifm = nlmsg_data(nlh);
+	ifm->ifa_family = AF_INET;
+	ifm->ifa_prefixlen = 32;
+	ifm->ifa_flags = IFA_F_PERMANENT;
+	ifm->ifa_scope = RT_SCOPE_UNIVERSE;
+	ifm->ifa_index = dev->ifindex;
+
+	ci.cstamp = (READ_ONCE(im->mca_cstamp) - INITIAL_JIFFIES) * 100UL / HZ;
+	ci.tstamp = ci.cstamp;
+	ci.ifa_prefered = INFINITY_LIFE_TIME;
+	ci.ifa_valid = INFINITY_LIFE_TIME;
+
+	if (nla_put_in_addr(skb, IFA_MULTICAST, im->multiaddr) < 0 ||
+	    nla_put(skb, IFA_CACHEINFO, sizeof(ci), &ci) < 0) {
+		nlmsg_cancel(skb, nlh);
+		return -EMSGSIZE;
+	}
+
+	nlmsg_end(skb, nlh);
+	return 0;
+}
+
+static void inet_ifmcaddr_notify(struct net_device *dev,
+				 const struct ip_mc_list *im, int event)
+{
+	struct net *net = dev_net(dev);
+	struct sk_buff *skb;
+	int err = -ENOMEM;
+
+	skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) +
+			nla_total_size(sizeof(__be32)), GFP_ATOMIC);
+	if (!skb)
+		goto error;
+
+	err = inet_fill_ifmcaddr(skb, dev, im, event);
+	if (err < 0) {
+		WARN_ON_ONCE(err == -EMSGSIZE);
+		nlmsg_free(skb);
+		goto error;
+	}
+
+	rtnl_notify(skb, net, 0, RTNLGRP_IPV4_MCADDR, NULL, GFP_ATOMIC);
+	return;
+error:
+	rtnl_set_sk_err(net, RTNLGRP_IPV4_MCADDR, err);
+}
 
 /*
  *	A socket has joined a multicast group on device dev.
@@ -1473,6 +1532,8 @@ static void ____ip_mc_inc_group(struct in_device *in_dev, __be32 addr,
 	im->interface = in_dev;
 	in_dev_hold(in_dev);
 	im->multiaddr = addr;
+	im->mca_cstamp = jiffies;
+	im->mca_tstamp = im->mca_cstamp;
 	/* initial mode is (EX, empty) */
 	im->sfmode = mode;
 	im->sfcount[mode] = 1;
@@ -1492,6 +1553,7 @@ static void ____ip_mc_inc_group(struct in_device *in_dev, __be32 addr,
 	igmpv3_del_delrec(in_dev, im);
 #endif
 	igmp_group_added(im);
+	inet_ifmcaddr_notify(in_dev->dev, im, RTM_NEWMULTICAST);
 	if (!in_dev->dead)
 		ip_rt_multicast_event(in_dev);
 out:
@@ -1705,6 +1767,8 @@ void __ip_mc_dec_group(struct in_device *in_dev, __be32 addr, gfp_t gfp)
 				*ip = i->next_rcu;
 				in_dev->mc_count--;
 				__igmp_group_dropped(i, gfp);
+				inet_ifmcaddr_notify(in_dev->dev, i,
+						     RTM_DELMULTICAST);
 				ip_mc_clear_src(i);
 
 				if (!in_dev->dead)