[PATCH] ipv4/udp: Verify multicast group is ours in upd_v4_early_demux()

[Shawn Bohrer <shawn.bohrer@gmail.com>]

From: Shawn Bohrer <sbohrer@rgmadvisors.com>

421b3885bf6d56391297844f43fb7154a6396e12 "udp: ipv4: Add udp early
demux" introduced a regression that allowed sockets bound to INADDR_ANY
to receive packets from multicast groups that the socket had not joined.
For example a socket that had joined 224.168.2.9 could also receive
packets from 225.168.2.9 despite not having joined that group if
ip_early_demux is enabled.

Fix this by calling ip_check_mc_rcu() in udp_v4_early_demux() to verify
that the multicast packet is indeed ours.

Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Reported-by: Yurij M. Plotnikov <Yurij.Plotnikov@oktetlabs.ru>
---
 net/ipv4/udp.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index d10b7e0..17d31f5 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -90,6 +90,7 @@
 #include <linux/socket.h>
 #include <linux/sockios.h>
 #include <linux/igmp.h>
+#include <linux/inetdevice.h>
 #include <linux/in.h>
 #include <linux/errno.h>
 #include <linux/timer.h>
@@ -1959,7 +1960,7 @@ void udp_v4_early_demux(struct sk_buff *skb)
 	struct net *net = dev_net(skb->dev);
 	const struct iphdr *iph;
 	const struct udphdr *uh;
-	struct sock *sk;
+	struct sock *sk = NULL;
 	struct dst_entry *dst;
 	int dif = skb->dev->ifindex;
 
@@ -1971,10 +1972,17 @@ void udp_v4_early_demux(struct sk_buff *skb)
 	uh = udp_hdr(skb);
 
 	if (skb->pkt_type == PACKET_BROADCAST ||
-	    skb->pkt_type == PACKET_MULTICAST)
-		sk = __udp4_lib_mcast_demux_lookup(net, uh->dest, iph->daddr,
-						   uh->source, iph->saddr, dif);
-	else if (skb->pkt_type == PACKET_HOST)
+	    skb->pkt_type == PACKET_MULTICAST) {
+		struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
+
+		if (in_dev) {
+			int our = ip_check_mc_rcu(in_dev, iph->daddr, iph->saddr,
+						  iph->protocol);
+			if (our)
+				sk = __udp4_lib_mcast_demux_lookup(net, uh->dest, iph->daddr,
+								   uh->source, iph->saddr, dif);
+		}
+	} else if (skb->pkt_type == PACKET_HOST)
 		sk = __udp4_lib_demux_lookup(net, uh->dest, iph->daddr,
 					     uh->source, iph->saddr, dif);
 	else
-- 
1.9.3