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

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 3 deletions

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 1c92ea67baef..83aa604f9273 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>
@@ -1960,6 +1961,7 @@ void udp_v4_early_demux(struct sk_buff *skb)
         struct sock *sk;
         struct dst_entry *dst;
         int dif = skb->dev->ifindex;
+        int ours;
 
         /* validate the packet */
         if (!pskb_may_pull(skb, skb_transport_offset(skb) + sizeof(struct udphdr)))
@@ -1969,14 +1971,24 @@ void udp_v4_early_demux(struct sk_buff *skb)
         uh = udp_hdr(skb);
 
         if (skb->pkt_type == PACKET_BROADCAST ||
-            skb->pkt_type == PACKET_MULTICAST)
+            skb->pkt_type == PACKET_MULTICAST) {
+                struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
+
+                if (!in_dev)
+                        return;
+
+                ours = ip_check_mc_rcu(in_dev, iph->daddr, iph->saddr,
+                                       iph->protocol);
+                if (!ours)
+                        return;
                 sk = __udp4_lib_mcast_demux_lookup(net, uh->dest, iph->daddr,
                                                    uh->source, iph->saddr, dif);
-        else if (skb->pkt_type == PACKET_HOST)
+        } else if (skb->pkt_type == PACKET_HOST) {
                 sk = __udp4_lib_demux_lookup(net, uh->dest, iph->daddr,
                                              uh->source, iph->saddr, dif);
-        else
+        } else {
                 return;
+        }
 
         if (!sk)
                 return;