[PATCH 3.2 113/140] net: igmp: Use correct source address on IGMPv3 reports

Ben Hutchings
2018-02-28T17:29:10Z

From: Kevin Cernekee <cernekee@chromium.org>

commit a46182b00290839fa3fa159d54fd3237bd8669f0 upstream.

Closing a multicast socket after the final IPv4 address is deleted
from an interface can generate a membership report that uses the
source IP from a different interface. The following test script, run
from an isolated netns, reproduces the issue:

#!/bin/bash

ip link add dummy0 type dummy
ip link add dummy1 type dummy
ip link set dummy0 up
ip link set dummy1 up
ip addr add 10.1.1.1/24 dev dummy0
ip addr add 192.168.99.99/24 dev dummy1

tcpdump -U -i dummy0 &
socat EXEC:"sleep 2" \
UDP4-DATAGRAM:239.101.1.68:8889,ip-add-membership=239.0.1.68:10.1.1.1 &

sleep 1
ip addr del 10.1.1.1/24 dev dummy0
sleep 5
kill %tcpdump

RFC 3376 specifies that the report must be sent with a valid IP source
address from the destination subnet, or from address 0.0.0.0. Add an
extra check to make sure this is the case.

Signed-off-by: Kevin Cernekee <cernekee@chromium.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv4/igmp.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)

--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -89,6 +89,7 @@
#include <linux/if_arp.h>
#include <linux/rtnetlink.h>
#include <linux/times.h>
+#include <linux/byteorder/generic.h>

#include <net/net_namespace.h>
#include <net/arp.h>
@@ -299,6 +300,23 @@ igmp_scount(struct ip_mc_list *pmc, int
return scount;
}

+/* source address selection per RFC 3376 section 4.2.13 */
+static __be32 igmpv3_get_srcaddr(struct net_device *dev,
+ const struct flowi4 *fl4)
+{
+ struct in_device *in_dev = __in_dev_get_rcu(dev);
+
+ if (!in_dev)
+ return htonl(INADDR_ANY);
+
+ for_ifa(in_dev) {
+ if (inet_ifa_match(fl4->saddr, ifa))
+ return fl4->saddr;
+ } endfor_ifa(in_dev);
+
+ return htonl(INADDR_ANY);
+}
+
static struct sk_buff *igmpv3_newpack(struct net_device *dev, unsigned int mtu)
{
struct sk_buff *skb;
@@ -345,7 +363,7 @@ static struct sk_buff *igmpv3_newpack(st
pip->frag_off = htons(IP_DF);
pip->ttl = 1;
pip->daddr = fl4.daddr;
- pip->saddr = fl4.saddr;
+ pip->saddr = igmpv3_get_srcaddr(dev, &fl4);
pip->protocol = IPPROTO_IGMP;
pip->tot_len = 0; /* filled in later */
ip_select_ident(skb, NULL);