From: Kevin Cernekee <cerne...@chromium.org>
Date: Mon, 11 Dec 2017 11:13:45 -0800
> 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 <cerne...@chromium.org>
...
> + return htonl(INADDR_ANY);
> +}
> +
> static struct sk_buff *igmpv3_newpack(struct net_device *dev, unsigned int
> mtu)
> {
> struct sk_buff *skb;
> @@ -368,7 +386,7 @@ static struct sk_buff *igmpv3_newpack(struct net_device
> *dev, unsigned int mtu)
> 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(net, skb, NULL);
Ok, and I checked that MC source address validation on the receiver
will pass because:
if (ipv4_is_zeronet(saddr)) {
if (!ipv4_is_local_multicast(daddr))
return -EINVAL;
that check in ip_mc_validate_source() won't trigger.
