On 02/07/14 07:30, Lung-Pin Chang wrote: > Hi folks, > > I'm currently using dnsmasq 2.70 (compiled from source) in my Linux > environment for IPv6 RA/DHCPv6. > > The following section is my dnsmasq config: > interface=lbr0 > dhcp-range=set:lbr0v60,2002:01ab:68c7:beef::5566,2002:01ab:68c7:beef::5600,64,86400 > dhcp-option=tag:lbr0v60,option6:dns-server,[2001:4860:4860::8888],[2001:4860:4860::8844] > enable-ra > dhcp-leasefile=/etc/dhcpd/dhcpd.conf.leases > dhcp-script=/usr/syno/etc/dhcpd/dhcpd-script.sh > > and my interface address configuration: > 8: lbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue > link/ether 00:00:15:69:67:15 brd ff:ff:ff:ff:ff:ff > inet6 2002:1ab:68c7:beef::1/64 scope global > valid_lft forever preferred_lft forever > inet6 fe80::200:15ff:fe69:6715/64 scope link > valid_lft forever preferred_lft forever > 66: 6in4: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1472 qdisc noqueue > link/sit 1.171.104.199 peer 192.88.99.1 > inet6 2002:1ab:68c7::1/16 scope global > valid_lft forever preferred_lft forever > inet6 fe80::1ab:68c7/128 scope link > valid_lft forever preferred_lft forever > > With logging facilities in my dhcp-script, I noticed that the script > is invoked by the "old" event when I kill -HUP <dnsmasq pid>. > > The problem is: when my script got invoked, the DNSMASQ_INTERFACE > environment is set to a wrong interface (i.e., 6in4, instead of the > incoming interface lbr0). > > After digging a while in the source code, I found that the > find_interface_v6 callback (src/lease.c) might be the cause: > > Given several interfaces share common prefix with different prefix length, > > current interface searching mechanism (lease_find_interfaces -> > iface_enumerate) would > > enumerate all the addresses on the host by netlink RTM_GETADDR > request, trying to figure out > > which interface is the packet originated from by checking if they're > in the same subnet. > > But with the netlink parsing flow, when multiple interfaces match, the > originated interface would > > always be the one that comes later in the netlink message. So in my > case, the originated > > interface would always be 6in4, even if the prefix length on it is > apparently shorter than lbr0.
Is that a legal interface configuration? IPv6 seems to be capable of generating endless surprises like this! > > I came up with a quick fix[1] to save the interface prefix length in > the lease context, > > so longer prefixes are always preferred and the script got invoked > with correct interface. I think that's fine. The only problem remaining is that lease_set_interface might be called with the wrong interface, before it's called with the right interface. I don't think that causes any serious problems, but it might be worth making the patch a bit more complex to avoid the problem, to save problems now or in the future. Determining the correct interface for each lease in a new_interface field in the lease structure,then calling lease_set_interface() on those values would do it. > > But I'm not sure if this also applies to IPv4, as I'm testing in a > IPv6-only environment in Linux > If the nested-prefixes condition can occur in IPv4, then the same thing will apply, and the same sort of fix would work. Note that this problem, if not fixed, will cause serious issues with the ra-names mode, which uses the interface to find the possible SLAAC addresses of host with a DHCPv4 lease. > (so I only traced the netlink part). > Cheers, Simon. Cheers _______________________________________________ Dnsmasq-discuss mailing list Dnsmasq-discuss@lists.thekelleys.org.uk http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
