[Dnsmasq-discuss] [PATCH] Issues with TCP queries on recreated interfaces.
pemensik at redhat.com
Wed Jul 10 11:01:00 BST 2019
On 7/9/19 10:00 PM, Vladislav Grishenko wrote:
> Hi Petr,
> Regarding 0002-Compare-address-and-interface-index-for-allowed-inte.patch, does it support case with different valid interfaces with the same address?
> For example:
> eth0 192.168.1.1/24
> tun0 192.168.1.1./16 (created/destroyed dynamically)
Not tested this specific case, but I think it should be handled
correctly, unlike previous code. Because it now compares also interface
index, it will mark existing entry as found only if interface index also
match. If it does not, new entry is created with correct index instead.
It should work, unlike previous code, it should keep both interface
addresses stored separately.
If tun0 is often destroyed and recreated, number of interfaces records
might grow. That is reason for patch #3, which removes dropped
interfaces after creating new ones.
> Regarding appearance, seems newly added code doesn’t fully follow dnsmasq code style in several places:
> * indentation (should be ident ==2 spaces, 8 spaces == \t)
> * brackets on the same code lines
Ok, I forgot to follow style on 3rd patch. Attached fixed formatting and
removed debug log on interface removal.
> * function args on the next line are not aligned with the first argument
> * prettyprint_addr() result is forcibly ignored with (void) unlike other places
I think that is better to state explicitly return value is not used.
> Best Regards, Vladislav Grishenko
> -----Original Message-----
> From: Dnsmasq-discuss <dnsmasq-discuss-bounces at lists.thekelleys.org.uk> On Behalf Of Petr Mensik
> Sent: Tuesday, July 9, 2019 5:31 PM
> To: dnsmasq-discuss at lists.thekelleys.org.uk
> Subject: [Dnsmasq-discuss] [PATCH] Issues with TCP queries on recreated interfaces.
> Hello Simon and others,
> we have discovered issues with TCP DNS query on dnsmasq, when running in bind-dynamic or bind-interfaces mode. dnsmasq scans automatically new interfaces or do that on new query in second case. However, because used speedup comparing only IP adresses in iface_allowed function, it never gets updated index of an interface.
> In case where named interface is destroyed and created again, that drops TCP queries on that interface. They are checked for incoming interface number. If such number is not found in interfaces list, query is denied.
> Luckily, there was a bug in checking, hiding this problem from usual configuration. If IPv6 address is enabled on the new device, new iface entry would be created, because scope_id of sockaddr_in6 does not match previous. That makes even IPv4 queries succeed.
> Bug on bugzilla  is partly private.
> I propose three changes. First is just helper to log what happens with listeners on bind-dynamic configuration.
> Second is the most important. Create new interface every time index changes. Also test address family of incoming TCP query when checking allowed clients.
> Third is cleanup of unused interfaces. On some virtual machines hosts, interfaces may often be created and destroyed. It might have negative effect on walking trough interfaces list. I think listeners should be garbage collected also on bind-interfaces configuration. But for now, release memory for unused interfaces at least for bind-dynamic.
> 1. https://bugzilla.redhat.com/show_bug.cgi?id=1721668
> Petr Menšík
> Software Engineer
> Red Hat, http://www.redhat.com/
> email: pemensik at redhat.com PGP: 65C6C973
Red Hat, http://www.redhat.com/
email: pemensik at redhat.com PGP: 65C6C973
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