LightDM - Apr 2016 - Error connecting to X server via IPv6

Hi list,

I've discovered a problem in lightdm XDMCP using link-local IPv6 
addresses without interface index to connect to X server.
It has been originally reported at 
https://bugzilla.redhat.com/show_bug.cgi?id=1322775.

The problem can be fixed by having the XDMCP client not transmitting 
link-local addresses in the request, but if it does, lightdm XDMCP 
server can be a lot smarter if the attached patch is applied.

It changes the X server address selection order to set the lowest 
preference to link-local addresses, even if matching the source address 
or family.

This is not 100% full-proof: if only link-local addresses have been 
received, one of them is used anyway. In this case, a complete solution 
would be to determine and set the address interface index if not ambiguous.

However, this patch fixes the problem for most of the non-pathological 
cases.

Regards,
Patrick
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Hi Patrick,

Thanks for this patch. Would you be able to open a bug on
https://launchpad.net/lightdm/ describing this? It makes it easier to track
the issue.

--Robert

On Fri, 8 Apr 2016 at 14:10 Patrick Monnerat <patrick.monnerat at dh.com>
wrote:
> Hi list,
>
> I've discovered a problem in lightdm XDMCP using link-local IPv6
> addresses without interface index to connect to X server.
> It has been originally reported at
> https://bugzilla.redhat.com/show_bug.cgi?id=1322775.
>
> The problem can be fixed by having the XDMCP client not transmitting
> link-local addresses in the request, but if it does, lightdm XDMCP
> server can be a lot smarter if the attached patch is applied.
>
> It changes the X server address selection order to set the lowest
> preference to link-local addresses, even if matching the source address
> or family.
>
> This is not 100% full-proof: if only link-local addresses have been
> received, one of them is used anyway. In this case, a complete solution
> would be to determine and set the address interface index if not ambiguous.
>
> However, this patch fixes the problem for most of the non-pathological
> cases.
>
> Regards,
> Patrick
> _______________________________________________
> LightDM mailing list
> LightDM at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/lightdm
>
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