[LightDM] LightDM as XDMCP server, multiple pathes to client

[Robert Ancell]

Oh, also I couldn't think of any workaround that would work without
patching.

On Wed, 5 Aug 2015 at 15:20 Robert Ancell <robert.ancell at gmail.com> wrote:

> Hi Lupe,
>
> I've filed a bug for this issue [1].
>
> I can't seem to find any documentation on exactly what you should do if
> you have multiple connections specified in the XDMCP Request. I'm not sure
> if LightDM should try them all or pick one based on some criteria. I can't
> tell it's actually wrong for the client to report an address that the
> daemon can't route to (I guess the client couldn't know in advance?).
>
> I've changed the behaviour for LightDM to use the address the Request came
> from if it is in the list. This will mean it matches the GDM behaviour in
> the simple case but also continues to work for other cases.
>
> Note that LightDM 1.6 is no longer supported. You will either need to
> upgrade to 1.10 or patch your version.
>
> Hope this helps,
> --Robert
>
> [1] https://bugs.launchpad.net/bugs/1481561
> [2] http://www.x.org/releases/X11R7.6/doc/libXdmcp/xdmcp.html
>
> On Wed, 5 Aug 2015 at 02:11 Lutz Christoph <
> lchristoph at extern.creativedata.de> wrote:
>
>> Hi!
>>
>>
>> This is part of a complicates scenario involving RHEL7, virtualization
>> with KVM, VMs with multiple interfaces, and Xorg on the hypervisor host.
>> The reason I'm trying to use LightDM is that the NVidia driver does not
>> work with GDM (black screen). (GDM is the only DM offered by RHEL7.)
>>
>>
>> The Xorg setup works OK when using Nouveau and GDM.
>>
>>
>> When I switch the VM to LightDM, the connection starts OK, but LightDM is
>> confused by the connection offerings of the client Xorg. GDM uses the
>> address the request came from, but LightDM uses the first connection
>> offering, which happens to be the outside interface of the hypervisor, and
>> we do not permit many things in the firewall for that interface.
>>
>>
>> I found no way to limit the connection offerings in the XDMCP Request
>> packet, and frankly I should not need to since the sending IPv4 address is
>> included in the list, but as #3.
>>
>>
>> This is with these EPEL RPMs:
>>
>> lightdm-gobject-1.6.3-4.el7.x86_64
>> lightdm-gtk-1.6.1-4.el7.x86_64
>> lightdm-1.6.3-4.el7.x86_64
>>
>>
>> Relevant log entries with IP addresses obfuscated (nice logging, BTW):
>>
>>
>> [+1952.58s] DEBUG: Got Query(authentication_names=[])
>> [+1952.58s] DEBUG: Send Willing(authentication_name='' hostname=''
>> status='')
>> [+1952.92s] DEBUG: Got Request(display_number=2 connections=[(0,
>> 0A11xxxx) (0, C0A8xxxx) (0, C0A8xxxx) (6, FE80xxxx...xxxx) (6,
>> FE80xxxx...xxxx) (6, FE80xxxx...xxxx) (6, FE80xxxx...xxxx) (6,
>> FE80xxxx...xxxx) (6, FE80xxxx...xxxx) (6, FE80xxxx...xxxx) (6,
>> FE80xxxx...xxxx)] authentication_name='' authentication_data=
>> authorization_names=['MIT-MAGIC-COOKIE-1' 'XDM-AUTHORIZATION-1'
>> 'SUN-DES-1'] manufacturer_display_id='')
>> [+1952.92s] DEBUG: Send Accept(session_id=1015 authentication_name=''
>> authentication_data= authorization_name='MIT-MAGIC-COOKIE-1'
>> authorization_data=3C46DEAE1D40A959820F497B1526DF38)
>> [+1952.92s] DEBUG: Got Manage(session_id=1015 display_number=2
>> display_class='MIT-unspecified')
>> [+1952.92s] DEBUG: Starting seat
>> [+1952.92s] DEBUG: Starting new display for greeter
>> [+1952.92s] DEBUG: Connecting to XServer 10.17.xx.xx:2
>> [+1952.92s] DEBUG: Error connecting to XServer 10.17.xx.xx:2
>> [+1952.92s] DEBUG: Send Failed(session_id=1015 status='Failed to connect
>> to display :2')
>>
>>
>> Any ideas how I can force LightDM to use the requesting address for the X
>> connection?
>>
>> Mit freundlichen Grüßen / Kind regards
>>
>> *Lupe Christoph*
>> im Auftrag von / on behalf of
>> *Creative Data AG*
>> - Standort Süddeutschland -
>> Otto-Lilienthal-Str. 36
>> D-71034 Böblingen
>>
>> Mobil:    +49 (0) 172 630 1004
>> E-Mail:   lchristoph at extern.creativedata.de
>> Web:www.creative-data.de
>>
>> Firmensitz: Robert-Bosch Str. 10 D-50769 Köln, Deutschland
>>
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>> Vorstand: Heinz Friebel, Aufsichtsratvorsitzender: Gerhard Böhm
>> _______________________________________________
>> LightDM mailing list
>> LightDM at lists.freedesktop.org
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>>
>
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