PAC parsing in Samba 4.1

[Andrew Bartlett]

On Tue, 2013-07-30 at 08:12 -0400, simo wrote:
> On Tue, 2013-07-30 at 15:13 +1200, Andrew Bartlett wrote:
> > On Thu, 2013-07-25 at 20:08 +0100, Tris Mabbs wrote:
> > > Good day, one and all ...
> > > 
> > > I just had to rebuild our main Samba server ("OpenSlowlaris" ->
> > > "Slowlaris 11.11"), during which I put the latest (at the time;
> > > currently 4.2.0pre1-GIT-b505111) Samba4 on there.  I thought that by
> > > now that Gunther's speculative changes to improve the PAC decode might
> > > have made their way into the trunk revision - obviously I was wrong,
> > > as I'm once again getting a load of "Can't parse the PAC:
> > > NT_STATUS_BUFFER_TOO_SMALL" messages and a user who can't access any
> > > Samba shares.
> > > 
> > > Whoops ...
> > > 
> > > So as we previously discussed looking into things in more detail
> > > (specifically finding out why there is no "client_principal" being
> > > passed into "kerberos_decode_pac()"), but nothing else ever happened,
> > > is there anything I can do to assist in getting the improved PAC
> > > decoding included into the trunk revision?  Whilst I can't guarantee
> > > immediate responses to any request, I'm quite happy to stick any code
> > > in anywhere you might want if you don't mind potentially waiting a day
> > > or so for the results :-)
> > 
> > GD:
> > 
> > What happened about your code here?  Can I merge your patch?
> > 
> > I see two branches in your git repo:
> > http://git.samba.org/?p=gd/samba/.git;a=shortlog;h=refs/heads/master-krb5pac_type12
> > http://git.samba.org/?p=gd/samba/.git;a=shortlog;h=refs/heads/master-krb5pac
> > 
> > Are either of these ready for merging?
> > 
> > Simo:
> > 
> > If these are not ready, can we revert your change, as this is a
> > regression in 4.1 vs 4.0?
> 
> What is the regression exactly ?
> We use this code in FreeIPA w/o issues, and removing it would break
> FreeIPA.
> 
> Simo.

It causes a reproducible segfault for every kerberos login (for a
particular user) for Tris Mabbs (CC'ed) that we were able to bisect down
to this patch:

> > commit a6be8a97f705247c1b1cbb0595887d8924740a71
> > Author: Simo Sorce <idra at samba.org>
> > Date:   Thu Sep 27 14:12:06 2012 -0400
> > 
> >     Support UPN_DNS_INFO in the PAC
> >     
> >     Previously marked as UNKNOWN_12 the UPN_DNS_INFO is defined in
> > MS-PAC
> >     
> >     Autobuild-User(master): Simo Sorce <idra at samba.org>
> >     Autobuild-Date(master): Fri Sep 28 01:13:44 CEST 2012 on
> > sn-devel-104
> > 
> > Thanks,
> > 
> > Andrew Bartlett
> > 

The failing PAC for feeding into ndrdump is available, and Tris agreed
to contribute it as a test case once we fix this. 

Andrew Bartlett

-- 
Andrew Bartlett
http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org
Samba Developer, Catalyst IT                   http://catalyst.net.nz