[PATCH] passdb: handle UPN in lookup_name correctly

Fri Feb 15 21:42:16 UTC 2019

On Fri, Feb 15, 2019 at 09:31:14PM +0000, Rowland Penny via samba-technical wrote:
> On Fri, 15 Feb 2019 18:07:40 +0100
> Ralph Wuerthner <ralphw at de.ibm.com> wrote:
> 
> > On 15.02.19 17:23, Rowland Penny wrote:
> > > On Fri, 15 Feb 2019 17:06:04 +0100
> > > Ralph Wuerthner via samba-technical
> > > <samba-technical at lists.samba.org> wrote:
> > > 
> > >> On 13.02.19 16:18, Andreas Schneider wrote:
> > >>> On Tuesday, February 12, 2019 1:38:09 PM CET Ralph Wuerthner via
> > >>> samba- technical wrote:
> > >>>> Hi Andreas!
> > >>>>
> > >>>> On 12.02.19 10:39, Andreas Schneider wrote:
> > >>>>> On Monday, February 11, 2019 5:39:33 PM CET Ralph Wuerthner
> > >>>>> wrote:
> > >>>>>> Hi Andreas!
> > >>>>>>
> > >>>>>> On 11.02.19 16:07, Andreas Schneider wrote:
> > >>>>>>> Hi Ralph,
> > >>>>>>>
> > >>>>>>>> Please see attached patchset:
> > >>>>>>>> The fix for Samba bugzilla 13312 (commit 1775ac8aa4) caused a
> > >>>>>>>> regression
> > >>>>>>>> when looking up names in UPN notation: Because
> > >>>>>>>> winbind_lookup_name is called with lp_workgroup as domain
> > >>>>>>>> name the lookup is now failing and the SID for an unmapped
> > >>>>>>>> Unix user is returned by lookup_name. Fixed by calling
> > >>>>>>>> winbind_lookup_name with an empty domain name in case the
> > >>>>>>>> name is in UPN notation.
> > >>>>>>>>
> > >>>>>>>> The patchset already passed a CI run:
> > >>>>>>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__gitlab.com_samba-2Dteam_devel_samba_pipelines_46689980&d=DwICAg&c=jf_iaSHvJObTbx-siA1ZOg&r=91G8BCIr_Gua7QkxI_O-dlz8T-mXwIVnjFb7EjeIK7M&m=cE08ROyNiXvMje49eaTVj5qguLqqeNc9L0waXJZlLU8&s=HzsOgBRt8y3O1Jco7WX-FCBZUY8W7L24Vwu5jmYeGP8&e=
> > >>>>>>>
> > >>>>>>> Thanks for your contribution!
> > >>>>>>>
> > >>>>>>> Please use DGB_DEBUG() instead of DEBUG(10, ...)
> > >>>>>>>
> > >>>>>>> In lookup_upn() use a helper variable 'bool ok'. And check
> > >>>>>>> talloc_strdup()
> > >>>>>>> for NULL.
> > >>>>>>
> > >>>>>> Thanks for your feedback! I prepared a new version of the
> > >>>>>> patchset with the following changes:
> > >>>>>> - using a helper variable in lookup_upn()
> > >>>>>> - use DBG_DEBUG() instead of DEBUG(10, ...)
> > >>>>>>
> > >>>>>> I didn't add a NULL check for talloc_strdup() because there is
> > >>>>>> already a NULL check right after the ok: label. This check is
> > >>>>>> used by other sequence steps in lookup_name() too.
> > >>>>>
> > >>>>> But then the function would need documentation that the caller
> > >>>>> is responsible for the NULL check.
> > >>>>>
> > >>>>> I think this is strange code and we should do the check in place
> > >>>>> and not defer it to later.
> > >>>>
> > >>>> Ahh, I got your point. I thought you were referring to the
> > >>>> talloc_strdup() call from patch #2 in lookup_name(), instead you
> > >>>> are referring to the talloc_strdup() call in lookup_upn(). You
> > >>>> are right, there should be a check in lookup_upn(). I didn't pay
> > >>>> much attention to this because patch #3 is elimination the
> > >>>> talloc_strdup() call in lookup_upn(). Please see the attached
> > >>>> patchset with the missing check (though it will be gone after
> > >>>> applying patch #3).
> > >>>
> > >>> This looks good. Now we need tests which verify this :-)
> > >>
> > >> This will be the harder part...
> > >>
> > >> I tried to recreate this in the ad_member test environment but
> > >> without success. Samba's AD DC seems to behave slightly different
> > >> than a Windows AD server. With or without my patchset I get the
> > >> same results:
> > >>
> > >> ./bin/rpcclient 127.0.0.29 -U% -c 'lookupnames "alice at ADDOMAIN"'
> > >> alice at ADDOMAIN S-1-5-21-2858285458-1632643436-2480850723-1106
> > >> (User: 1)
> > >>
> > >> But when doing this on my test system (without my patchset) I get a
> > >> Unix SID when querying a Samba AD member:
> > >>
> > >> rpcclient localhost -U'virtual1\administrator%*****' -c
> > >> 'lookupnames "testuser1 at virtual1.com"'
> > >> testuser1 at virtual1.com S-1-22-1-12001118 (User: 1)
> > >>
> > >> and the expected SID when querying the AD server directly:
> > >>
> > >> rpcclient 10.0.100.8 -U'virtual1\administrator%*****' -c
> > >> 'lookupnames "testuser1 at virtual1.com"'
> > >> testuser1 at virtual1.com
> > >> S-1-5-21-3478218634-1770281059-659661689-1118 (User: 1)
> > >>
> > >> Do we have to change the behavior of the Samba AD DC or what's the
> > >> way forward here?
> > >>
> > >>
> > > 
> > > Could there be something wrong with your test system:
> > > 
> > > rowland at devstation:~$ rpcclient localhost
> > > -U'samdom\administrator%xxxxxxxxxx' -c 'lookupnames
> > > "rowland at samdom.example.com"' rowland at samdom.example.com
> > > S-1-5-21-1768301897-3342589593-1064908849-1107 (User: 1)
> > > rowland at devstation:~$ rpcclient 192.168.0.6
> > > -U'samdom\administrator%xxxxxxxxxx' -c 'lookupnames
> > > "rowland at samdom.example.com"' rowland at samdom.example.com
> > > S-1-5-21-1768301897-3342589593-1064908849-1107 (User: 1)
> > > 
> > > devstation is a Unix domain member
> > > 192.168.0.6 is a Samba AD DC
> > 
> > Maybe I was not precises enough above: when querying a Samba domain 
> > member joined to a Samba AD DC everything is fine. But when querying
> > a Samba domain member joined to a Windows AD server I get a Unix SID.
> > 
> 
> I have been doing further testing (just out of curiosity) with a 2012R2
> DC and a Samba Unix domain member:
> 
> root at fileserver:~# rpcclient 192.168.0.43 -U'example\administrator%xxxxxxxxxx' -c 'lookupnames "rowland at example.com"'
> rowland at example.com S-1-5-21-1739413417-3060112075-1959733387-1104 (User: 1)
> 
> fileserver is the Samba Unix domain member
> 192.168.0.43 is the 2012R2 DC
> 
> So I repeat, could there be something wrong with the test or the Unix
> domain member ?

The scenario is that the initial 'rpcclient' call asks for
user at domain.com. That goes to smbd, which sends a request for
domain\user at domain.com to winbindd, which gets forwarded to the DC.

The Samba DC seems to silently accept this request. I assume that a
Windows DC would reject a lookupname for domain\user at domain.com.
Then the additional fix required would be having the Samba DC also
reject queries for domain\user at domain.com.

Christof