[Samba] winbindd losing track of RFC2307 UIDs

Achim Gottinger achim at ag-web.biz
Tue Oct 4 14:09:40 UTC 2016

Am 04.10.2016 um 15:43 schrieb Rowland Penny via samba:
> On Tue, 4 Oct 2016 15:16:17 +0200
> Achim Gottinger via samba <samba at lists.samba.org> wrote:
>> Am 04.10.2016 um 10:21 schrieb Rowland Penny:
>>> On Tue, 4 Oct 2016 02:35:21 +0200
>>> Achim Gottinger via samba <samba at lists.samba.org> wrote:
>>>> Am 03.10.2016 um 18:57 schrieb Rob via samba:
>>>>> Hi all,
>>>>> I've been experiencing an intermittent problem where some UIDs on
>>>>> a member server spontaneously change from being their AD-derived
>>>>> values to being allocated from the default idmap space, even when
>>>>> there is no change to the AD user information.
>>>>> Specifically, I have a member server running Samba 4.4.5 on CentOS
>>>>> 6.8. AD service is provided by two Samba 4.4.5 servers.
>>>>> The member server's smb.conf has (in part):
>>>>> [global]
>>>>>           netbios name = memberserver
>>>>>           security = ADS
>>>>>           workgroup = MYDOMAIN
>>>>>           realm = MY.AD.REALM.COM
>>>>>           server role = member server
>>>>>           interfaces = em1
>>>>>           bind interfaces only = yes
>>>>>           idmap config *:backend = tdb
>>>>>           idmap config *:range = 2000-9999
>>>>>           # idmap config for domain
>>>>>           idmap config MY.AD.REALM.COM:backend = ad
>>>>>           idmap config MY.AD.REALM.COM:schema_mode = rfc2307
>>>>>           idmap config MY.AD.REALM.COM:range = 10000-99999
>>>>>           # Use template settings for login shell and home
>>>>> directory winbind nss info = template
>>>>>           template shell = /bin/bash
>>>>>           template homedir = /home/%U
>>>>>           winbind use default domain = yes
>>>>> [...]
>>>>> This generally works fine... user mappings are like:
>>>>> $ wbinfo -i auser
>>>>> auser:*:10028:10000:User Name:/home/auser:/bin/bash
>>>>> $ id auser
>>>>> uid=10028(auser) gid=10000(agroup)
>>>>> groups=10000(agroup),10007(othergroup)
>>>>> After a while (generally a couple days, though sometimes much
>>>>> sooner), this starts happening:
>>>>> $ wbinfo -i auser
>>>>> auser:*:2018:10000:User Name:/home/auser:/bin/bash
>>>>> $ id auser
>>>>> uid=2018(auser) gid=10000(agroup)
>>>>> groups=10000(agroup),10007(othergroup)
>>>>> and this persists until I do "net cache flush" on the member!
>>>>> Any thoughts on why the winbindd cache is getting corrupted?  I
>>>>> tried running winbindd with log level 7, but nothing jumped out at
>>>>> me: just normal queries returning 10028 and then normal queries
>>>>> returning 2018. Other suggestions to try?
>>>>> Thanks!
>>>>> -Rob
>>>>> PS. At one point in the past, this member server was also a DC and
>>>>> this problem never happened then.
>>>> Been having this issue on an dc after i updated from 4.1 to 4.2. It
>>>> turned out some users with defined uid also had mappings from
>>>> winbind in idmap.tdb. At firt the uid attributre gets used but
>>>> afetr a while the value fromidmap.tdb was used. The fix was to
>>>> delete the mappings in idmap.tdb.
>>>> On an member server you can use net idmap set/get/dump to test
>>>> this.
>>> You are missing the fact that the OP is using the REALM name
>>> instead of the NETBios domain name and for some reason winbind is
>>> starting to allocate the user a UID from the '*' range.
>>> Rowland
>> It's jumping from using rfc uid's gid's in ad to the "*" range. Would
>> it dynamic assign from the ad range it would still be an error.
> If you look at the smb.conf the OP posted, you will find the ranges are
> set to:
> idmap config *:range = 2000-9999
> idmap config MY.AD.REALM.COM:range = 10000-99999
> His user 'auser' intially has this 'uid=10028', it then changes to
> 'uid=2018'
> I do not really understand how he got the first as the second 'idmap
> config' line is wrong, the user should have had the second id all the
> time, because the user is outside the domain 'MYDOMAIN'.
> '10028' is inside the second range, but shouldn't have been used
> because the DOMAIN name is wrong.
> '2018' is inside the range set for '*' i.e. everything outside the
> Rowland
I assume he has configured 10028 as uid in the ad for that user.
Using the realm as the domain name is not wrong seen from the windows 
side of things where the netbios name is there for backward 
compatibility. For example i can use [realm]\[username] or [netbios 
domain name]\[username] to logon to a windows domain member.

In my case I had a few users to whom i added the rfc uid attribute abit 
later so they already had mappings in idmap.tdb. This did not cause any 
issues with samba 4.1 it always used the uid values. With 4.2 and the 
switch to winbindd however it sometimes used the old mappings from 
idmap.tdb. An good test case was a second logon on an windows client. On 
the first logon the users homedir was accessible at the second logon 
samba had picked the vlaue from idmap.tdb and the user had no access to 
it's homedir. net cache flush or an samba restart fixed the mapping 
temporary. The OP may have eigther this issue or like you said the cause 
is samba has not yet fully imlemented using the REALM as the domain name.

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