[Samba] Samba 4 security

steve steve at steve-ss.com
Sun Dec 4 11:04:04 MST 2011

On 04/12/11 09:04, steve wrote:
> On 03/12/11 17:32, Matthieu Patou wrote:
>> Steve
>>>> Beware that on your machine where samba 4 DC is running file / folders
>>>> needs to have guid/uid of your AD users not your linux users.
>> Did you read this ^.
>>> Did a git pull ./configure.developer make and make install about an
>>> hour ago.
>>> And, well, something has changed. Now neither user can create nor
>>> delete files!
>>> smbclient //hh3/homes
>>> Password for [HH1\steve]:
>>> smb: \> ls
>>> . D 0 Wed Nov 30 20:37:48 2011
>>> .. D 0 Fri Dec 2 07:15:17 2011
>>> lynn D 0 Thu Dec 1 13:25:45 2011
>>> steve D 0 Fri Dec 2 11:50:09 2011
>>> 29284192 blocks of size 512. 10550432 blocks available
>>> smb: \> cd lynn
>>> smb: \lynn\> mkdir h
>>> NT_STATUS_ACCESS_DENIED making remote directory \lynn\h
>>> smb: \lynn\> cd ../steve
>>> smb: \steve\> mkdir h
>>> NT_STATUS_ACCESS_DENIED making remote directory \steve\h
>>> smb: \steve\>
>>> This has something to do with uid/gid no? But wait, both steve and
>>> lynn _are_ AD users who just happen to have linux accounts.
>> No there is something that you missunderstand, the thing is that in
>> order to do the file access control samba needs to know on the behalf of
>> which uid/gid the access are done.
>> With series of samba 3.x you have different way of doing this mapping or
>> to create unix users that have the same name as the user declared in
>> Samba (either in the local sam or in the NT domain sam), but most of the
>> time now it's winbind that is used. In Samba AD there is just the
>> winbind solution as other solution didn't have a real interest in the
>> context of an active directory domain.
>> So what winbind does ? it allocate a UID to users and GID to groups in a
>> database it stores the association SID<->UID/GID and next time it is
>> asked to translate the same SID to a UID/GID it will use the value in
>> its database.
>> In your particular case, when you connect to the samba AD with smbclient
>> as AD user steve and try to create a dir the server checks the
>> security.NTACL extended attribute, as it didn't exists it knows that it
>> will have to translate posix rights to NT ACLs. At this moment in order
>> to know if you are the owner of the parent directory or in group of the
>> parent directory it will ask its internal winbind to translate user's
>> SID and the SID of user's groups to UID and GID, and it will turn out
>> that the UID of unix user steve is not at all the UID of AD user steve
>> (which is in the 3000000+ range), as other translated posix rights
>> didn't give any write rights to the AD user the directory creation was
>> not created.
>>> How do I change the gid/uid of my linux users to gid/uid AD users? Is
>>> there a script? But that shouldn't matter no?
>>> Thinking you may want more info I'll leave it as it is for now. The
>>> users are the same as they were before the new build. I did not delete
>>> and recreate them.
>> Sure this is the expected behavior, before there was a bug in the posix
>> to NT ACLs translation that granted the write right even if you had just
>> the read and execute right you can have the detail by looking at this
>> changeset: d1274f7f6236b47a1c6aa1737b054ed521d31b67
>> I don't really know your case but I think it's not such a problem at
>> least so far nobody complained, on the DC you don't need to create unix
>> account for the AD users. As you need to create directory for each user
>> there is a couple of solution:
>> 1) change the rights on the directory that is shared as "home" so that
>> the group has a write right, then change group to be users (that's
>> because we map the domain users group to the user unix group)
>> 2) for each user connect using smbclient and create the directory of
>> this user
>> or
>> For each user, use wbinfo -i <ad_user> and then create a folder for this
>> user and use the uid obtained with wbinfo to set the owner of the
>> directory.
>> For instance on my test server I have:
>> ./bin/wbinfo -i steve
>> MATWS\steve:*:3000010:100::/home/MATWS/steve:/bin/false
>> Note: first you have to do a ./bin/wbinfo -u and beware the first time
>> it is _slow_
>> Matthieu.
> Hi Matthieu
> Thanks for your patience. Yes, your clear explanation is excellent. I'm
> going to try it as soon as I get Samba 4 running again.
> I reinstalled from nothing to get a clean slate. Now, DNS isn't working.
> The method of configuring as outlined in the wiki doesn't work anymore.
> The dns files in /usr/local/samba/private have changed since my first
> install last week:( I've another thread open on this.
> Thanks again
> Steve.
Almost there at the command line. Permissions are respected. Following 
your method to create a user and allocate them a home folder:

cat /usr/local/samba/etc/smb.conf
# Global parameters
         server role = domain controller
         workgroup = HH1
         realm = hh3.site
         netbios name = HH3
         passdb backend = samba4

         path = /home
         read only = No

         path = /usr/local/samba/var/locks/sysvol/hh3.site/scripts
         read only = No

         path = /usr/local/samba/var/locks/sysvol
         read only = No

samba-tool user add lynn 123 at 456
User 'lynn' created successfully

wbinfo -i lynn

mkdir /home/HH1

mkdir /home/HH1/lynn

chown 3000009:100 /home/HH1/lynn

  ls -la /home/HH1/lynn
total 8
drwxr-xr-x 2 3000009 users 4096 Dec  4 18:24 .
drwxr-xr-x 3 root    root  4096 Dec  4 18:24 ..

wbinfo -u

smbclient //hh3/home/HH1/lynn -Ulynn
Password for [HH1\lynn]:

smb: \> ls
   .                                   D        0  Sun Dec  4 18:23:31 2011
   ..                                  D        0  Sun Dec  4 16:31:38 2011
   HH1                                 D        0  Sun Dec  4 18:24:
mkdir h
NT_STATUS_ACCESS_DENIED making remote directory \h

smb: \HH1\> cd lynn
smb: \HH1\lynn\> mkdir h
smb: \HH1\lynn\> ls
   .                                   D        0  Sun Dec  4 18:40:36 2011
   ..                                  D        0  Sun Dec  4 18:24:28 2011
   h                                   D        0  Sun Dec  4 18:40:36 2011

                 29284192 blocks of size 512. 10467776 blocks available

ls -la /home/HH1
total 12
drwxr-xr-x 3 root    root  4096 Dec  4 18:24 .
drwxr-xr-x 4 root    root  4096 Dec  4 18:23 ..
drwxr-xr-x 3 3000009 users 4096 Dec  4 18:40 lynn


This only works at the command line.

In konqueror smb://hh3/home/HH1/lynn

lynn is NOT prompted for a password, is allowed entry to her folder but 
can neither create nor delete files.

It seems as though lynn would still need a linux account if she wanted 
to work on a linux computer. If I nfs'd her /home over to the linux 
boxes, is here any way lynn could authenticate against the Samba AD? 
Would the linux client have to join the AD? Can linux clients join AD?

Thanks so much for getting me this far.

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