Samba and krb5.conf

[Simo]

On Fri, 2015-04-17 at 14:16 -0700, Kenny Dinh wrote:
> Richard,
> 
> It is possible to run the conflicting application in a container, but I
> cannot prevent future applications.
> 
> I will look into the alternative method, make the kerberos libraries linked
> to Samba use a different location of krb5.conf rather than /etc/krb5.conf.
> I have been looking at the wrong place all this time.
> 
> Thanks for the pointer!
> ~Kenny

Set the environment variable KRB5_CONFIG to another file in the samba
unit file/startup script ?

Simo.

> On Fri, Apr 17, 2015 at 2:02 PM, Richard Sharpe <realrichardsharpe at gmail.com
> > wrote:
> 
> > On Fri, Apr 17, 2015 at 1:09 PM, Kenny Dinh <kdinh at peaxy.net> wrote:
> > > Greeting,
> > >
> > > We are using Samba 4.1.13 on CentOS and was having issue authenticating
> > > user that was created in a subdomain.
> > >
> > > We found out that another application had updated the /etc/krb5.conf to
> > > match its need, and Samba was not happy about it.  When we deleted the
> > > /etc/krb5.conf, Samba was able to authenticate user from a subdomain
> > > (smbclient //localhost/share -U<subdomain>\\<user>%<password>)
> > >
> > > Note that SAMBA4_USES_HEIMDAL was not defined.
> > > This is my smb.conf
> > >
> > > # net conf list
> > > [global]
> > > idmap config *:backend = tdb
> > > idmap config *:range = 1000000-100000000
> > > idmap config *:script = /usr/mydir/bin/idmap
> > > workgroup = REPUBLIC
> > > realm = REPUBLIC.WINDC
> > > security = ads
> > > netbios name = testbox1
> > > log level = 10
> > >
> > > [blah]
> > > path = /
> > > comment = sdakjhkjh
> > > guest ok = no
> > > read only = no
> > > browseable = yes
> > >
> > > I noticed that the code path went
> > > through create_local_private_krb5_conf_for_domain() function and created
> > > its own krb5.conf.  Toward the end of the function, the code also set the
> > > KRB5_CONFIG environment variable to "
> > > /var/lib/samba/smb_krb5/krb5.conf.REPUBLIC"
> > >
> > > Here's a snippet of the log:
> > > /var/log/samba/log.smbd:[2015/04/17 10:19:25.083196,  5, pid=9003,
> > > effective(0, 0), real(0, 0)]
> > >
> > ../source3/libads/kerberos.c:925(create_local_private_krb5_conf_for_domain)
> > > /var/log/samba/log.smbd:  create_local_private_krb5_conf_for_domain:
> > wrote
> > > file /var/lib/samba/smb_krb5/krb5.conf.REPUBLIC with realm REPUBLIC.WINDC
> > > KDC list = kdc = 10.0.3.1
> > >
> > > I searched through samba code for krb5.conf and found that
> > > "krb5_config_file" in source4\heimdal\lib\krb5\constants.c seems to be
> > the
> > > only place that make use of krb5.conf files location.  Also the function
> > > where "krb5_config_file" is used in krb5_init_context() defined in
> > > source4\heimdal\lib\krb5\context.c.  However, it seems that the code was
> > > never executed.  I place additional DEBUG message in that code path but
> > > none appear.
> > >
> > > This is the variable I was referring to.
> > > KRB5_LIB_VARIABLE const char *krb5_config_file =
> > >
> > > It seems Samba expects the default location for krb5.conf to be located
> > at
> > > /etc/krb5.conf.  However, I couldn't find the location in the code where
> > > Samba is looking for /etc/krb5.conf.  Another thing that confuses me is
> > why
> > > does Samba look into /etc/krb5.conf when it was already creating its own
> > > krb5.conf file.
> > >
> > > My goal is to prevent Samba from looking at /etc/krb5.conf to avoid
> > > conflicts between Samba and any other applications that would modify
> > > /etc/krb5.conf.
> > >
> > > Could someone point me to the code to do that?
> >
> > It's likely the kerberos libraries that are looking in that file.
> > Samba really works best if you tell it to use DNS to look up services
> > and realms, so an empty krb5.conf file works.
> >
> > However, if you need a krb5.conf for another application, is it
> > possible to run that application in a jail or container?
> >
> > Alternatively, you might have to make the kerberos libraries linked to
> > Samba use a different location or not use krb5.conf.
> >
> > --
> > Regards,
> > Richard Sharpe
> > (何以解憂？唯有杜康。--曹操)
> >


-- 
Simo Sorce