Re: Question about newrole

[Dennis Wronka <linuxweb@gmx.net>]

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On Tuesday 05 August 2008 23:36:40 Stephen Smalley wrote:
> On Tue, 2008-08-05 at 23:23 +0800, Dennis Wronka wrote:
> > On Tuesday 05 August 2008 22:48:55 Stephen Smalley wrote:
> > > On Tue, 2008-08-05 at 22:32 +0800, Dennis Wronka wrote:
> > > > Thanks.
> > > > That seems to help quite a bit.
> > > > I now get some messages. For example it seems that newrole wants to
> > > > read /etc/shadow directly.
> > > > Will check those messages and play around with the policy.
> > >
> > > The way it works is that pam_unix attempts to open /etc/shadow directly
> > > for reading, and if it fails, it falls back to running unix_chkpwd to
> > > perform the password check.  SELinux policy prohibits most programs
> > > from directly reading /etc/shadow, including even ones that run as
> > > root, and forces them to go through unix_chkpwd instead, in order to
> > > limit the set of processes that have full read access to the shadow
> > > password file.
> > >
> > > The logic to try to open /etc/shadow and fall back to unix_chkpwd
> > > already existed before SELinux in order to support non-root processes
> > > re-authenticating the current user.  What changed with SELinux was that
> > > it could also happen for root processes.
> > >
> > > The current policy dontaudit's the attempt to directly read /etc/shadow
> > > to avoid noise.  When you did semodule -DB, you turned on that
> > > auditing. But those denials are what is expected, and allowing them
> > > will mean giving newrole direct read access to /etc/shadow (although
> > > that will only work if running as root, of course, as otherwise it has
> > > to use a suid helper like unix_chkpwd anyway).
> > >
> > > Does newrole work for you as a non-root user?
> >
> > Okay, it looks like that unix_chkpwd is not allowed to read /etc/shadow
> > when running in newrole_t.
> >
> > Here's the message:
> > type=1400 audit(1217920543.235:26): avc: denied { read } for pid=1210
> > comm="unix_chkpwd" name="shadow" dev=dm-0 ino=29366926
> > scontext=staff_u:staff_r:newrole_t tcontext=system_u:object_r:shadow_t
> > tclass=file
> >
> > Is it safe to add the rule suggested by audit2allow "allow newrole_t
> > shadow_t:file read;" to the policy or would there be a better way?
> >
> > Wouldn't it in general be better if unix_chkpwd would transition into a
> > domain for itself which then in turn is allowed to access /etc/shadow?
>
> unix_chkpwd is supposed to transition into its own domain already.  Is
> it properly labeled (ls -Z /sbin/unix_chkpwd)?  It should have the
> chkpwd_exec_t type.  And newrole_t should transition to the
> system_chkpwd_t domain upon executing it.

Thanks Stephen, that was the magic hint I believe.
My unix_chkpwd and unix_update were still in the position they got put by the 
PAM-installation (gotta check the install-script if there's a way to put them 
directly into /sbin). I moved them over, checked with restorecon and now it 
works.
Just had to put symlinks back to the original place because otherwise login 
didn't work. Will have to check if I really need these symlinks or if I can 
do without (Fedora 9 seems to get along without, so there must be a way for 
me to do it too).

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