Re: [PATCH] SELinux: Measure state and hash of policy using IMA

[Lakshmi Ramasubramanian]

On 8/24/20 1:01 PM, Ondrej Mosnacek wrote:
> On Mon, Aug 24, 2020 at 9:30 PM Stephen Smalley
> <stephen.smalley.work@xxxxxxxxx> wrote:
> > On Mon, Aug 24, 2020 at 2:13 PM Lakshmi Ramasubramanian
> > <nramas@xxxxxxxxxxxxxxxxxxx> wrote:
> > > On 8/24/20 7:00 AM, Stephen Smalley wrote:
> > >
> > > > > +int security_read_policy_kernel(struct selinux_state *state,
> > > > > +                               void **data, size_t *len)
> > > > > +{
> > > > > +       int rc;
> > > > > +
> > > > > +       rc = security_read_policy_len(state, len);
> > > > > +       if (rc)
> > > > > +               return rc;
> > > > > +
> > > > > +       *data = vmalloc(*len);
> > > > > +       if (!*data)
> > > > > +               return -ENOMEM;
> > > > >
> > > > > +       return security_read_selinux_policy(state, data, len);
> > > > >    }
> > > >
> > > > See the discussion here:
> > > > https://lore.kernel.org/selinux/20200824113015.1375857-1-omosnace@xxxxxxxxxx/T/#t
> > > >
> > > > In order for this to be safe, you need to ensure that all callers of
> > > > security_read_policy_kernel() have taken fsi->mutex in selinuxfs and
> > > > any use of security_read_policy_len() occurs while holding the mutex.
> > > > Otherwise, the length can change between security_read_policy_len()
> > > > and security_read_selinux_policy() if policy is reloaded.
> > >
> > > "struct selinux_fs_info" is available when calling
> > > security_read_policy_kernel() - currently in measure.c.
> > > Only "struct selinux_state" is.
> > >
> > > Is Ondrej's re-try approach I need to use to workaround policy reload issue?
> >
> > No, I think perhaps we should move the mutex to selinux_state instead
> > of selinux_fs_info.  selinux_fs_info has a pointer to selinux_state so
> > it can then use it indirectly.  Note that your patches are going to
> > conflict with other ongoing work in the selinux next branch that is
> > refactoring policy load and converting the policy rwlock to RCU.
>
> Yeah, and I'm experimenting with a patch on top of Stephen's RCU work
> that would allow you to do this in a straightforward way without even
> messing with the fsi->mutex. My patch may or may not be eventually
> committed, but either way I'd recommend holding off on this for a
> while until the dust settles around the RCU conversion.

I can make the SELinux\IMA changes in "selinux next branch" taking 
dependencies on Stephen's patches + relevant IMA patches.

Could you please let me know the URL to the "selinux next branch"?

thanks,
 -lakshmi