Re: [PATCH] capabilities: introduce per-process capability bounding set (v10)

[KaiGai Kohei <kaigai@ak.jp.nec.com>]

Andrew Morgan wrote:
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> KaiGai Kohei wrote:
> > Serge,
> >
> > Please tell me the meanings of the following condition.
> >
> > > diff --git a/security/commoncap.c b/security/commoncap.c
> > > index 3a95990..cb71bb0 100644
> > > --- a/security/commoncap.c
> > > +++ b/security/commoncap.c
> > > @@ -133,6 +119,12 @@ int cap_capset_check (struct task_struct *target,
> > > kernel_cap_t *effective,
> > >          /* incapable of using this inheritable set */
> > >          return -EPERM;
> > >      }
> > > +    if (!!cap_issubset(*inheritable,
> > > +               cap_combine(target->cap_inheritable,
> > > +                       current->cap_bset))) {
> > > +        /* no new pI capabilities outside bounding set */
> > > +        return -EPERM;
> > > +    }
> > >  
> > >      /* verify restrictions on target's new Permitted set */
> > >      if (!cap_issubset (*permitted,
> > It seems to me this condition requires the new inheritable capability
> > set must have a capability more than bounding set, at least.
> > What is the purpose of this checking?
>
> Yes, the !! was a bug. The correct check is a single !.

I was in trouble with getting -EPERM at pam_cap.so :-)

> (Thus, the correct check says no 'new' pI bits can be outside cap_bset.)

If this condition intends to dominate 'new' pI bits by 'old' pI bits masked
with bounding set, we should not apply cap_combine() here.
I think applying cap_intersect() is correct for the purpose.

Thanks,
--
KaiGai Kohei
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