On Wed, Nov 24, 2021 at 04:31:22PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Nov 24, 2021 at 04:22:50PM +0200, Jari Ruusu wrote:
> > Greg Kroah-Hartman wrote:
> > > From: Alistair Delva <adelva@xxxxxxxxxx>
> > >
> > > commit 94c4b4fd25e6c3763941bdec3ad54f2204afa992 upstream.
> > [SNIP]
> > > --- a/block/ioprio.c
> > > +++ b/block/ioprio.c
> > > @@ -69,7 +69,14 @@ int ioprio_check_cap(int ioprio)
> > >
> > > switch (class) {
> > > case IOPRIO_CLASS_RT:
> > > - if (!capable(CAP_SYS_NICE) && !capable(CAP_SYS_ADMIN))
> > > + /*
> > > + * Originally this only checked for CAP_SYS_ADMIN,
> > > + * which was implicitly allowed for pid 0 by security
> > > + * modules such as SELinux. Make sure we check
> > > + * CAP_SYS_ADMIN first to avoid a denial/avc for
> > > + * possibly missing CAP_SYS_NICE permission.
> > > + */
> > > + if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
> > > return -EPERM;
> > > fallthrough;
> > > /* rt has prio field too */
> >
> > What exactly is above patch trying to fix?
> > It does not change control flow at all, and added comment is misleading.
>
> See the thread on the mailing list for what it does and why it is
> needed.
>
> It does change the result when selinux is enabled.
>
> thanks,
>
> greg k-h
The case where we create a newer more fine grained capability which is a
sub-cap of a broader capability like CAP_SYS_ADMIN is analogous. See
check_syslog_permissions() for instance.
So I think a helper like
int capable_either_or(int cap1, int cap2) {
if (has_capability_noaudit(current, cap1))
return 0;
return capable(cap2);
}
might be worthwhile.
