About this list Date view Thread view Subject view Author view Attachment view

From: Herbert Poetzl (herbert_at_13thfloor.at)
Date: Tue 28 Dec 2004 - 02:21:39 GMT

On Mon, Dec 27, 2004 at 03:22:32PM -0800, Ulrich Drepper wrote:
> On Mon, 27 Dec 2004 02:40:41 +0100, Herbert Poetzl <herbert_at_13thfloor.at> wrote:
> > II) add 32 (or more) sub-capabilities which depend
> > on the parent capability to be usable, and add
> > appropriate syscalls for them.
> >
> > example: CAP_IPC_LOCK gets two subcapabilities
> > (e.g. SCAP_SHM_LOCK and SCAP_MEM_LOCK) which
> I won't try to say anything about III, but I is not really suitable,
> it breaks code currently using capabilities. Or at least makes them
> less secure.

let me assure you that III) does neither break the existing code
nor reduce security, for the following reasons:

  a) the per process capability is a requirement for
     _all_ subcapabilities (when the cap is in the cap_mask)

  b) the capability system isn't changed for caps not
     in the cap_mask

  c) reducing a cap by removing a subcapability can only
     increase security not lower it

> With sub-capabilities the interface diverges from the
> POSIX capabilities interfaces, but at least one can keep backward
> compatibilities.

to some extend, yes ...

> An alternative would be to keep the existing capabilities, and add new
> ones for all the cases which need splitting. If the old value is
> set/reset, all the split-out values are "magically" affected as well.

I consider the 'magically' part another solution I didn't
list in my previous mail, but it is a kind of variation
from II) where we do not necessarily need subcaps for _all_
aspects of a capability (as a matter of fact it's one less)

> This would help keeping the interfaces in line with POSIX and no
> additions to the userlevel libcap would be needed. Yes, new cap[gs]et
> syscalls would be needed, but this fact is hidden from the user.

I guess it might be doable, although the 'magically' part
would require to keep masks for all caps which got split
to select the corresponding sub-capabilities ...


> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo_at_vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
Vserver mailing list

About this list Date view Thread view Subject view Author view Attachment view
[Next/Previous Months] [Main vserver Project Homepage] [Howto Subscribe/Unsubscribe] [Paul Sladen's vserver stuff]
Generated on Tue 28 Dec 2004 - 02:21:52 GMT by hypermail 2.1.3