Messages in this thread | | | Date | Tue, 28 Dec 2004 03:21:39 +0100 | From | Herbert Poetzl <> | Subject | Re: The Future of Linux Capabilities ... |
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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@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 ...
thanks, Herbert
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