On Sun, Jul 16, 2006 at 12:31:51PM +0200, Blaisorblade wrote: > On Saturday 15 July 2006 17:23, Frank v Waveren wrote: > > I was trying to limit some unecessary capabilities in a UML instance > > with /proc/sys/kernel/cap-bound, but it turned out not to take. > > To remove capabilities from the whole system (i.e. all processes) the > recommended way wasn't to use lcap (or a similar program bundled with > libcap)? Yup, lcap is just an interface to /proc/sys/kernel/cap-bound.
> > The source of the problem (or at least something a bit of the way up
> > the garden path of the problem) is at security/commoncap.c:140 at the
> > top of cap_bprm_apply_creds(bprm, unsafe):
> >
> > void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
> > {
> > /* Derived from fs/exec.c:compute_creds. */
> > kernel_cap_t new_permitted, working;
> >
> > new_permitted = cap_intersect (bprm->cap_permitted, cap_bset);
> > working = cap_intersect (bprm->cap_inheritable,
> > current->cap_inheritable);
> > new_permitted = cap_combine (new_permitted, working);
> > ...
> >
> > Here the new permitted set gets limited to the bits in cap_bset, which
> > is as it should be, but then the intersection of the of the current
> > and exec inheritable masks get added to that set, whereas as I
> > understand it, cap_bset should always be the bounding set.
> >
> > I've tried commenting out that bit and everything worked as I'd hoped
> > (I haven't done extensive testing, but bounding the caps worked, as
> > did suids and such).
> >
> > That doesn't explain why it works with those lines left in on a
> > non-UML kernel though, so I assume I'm missing something fundamental.
> >
> > (My guest kernel is
> > Linux version 2.6.16.24 ([EMAIL PROTECTED]) (gcc version 4.0.3 20051201
> > (prerelease) (Debian 4.0.2-5)) #3 Sat Jul 15 16:54:20 CEST 2006
> > , should it matter)
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