Messages in this thread | | | Date | Thu, 5 Feb 2015 01:03:09 +0100 | From | "Serge E. Hallyn" <> | Subject | Re: [RFC] Implement ambient capability set. |
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Quoting Andy Lutomirski (luto@amacapital.net): > On Wed, Feb 4, 2015 at 2:02 PM, Serge E. Hallyn <serge@hallyn.com> wrote: > > Quoting Serge E. Hallyn (serge@hallyn.com): > >> Quoting Andy Lutomirski (luto@amacapital.net): > >> > On Wed, Feb 4, 2015 at 1:27 PM, Serge E. Hallyn <serge@hallyn.com> wrote: > >> > > Quoting Andy Lutomirski (luto@amacapital.net): > >> > >> On Wed, Feb 4, 2015 at 1:16 PM, Serge E. Hallyn <serge@hallyn.com> wrote: > >> > >> > Quoting Andy Lutomirski (luto@amacapital.net): > >> > >> >> On Wed, Feb 4, 2015 at 10:49 AM, Christoph Lameter <cl@linux.com> wrote: > >> > >> >> > + > >> > >> >> > + if (!cap_valid(arg2)) > >> > >> >> > + return -EINVAL; > >> > >> >> > + > >> > >> >> > + new =prepare_creds(); > >> > >> >> > + if (arg3 == 0) > >> > >> >> > + cap_lower(new->cap_ambient, arg2); > >> > >> >> > + else > >> > >> >> > + cap_raise(new->cap_ambient, arg2); > >> > >> >> > + return commit_creds(new); > >> > >> >> > + > >> > >> >> > >> > >> >> This let you add capabilities you don't even have to cap_ambient. I'm > >> > >> >> fine with that as long as the cap evolution rule changes, as above. > >> > >> > > >> > >> > How about if instead we do restrict it to what's in pP? I don't > >> > >> > want CAP_SETPCAP to become a cheap way to get all caps back. With > >> > >> > or without NNP. > >> > >> > >> > >> We'd also have to modify everything that can change pP to change pA as > >> > >> well if we went this route. I'd be okay with that, but it would make > >> > >> the patch much larger, and I'm not entirely sure I see the benefit. > >> > >> It would keep the number of possible states smaller, which could be > >> > >> nice. > >> > > > >> > > Do you mean if we didn't require NNP? I'm suggesting that even if > >> > > we require NNP we should restrict any new bits added to pA to be > >> > > in pP at the prctl call. Then whether or not to drop them from > >> > > pA when they are dropped from pP, I'm not yet certain. > >> > > >> > I mean regardless of whether we require NNP. > >> > > >> > I think that, unless we change the evolution rule, we would need to > >> > drop from pA when bits are dropped from pP to preserve the idea that > >> > dropping bits from pP drops them for good (as long as ruid != 0 or > >> > some securebit is set). > >> > >> Ok, so iiuc the rules would be: > >> > >> 1. must set nnp and have ns_capable(CAP_SETPCAP) to > >> call prctl(PR_SET_AMBIENT_WHATEVER) > >> > >> 2. adding bits to pA requires they be in pP at prctl time > >> > >> 3. dropping bits from pP drops them also from pA > > I'm still unconvinced that 2 and 3 is better than using pP & pA in > execve, but I could go either way on that. > > >> > >> 4. at exec, fP |= pA; pA' = pA > > > > Actually I'm tempted to say that if fP is not empty, then we stick with current > > rules for fP/pP and clear out pA. If fP is empty, then fP = pA > > > > Then, if fP is not empty on the file, we either drop nnp at exec (or > > don't use nnp at all), or we refuse exec if fP > pA. > > We can't drop nnp at exec. > > > > > We definately do not want to run a file which has capability X > > in fP, when X is not in pA. > > Confused. This will break everything, including Christoph's use case. > The status quo for running ping from bash has pA == 0 and fP != 0.
Sorry, I meant only if pA is not empty.
But it sounds like we've in any case not hit on anything that will actually work for Christoph.
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