linux-kernel - Re: [RFC] Implement ambient capability set.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150204220211.GB21613@mail.hallyn.com>
Date:	Wed, 4 Feb 2015 23:02:11 +0100
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Christoph Lameter <cl@...ux.com>,
	"Andrew G. Morgan" <morgan@...nel.org>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Jonathan Corbet <corbet@....net>,
	Aaron Jones <aaronmdjones@...il.com>, Ted Ts'o <tytso@....edu>,
	LSM List <linux-security-module@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...uxfoundation.org>
Subject: Re: [RFC] Implement ambient capability set.

Quoting Serge E. Hallyn (serge@...lyn.com):
> Quoting Andy Lutomirski (luto@...capital.net):
> > On Wed, Feb 4, 2015 at 1:27 PM, Serge E. Hallyn <serge@...lyn.com> wrote:
> > > Quoting Andy Lutomirski (luto@...capital.net):
> > >> On Wed, Feb 4, 2015 at 1:16 PM, Serge E. Hallyn <serge@...lyn.com> wrote:
> > >> > Quoting Andy Lutomirski (luto@...capital.net):
> > >> >> On Wed, Feb 4, 2015 at 10:49 AM, Christoph Lameter <cl@...ux.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
> 
> 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 definately do not want to run a file which has capability X
in fP, when X is not in pA.

> Christoph, would these suffice for your use caes?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/