Messages in this thread | | | Date | Thu, 5 Nov 2015 16:08:43 -0600 | From | "Serge E. Hallyn" <> | Subject | Re: [KERNEL] Re: [KERNEL] Re: [KERNEL] Re: [KERNEL] Re: Kernel 4.3 breaks security in systems using capabilities |
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On Thu, Nov 05, 2015 at 11:01:07AM -0800, Andy Lutomirski wrote: > On Thu, Nov 5, 2015 at 9:48 AM, Klaus Ethgen <Klaus+lkml@ethgen.de> wrote: > > -----BEGIN PGP SIGNED MESSAGE----- > > Hash: SHA512 > > > > Am Do den 5. Nov 2015 um 18:34 schrieb Serge E. Hallyn: > >> > Am Do den 5. Nov 2015 um 17:15 schrieb Serge E. Hallyn: > >> > > I think if you follow your idea to its logical conclusions, you end > >> > > up wanting set SECURE_ALL_BITS | SECURE_ALL_LOCKS, which will include > >> > > SECURE_NO_CAP_AMBIENT_RAISE, disabling ambient capabilities. > >> > > >> > That I did miss out and seems to be the solution for the problem. So > >> > adding cap_secure_all_bits,cap_secure_all_locks=ep to every binary that > >> > gets other caps should solve it? > >> > >> No that doesn't work, you have to use prctl to set those bits. If you > >> can get your system to be fully rootless, you can have init or initramfs > >> do this for you. It'll mean that root and setuid-root binaries have no > >> automatic privileges beside owning host (proc/sys) files. > > > > So this is not helping much. But for me it is at least an idea to how to > > have abient capabilities _and_ full control for admin. It would be an > > un-capability but at least would allow the admin to change the > > behaviour. > > > > Another one, that would be much better would be something like > > cap_ambient_cap capability to explicitly allow the use of ambient > > capabilities. > > > > I have to say that I do not know much about prctl. Just reading the man > > page currently. But this seems to be about the second way of taking away > > rights from UID 0 instead of explicitly giving rights to selective > > binaries.
Not exactly. It's restoring the full unadulterated use of posix capabilities.
> OK, everyone, take a deep breath please. > > Somewhere very high up on my personal list of generally applicable > security advice: do not turn security knobs for the warm fully > feelings. Let me repeat that in all caps: DO NOT TURN SECURITY KNOBS > FOR THE WARM FUZZY FEELINGS. > > When a whole bunch of us designed and iterated on how ambient caps > would work, we were very careful that they would *not* break > pre-existing assumptions that SUID programs could make. Securebits > are very different: they very much do break pre-existing assumptions.
... thought i was clear about that.
> See, for example, CVE-2014-3215 [1], which is a local privilege > escalation made possible a because setuid binary turned security knobs > for the warm fuzzy feelings.
Which is why I wonder whether a mailing list - a very slow one - where projects wanting to discuss how to best integrate with capabilities and nnp could go for discussion, would be useful. Very slow because for each project 1+ people on the list would need to put in some time to figure out what the project really needs.
> So, no, barring a really good reason and a very convincing argument > about why it would be safe, I won't ack any attempt to add xattr knobs > to change privilege evolution rules like that. If you really want to > turn knobs to make your system feel safer and be safe at the same > time, please learn exactly what all the knobs do first and, while > you're at it, please think carefully about how they interact. > > --Andy > > [1] See http://openwall.com/lists/oss-security/2014/04/29/7 and much > related discussion
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