Re: [KERNEL] Re: [KERNEL] Re: [KERNEL] Re: [KERNEL] Re: Kernel 4.3 breaks security in systems using capabilities

From: Klaus Ethgen <Klaus+lkml@ethgen.de>
To: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Richard Weinberger <richard.weinberger@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Christoph Lameter <cl@linux.com>,
	Andy Lutomirski <luto@kernel.org>,
	Serge Hallyn <serge.hallyn@ubuntu.com>,
	Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [KERNEL] Re: [KERNEL] Re: [KERNEL] Re: [KERNEL] Re: Kernel 4.3 breaks  security in systems  using capabilities
Date: Thu, 5 Nov 2015 18:48:24 +0100	[thread overview]
Message-ID: <20151105174823.GD9307@ikki.ethgen.ch> (raw)
In-Reply-To: <20151105173438.GA3378@mail.hallyn.com>

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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.

Regards
   Klaus
- -- 
Klaus Ethgen                              http://www.ethgen.ch/
pub  4096R/4E20AF1C 2011-05-16   Klaus Ethgen <Klaus@Ethgen.de>
Fingerprint: 85D4 CA42 952C 949B 1753  62B3 79D0 B06F 4E20 AF1C
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