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

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Message-ID: <20151105172259.GC9307@ikki.ethgen.ch>
Date:	Thu, 5 Nov 2015 18:22:59 +0100
From:	Klaus Ethgen <Klaus+lkml@...gen.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Richard Weinberger <richard.weinberger@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Andy Lutomirski <luto@...nel.org>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [KERNEL] Re: [KERNEL] Re: [KERNEL] Re: Kernel 4.3 breaks
 security in systems  using capabilities

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Hi,

Am Do den  5. Nov 2015 um 17:19 schrieb Andy Lutomirski:
> > With the present way, that was no problem (for OSS). You take away the
> > SUID, set the capabilities and if the tool complains about not being
> > root, look into the code and remove that stupid thing. With ambient
> > capabilities, no one will see that the tool is doing such stupid thing
> > as setting all capabilities unless some trouble is seen.
> 
> SUID is, always has been, and always will be a minefield.  People
> writing SUID programs need to do it right.  When the kernel adds a new
> API, doing it right includes not adding a buggy call to the API.

Thats right. But real world is not optimal.

> The ambient capability code explicitly zeros pA when running a SUID
> binary to avoid problems in which a SUID binary has unexpected ambient
> capabilities.

That is not the point. I do not talk about combining SUID and
capabilities. I even seen that it was implemented that way. I talk about
taking away rights from tools that don't need it.

> IMO the right long term solution is to just stop using SUID and to
> stop using any other mechanism that grants new privileges of any sort
> when execve is called.

Right. That is my intention.

> When you can boot a distro with no_new_privs
> set everywhere (including init) and everything works, then I'll think
> we've made considerable progress.

That might be a longer way to go. I also don't think it it fully doable.
You do always need some applications having special rights. But I like
to pick exactly that rights instead using sudo or SUID.

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