linux-kernel - Re: [capabilities] Allow normal inheritance for a configurable set of capabilities

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Date:	Mon, 02 Feb 2015 11:00:18 -0800
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Serge Hallyn <serge.hallyn@...ntu.com>
CC:	Christoph Lameter <cl@...ux.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	Jonathan Corbet <corbet@....net>,
	Aaron Jones <aaronmdjones@...il.com>, Ted Ts'o <tytso@....edu>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, akpm@...uxfoundation.org,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [capabilities] Allow normal inheritance for a configurable set
 of capabilities

On 2/2/2015 10:08 AM, Serge Hallyn wrote:
> Quoting Casey Schaufler (casey@...aufler-ca.com):
>> I'm game to participate in such an effort. The POSIX scheme
>> is workable, but given that it's 20 years old and hasn't
>> developed real traction it's hard to call it successful.
> Over the years we've several times discussed possible reasons for this
> and how to help.  I personally think it's two things:  1. lack of
> toolchain and fs support.  The fact that we cannot to this day enable
> ping using capabilities by default because of cpio, tar and non-xattr
> filesystems is disheartening.  2. It's hard for users and applications
> to know what caps they need.  yes the API is a bear to use, but we can
> hide that behind fancier libraries.  But using capabilities requires too
> much in-depth knowledge of precisely what caps you might need for
> whatever operations library may now do when you asked for something.

The fix for that is to a change to the audit system. If the audit system
reported the capabilities relevant to the decision you'd have what you
need. If you failed because you didn't have CAP_CHMOD or you succeeded
because you had CAP_SYS_ADMIN it should show up in the audit record.
Other systems have used this approach.

You could, of course, create a separate capability result log, and I
believe that Nokia had done something along those lines. I think that
adding it to the audit trail is a more rational approach.

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