linux-kernel - Re: [RFC][PATCH] Fix cap_capable to only allow owners in the parent user namespace to have caps.

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Message-ID: <87bodww9hv.fsf@xmission.com>
Date:	Fri, 14 Dec 2012 14:32:12 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	containers@...ts.linux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	linux-security-module@...r.kernel.org
Subject: Re: [RFC][PATCH] Fix cap_capable to only allow owners in the parent user namespace to have caps.

"Serge E. Hallyn" <serge@...lyn.com> writes:

> Quoting Eric W. Biederman (ebiederm@...ssion.com):

>> A child user namespace having capabilities against processes in it's
>> parent seems totally bizarre and pretty dangerous from a capabilities
>> standpoint.
>
> How would it have them against its parent?

init_user_ns
   userns a --- created by kuid 1
     userns b -- created by kuid 2
        process c in userns b with kuid 1

Serge read the first permisison check in common_cap. 
Think what happens in the above example.

For the rest I understand your concern.

Serge please read and look at the patches I have posted to fix
the issues Andy found with the user namespace tree.  Especially
the fix to commit_creds.

After you have looked at the patches to fix the issues I will
be happy to discuss things further with you.

Eric

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