linux-kernel - Re: [PATCH 2/9] security: Make capabilities relative to the user namespace.

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Message-ID: <29256.1298461209@redhat.com>
Date:	Wed, 23 Feb 2011 11:40:09 +0000
From:	David Howells <dhowells@...hat.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	dhowells@...hat.com, LSM <linux-security-module@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	James Morris <jmorris@...ei.org>,
	Kees Cook <kees.cook@...onical.com>,
	containers@...ts.linux-foundation.org,
	kernel list <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Michael Kerrisk <mtk.manpages@...il.com>, xemul@...allels.com
Subject: Re: [PATCH 2/9] security: Make capabilities relative to the user namespace.

Serge E. Hallyn <serge@...lyn.com> wrote:

>  	int (*capable) (struct task_struct *tsk, const struct cred *cred,
> -			int cap, int audit);
> +			struct user_namespace *ns, int cap, int audit);

Hmmm...  A chunk of the contents of the cred struct are user-namespaced.
Could you add the user_namespace pointer to the cred struct and thus avoid
passing it as an argument to other things.

In fact, I think you probably have to do this so that cachefiles, for example,
can override the user namespace when it operates on behalf of a process that's
in another namespace.

In fact, looking later on in your patch, I see:

> -		    || (cap_capable(current, current_cred(), CAP_SETPCAP,
> +		    || (cap_capable(current, current_cred(),
> +				    current_cred()->user->user_ns, CAP_SETPCAP,

so the user_ns _is_ already available through the creds.  So is there really a
need to pass it as an argument to anything that already takes a cred?

>   *	@cred contains the credentials to use.
> + *      @ns contains the user namespace we want the capability in
>   *	@cap contains the capability <include/linux/capability.h>.

That should be tabbed to match the lines either side.

David
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