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Date: Mon, 10 Jan 2011 22:52:40 +0100
From: Bastian Blank <bastian@waldi.eu.org>
To: "Serge E. Hallyn" <serge@hallyn.com>
Cc: containers@lists.linux-foundation.org,
        kernel list <linux-kernel@vger.kernel.org>,
        LSM <linux-security-module@vger.kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Kees Cook <kees.cook@canonical.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: [PATCH 4/7] allow killing tasks in your own or child userns
Message-ID: <20110110215240.GA21351@wavehammer.waldi.eu.org>
Mail-Followup-To: Bastian Blank <bastian@waldi.eu.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	containers@lists.linux-foundation.org,
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	LSM <linux-security-module@vger.kernel.org>,
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	Alexey Dobriyan <adobriyan@gmail.com>,
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References: <20110110211135.GA22446@mail.hallyn.com>
 <20110110211334.GD22564@mail.hallyn.com>
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On Mon, Jan 10, 2011 at 09:13:34PM +0000, Serge E. Hallyn wrote:
> +	const struct cred *cred = current_cred();
> +	const struct cred *tcred = __task_cred(t);
> +
> +	if (cred->user->user_ns != tcred->user->user_ns) {
> +		/* userids are not equivalent - either you have the
> +		   capability to the target user ns or you don't */
> +		if (ns_capable(tcred->user->user_ns, CAP_KILL))
> +			return 1;
> +		return 0;
> +	}
> +
> +	/* same user namespace - usual credentials checks apply */
> +	if ((cred->euid ^ tcred->suid) &&
> +	    (cred->euid ^ tcred->uid) &&
> +	    (cred->uid  ^ tcred->suid) &&
> +	    (cred->uid  ^ tcred->uid) &&
> +	    !ns_capable(tcred->user->user_ns, CAP_KILL))
> +		return 0;
> +
> +	return 1;

Isn't that equal to this?

	if (ns_capable(tcred->user->user_ns, CAP_KILL))
		return 1;

	if (cred->user->user_ns == tcred->user->user_ns &&
	    (cred->euid == tcred->suid ||
	     cred->euid == tcred->uid ||
	     cred->uid == tcred->suid ||
	     cred->uid == tcred->uid))
		return 1;

	return 0;

I would consider this much easier to read.

Bastian

-- 
I'm a soldier, not a diplomat.  I can only tell the truth.
		-- Kirk, "Errand of Mercy", stardate 3198.9