From owner-freebsd-security@FreeBSD.ORG  Tue May 10 10:57:04 2011
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To: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Tue, 10 May 2011 12:28:28 +0200."
	<86zkmu26k3.fsf@ds4.des.no> 
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Date: Tue, 10 May 2011 10:37:44 +0000
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Cc: Jamie Landeg Jones <jamie@bishopston.net>,
	Jason Hellenthal <jhell@DataIX.net>, feld@feld.me,
	Edho P Arief <edhoprima@gmail.com>, freebsd-security@freebsd.org,
	utisoft@gmail.com
Subject: Re: Rooting FreeBSD , Privilege Escalation using Jails (P??????tur) 
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In message <86zkmu26k3.fsf@ds4.des.no>, =?utf-8?Q?Dag-Erling_Smørgrav?= wr
ites:
>Jason Hellenthal <jhell@DataIX.net> writes:
>> Do you know if there is a way that chmod on / from within the jail could
> 
>> be prevented easily without breaking something ? Maybe not failing but 
>> falling though and return 0 for any operation with the sole argument of /.
>
>Not without adding explicit checks in the kernel.

I identified this issue back when I implemented jails and though long
and hard about adding a kernel hack to paste over this.

My conclusion was that there were not enough justification for it,
based on the usage model envisioned then: virtual-machines-light.

Gettys first rule says:

	1. Do not add new functionality unless an implementor
	   cannot complete a real application without it.

and I think we should stick to that before adding more or less
random pieces of magic to the kernel.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.