linux-kernel - Re: [PATCH 01/12] Security: Add CAP_COMPROMISE

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Message-ID: <51490ABD.3050205@zytor.com>
Date:	Tue, 19 Mar 2013 18:02:53 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matthew Garrett <matthew.garrett@...ula.com>
CC:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
	kexec@...ts.infradead.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 01/12] Security: Add CAP_COMPROMISE_KERNEL

On 03/18/2013 02:32 PM, Matthew Garrett wrote:
> 
> This means we can return our focus to the kernel. There's currently a number
> of kernel interfaces that permit privileged userspace to modify the running
> kernel. These are currently protected by CAP_SYS_RAWIO, but unfortunately
> the semantics of this capability are poorly defined and it now covers a large
> superset of the desired behaviour.
> 

... except it doesn't.

Looking at it in detail, EVERYTHING in CAP_SYS_RAWIO has the possibility
of compromising the kernel, because they let device drivers be bypassed,
which means arbitrary DMA, which means you have everything.

Now, a lot of the abuses of CAP_SYS_RAWIO have clearly been added by
people who had *no bloody clue* what that capability meant, but it
really doesn't change the fact that pretty much if you have
CAP_SYS_RAWIO you have the machine.

So just reject CAP_SYS_RAWIO.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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