linux-kernel - Re: Security fix for remapping of page 0 (was [PATCH] Change ZERO_SIZE

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Message-ID: <20090603202117.39b070d5@lxorguk.ukuu.org.uk>
Date:	Wed, 3 Jun 2009 20:21:17 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Larry H." <research@...reption.com>, linux-mm@...ck.org,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	pageexec@...email.hu
Subject: Re: Security fix for remapping of page 0 (was [PATCH] Change
 ZERO_SIZE_PTR to point at unmapped space)

On Wed, 3 Jun 2009 14:59:51 -0400 (EDT)
Christoph Lameter <cl@...ux-foundation.org> wrote:

> We could just move the check for mmap_min_addr out from
> CONFIG_SECURITY?
> 
> 
> Use mmap_min_addr indepedently of security models
> 
> This patch removes the dependency of mmap_min_addr on CONFIG_SECURITY.
> It also sets a default mmap_min_addr of 4096.
> 
> mmapping of addresses below 4096 will only be possible for processes
> with CAP_SYS_RAWIO.

This appears to break the security models as they can no longer replace
the CAP_SYS_RAWIO check with something based on the security model.

> @@ -1043,6 +1046,9 @@ unsigned long do_mmap_pgoff(struct file
>  		}
>  	}
> 
> +	if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
> +		return -EACCES;
> +

You can't move this bit here

>  	error = security_file_mmap(file, reqprot, prot, flags, addr, 0);

You need it in the default (no security) version of security_file_mmap()
in security.h not hard coded into do_mmap_pgoff, and leave the one in
cap_* alone.

So NAK - not to the idea but to the fact the patch is buggy.

Alan
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