linux-kernel - Re: [patch 1/1] personality handling: fix PER_CLEAR_ON

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Date:	Sun, 28 Jun 2009 16:40:46 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Julien Tinnes <jt@....org>
Cc:	hch@...radead.org, security@...nel.org, taviso@....lonestar.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/1] personality handling: fix PER_CLEAR_ON_SETID for
	security reasons

On Fri, Jun 26, 2009 at 08:27:40PM +0200, Julien Tinnes wrote:
> Hello,
> 
> We have found that the current PER_CLEAR_ON_SETID mask on Linux
> doesn't include neither ADDR_COMPAT_LAYOUT, nor MMAP_PAGE_ZERO.
> 
> The current mask is READ_IMPLIES_EXEC|ADDR_NO_RANDOMIZE.
> 
> We believe it is important to add MMAP_PAGE_ZERO, because by using
> this personality it is possible to have the first page mapped inside a
> process running as setuid root. This could be used in those scenarios:

I agree.

> Less importantly, we believe ADDR_COMPAT_LAYOUT should also be added
> since on x86 32bits it will in practice disable most of the address
> space layout randomization (only the stack will remain randomized).

Agree on this on, too.

> -#define PER_CLEAR_ON_SETID (READ_IMPLIES_EXEC|ADDR_NO_RANDOMIZE)
> +#define PER_CLEAR_ON_SETID
> (READ_IMPLIES_EXEC|ADDR_NO_RANDOMIZE|ADDR_COMPAT_LAYOUT|MMAP_PAGE_ZERO)

#define PER_CLEAR_ON_SETID \
	(READ_IMPLIES_EXEC | \
	 ADDR_NO_RANDOMIZE | \
	 ADDR_COMPAT_LAYOUT | \
	 MMAP_PAGE_ZERO)

to make it a little more readable (and work around your mailer
corrupting long lines :))
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