linux-kernel - Re: [PATCH] get_random_long() and AT

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Date:	Mon, 25 Jun 2007 17:02:01 +0200
From:	Alexander Gabert <pappy@...too.org>
To:	Matt Mackall <mpm@...enic.com>
CC:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	Arjan van de Ven <arjan@...radead.org>,
	libc-alpha@...rceware.org, hardened@...too.org
Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

Hi Matt,
sorry for not answering your questions in the first place, i hope this 
did not mean to make a bad impression
Matt Mackall schrieb:
> On Sun, Jun 24, 2007 at 07:45:04PM +0200, Alexander Gabert wrote:
>   
>> Hi Linus,
>> hi LKML,
>>
>> i would like to thank LKML and especially Eric (thanks for the per_cpu 
>> macro tips and design guidelines!) and the other contributors to this idea.
>>
>> This time the patch is rather big because it also removes 
>> get_random_int() and introduces get_random_long() throughout the kernel.
>>     
>
> Stop right there. You still haven't answered my original question.
> What is the point of this exercise in the first place, please?
>
> Am I right in thinking you have three unrelated patches here?
>   
I don't think so but you may be right nonetheless if my opinion.
> - something to do with aux vector headers
>   
Adding the new field
> - something to do with get_random_int repeating itself
>   
Found while adding the new field and testing it.
> - sweeping change of get_random_int to get_random_long for no obvious reason
>   
It is needed for properly initializing a SSP guard which is (afaik) a 
long value.
> These should be three completely separate patches.
>   
Probably ... but bear in mind that the goal is still the same: allowing 
glibc to use SSP with /proc/self/auxv instead of fopen(/dev/urandom) as 
it is now.
Effectively saving three syscalls (open,read,close) and making life 
easier for glibc because randomization "generated" in the kernel does 
not deplete /dev/urandom too much for high coverage SSP userlands (i.e. 
Gentoo Hardened).

I can imagine that Redhat would do the same with the SSP implementation 
in glibc, i think if this patch moves into kernel, they will bring out a 
glibc patch that is checking for AT_ENTROPY and using the opening of 
/dev/urandom for retrieving randomized data as a fallback for machines 
where such a kernel is not available.  This is a win-win situation for 
both sides- the kernel wins because the pressure on /dev/urandom is 
released a bit (applicable to SSP environments) and the glibc wins 
because it has a reliable, fast, cheap and easy to use source for 
randomization.


Thank you,

Alex

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