linux-kernel - Re: [RFC PATCH] crypto: add buffer overflow checks to testmgr

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Message-ID: <20090529221055.GA17957@gondor.apana.org.au>
Date:	Sat, 30 May 2009 08:10:55 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Jarod Wilson <jarod@...hat.com>
Cc:	linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Neil Horman <nhorman@...driver.com>
Subject: Re: [RFC PATCH] crypto: add buffer overflow checks to testmgr

On Fri, May 29, 2009 at 11:32:54AM -0400, Jarod Wilson wrote:
> At present, its entirely possible to add a test vector to testmgr with
> an input longer than a page in length w/o specifying a .np option, and
> overflow the page of memory allocated to {a,}xbuf[0], silently
> corrupting memory. I know, because I've accidentally done it. :)
> 
> While this doesn't currently happen in practice w/the existing code,
> due to all !np vectors being less than a 4k page in length (and the
> page allocation loop often returns contiguous pages anyway), explicit
> checks or a way to remove the 4k limit would be a good idea.
> 
> A few ways to fix and/or work around this:
> 
> 1) allocate some larger guaranteed contiguous buffers using
> __get_free_pages() or kmalloc and use them in the !np case
> 
> 2) catch the > PAGE_SIZE && !np case and then do things similar to how
> they are done in the np case
> 
> 3) catch the > PAGE_SIZE && !np case and simply exit with an error
> 
> Since there currently aren't any test vectors that are actually larger
> than a page and not tagged np, option 1 seems like a waste of memory
> and option 2 sounds like unnecessary complexity, so I'd offer up
> option 3 as the most viable alternative right now.
> 
> Signed-off-by: Jarod Wilson <jarod@...hat.com>

I just posted exactly the same thing yesterday :)
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