linux-kernel - Re: [v2.6.34-stable 71/77] crypto: ghash - Avoid null pointer dereference if no key is set

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Message-ID: <20130109025631.GA12832@elliptictech.com>
Date:	Tue, 8 Jan 2013 21:56:31 -0500
From:	Nick Bowler <nbowler@...iptictech.com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	stable@...r.kernel.org, linux-kernel@...r.kernel.org,
	Herbert Xu <herbert@...dor.hengli.com.au>
Subject: Re: [v2.6.34-stable 71/77] crypto: ghash - Avoid null pointer
 dereference if no key is set

On 2013-01-08 18:35 -0500, Paul Gortmaker wrote:
> From: Nick Bowler <nbowler@...iptictech.com>
> 
>                    -------------------
>     This is a commit scheduled for the next v2.6.34 longterm release.
>     http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
>     If you see a problem with using this for longterm, please comment.
>                    -------------------
> 
> commit 7ed47b7d142ec99ad6880bbbec51e9f12b3af74c upstream.
> 
> The ghash_update function passes a pointer to gf128mul_4k_lle which will
> be NULL if ghash_setkey is not called or if the most recent call to
> ghash_setkey failed to allocate memory.  This causes an oops.  Fix this
> up by returning an error code in the null case.
> 
> This is trivially triggered from unprivileged userspace through the
> AF_ALG interface by simply writing to the socket without setting a key.

I haven't been following 2.6.34-longterm development, but unless
you've also backported the AF_ALG userspace interface from 2.6.38,
this sequence can only be triggered by kernel code.  So while this
patch shouldn't break anything, it isn't really necessary.

Cheers,
-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)
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