linux-kernel - Re: [PATCH v2] crypto: AES-NI - fix memory usage in GCM decryption

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Message-ID: <20150313103306.GA1559@gondor.apana.org.au>
Date:	Fri, 13 Mar 2015 21:33:06 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	tadeusz.struk@...el.com, linux-crypto@...r.kernel.org,
	'LKML' <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] crypto: AES-NI - fix memory usage in GCM decryption

On Thu, Mar 12, 2015 at 09:17:51AM +0100, Stephan Mueller wrote:
> The kernel crypto API logic requires the caller to provide the
> length of (ciphertext || authentication tag) as cryptlen for the
> AEAD decryption operation. Thus, the cipher implementation must
> calculate the size of the plaintext output itself and cannot simply use
> cryptlen.
> 
> The RFC4106 GCM decryption operation tries to overwrite cryptlen memory
> in req->dst. As the destination buffer for decryption only needs to hold
> the plaintext memory but cryptlen references the input buffer holding
> (ciphertext || authentication tag), the assumption of the destination
> buffer length in RFC4106 GCM operation leads to a too large size. This
> patch simply uses the already calculated plaintext size.
> 
> In addition, this patch fixes the offset calculation of the AAD buffer
> pointer: as mentioned before, cryptlen already includes the size of the
> tag. Thus, the tag does not need to be added. With the addition, the AAD
> will be written beyond the already allocated buffer.
> 
> Note, this fixes a kernel crash that can be triggered from user space
> via AF_ALG(aead) -- simply use the libkcapi test application
> from [1] and update it to use rfc4106-gcm-aes.
> 
> Using [1], the changes were tested using CAVS vectors to demonstrate
> that the crypto operation still delivers the right results.
> 
> [1] http://www.chronox.de/libkcapi.html
> 
> CC: Tadeusz Struk <tadeusz.struk@...el.com>
> Signed-off-by: Stephan Mueller <smueller@...onox.de>

Patch applied.  Thanks!
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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