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

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Date:	Tue, 10 Mar 2015 20:45:43 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	Tadeusz Struk <tadeusz.struk@...el.com>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: AES-NI: fix memory usage in GCM decryption

On Sun, Mar 08, 2015 at 07:49:58PM +0100, Stephan Mueller wrote:
> 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 subtracts the authentication tag size from cryptlen.
> 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
> caculate the size of the plaintext output itself and cannot simply use
> cryptlen.
> 
> Note, this fixes a kernel crash that can be triggered from user space
> via AF_ALG(aead)  without it (simply use the libkcapi test application
> from [1] and update it to use rfc4106-gcm-aes).
> 
> [1] http://www.chronox.de/libkcapi.html
> 
> CC: Tadeusz Struk <tadeusz.struk@...el.com>
> Signed-off-by: Stephan Mueller <smueller@...onox.de>

Good catch.  However, I think the same confusion exists in the
code that allocates src which may also trigger a crash.  So could
you fix that as well?

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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