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Re: [dm-devel] [PATCH v7 2/9] crypto: cbc: Remove VLA usage



On Thu, Aug 02, 2018 at 03:51:45PM -0700, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> uses the upper bounds on blocksize. Since this is always a cipher
> blocksize, use the existing cipher max blocksize.
> 
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA mail gmail com
> 
> Signed-off-by: Kees Cook <keescook chromium org>
> ---
>  include/crypto/cbc.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/crypto/cbc.h b/include/crypto/cbc.h
> index f5b8bfc22e6d..47db0aac2ab9 100644
> --- a/include/crypto/cbc.h
> +++ b/include/crypto/cbc.h
> @@ -113,7 +113,9 @@ static inline int crypto_cbc_decrypt_inplace(
>  	unsigned int bsize = crypto_skcipher_blocksize(tfm);
>  	unsigned int nbytes = walk->nbytes;
>  	u8 *src = walk->src.virt.addr;
> -	u8 last_iv[bsize];
> +	u8 last_iv[MAX_CIPHER_BLOCKSIZE];
> +
> +	BUG_ON(bsize > sizeof(last_iv));

Ugh, please don't add these BUG_ONs.  Add them to the places where
the algorithm is created (if they aren't checking that already).

Thanks,
-- 
Email: Herbert Xu <herbert gondor 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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