Re: [PATCH 4/7] crypto/hmac_sha256: Remove undefined memset()

[Rusty Russell <rusty@rustcorp.com.au>]

David Gibson <david@gibson.dropbear.id.au> writes:
> A memset() with a zero length argument isn't well defined.  It *might* be
> a no-op, but then it might not.  So, test for this case in
> hmac_sha256_init().

Huh?  That seems really odd.

Rusty.

> Found by Coverity.
>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  ccan/crypto/hmac_sha256/hmac_sha256.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/ccan/crypto/hmac_sha256/hmac_sha256.c b/ccan/crypto/hmac_sha256/hmac_sha256.c
> index 0392afe..70ca3b2 100644
> --- a/ccan/crypto/hmac_sha256/hmac_sha256.c
> +++ b/ccan/crypto/hmac_sha256/hmac_sha256.c
> @@ -36,7 +36,9 @@ void hmac_sha256_init(struct hmac_sha256_ctx *ctx,
>  	 *   appended with 44 zero bytes 0x00)
>  	 */
>  	memcpy(k_ipad, k, ksize);
> -	memset((char *)k_ipad + ksize, 0, HMAC_SHA256_BLOCKSIZE - ksize);
> +	if (ksize < HMAC_SHA256_BLOCKSIZE)
> +		memset((char *)k_ipad + ksize, 0,
> +		       HMAC_SHA256_BLOCKSIZE - ksize);
>  
>  	/*
>  	 * (2) XOR (bitwise exclusive-OR) the B byte string computed
> -- 
> 2.9.3
>
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