Re: [PATCH] crypto: drbg: check blocklen is non zero

[Herbert Xu]

On Sun, Aug 02, 2020 at 10:12:47AM -0700, trix@xxxxxxxxxx wrote:
> From: Tom Rix <trix@xxxxxxxxxx>
> 
> Clang static analysis reports this error
> 
> crypto/drbg.c:441:40: warning: Division by zero
>         padlen = (inputlen + sizeof(L_N) + 1) % (drbg_blocklen(drbg));
>                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
> 
> When drbg_bocklen fails it returns 0.
> 
> 	if (drbg && drbg->core)
> 		return drbg->core->blocklen_bytes;
> 	return 0;

Yes but it can only fail if the drbg is not instantiated.  If
you're hitting the generate path with an uninstantiated drbg you've
got bigger problems than a divide by zero.

So how is this even possible?

Cheers,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
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