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

[Tom Rix]

There are many divide by 0 reports.  This one got attention because it is in crypto, where i believe problems, even false positives, should be fixed.

Tom

On 8/20/20 12:15 AM, Herbert Xu wrote:
> 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,