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

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Message-ID: <20200820071522.GA21511@gondor.apana.org.au>
Date:   Thu, 20 Aug 2020 17:15:22 +1000
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     trix@...hat.com
Cc:     davem@...emloft.net, smueller@...onox.de,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: drbg: check blocklen is non zero

On Sun, Aug 02, 2020 at 10:12:47AM -0700, trix@...hat.com wrote:
> From: Tom Rix <trix@...hat.com>
> 
> 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@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt