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[75.142.250.213]) by smtp.gmail.com with ESMTPSA id k31sm2798255qtd.60.2020.08.20.06.27.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Aug 2020 06:27:37 -0700 (PDT) Subject: Re: [PATCH] crypto: drbg: check blocklen is non zero To: Herbert Xu Cc: davem@davemloft.net, smueller@chronox.de, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200802171247.16558-1-trix@redhat.com> <20200820071522.GA21511@gondor.apana.org.au> From: Tom Rix Message-ID: <97371bc7-ebb6-92f2-bbaa-6b444e27cb8b@redhat.com> Date: Thu, 20 Aug 2020 06:27:36 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200820071522.GA21511@gondor.apana.org.au> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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@redhat.com wrote: >> From: Tom Rix >> >> 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,