From: Stephan Mueller Subject: Re: [PATCH v6 3/6] crypto: AF_ALG -- add asymmetric cipher interface Date: Wed, 08 Jun 2016 07:31:14 +0200 Message-ID: <6401187.24v903AfyY@tauon.atsec.com> References: <20160515041645.15888.94903.stgit@tstruk-mobl1> <20160515041701.15888.53830.stgit@tstruk-mobl1> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: Tadeusz Struk , dhowells@redhat.com, herbert@gondor.apana.org.au, linux-api@vger.kernel.org, marcel@holtmann.org, linux-kernel@vger.kernel.org, keyrings@vger.kernel.org, linux-crypto@vger.kernel.org, dwmw2@infradead.org, davem@davemloft.net To: Mat Martineau Return-path: Received: from mail.eperm.de ([89.247.134.16]:36036 "EHLO mail.eperm.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161600AbcFHFbT (ORCPT ); Wed, 8 Jun 2016 01:31:19 -0400 In-Reply-To: Sender: linux-crypto-owner@vger.kernel.org List-ID: Am Dienstag, 7. Juni 2016, 17:28:07 schrieb Mat Martineau: Hi Mat, > > + used = ctx->used; > > + > > + /* convert iovecs of output buffers into scatterlists */ > > + while (iov_iter_count(&msg->msg_iter)) { > > + /* make one iovec available as scatterlist */ > > + err = af_alg_make_sg(&ctx->rsgl[cnt], &msg->msg_iter, > > + iov_iter_count(&msg->msg_iter)); > > + if (err < 0) > > + goto unlock; > > + usedpages += err; > > + /* chain the new scatterlist with previous one */ > > + if (cnt) > > + af_alg_link_sg(&ctx->rsgl[cnt - 1], &ctx->rsgl[cnt]); > > + > > + iov_iter_advance(&msg->msg_iter, err); > > + cnt++; > > + } > > + > > + /* ensure output buffer is sufficiently large */ > > + if (usedpages < akcipher_calcsize(ctx)) { > > + err = -EMSGSIZE; > > + goto unlock; > > + } > > Why is the size of the output buffer enforced here instead of depending on > the algorithm implementation? akcipher_calcsize calls crypto_akcipher_maxsize to get the maximum size the algorithm generates as output during its operation. The code ensures that the caller provided at least that amount of memory for the kernel to store its data in. This check therefore is present to ensure the kernel does not overstep memory boundaries in user space. What is your concern? Thanks Ciao Stephan