From: James Morris Subject: Re: [PATCH] dh key: fix rounding up KDF output length Date: Fri, 8 Jun 2018 05:28:01 +1000 (AEST) Message-ID: References: <0000000000009c221d056e0cf53a@google.com> <20180607191201.97080-1-ebiggers3@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: Eric Biggers , David Howells , keyrings@vger.kernel.org, linux-security-module , linux-crypto , LKML , syzkaller-bugs@googlegroups.com, Tycho Andersen , Stephan Mueller , Eric Biggers To: Kees Cook Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On Thu, 7 Jun 2018, Kees Cook wrote: > On Thu, Jun 7, 2018 at 12:12 PM, Eric Biggers wrote: > > From: Eric Biggers > > > > Commit 383203eff718 ("dh key: get rid of stack allocated array") changed > > kdf_ctr() to assume that the length of key material to derive is a > > multiple of the digest size. The length was supposed to be rounded up > > accordingly. However, the round_up() macro was used which only gives > > the correct result on power-of-2 arguments, whereas not all hash > > algorithms have power-of-2 digest sizes. In some cases this resulted in > > a write past the end of the 'outbuf' buffer. > > > > Fix it by switching to roundup(), which works for non-power-of-2 inputs. > > round_up() vs roundup(). Wow, that's not confusing. :( I wonder if we > should rename the former to roundup_pow2() or something? Good idea, in a separate patch(set). -- James Morris