From: Pavel Machek Subject: Re: [PATCH 07/18] asymmetric keys: explicitly add the leading zero byte to encoded message Date: Sun, 25 Aug 2013 18:13:13 +0200 Message-ID: <20130825161313.GD5171@amd.pavel.ucw.cz> References: <1377169317-5959-1-git-send-email-jlee@suse.com> <1377169317-5959-8-git-send-email-jlee@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-efi@vger.kernel.org, linux-pm@vger.kernel.org, linux-crypto@vger.kernel.org, opensuse-kernel@opensuse.org, David Howells , "Rafael J. Wysocki" , Matthew Garrett , Len Brown , Josh Boyer , Vojtech Pavlik , Matt Fleming , James Bottomley , Greg KH , JKosina@suse.com, Rusty Russell , Herbert Xu , "David S. Miller" , "H. Peter Anvin" , Michal Marek , Gary Lin , Vivek Goyal , "Lee, Chun-Yi" To: "Lee, Chun-Yi" Return-path: Content-Disposition: inline In-Reply-To: <1377169317-5959-8-git-send-email-jlee@suse.com> Sender: linux-security-module-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On Thu 2013-08-22 19:01:46, Lee, Chun-Yi wrote: > Per PKCS1 spec, the EMSA-PKCS1-v1_5 encoded message is leading by 0x00 0x01 in > its first 2 bytes. The leading zero byte is suppressed by MPI so we pass a > pointer to the _preceding_ byte to RSA_verify() in original code, but it has > risk for the byte is not zero because it's not in EM buffer's scope, neither > RSA_verify() nor mpi_get_buffer() didn't take care the leading byte. > > To avoid the risk, that's better we explicitly add the leading zero byte to EM > for pass to RSA_verify(). This patch allocate a _EM buffer to capture the > result from RSA_I2OSP(), then set the first byte to zero in EM and copy the > remaining bytes from _EM. > > Reviewed-by: Jiri Kosina > Signed-off-by: Lee, Chun-Yi > - ret = RSA_verify(H, EM - 1, k, sig->digest_size, > + EM = kmalloc(k, GFP_KERNEL); > + memset(EM, 0, 1); > + memcpy(EM + 1, _EM, k-1); > + kfree(_EM); Spot a crash waiting to happen. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html