From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751701AbcGRPrQ (ORCPT ); Mon, 18 Jul 2016 11:47:16 -0400 Received: from mail-qk0-f170.google.com ([209.85.220.170]:33284 "EHLO mail-qk0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751396AbcGRPrP (ORCPT ); Mon, 18 Jul 2016 11:47:15 -0400 Date: Mon, 18 Jul 2016 11:45:53 -0400 (EDT) From: Nicolas Pitre To: One Thousand Gnomes cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Viro , David Howells , Greg Ungerer Subject: Re: [PATCH v2 10/10] binfmt_flat: allow compressed flat binary format to work on MMU systems In-Reply-To: <20160718124707.6adfa9a1@lxorguk.ukuu.org.uk> Message-ID: References: <1468812716-30537-1-git-send-email-nicolas.pitre@linaro.org> <1468812716-30537-11-git-send-email-nicolas.pitre@linaro.org> <20160718124707.6adfa9a1@lxorguk.ukuu.org.uk> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 18 Jul 2016, One Thousand Gnomes wrote: > On Sun, 17 Jul 2016 23:31:56 -0400 > Nicolas Pitre wrote: > > > Let's take the simple and obvious approach by decompressing the binary > > into a kernel buffer and then copying it to user space. Those who are > > looking for more performance on a MMU system are unlikely to choose this > > executable format anyway. > > The flat loader takes a very casual attitude to overruns and corrupted > binaries. It's after all MMUless so has no real security model. If you > enable flat for an MMU system then IMHO those all need to be fixed > including all the missing overflow checks on the maths on textlen and the > like. What about the following patch? This with existing user accessors and allocation error checks should cover it all. ----- >8 commit cc1051c9c57202772568600e96b75229a2a7cf19 Author: Nicolas Pitre Date: Mon Jul 18 11:28:57 2016 -0400 binfmt_flat: prevent kernel dammage from corrupted executable headers Signed-off-by: Nicolas Pitre diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c index 24deae4dcb..fa0054c1c3 100644 --- a/fs/binfmt_flat.c +++ b/fs/binfmt_flat.c @@ -498,6 +498,17 @@ static int load_flat_file(struct linux_binprm * bprm, } /* + * Make sure the header params are sane. + * 28 bits (256 MB) is way more than reasonable in this case. + * If some top bits are set we have probable binary corruption. + */ + if ((text_len | data_len | bss_len | stack_len | full_data) >> 28) { + printk("BINFMT_FLAT: bad header\n"); + ret = -ENOEXEC; + goto err; + } + + /* * fix up the flags for the older format, there were all kinds * of endian hacks, this only works for the simple cases */ >