From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f179.google.com ([209.85.220.179]:35009 "EHLO mail-qk0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751364AbcGRQ6h (ORCPT ); Mon, 18 Jul 2016 12:58:37 -0400 Received: by mail-qk0-f179.google.com with SMTP id s63so162801401qkb.2 for ; Mon, 18 Jul 2016 09:58:37 -0700 (PDT) Date: Mon, 18 Jul 2016 12:58:34 -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: <20160718175158.74676924@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> <20160718175158.74676924@lxorguk.ukuu.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Mon, 18 Jul 2016, One Thousand Gnomes wrote: > On Mon, 18 Jul 2016 11:45:53 -0400 (EDT) > Nicolas Pitre wrote: > > > 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"); > > Apart from the printk that looks good for the header but I think the rest > could do with a fair bit more review (eg relocations in range checks). Given that they all go through put_user() now, the worst that could happen is an executable that craps onto itself. I don't think there is much we can do here besides letting the user task crash. Nicolas