From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754632Ab2B0SgS (ORCPT ); Mon, 27 Feb 2012 13:36:18 -0500 Received: from mail-gx0-f174.google.com ([209.85.161.174]:39371 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754587Ab2B0SgQ convert rfc822-to-8bit (ORCPT ); Mon, 27 Feb 2012 13:36:16 -0500 MIME-Version: 1.0 In-Reply-To: <20120227181434.GA13903@redhat.com> References: <1330140111-17201-1-git-send-email-wad@chromium.org> <1330140111-17201-7-git-send-email-wad@chromium.org> <20120227171132.GB10608@redhat.com> <20120227181434.GA13903@redhat.com> From: Andrew Lutomirski Date: Mon, 27 Feb 2012 10:35:55 -0800 X-Google-Sender-Auth: l9Nl6kkeWBizvOA3KZFSP_UnNa4 Message-ID: Subject: Re: [PATCH v11 07/12] seccomp: add SECCOMP_RET_ERRNO To: Oleg Nesterov Cc: Kees Cook , Will Drewry , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, kernel-hardening@lists.openwall.com, netdev@vger.kernel.org, x86@kernel.org, arnd@arndb.de, davem@davemloft.net, hpa@zytor.com, mingo@redhat.com, peterz@infradead.org, rdunlap@xenotime.net, mcgrathr@chromium.org, tglx@linutronix.de, eparis@redhat.com, serge.hallyn@canonical.com, djm@mindrot.org, scarybeasts@gmail.com, indan@nul.nu, pmoore@redhat.com, akpm@linux-foundation.org, corbet@lwn.net, eric.dumazet@gmail.com, markus@chromium.org, coreyb@linux.vnet.ibm.com Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 27, 2012 at 10:14 AM, Oleg Nesterov wrote: > On 02/27, Kees Cook wrote: >> >> On Mon, Feb 27, 2012 at 9:11 AM, Oleg Nesterov wrote: >> > On 02/24, Will Drewry wrote: >> >> >> >>  static u32 seccomp_run_filters(int syscall) >> >>  { >> >>       struct seccomp_filter *f; >> >> -     u32 ret = SECCOMP_RET_KILL; >> >>       static const struct bpf_load_fn fns = { >> >>               bpf_load, >> >>               sizeof(struct seccomp_data), >> >>       }; >> >> +     u32 ret = SECCOMP_RET_ALLOW; >> >>       const void *sc_ptr = (const void *)(uintptr_t)syscall; >> >> >> >> +     /* Ensure unexpected behavior doesn't result in failing open. */ >> >> +     if (unlikely(current->seccomp.filter == NULL)) >> >> +             ret = SECCOMP_RET_KILL; >> > >> > Is "seccomp.filter == NULL" really possible? >> >> It should not be, but I'm much more comfortable with this failing >> closed. I think it's important to be as defensive as possible with >> this code given its intended use. > > Can't resists... Sorry, I know I am troll but personally I think > in this case the most defensive code is BUG_ON(->filter == NULL) > or at least WARN_ON(). Linus will probably object because he objected (correctly) to a very similar problem in my old vsyscall emulation series. A userspace security feature shouldn't have a failure mode in which it confuses the kernel and results in an oops, unless the situation is really unrecoverable. So WARN_ON plus do_exit would be okay but BUG_ON would not. --Andy