linux-kernel - Re: [PATCH v11 07/12] seccomp: add SECCOMP_RET

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Date:	Mon, 27 Feb 2012 19:14:34 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
	kernel-hardening@...ts.openwall.com, netdev@...r.kernel.org,
	x86@...nel.org, arnd@...db.de, davem@...emloft.net, hpa@...or.com,
	mingo@...hat.com, peterz@...radead.org, rdunlap@...otime.net,
	mcgrathr@...omium.org, tglx@...utronix.de, luto@....edu,
	eparis@...hat.com, serge.hallyn@...onical.com, djm@...drot.org,
	scarybeasts@...il.com, indan@....nu, pmoore@...hat.com,
	akpm@...ux-foundation.org, corbet@....net, eric.dumazet@...il.com,
	markus@...omium.org, coreyb@...ux.vnet.ibm.com
Subject: Re: [PATCH v11 07/12] seccomp: add SECCOMP_RET_ERRNO

On 02/27, Kees Cook wrote:
>
> On Mon, Feb 27, 2012 at 9:11 AM, Oleg Nesterov <oleg@...hat.com> 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().

Nevermind, I won't pretend I really understand the intended use,
please ignore.

Oleg.

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