Date: Mon, 27 Feb 2012 19:14:34 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: Will Drewry <wad@chromium.org>, 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, luto@mit.edu,
        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
Subject: Re: [PATCH v11 07/12] seccomp: add SECCOMP_RET_ERRNO
Message-ID: <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> <CAGXu5jJQhfSSwTU5fSGR_Q57LAQBFW25A_FtR2GFsxyT_ibnzQ@mail.gmail.com>
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On 02/27, Kees Cook wrote:
>
> On Mon, Feb 27, 2012 at 9:11 AM, Oleg Nesterov <oleg@redhat.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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