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From: Andy Lutomirski <luto@amacapital.net>
Date: Wed, 16 Jul 2014 14:27:38 -0700
Message-ID: <CALCETrUXRszBEhB7aOu6nXtCj09zofY_b_5BUNbJk-EFefA6fw@mail.gmail.com>
Subject: Re: [PATCH v10 0/11] seccomp: add thread sync ability
To: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Alexei Starovoitov <ast@plumgrid.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Daniel Borkmann <dborkman@redhat.com>, Will Drewry <wad@chromium.org>,
        Julien Tinnes <jln@chromium.org>, David Drysdale <drysdale@google.com>,
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        "x86@kernel.org" <x86@kernel.org>,
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	<linux-arm-kernel@lists.infradead.org>,
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        linux-arch <linux-arch@vger.kernel.org>,
        linux-security-module <linux-security-module@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org

On Wed, Jul 16, 2014 at 2:23 PM, Kees Cook <keescook@chromium.org> wrote:
> On Wed, Jul 16, 2014 at 12:45 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> In seccomp_prepare_user_filter, would it make sense to return -EINVAL
>> if !user_filter?  That will make it slightly more pleasant to
>> implement TSYNC-without-change if anyone ever wants it.  (This isn't
>> really necessary -- it's just slightly more polite.)
>
> I can't do this since EFAULT is already used to detect seccomp
> capabilities from userspace.

Aha.  In that case, can you (separately) send a prctl.2 manpage patch
documenting that?  Also, I'm pretty sure you can get away with doing
this for seccomp(2) -- EINVAL and ENOSYS are easily distinguishable,
but the current behavior is IMO also fine if documented.

--Andy
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