linux-kernel - Re: [PATCH] ptrace, seccomp: add support for retrieving seccomp flags

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Message-ID: <CAGXu5jJGPLi0Pc_KHADhCmo9peivN6HP-BDJ5=BJsyMbo3VzWA@mail.gmail.com>
Date:   Tue, 19 Sep 2017 14:43:51 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Tycho Andersen <tycho@...ker.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, criu@...nvz.org,
        Andy Lutomirski <luto@...capital.net>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] ptrace, seccomp: add support for retrieving seccomp flags

On Tue, Sep 19, 2017 at 2:09 PM, Tycho Andersen <tycho@...ker.com> wrote:
> Hi Kees,
>
> On Tue, Sep 19, 2017 at 01:08:28PM -0700, Kees Cook wrote:
>> On Tue, Sep 19, 2017 at 10:47 AM, Tycho Andersen <tycho@...ker.com> wrote:
>> > With the new SECCOMP_FILTER_FLAG_LOG, we need to be able to extract these
>> > flags for checkpoint restore, since they describe the state of a filter.
>> >
>> > So, let's add PTRACE_SECCOMP_GET_FLAGS, similar to ..._GET_FILTER, which
>> > returns the flags of the nth filter.
>>
>> Can you split this up into factoring out the nth helper, and then
>> adding the new get?
>>
>> For naming, perhaps "GET_FILTER_FLAGS" instead of "GET_FLAGS" since
>> there may be seccomp flags in the future, etc.
>
> Sure, I'll do both of these.
>
>> Is there any sane way to add the flags to the existing GET_FILTER?
>
> I looked at this, and I don't think so. Unfortunately, we didn't use
> any structure for the output, it's just the raw bytes of the filter
> with the length used as the return value. I suppose we could append
> the flags after the bytes of the filter, but that seems... very ugly
> :). Let me know if you want to go that route.

I think if we can make the new GET_FILTER_stuff interface more
extensible, we should cover any future needs for per-filter content.
BUt yeah, I agree, when I looked at this when I first mailed you about
it, I agree: it looked more ugly to extend the existing GET_FILTER.

-Kees

-- 
Kees Cook
Pixel Security