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

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Message-ID: <20170919210916.6r5janszdtx7eoes@smitten>
Date:   Tue, 19 Sep 2017 15:09:16 -0600
From:   Tycho Andersen <tycho@...ker.com>
To:     Kees Cook <keescook@...omium.org>
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

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.

Tycho