linux-kernel - Re: [PATCH v8 1/2] seccomp: add a return code to trap to userspace

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Date:   Tue, 30 Oct 2018 11:21:43 -0600
From:   Tycho Andersen <tycho@...ho.ws>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Christian Brauner <christian@...uner.io>,
        Tyler Hicks <tyhicks@...onical.com>,
        Akihiro Suda <suda.akihiro@....ntt.co.jp>,
        Aleksa Sarai <asarai@...e.de>, linux-kernel@...r.kernel.org,
        containers@...ts.linux-foundation.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v8 1/2] seccomp: add a return code to trap to userspace

On Tue, Oct 30, 2018 at 05:39:26PM +0100, Oleg Nesterov wrote:
> On 10/30, Oleg Nesterov wrote:
> >
> > On 10/30, Tycho Andersen wrote:
> > >
> > > @@ -828,6 +823,11 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
> > >  	 */
> > >  	rmb();
> > >
> > > +	if (!sd) {
> > > +		populate_seccomp_data(&sd_local);
> > > +		sd = &sd_local;
> > > +	}
> > > +
> >
> > To me it would be more clean to remove the "if (!sd)" check, case(SECCOMP_RET_TRACE)
> > in __seccomp_filter() can simply do populate_seccomp_data(&sd_local) unconditionally
> > and pass &sd_local to __seccomp_filter().
> 
> Ah, please ignore, emulate_vsyscall() does secure_computing(NULL).
> 
> Btw. why __seccomp_filter() doesn't return a boolean?
> 
> Or at least, why can't case(SECCOMP_RET_TRACE) simply do
> 
> 	return __seccomp_filter(this_syscall, NULL, true);
> 
> ?

Yeah, at least the second one definitely makes sense. I can add that
as a patch in the next version of this series unless Kees does it
before.

Thanks for your help, Oleg!

Tycho