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

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Date:   Wed, 31 Oct 2018 14:04:42 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Tycho Andersen <tycho@...ho.ws>,
        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>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v8 1/2] seccomp: add a return code to trap to userspace

On 10/30, Kees Cook wrote:
>
> I'd like to avoid changing the return value of __secure_computing() to
> just avoid having to touch all the callers. And I'd prefer not to
> change __seccomp_filter() to a bool, since I'd like the return values
> to be consistent through the call chain.

Sure, please forget.

> I find the existing code more readable than a single-line return, just
> because it's very explicit. I don't want to have to think any harder
> when reading seccomp. ;)

Heh ;) Again, please forget, this is cosmetic.

But I simply can't resist. I asked this question exactly because I was
confused by these 2 lines:

		if (__seccomp_filter(this_syscall, NULL, true))
			return -1;

		return 0;

to me it looks as if we need to filter out some non-zero return values and
turn them into -1. I had to spend some time (and think harder ;) to verify
that this is just the recursive call and nothing more.

nevermind, please ignore.

Oleg.