linux-kernel - Re: [PATCH v2 1/2] seccomp: notify user trap about unused filter

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <202005290102.3BB21C875@keescook>
Date:   Fri, 29 May 2020 01:06:59 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Tycho Andersen <tycho@...ho.ws>,
        Matt Denton <mpdenton@...gle.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Jann Horn <jannh@...gle.com>, Chris Palmer <palmer@...gle.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Robert Sesek <rsesek@...gle.com>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH v2 1/2] seccomp: notify user trap about unused filter

On Fri, May 29, 2020 at 09:56:41AM +0200, Christian Brauner wrote:
> On Thu, May 28, 2020 at 04:11:00PM -0700, Kees Cook wrote:
> > void seccomp_filter_release(const struct task_struct *tsk)
> > {
> > 	struct seccomp_filter *orig = READ_ONCE(tsk->seccomp.filter);
> > 
> > 	smp_store_release(&tsk->seccomp.filter, NULL);
> 
> I need to go through the memory ordering requirements before I can say
> yay or nay confidently to this. :)
> 
> > 	__seccomp_filter_release(orig);
> > }

The only caller will be release_task() after dethread, so honestly this
was just me being paranoid. I don't think it actually needs the
READ_ONCE() nor the store_release. I think I wrote all that before I'd
convinced myself it was safe to remove a filter then. But I'm still
suspicious given the various ways release_task() gets called... I just
know that if mode 2 is set and filter == NULL, seccomp will fail closed,
so I went the paranoid route. :)

-- 
Kees Cook