linux-kernel - Re: [PATCH v6 4/5] seccomp: add support for passing fds via USER

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Date:   Tue, 25 Sep 2018 06:53:27 -0600
From:   Tycho Andersen <tycho@...ho.ws>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Linux API <linux-api@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Tyler Hicks <tyhicks@...onical.com>,
        Akihiro Suda <suda.akihiro@....ntt.co.jp>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v6 4/5] seccomp: add support for passing fds via
 USER_NOTIF

On Thu, Sep 20, 2018 at 07:18:45PM -0700, Andy Lutomirski wrote:
> Hmm.  This does mean that we need a test case for a user notifier
> returning -ERESTARTSYS.  It should Just Work (tm), but those are
> famous last words.

Just to confirm, I've got a test case that works like this:

1. fork and install a SIGUSR1 handler
2. tracee does a syscall that gets trapped
3. send SIGUSR1
4. respond from the listener with -ERESTARTSYS
5. see another of the same syscall, even though the tracee still thinks
   its in the first one
6. respond with something reasonable, the tracee sees this response

I think that's the intended behavior. Note that when the listener
responds with -ERESTARTSYS and there is no signal pending, the task
just dies. That might be reasonable, I'm not sure.

Tycho