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

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Date:   Fri, 30 Nov 2018 11:17:51 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Tycho Andersen <tycho@...ho.ws>
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 11/29, Tycho Andersen wrote:
>
> /*
>  * These should never be seen by user programs.  To return one of ERESTART*
>  * codes, signal_pending() MUST be set.  Note that ptrace can observe these
>  * at syscall exit tracing, but they will never be left for the debugged user
>  * process to see.
>  */
> #define ERESTARTSYS     512
>
> So basically, if you respond with -ERESTARTSYS with no signal pending, you'll
> leak it to userspace.

Yes,

> It turns out this is already possible with
> SECCOMP_RET_TRAP (and probably ptrace alone,

Yes,

> The question is: do we care?

I think we do not care, debugger can do anything with the tracee.

Oleg.