linux-kernel - Re: [PATCH 10/11] ptrace: move JOBCTL_TRAPPING wait to wait(2) and ptrace_check

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]

Date:	Thu, 12 May 2011 18:06:49 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	jan.kratochvil@...hat.com, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu
Subject: Re: [PATCH 10/11] ptrace: move JOBCTL_TRAPPING wait to wait(2) and
	ptrace_check_attach()

On 05/12, Tejun Heo wrote:
>
> Hello, Oleg.
>
> On Wed, May 11, 2011 at 09:53:33PM +0200, Tejun Heo wrote:
> > > As for ptrace_check_attach(), it can simply do wait_event(), we
> > > only need to verify the caller is the tracer. No need to play with
> > > lock/unlock/retry.
> > >
> > > What do you think?
> >
> > Hmmm... interesting.  Yeah, the state is visible only through wait(2)
> > and ptrace(2) and for wait(2) TRAPPING is as good as STOPPED/TRACED
> > and we can wait all we want in ptrace_check_attach().  I'll think more
> > about it but seems like a nice idea.
>
> Eh, problem.  Please consider the following scenario.
>
> * A task is in TASK_STOPPED.  current->exit_code contains zero.
>
> * Tracer seizes the task which triggers TRAPPING.
>
> * Tracer wait(2)s which sees TRAPPING but tracee->exit_code is still
>   zero.

At first glance, this is easy to fix. do_signal_stop() can set
->exit_code unconditionally as it did before.

> I think retrying and ensuring that tracee is in the expected state
> after going through the regular trapping procedure is better way to
> handle this.  Bypassing wait(2) seems smart and simple but it entails
> much more subtleties than simple stupid waiting/retrying.

Agreed. But this wait_event(!TRAPPING) logic has a lot of subtleties
too.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/