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]

Message-ID: <20110511170058.GB26383@redhat.com>
Date:	Wed, 11 May 2011 19:00:58 +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 05/11, Oleg Nesterov wrote:
>
> You know, I'd wish I could find the serious bugs in this patch. The
> code becomes really hairy. -EAGAIN in do_wait() doesn't make it more
> simple ;)

Mwahaha! I seem to see the bug ;)

	bool ptrace_wait_trapping(struct task_struct *child)
		__releases(&child->sighand->siglock)
		__releases(&tasklist_lock)
	{
		if (likely(!(child->jobctl & JOBCTL_TRAPPING)))
			return false;

		spin_unlock_irq(&child->sighand->siglock);
		get_task_struct(child);
		read_unlock(&tasklist_lock);

--> WINDOW

		wait_event(current->signal->wait_chldexit,
			   !(child->jobctl & JOBCTL_TRAPPING));
		put_task_struct(child);
		return true;
	}

When the caller is do_wait(), we can't assume we are the tracer when
we drop tasklist. Original tracer can detach, then another unrelated
process can attach again and provoke JOBCTL_TRAPPING. wait_event()
can hang forever.

Unfortunately, this is easy to fix :/

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/