linux-kernel - Re: Race in ptrace.

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Message-ID: <20100209112700.GA4258@redhat.com>
Date:	Tue, 9 Feb 2010 12:27:00 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Salman Qazi <sqazi@...gle.com>
Cc:	Roland Dreier <rolandd@...co.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Race in ptrace.

Salman Qazi wrote:
>
> A race in ptrace was pointed to us by a fellow Google engineer, Tavis
> Ormandy.  The race involves interaction between a tracer, a tracee and
> an antagonist.  The tracer is tracing the tracee with PTRACE_SYSCALL and
> waits on the tracee.  In the mean time, an antagonist blasts the tracee
> with SIGCONTs.

Could you please explain how did observe this race? Do you have a
test-case, or could you explain how we can reproduce it?

Because,

> It turns out that a SIGCONT wakes up the
> tracee in kernel mode,

SIGCONT must not wake up a TASK_TRACED task.


Yes, there are some know problems with SIGCONT && ptrace, but I don't
see anthing related to the described problem.

Thanks,

Oleg.

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