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Date: Wed, 22 Feb 2017 17:55:39 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: bsegall@google.com
Cc: linux-kernel@vger.kernel.org, Roland McGrath <roland@hack.frob.com>
Subject: Re: [PATCH] ptrace: fix PTRACE_LISTEN race corrupting task->state
Message-ID: <20170222165538.GA15968@redhat.com>
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On 02/21, bsegall@google.com wrote:
>
> In PT_SEIZED + LISTEN mode SIGSTOP/SIGCONT signals cause a wakeup
> against __TASK_TRACED. If this races with the ptrace_unfreeze_traced at
> the end of a PTRACE_LISTEN, this can wake the task /after/ the check
> against __TASK_TRACED, but before the reset of state to TASK_TRACED.

Oh, thanks...

note also that PTRACE_LISTEN itself can do ptrace_signal_wake_up(true),

> This causes it to instead clobber TASK_WAKING,

even if it is already TASK_RUNNING it is simply wrong to set TASK_TRACED
in both cases, right?

Thanks. The patch looks good at first glance, but let me think a bit...
perhaps we should change PTRACE_LISTEN instead, not sure.

Oleg.