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Date:   Tue, 4 Apr 2017 14:53:10 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     bsegall@...gle.com
Cc:     Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
        Roland McGrath <roland@...k.frob.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [PATCHv2] ptrace: fix PTRACE_LISTEN race corrupting task->state

On Tue, 04 Apr 2017 14:47:34 -0700 bsegall@...gle.com wrote:

> In PT_SEIZED + LISTEN mode STOP/CONT 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. This causes
> it to instead clobber TASK_WAKING, allowing a subsequent wakeup against
> TRACED while the task is still on the rq wake_list, corrupting it.

The changelog doesn't convey the urgency of the fix.  To understand
this we'll need to know the user-visible impact of the bug and the
likelihood of someone hitting it.

Also your suggestion regarding which kernel version(s) should be fixed
(and the reasoning) is always valuable.

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