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Date:   Wed, 12 May 2021 16:38:56 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Jan Kratochvil <jan.kratochvil@redhat.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Pedro Alves <palves@redhat.com>,
        Simon Marchi <simon.marchi@efficios.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RESEND2] ptrace: make ptrace() fail if the tracee changed
 its pid unexpectedly
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Hi Mathieu,

On 05/12, Mathieu Desnoyers wrote:
>
> Out of curiosity: what makes it OK to use either the current task or its
> parent's pid namespace in this specific case ? What happens if they are
> in different pid namespaces ?

Because in this case current == task->parent == debugger.

Just in case... task->real_parent is, well, "real parent", the parent which
forked this task.

task->parent == task->real_parent unless this task is ptraced, in this case
task->parent == debugger.

Oleg.