linux-kernel - Re: [RFC PATCH] ptrace: make ptrace() fail if the tracee changed its pid unexpectedly

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Message-ID: <e8644e25-042f-6c52-533a-da097fc566e9@efficios.com>
Date:   Sat, 19 Dec 2020 23:48:03 -0500
From:   Simon Marchi <simon.marchi@...icios.com>
To:     Oleg Nesterov <oleg@...hat.com>, Pedro Alves <palves@...hat.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Jan Kratochvil <jan.kratochvil@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ptrace: make ptrace() fail if the tracee changed its
 pid unexpectedly

On 2020-12-19 2:33 p.m., Oleg Nesterov wrote:
> OOPS! Sorry Simon, yes I forgot to add reported-by. Andrew, or Eric, if
> you take this patch, could you also add
> 
> 	Reported-by: Simon Marchi <simon.marchi@...icios.com>

I tried the original reproducer on a patched kernel, and it looks good.
GDB's behavior is still not super clean when this situation happens: a
PTRACE_GETREGS on the (disappeared) leader now fails with ESRCH (that's
what we want), and that interrupts the "continue" command and
unexpectedly brings back the prompt while leaving the other thread
running.  But that is all logic that will have to be fixed inside GDB.

So, feel free to add

  Acked-by: Simon Marchi <simon.marchi@...icios.com>

too.

Thanks!

Simon