linux-kernel - Re: [PATCH 08/16] ptrace: Only populate last

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Date:   Mon, 06 Jun 2022 17:16:01 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     linux-kernel@...r.kernel.org, rjw@...ysocki.net, mingo@...nel.org,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, mgorman@...e.de, bigeasy@...utronix.de,
        Will Deacon <will@...nel.org>, tj@...nel.org,
        linux-pm@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        linux-um@...ts.infradead.org, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org, Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, linux-ia64@...r.kernel.org,
        Robert OCallahan <roc@...nos.co>, Kyle Huey <khuey@...nos.co>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        Douglas Miller <dougmill@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 08/16] ptrace: Only populate last_siginfo from ptrace

Oleg Nesterov <oleg@...hat.com> writes:

> On 05/18, Eric W. Biederman wrote:
>>
>> The code in ptrace_signal to populate siginfo if the signal number
>> changed is buggy.  If the tracer contined the tracee using
>> ptrace_detach it is guaranteed to use the real_parent (or possibly a
>> new tracer) but definitely not the origional tracer to populate si_pid
>> and si_uid.
>
> I guess nobody cares. As the comment says
>
> 	 If the debugger wanted something
> 	 specific in the siginfo structure then it should
> 	 have updated *info via PTRACE_SETSIGINFO.
>
> otherwise I don't think si_pid/si_uid have any value.

No one has complained so it is clearly no one cares.  So it is
definitely not a regression.  Or even anything that needs to be
backported.

However si_pid and si_uid are defined with SI_USER are defined
to be whomever sent the signal.  So I would argue by definition
those values are wrong.

> However the patch looks fine to me, just the word "buggy" looks a bit
> too strong imo.

I guess I am in general agreement.  Perhaps I can just say they values
are wrong by definition?

Eric