linux-kernel - Re: [PATCH 6/9] signal: Always call do_notify_parent

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Date:   Wed, 27 Apr 2022 16:43:00 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.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>,
        inux-xtensa@...ux-xtensa.org, Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH 6/9] signal: Always call do_notify_parent_cldstop with
 siglock held

On 04/27, Eric W. Biederman wrote:
>
> The ptrace parental relationship definitely has the potential to be a
> graph with cycles.  Which as you point out is not fine.
>
> The result is very nice and I don't want to give it up.  I suspect
> something ptrace cycles are always a problem and can simply be
> forbidden.

OK, please consider another case.

We have a parent P and its child C. C traces P.

This is not that unusual, I don't think we can forbid this case.

P reports an event and calls do_notify_parent_cldstop().

C receives SIGSTOP and calls do_notify_parent_cldstop() too.

Oleg.