Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
From:   "Eric W. Biederman" <ebiederm@xmission.com>
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     linux-kernel@vger.kernel.org, rjw@rjwysocki.net, mingo@kernel.org,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de,
        Will Deacon <will@kernel.org>, tj@kernel.org,
        linux-pm@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Richard Weinberger <richard@nod.at>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-um@lists.infradead.org, Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>,
        inux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>
In-Reply-To: <20220427160901.GI17421@redhat.com> (Oleg Nesterov's message of
        "Wed, 27 Apr 2022 18:09:03 +0200")
References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org>
        <20220426225211.308418-9-ebiederm@xmission.com>
        <20220427160901.GI17421@redhat.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux)
Date:   Wed, 27 Apr 2022 11:33:40 -0500
Message-ID: <87o80m7afv.fsf@email.froward.int.ebiederm.org>
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [PATCH 9/9] ptrace: Don't change __state
Precedence: bulk

Oleg Nesterov <oleg@redhat.com> writes:

> On 04/26, Eric W. Biederman wrote:
>>
>> @@ -253,7 +252,7 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state)
>>  	 */
>>  	if (lock_task_sighand(child, &flags)) {
>>  		if (child->ptrace && child->parent == current) {
>> -			WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED);
>> +			WARN_ON(child->jobctl & JOBCTL_DELAY_WAKEKILL);
>
> This WARN_ON() doesn't look right.
>
> It is possible that this child was traced by another task and PTRACE_DETACH'ed,
> but it didn't clear DELAY_WAKEKILL.

That would be a bug.  That would mean that PTRACE_DETACHED process can
not be SIGKILL'd.

> If the new debugger attaches and calls ptrace() before the child takes siglock
> ptrace_freeze_traced() will fail, but we can hit this WARN_ON().

Eric