From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out01.mta.xmission.com ([166.70.13.231]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1njlVa-002gNn-4d for linux-um@lists.infradead.org; Wed, 27 Apr 2022 17:31:23 +0000 From: "Eric W. Biederman" References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-9-ebiederm@xmission.com> <20220427160901.GI17421@redhat.com> <87o80m7afv.fsf@email.froward.int.ebiederm.org> <20220427171829.GJ17421@redhat.com> <20220427172109.GK17421@redhat.com> Date: Wed, 27 Apr 2022 12:31:09 -0500 In-Reply-To: <20220427172109.GK17421@redhat.com> (Oleg Nesterov's message of "Wed, 27 Apr 2022 19:21:10 +0200") Message-ID: <87wnfa5t7m.fsf@email.froward.int.ebiederm.org> MIME-Version: 1.0 Subject: Re: [PATCH 9/9] ptrace: Don't change __state List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: Oleg Nesterov 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 , tj@kernel.org, linux-pm@vger.kernel.org, Peter Zijlstra , Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , inux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn Oleg Nesterov writes: > On 04/27, Oleg Nesterov wrote: >> >> On 04/27, Eric W. Biederman wrote: >> > >> > Oleg Nesterov 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. >> >> Why? The tracee will take siglock, clear JOBCTL_DELAY_WAKEKILL and notice >> SIGKILL after that. > > Not to mention that the tracee is TASK_RUNNING after PTRACE_DETACH wakes it > up, so the pending JOBCTL_DELAY_WAKEKILL simply has no effect. Oh. You are talking about the window when between clearing the traced state and when tracee resumes executing and clears JOBCTL_DELAY_WAKEKILL. I thought you were thinking about JOBCTL_DELAY_WAKEKILL being leaked. That requires both ptrace_attach and ptrace_check_attach for the new tracer to happen before the tracee is scheduled to run. I agree. I think the WARN_ON could reasonably be moved a bit later, but I don't know that the WARN_ON is important. I simply kept it because it seemed to make sense. Eric _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um