From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71947C433F5 for ; Wed, 27 Apr 2022 23:06:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233901AbiD0XJY (ORCPT ); Wed, 27 Apr 2022 19:09:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35416 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237842AbiD0XJN (ORCPT ); Wed, 27 Apr 2022 19:09:13 -0400 Received: from out02.mta.xmission.com (out02.mta.xmission.com [166.70.13.232]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 120FF4EF42; Wed, 27 Apr 2022 16:05:59 -0700 (PDT) Received: from in02.mta.xmission.com ([166.70.13.52]:51442) by out02.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1njqjL-004GYP-WE; Wed, 27 Apr 2022 17:05:56 -0600 Received: from ip68-227-174-4.om.om.cox.net ([68.227.174.4]:36000 helo=email.froward.int.ebiederm.org.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1njqjK-00DmT9-Ut; Wed, 27 Apr 2022 17:05:55 -0600 From: "Eric W. Biederman" To: linux-kernel@vger.kernel.org Cc: rjw@rjwysocki.net, Oleg Nesterov , 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 References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-9-ebiederm@xmission.com> Date: Wed, 27 Apr 2022 18:05:47 -0500 In-Reply-To: <20220426225211.308418-9-ebiederm@xmission.com> (Eric W. Biederman's message of "Tue, 26 Apr 2022 17:52:11 -0500") Message-ID: <87czh2160k.fsf@email.froward.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1njqjK-00DmT9-Ut;;;mid=<87czh2160k.fsf@email.froward.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.174.4;;;frm=ebiederm@xmission.com;;;spf=softfail X-XM-AID: U2FsdGVkX1/koGqdANEmvAjzDoG/4Ztqacq2eIk+J9E= X-SA-Exim-Connect-IP: 68.227.174.4 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 9/9] ptrace: Don't change __state X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Eric W. Biederman" writes: > diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h > index 3c8b34876744..1947c85aa9d9 100644 > --- a/include/linux/sched/signal.h > +++ b/include/linux/sched/signal.h > @@ -437,7 +437,8 @@ extern void signal_wake_up_state(struct task_struct *t, unsigned int state); > > static inline void signal_wake_up(struct task_struct *t, bool resume) > { > - signal_wake_up_state(t, resume ? TASK_WAKEKILL : 0); > + bool wakekill = resume && !(t->jobctl & JOBCTL_DELAY_WAKEKILL); > + signal_wake_up_state(t, wakekill ? TASK_WAKEKILL : 0); > } > static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume) > { Grrr. While looking through everything today I have realized that there is a bug. Suppose we have 3 processes: TRACER, TRACEE, KILLER. Meanwhile TRACEE is in the middle of ptrace_stop, just after siglock has been dropped. The TRACER process has performed ptrace_attach on TRACEE and is in the middle of a ptrace operation and has just set JOBCTL_DELAY_WAKEKILL. Then comes in the KILLER process and sends the TRACEE a SIGKILL. The TRACEE __state remains TASK_TRACED, as designed. The bug appears when the TRACEE makes it to schedule(). Inside schedule there is a call to signal_pending_state() which notices a SIGKILL is pending and refuses to sleep. I could avoid setting TIF_SIGPENDING in signal_wake_up but that is insufficient as another signal may be pending. I could avoid marking the task as __fatal_signal_pending but then where would the information that the task needs to become __fatal_signal_pending go. Hmm. This looks like I need my other pending cleanup which introduces a helper to get this idea to work. Eric From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out02.mta.xmission.com ([166.70.13.232]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1njqjQ-003u0A-4M for linux-um@lists.infradead.org; Wed, 27 Apr 2022 23:06:02 +0000 From: "Eric W. Biederman" References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-9-ebiederm@xmission.com> Date: Wed, 27 Apr 2022 18:05:47 -0500 In-Reply-To: <20220426225211.308418-9-ebiederm@xmission.com> (Eric W. Biederman's message of "Tue, 26 Apr 2022 17:52:11 -0500") Message-ID: <87czh2160k.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: linux-kernel@vger.kernel.org Cc: rjw@rjwysocki.net, Oleg Nesterov , 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 "Eric W. Biederman" writes: > diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h > index 3c8b34876744..1947c85aa9d9 100644 > --- a/include/linux/sched/signal.h > +++ b/include/linux/sched/signal.h > @@ -437,7 +437,8 @@ extern void signal_wake_up_state(struct task_struct *t, unsigned int state); > > static inline void signal_wake_up(struct task_struct *t, bool resume) > { > - signal_wake_up_state(t, resume ? TASK_WAKEKILL : 0); > + bool wakekill = resume && !(t->jobctl & JOBCTL_DELAY_WAKEKILL); > + signal_wake_up_state(t, wakekill ? TASK_WAKEKILL : 0); > } > static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume) > { Grrr. While looking through everything today I have realized that there is a bug. Suppose we have 3 processes: TRACER, TRACEE, KILLER. Meanwhile TRACEE is in the middle of ptrace_stop, just after siglock has been dropped. The TRACER process has performed ptrace_attach on TRACEE and is in the middle of a ptrace operation and has just set JOBCTL_DELAY_WAKEKILL. Then comes in the KILLER process and sends the TRACEE a SIGKILL. The TRACEE __state remains TASK_TRACED, as designed. The bug appears when the TRACEE makes it to schedule(). Inside schedule there is a call to signal_pending_state() which notices a SIGKILL is pending and refuses to sleep. I could avoid setting TIF_SIGPENDING in signal_wake_up but that is insufficient as another signal may be pending. I could avoid marking the task as __fatal_signal_pending but then where would the information that the task needs to become __fatal_signal_pending go. Hmm. This looks like I need my other pending cleanup which introduces a helper to get this idea to work. Eric _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um