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 11984C433EF for ; Thu, 28 Apr 2022 15:11:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348888AbiD1POk (ORCPT ); Thu, 28 Apr 2022 11:14:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58148 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348757AbiD1POh (ORCPT ); Thu, 28 Apr 2022 11:14:37 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3CB5965D22 for ; Thu, 28 Apr 2022 08:11:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1651158682; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=oLKNKGr8DCgjevzFl33k7TMRU8EM/aNPYmQT5R2S5w8=; b=UbgFSNqncYGJUmuLeDpMMUN1CLTAWQc69dv44n8yh3a+FVTiNOsldZisWi4ZySUYmBdJxS g1STj1/ZMyX/UK/Ld/fkzO6XwtKnDCpMZio4zmHYEVCf61u5BrHDUTJfM+HJqxFR60KoRM xBrTHgGro0+0bMEAsIH6A+usAN4GwcU= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-529-N8lcjA7HMeetaX_6BRAbgw-1; Thu, 28 Apr 2022 11:11:18 -0400 X-MC-Unique: N8lcjA7HMeetaX_6BRAbgw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BB1D81014A67; Thu, 28 Apr 2022 15:11:17 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.151]) by smtp.corp.redhat.com (Postfix) with SMTP id CBFF2414A7E7; Thu, 28 Apr 2022 15:11:12 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 28 Apr 2022 17:11:17 +0200 (CEST) Date: Thu, 28 Apr 2022 17:11:11 +0200 From: Oleg Nesterov To: "Eric W. Biederman" 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 Subject: Re: [PATCH 9/9] ptrace: Don't change __state Message-ID: <20220428151110.GB15485@redhat.com> References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-9-ebiederm@xmission.com> <87czh2160k.fsf@email.froward.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87czh2160k.fsf@email.froward.int.ebiederm.org> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/27, Eric W. Biederman wrote: > > "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. And I think this is fine. This doesn't really differ from the case when the tracee was killed before it takes siglock. The only problem (afaics) is that, once we introduce JOBCTL_TRACED, ptrace_stop() can leak this flag. That is why I suggested to clear it along with LISTENING/DELAY_WAKEKILL before return, exactly because schedule() won't block if fatal_signal_pending() is true. But may be I misunderstood you concern? Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nk5nh-007cIL-Ca for linux-um@lists.infradead.org; Thu, 28 Apr 2022 15:11:26 +0000 Date: Thu, 28 Apr 2022 17:11:11 +0200 From: Oleg Nesterov Subject: Re: [PATCH 9/9] ptrace: Don't change __state Message-ID: <20220428151110.GB15485@redhat.com> References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-9-ebiederm@xmission.com> <87czh2160k.fsf@email.froward.int.ebiederm.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <87czh2160k.fsf@email.froward.int.ebiederm.org> 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: "Eric W. Biederman" 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 On 04/27, Eric W. Biederman wrote: > > "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. And I think this is fine. This doesn't really differ from the case when the tracee was killed before it takes siglock. The only problem (afaics) is that, once we introduce JOBCTL_TRACED, ptrace_stop() can leak this flag. That is why I suggested to clear it along with LISTENING/DELAY_WAKEKILL before return, exactly because schedule() won't block if fatal_signal_pending() is true. But may be I misunderstood you concern? Oleg. _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um