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 ED4D9C433F5 for ; Wed, 25 May 2022 14:33:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244849AbiEYOdj (ORCPT ); Wed, 25 May 2022 10:33:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53600 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244853AbiEYOdc (ORCPT ); Wed, 25 May 2022 10:33:32 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id A1ADEA88A1 for ; Wed, 25 May 2022 07:33:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1653489207; 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=9TKWXPVOyy27jggL+/cJXYJRt9uEdXRrwGp2as9PzGY=; b=PgOLgZk1zDCjho1yLJGQZDGxT/cT5s+ZWvASufOr6AbI7RKeMjPNUsbVeU+8qItK00WB9c rDUCJ2wZleC+grwv6zXCAWMexJyZvpf9I1D/vSpTSOKXcl38DXP3HJhgMCrV8RX8VliApu bUyb0wxYII1e/zvIjnV/Y2sXiUX9GbM= 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-396-1WAZ6LSpP8WakQXx6X-awA-1; Wed, 25 May 2022 10:33:24 -0400 X-MC-Unique: 1WAZ6LSpP8WakQXx6X-awA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A921E858EFE; Wed, 25 May 2022 14:33:22 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.193.81]) by smtp.corp.redhat.com (Postfix) with SMTP id BC570112131B; Wed, 25 May 2022 14:33:04 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 25 May 2022 16:33:22 +0200 (CEST) Date: Wed, 25 May 2022 16:33:03 +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 , linux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn , linux-ia64@vger.kernel.org, Robert OCallahan , Kyle Huey , Richard Henderson , Ivan Kokshaysky , Matt Turner , Jason Wessel , Daniel Thompson , Douglas Anderson , Douglas Miller , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras Subject: Re: [PATCH 05/16] ptrace: Remove dead code from __ptrace_detach Message-ID: <20220525143303.GB2687@redhat.com> References: <871qwq5ucx.fsf_-_@email.froward.int.ebiederm.org> <20220518225355.784371-5-ebiederm@xmission.com> <20220524114250.GB14347@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220524114250.GB14347@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/24, Oleg Nesterov wrote: > > Sorry for delay. > > On 05/18, Eric W. Biederman wrote: > > > > Ever since commit 28d838cc4dfe ("Fix ptrace self-attach rule") it has > > been impossible to attach another thread in the same thread group. > > > > Remove the code from __ptrace_detach that was trying to support > > detaching from a thread in the same thread group. > > may be I am totally confused, but I think you misunderstood this code > and thus this patch is very wrong. > > The same_thread_group() check does NOT try to check if debugger and > tracee is in the same thread group, this is indeed impossible. > > We need this check to know if the tracee was ptrace_reparented() before > __ptrace_unlink() or not. > > > > -static int ignoring_children(struct sighand_struct *sigh) > > -{ > > - int ret; > > - spin_lock(&sigh->siglock); > > - ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) || > > - (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT); > > - spin_unlock(&sigh->siglock); > > - return ret; > > -} > > ... > > > @@ -565,14 +552,9 @@ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p) > > > > dead = !thread_group_leader(p); > > > > - if (!dead && thread_group_empty(p)) { > > - if (!same_thread_group(p->real_parent, tracer)) > > - dead = do_notify_parent(p, p->exit_signal); > > - else if (ignoring_children(tracer->sighand)) { > > - __wake_up_parent(p, tracer); > > - dead = true; > > - } > > - } > > So the code above does: > > - if !same_thread_group(p->real_parent, tracer), then the tracee was > ptrace_reparented(), and now we need to notify its natural parent > to let it know it has a zombie child. > > - otherwise, the tracee is our natural child, and it is actually dead. > however, since we are going to reap this task, we need to wake up our > sub-threads possibly sleeping on ->wait_chldexit wait_queue_head_t. > > See? > > > + if (!dead && thread_group_empty(p)) > > + dead = do_notify_parent(p, p->exit_signal); > > No, this looks wrong. Or I missed something? Yes, but... That said, it seems that we do not need __wake_up_parent() if it was our natural child? I'll recheck. Eric, I'll continue to read this series tomorrow, can't concentrate on ptrace today. Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nts4n-00BR6Q-Sd for linux-um@lists.infradead.org; Wed, 25 May 2022 14:33:31 +0000 Date: Wed, 25 May 2022 16:33:03 +0200 From: Oleg Nesterov Subject: Re: [PATCH 05/16] ptrace: Remove dead code from __ptrace_detach Message-ID: <20220525143303.GB2687@redhat.com> References: <871qwq5ucx.fsf_-_@email.froward.int.ebiederm.org> <20220518225355.784371-5-ebiederm@xmission.com> <20220524114250.GB14347@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220524114250.GB14347@redhat.com> 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 , linux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn , linux-ia64@vger.kernel.org, Robert OCallahan , Kyle Huey , Richard Henderson , Ivan Kokshaysky , Matt Turner , Jason Wessel , Daniel Thompson , Douglas Anderson , Douglas Miller , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras On 05/24, Oleg Nesterov wrote: > > Sorry for delay. > > On 05/18, Eric W. Biederman wrote: > > > > Ever since commit 28d838cc4dfe ("Fix ptrace self-attach rule") it has > > been impossible to attach another thread in the same thread group. > > > > Remove the code from __ptrace_detach that was trying to support > > detaching from a thread in the same thread group. > > may be I am totally confused, but I think you misunderstood this code > and thus this patch is very wrong. > > The same_thread_group() check does NOT try to check if debugger and > tracee is in the same thread group, this is indeed impossible. > > We need this check to know if the tracee was ptrace_reparented() before > __ptrace_unlink() or not. > > > > -static int ignoring_children(struct sighand_struct *sigh) > > -{ > > - int ret; > > - spin_lock(&sigh->siglock); > > - ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) || > > - (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT); > > - spin_unlock(&sigh->siglock); > > - return ret; > > -} > > ... > > > @@ -565,14 +552,9 @@ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p) > > > > dead = !thread_group_leader(p); > > > > - if (!dead && thread_group_empty(p)) { > > - if (!same_thread_group(p->real_parent, tracer)) > > - dead = do_notify_parent(p, p->exit_signal); > > - else if (ignoring_children(tracer->sighand)) { > > - __wake_up_parent(p, tracer); > > - dead = true; > > - } > > - } > > So the code above does: > > - if !same_thread_group(p->real_parent, tracer), then the tracee was > ptrace_reparented(), and now we need to notify its natural parent > to let it know it has a zombie child. > > - otherwise, the tracee is our natural child, and it is actually dead. > however, since we are going to reap this task, we need to wake up our > sub-threads possibly sleeping on ->wait_chldexit wait_queue_head_t. > > See? > > > + if (!dead && thread_group_empty(p)) > > + dead = do_notify_parent(p, p->exit_signal); > > No, this looks wrong. Or I missed something? Yes, but... That said, it seems that we do not need __wake_up_parent() if it was our natural child? I'll recheck. Eric, I'll continue to read this series tomorrow, can't concentrate on ptrace today. Oleg. _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Date: Wed, 25 May 2022 14:33:03 +0000 Subject: Re: [PATCH 05/16] ptrace: Remove dead code from __ptrace_detach Message-Id: <20220525143303.GB2687@redhat.com> List-Id: References: <871qwq5ucx.fsf_-_@email.froward.int.ebiederm.org> <20220518225355.784371-5-ebiederm@xmission.com> <20220524114250.GB14347@redhat.com> In-Reply-To: <20220524114250.GB14347@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 , linux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn , linux-ia64@vger.kernel.org, Robert OCallahan , Kyle Huey , Richard Henderson , Ivan Kokshaysky , Matt Turner , Jason Wessel , Daniel Thompson , Douglas Anderson , Douglas Miller , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras On 05/24, Oleg Nesterov wrote: > > Sorry for delay. > > On 05/18, Eric W. Biederman wrote: > > > > Ever since commit 28d838cc4dfe ("Fix ptrace self-attach rule") it has > > been impossible to attach another thread in the same thread group. > > > > Remove the code from __ptrace_detach that was trying to support > > detaching from a thread in the same thread group. > > may be I am totally confused, but I think you misunderstood this code > and thus this patch is very wrong. > > The same_thread_group() check does NOT try to check if debugger and > tracee is in the same thread group, this is indeed impossible. > > We need this check to know if the tracee was ptrace_reparented() before > __ptrace_unlink() or not. > > > > -static int ignoring_children(struct sighand_struct *sigh) > > -{ > > - int ret; > > - spin_lock(&sigh->siglock); > > - ret = (sigh->action[SIGCHLD-1].sa.sa_handler = SIG_IGN) || > > - (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT); > > - spin_unlock(&sigh->siglock); > > - return ret; > > -} > > ... > > > @@ -565,14 +552,9 @@ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p) > > > > dead = !thread_group_leader(p); > > > > - if (!dead && thread_group_empty(p)) { > > - if (!same_thread_group(p->real_parent, tracer)) > > - dead = do_notify_parent(p, p->exit_signal); > > - else if (ignoring_children(tracer->sighand)) { > > - __wake_up_parent(p, tracer); > > - dead = true; > > - } > > - } > > So the code above does: > > - if !same_thread_group(p->real_parent, tracer), then the tracee was > ptrace_reparented(), and now we need to notify its natural parent > to let it know it has a zombie child. > > - otherwise, the tracee is our natural child, and it is actually dead. > however, since we are going to reap this task, we need to wake up our > sub-threads possibly sleeping on ->wait_chldexit wait_queue_head_t. > > See? > > > + if (!dead && thread_group_empty(p)) > > + dead = do_notify_parent(p, p->exit_signal); > > No, this looks wrong. Or I missed something? Yes, but... That said, it seems that we do not need __wake_up_parent() if it was our natural child? I'll recheck. Eric, I'll continue to read this series tomorrow, can't concentrate on ptrace today. Oleg.