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 X-Spam-Level: X-Spam-Status: No, score=-8.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3286C433ED for ; Tue, 11 May 2021 17:54:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9092761353 for ; Tue, 11 May 2021 17:54:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231693AbhEKRzF (ORCPT ); Tue, 11 May 2021 13:55:05 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:23027 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231439AbhEKRzD (ORCPT ); Tue, 11 May 2021 13:55:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620755636; 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=TMmnYi2R2rpijnadia4P/sKG3RmewE+fpb6vPJAQNH4=; b=ZiiAoLYF0/wwuWwZzzDeAk027Az9FnVUVoRP2WgEdjawXdF5rVJNXX1kiHlnMHq9GW/Rk+ EWCpr3FhnLwf0fRBY5JI26yvdjwWH5V/HHdSAFyZq0s/ofxUP0BSC3sOZIqNF3wi9e32aP 4fQKM+om6wfc0WzJZOMT2ZUf0yOebOo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-165-0Ghno32cNDCf2rniGd5djw-1; Tue, 11 May 2021 13:53:55 -0400 X-MC-Unique: 0Ghno32cNDCf2rniGd5djw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 55ED3106BB24; Tue, 11 May 2021 17:53:53 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.124]) by smtp.corp.redhat.com (Postfix) with SMTP id C8EAF2B431; Tue, 11 May 2021 17:53:43 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 11 May 2021 19:53:52 +0200 (CEST) Date: Tue, 11 May 2021 19:53:42 +0200 From: Oleg Nesterov To: Linus Torvalds Cc: Andrew Morton , "Eric W. Biederman" , Eugene Syromiatnikov , Jan Kratochvil , Mathieu Desnoyers , Michael Kerrisk , Pedro Alves , Simon Marchi , Linux Kernel Mailing List Subject: Re: [PATCH RESEND2] ptrace: make ptrace() fail if the tracee changed its pid unexpectedly Message-ID: <20210511175341.GA14488@redhat.com> References: <20210511165626.GA13720@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/11, Linus Torvalds wrote: > > On Tue, May 11, 2021 at 9:56 AM Oleg Nesterov wrote: > > > > This patch makes ptrace() fail in this case until debugger does wait() > > and consumes PTHREAD_EVENT_EXEC which reports old_pid. > > I'm ok with the patch, just wondering which way it's supposed to come > to me. Should I just apply it directly? would be nice! > That said, why this: > > > + rcu_read_lock(); > > + pid = task_pid_nr_ns(task, task_active_pid_ns(task->parent)); > > + rcu_read_unlock(); > > I don't see why the RCU read lock would be needed? task_pid_nr_ns() > does any required locking itself, afaik. > > And even if it wasn't, this all happens with siglock held, can > anything actually change. ... and with tasklist_lock held. Hmm. Linus, I am shy to admit I can't answer immediately, I'll recheck tomorrow after sleep. But it seems you are right. Thanks! Oleg.