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=-9.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 D06E6C433E2 for ; Fri, 11 Sep 2020 07:49:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6575E2076C for ; Fri, 11 Sep 2020 07:49:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IDgsuAR7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725800AbgIKHtp (ORCPT ); Fri, 11 Sep 2020 03:49:45 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:38317 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725730AbgIKHtm (ORCPT ); Fri, 11 Sep 2020 03:49:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1599810581; 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=F74XmnvmIOv7/0c83mboFgtyfFoiNlg6s2uPMowubsw=; b=IDgsuAR7Z2RA9lyNW23cfJfzWIc4pkLJDk5puAhtgGKsGhDyXxrsIYx9xxb0Nk7CHeJlsT SQu3C2b7JuuTxulfmv6w4qvIFUOxxFhYrpxqFvfqsWEw1vUmnzmB73k0nRkmg9GOLWz2xS J6YJpCSSNP13A7tUQZSuLQGs5hNnAIY= 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-402-MTOhIK0iOxCrDHiCDOuZuA-1; Fri, 11 Sep 2020 03:49:37 -0400 X-MC-Unique: MTOhIK0iOxCrDHiCDOuZuA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2FDF91017DC7; Fri, 11 Sep 2020 07:49:36 +0000 (UTC) Received: from krava (unknown [10.40.192.120]) by smtp.corp.redhat.com (Postfix) with SMTP id B2A2181C40; Fri, 11 Sep 2020 07:49:32 +0000 (UTC) Date: Fri, 11 Sep 2020 09:49:31 +0200 From: Jiri Olsa To: Namhyung Kim Cc: Jiri Olsa , Peter Zijlstra , Arnaldo Carvalho de Melo , lkml , Ingo Molnar , Alexander Shishkin , Michael Petlan , Wade Mealing Subject: Re: [PATCH] perf: Fix race in perf_mmap_close function Message-ID: <20200911074931.GA1714160@krava> References: <20200910104153.1672460-1-jolsa@kernel.org> <20200910144744.GA1663813@krava> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 11, 2020 at 12:05:10PM +0900, Namhyung Kim wrote: > Hi Jiri, > > On Thu, Sep 10, 2020 at 11:50 PM Jiri Olsa wrote: > > > > On Thu, Sep 10, 2020 at 10:48:02PM +0900, Namhyung Kim wrote: > > > > SNIP > > > > > > _do_fork+0x83/0x3a0 > > > > __do_sys_wait4+0x83/0x90 > > > > __do_sys_clone+0x85/0xa0 > > > > do_syscall_64+0x5b/0x1e0 > > > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > > > > > Using atomic decrease and check instead of separated calls. > > > > This fixes CVE-2020-14351. > > > > > > > > Signed-off-by: Jiri Olsa > > > > --- > > > > kernel/events/core.c | 4 +--- > > > > 1 file changed, 1 insertion(+), 3 deletions(-) > > > > > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > > > index 7ed5248f0445..29313cc54d9e 100644 > > > > --- a/kernel/events/core.c > > > > +++ b/kernel/events/core.c > > > > @@ -5903,8 +5903,6 @@ static void perf_mmap_close(struct vm_area_struct *vma) > > > > mutex_unlock(&event->mmap_mutex); > > > > } > > > > > > > > - atomic_dec(&rb->mmap_count); > > > > - > > > > if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) > > > > goto out_put; > > > > > > But when it takes the goto, rb->mmap_count won't decrement anymore.. > > > > event->mmap_count is per event, so if we have have race in here, > > 2 threads can go through with each event->mmap_count reaching zero > > Maybe I'm missing something. > > But as far as I can see, perf_mmap_close() always decremented both > rb->mmap_count and event->mmap_count. But with this change, > it seems not decrement rb->mmap_count when event->mmap_count > doesn't go to zero, right? ugh, that's right.. how about change below jirka --- diff --git a/kernel/events/core.c b/kernel/events/core.c index 7ed5248f0445..8ab2400aef55 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5868,11 +5868,11 @@ static void perf_pmu_output_stop(struct perf_event *event); static void perf_mmap_close(struct vm_area_struct *vma) { struct perf_event *event = vma->vm_file->private_data; - struct perf_buffer *rb = ring_buffer_get(event); struct user_struct *mmap_user = rb->mmap_user; int mmap_locked = rb->mmap_locked; unsigned long size = perf_data_size(rb); + bool detach_rest = false; if (event->pmu->event_unmapped) event->pmu->event_unmapped(event, vma->vm_mm); @@ -5903,7 +5903,8 @@ static void perf_mmap_close(struct vm_area_struct *vma) mutex_unlock(&event->mmap_mutex); } - atomic_dec(&rb->mmap_count); + if (atomic_dec_and_test(&rb->mmap_count)) + detach_rest = true; if (!atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) goto out_put; @@ -5912,7 +5913,7 @@ static void perf_mmap_close(struct vm_area_struct *vma) mutex_unlock(&event->mmap_mutex); /* If there's still other mmap()s of this buffer, we're done. */ - if (atomic_read(&rb->mmap_count)) + if (!detach_rest) goto out_put; /*