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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 1EC76C43461 for ; Thu, 10 Sep 2020 14:58:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DAD0E2075A for ; Thu, 10 Sep 2020 14:58:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599749911; bh=FYttYrZtuK5BwOL7MlOFary7ccNNYwSvTguucnlrJ+Q=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=BoGekT63CnpM0tIdSdYaJzerzCrLw1N8dLObxr5jvhgvPsKo9yuxe5gzOzCMUnRv2 EvDrZn+CnFHcIbKy/iu5doxx/rvEyU7q0K4rpKzfwcxF3Z5Islxya2vmGxoatXk7Fy V4ydsLdz2ySrqsIafwlIAfxkj2Y0vtJK2ma8eGw8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730940AbgIJO6X (ORCPT ); Thu, 10 Sep 2020 10:58:23 -0400 Received: from mail-ej1-f65.google.com ([209.85.218.65]:43931 "EHLO mail-ej1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730438AbgIJO5P (ORCPT ); Thu, 10 Sep 2020 10:57:15 -0400 Received: by mail-ej1-f65.google.com with SMTP id o8so9150813ejb.10 for ; Thu, 10 Sep 2020 07:57:13 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=SP185hc4qqDaCocuE1o9/q6QIwRYkBlPfsR5unwg+tw=; b=r0k7ErdCjNm8aC+5fpE+k+OlNn6yxK9eUdB1n2q2rM+VsWlKr5L+PNJ0c/7Fd1oV4G FrqeZPLmQDDeB7Der4Q2mOoFkkQAD4dbKDXcbNLr7DrkOrV2VsgQXeHLrmiCfWyXCiYF Jh8MCcCATk1/zvyqHCUWLxuD2Lls1EePCSLIb+IW9lyn6y4m6PJ98OV5SlqO4YcKLkMr 3Wa4QH7Byd4vtyHfLRO/n58vvq4XCV0iCaJw++WPKOmd5fhGO/7UikO74pKT69rAg0DA Qywf8CEzDbq2IMKi+1lryta0eBjAJT3hUBTHOS/wNt7mMZferklkzycNKiljmo3+LiST b0Kw== X-Gm-Message-State: AOAM533mBcTwZF8kPYy3yXpC3b2ENONCFUSXhETfjfMPbUZJhvG8ufmJ eEzKskNgun/0XRpdAeCWoeWr3zPX7t7MsWMiboVMUDAyH8A= X-Google-Smtp-Source: ABdhPJxxh+toO9w+3Xk3Z8n0cYqYrf9qTBRvR8yTvjyobzGOq0dcjT8+GZp2gyhK4BYyVpUdX8kM0Z8tNlCc7xLEmgU= X-Received: by 2002:adf:8b48:: with SMTP id v8mr9157976wra.21.1599745693134; Thu, 10 Sep 2020 06:48:13 -0700 (PDT) MIME-Version: 1.0 References: <20200910104153.1672460-1-jolsa@kernel.org> In-Reply-To: <20200910104153.1672460-1-jolsa@kernel.org> From: Namhyung Kim Date: Thu, 10 Sep 2020 22:48:02 +0900 Message-ID: Subject: Re: [PATCH] perf: Fix race in perf_mmap_close function To: Jiri Olsa Cc: Peter Zijlstra , Arnaldo Carvalho de Melo , lkml , Ingo Molnar , Alexander Shishkin , Michael Petlan , Wade Mealing Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 10, 2020 at 7:42 PM Jiri Olsa wrote: > > There's a possible race in perf_mmap_close when checking ring buffer's > mmap_count refcount value. The problem is that the mmap_count check is > not atomic because we call atomic_dec and atomic_read separately. > > perf_mmap_close: > ... > atomic_dec(&rb->mmap_count); > ... > if (atomic_read(&rb->mmap_count)) > goto out_put; > > > free_uid > > out_put: > ring_buffer_put(rb); /* could be last */ > > The race can happen when we have two (or more) events sharing same ring > buffer and they go through atomic_dec and then they both see 0 as refcount > value later in atomic_read. Then both will go on and execute code which > is meant to be run just once. > > The code that detaches ring buffer is probably fine to be executed more > than once, but the problem is in calling free_uid, which will later on > demonstrate in related crashes and refcount warnings, like: > > refcount_t: addition on 0; use-after-free. > ... > RIP: 0010:refcount_warn_saturate+0x6d/0xf > ... > Call Trace: > prepare_creds+0x190/0x1e0 > copy_creds+0x35/0x172 > copy_process+0x471/0x1a80 > _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.. Thanks Namhyung > > @@ -5912,7 +5910,7 @@ 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 (!atomic_dec_and_test(&rb->mmap_count)) > goto out_put; > > /* > -- > 2.26.2 >