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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 9F7F3ECDFB3 for ; Mon, 16 Jul 2018 14:04:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 653E920870 for ; Mon, 16 Jul 2018 14:04:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 653E920870 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730375AbeGPOcO (ORCPT ); Mon, 16 Jul 2018 10:32:14 -0400 Received: from mga18.intel.com ([134.134.136.126]:41577 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727843AbeGPOcN (ORCPT ); Mon, 16 Jul 2018 10:32:13 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Jul 2018 07:04:37 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,361,1526367600"; d="scan'208";a="73171203" Received: from black.fi.intel.com ([10.237.72.28]) by orsmga001.jf.intel.com with ESMTP; 16 Jul 2018 07:04:35 -0700 Received: by black.fi.intel.com (Postfix, from userid 1000) id 7C09D12D; Mon, 16 Jul 2018 17:04:41 +0300 (EEST) Date: Mon, 16 Jul 2018 17:04:41 +0300 From: "Kirill A. Shutemov" To: Michal Hocko Cc: Andrew Morton , Dmitry Vyukov , Oleg Nesterov , Andrea Arcangeli , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/2] mm: Fix vma_is_anonymous() false-positives Message-ID: <20180716140440.fd3sjw5xys5wozw7@black.fi.intel.com> References: <20180710134821.84709-1-kirill.shutemov@linux.intel.com> <20180710134821.84709-2-kirill.shutemov@linux.intel.com> <20180710134858.3506f097104859b533c81bf3@linux-foundation.org> <20180716133028.GQ17280@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180716133028.GQ17280@dhcp22.suse.cz> User-Agent: NeoMutt/20170714-126-deb55f (1.8.3) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 16, 2018 at 01:30:28PM +0000, Michal Hocko wrote: > On Tue 10-07-18 13:48:58, Andrew Morton wrote: > > On Tue, 10 Jul 2018 16:48:20 +0300 "Kirill A. Shutemov" wrote: > > > > > vma_is_anonymous() relies on ->vm_ops being NULL to detect anonymous > > > VMA. This is unreliable as ->mmap may not set ->vm_ops. > > > > > > False-positive vma_is_anonymous() may lead to crashes: > > > > > > ... > > > > > > This can be fixed by assigning anonymous VMAs own vm_ops and not relying > > > on it being NULL. > > > > > > If ->mmap() failed to set ->vm_ops, mmap_region() will set it to > > > dummy_vm_ops. This way we will have non-NULL ->vm_ops for all VMAs. > > > > Is there a smaller, simpler fix which we can use for backporting > > purposes and save the larger rework for development kernels? > > Why cannot we simply keep anon vma with null vm_ops and set dummy_vm_ops > for all users who do not initialize it in their mmap callbacks? > Basically have a sanity check&fixup in call_mmap? As I said, there's a corner case of MAP_PRIVATE of /dev/zero. It has to produce anonymous VMA, but in map_region() we cannot distinguish it from broken ->mmap handler. See my attempt 6dc296e7df4c ("mm: make sure all file VMAs have ->vm_ops set") and it's revert 28c553d0aa0a ("revert "mm: make sure all file VMAs have ->vm_ops set"") -- Kirill A. Shutemov