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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT 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 67DD9ECDFAA for ; Mon, 16 Jul 2018 14:22:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 177B120873 for ; Mon, 16 Jul 2018 14:22:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 177B120873 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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 S1727843AbeGPOu1 (ORCPT ); Mon, 16 Jul 2018 10:50:27 -0400 Received: from mx2.suse.de ([195.135.220.15]:55204 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727374AbeGPOu0 (ORCPT ); Mon, 16 Jul 2018 10:50:26 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 941C0AD31; Mon, 16 Jul 2018 14:22:45 +0000 (UTC) Date: Mon, 16 Jul 2018 16:22:45 +0200 From: Michal Hocko To: "Kirill A. Shutemov" 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: <20180716142245.GT17280@dhcp22.suse.cz> 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> <20180716140440.fd3sjw5xys5wozw7@black.fi.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180716140440.fd3sjw5xys5wozw7@black.fi.intel.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 16-07-18 17:04:41, Kirill A. Shutemov wrote: > 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. This is really creative. I really didn't think about that. I am wondering whether this really has to be handled as a private anonymous mapping implicitly. Why does vma_is_anonymous has to succeed for these mappings? Why cannot we simply handle it as any other file backed PRIVATE mapping? -- Michal Hocko SUSE Labs