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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,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 DE0CBECDE32 for ; Wed, 17 Oct 2018 09:51:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A4F232151D for ; Wed, 17 Oct 2018 09:51:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="oQCkdoiC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A4F232151D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.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 S1727223AbeJQRqu (ORCPT ); Wed, 17 Oct 2018 13:46:50 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:60028 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726994AbeJQRqu (ORCPT ); Wed, 17 Oct 2018 13:46:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=vrlzfuBdGYThbkt5/Dl0UF+Kh8QDAIWULWWa5+4RWMs=; b=oQCkdoiCCct0VLXVGE2dZoTlB BEyUtwVATal6prOLgWk6bvg3ESpkbSnjeC/xdu3bwylsTXofrT1JfblaFi6yTjn+c05dA9046X+bR 8XCtflxOLEZYK0IJxTR9EP3sY6euwvm52iL+oXzdTqSZCyw+V0mU7cfAThZ+z8Ek7ebvQYlNlWwRH RPVE3qsMlzKRN0E0mSH/LClkbC5jben2L//OMucrLjaxfN/MFGUtiK1pfiSabaIqr0qQKBENubVvL EWeA0amZjfTGwCZQudI5SwRfeIi19+r8fVCoFoVkFz4g3g3AKPkbQ4NeRManRDtMi7RZc/VUm2g65 YPX291IQw==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gCiUd-0001zQ-Bf; Wed, 17 Oct 2018 09:51:55 +0000 Date: Wed, 17 Oct 2018 02:51:55 -0700 From: Christoph Hellwig To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, kernel-team@android.com, jreck@google.com, john.stultz@linaro.org, tkjos@google.com, gregkh@linuxfoundation.org, Andrew Morton , dancol@google.com, "J. Bruce Fields" , Jeff Layton , Khalid Aziz , linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, Mike Kravetz , minchan@google.com, Shuah Khan Subject: Re: [PATCH v2 1/2] mm: Add an F_SEAL_FS_WRITE seal to memfd Message-ID: <20181017095155.GA354@infradead.org> References: <20181009222042.9781-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181009222042.9781-1-joel@joelfernandes.org> User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 09, 2018 at 03:20:41PM -0700, Joel Fernandes (Google) wrote: > One of the main usecases Android has is the ability to create a region > and mmap it as writeable, then drop its protection for "future" writes > while keeping the existing already mmap'ed writeable-region active. s/drop/add/ ? Otherwise this doesn't make much sense to me. > This usecase cannot be implemented with the existing F_SEAL_WRITE seal. > To support the usecase, this patch adds a new F_SEAL_FS_WRITE seal which > prevents any future mmap and write syscalls from succeeding while > keeping the existing mmap active. The following program shows the seal > working in action: Where does the FS come from? I'd rather expect this to be implemented as a 'force' style flag that applies the seal even if the otherwise required precondition is not met. > Note: This seal will also prevent growing and shrinking of the memfd. > This is not something we do in Android so it does not affect us, however > I have mentioned this behavior of the seal in the manpage. This seems odd, as that is otherwise split into the F_SEAL_SHRINK / F_SEAL_GROW flags. > static int memfd_add_seals(struct file *file, unsigned int seals) > { > @@ -219,6 +220,9 @@ static int memfd_add_seals(struct file *file, unsigned int seals) > } > } > > + if ((seals & F_SEAL_FS_WRITE) && !(*file_seals & F_SEAL_FS_WRITE)) > + file->f_mode &= ~(FMODE_WRITE | FMODE_PWRITE); > + This seems to lack any synchronization for f_mode.