From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751448AbbLJBV6 (ORCPT ); Wed, 9 Dec 2015 20:21:58 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:52014 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910AbbLJBV5 (ORCPT ); Wed, 9 Dec 2015 20:21:57 -0500 Date: Wed, 9 Dec 2015 17:21:30 -0800 From: Christoph Hellwig To: Kees Cook Cc: Andrew Morton , Jan Kara , yalin wang , Willy Tarreau , "Eric W. Biederman" , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5] fs: clear file privilege bits when mmap writing Message-ID: <20151210012130.GA17673@infradead.org> References: <20151209225148.GA14794@www.outflux.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151209225148.GA14794@www.outflux.net> User-Agent: Mutt/1.5.23 (2014-03-12) 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Changing the bits requires holding inode->i_mutex, so it cannot be done > during the page fault (due to mmap_sem being held during the fault). We > could do this during vm_mmap_pgoff, but that would need coverage in > mprotect as well, but to check for MAP_SHARED, we'd need to hold mmap_sem > again. We could clear at open() time, but it's possible things are > accidentally opening with O_RDWR and only reading. Better to clear on > close and error failures (i.e. an improvement over now, which is not > clearing at all). > > Instead, detect the need to clear the bits during the page fault, and > actually remove the bits during final fput. Since the file was open for > writing, it wouldn't have been possible to execute it yet. > > Signed-off-by: Kees Cook > --- > I think this is the best we can do; everything else is blocked by mmap_sem. It should be done at mmap time, before even taking mmap_sem. Adding a new field for this to strut file isn't really acceptable.