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=-8.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 671C2C433E1 for ; Tue, 18 Aug 2020 20:07:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B82620786 for ; Tue, 18 Aug 2020 20:07:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726408AbgHRUH3 (ORCPT ); Tue, 18 Aug 2020 16:07:29 -0400 Received: from verein.lst.de ([213.95.11.211]:34984 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725554AbgHRUH3 (ORCPT ); Tue, 18 Aug 2020 16:07:29 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 7B5EB68AFE; Tue, 18 Aug 2020 22:07:25 +0200 (CEST) Date: Tue, 18 Aug 2020 22:07:25 +0200 From: Christoph Hellwig To: Kees Cook Cc: Christoph Hellwig , Al Viro , Michael Ellerman , x86@kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH 03/11] fs: don't allow splice read/write without explicit ops Message-ID: <20200818200725.GA1081@lst.de> References: <20200817073212.830069-1-hch@lst.de> <20200817073212.830069-4-hch@lst.de> <202008181239.E51B80265@keescook> <20200818195446.GA32691@lst.de> <202008181256.CABD56782@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202008181256.CABD56782@keescook> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Aug 18, 2020 at 12:58:07PM -0700, Kees Cook wrote: > On Tue, Aug 18, 2020 at 09:54:46PM +0200, Christoph Hellwig wrote: > > On Tue, Aug 18, 2020 at 12:39:34PM -0700, Kees Cook wrote: > > > On Mon, Aug 17, 2020 at 09:32:04AM +0200, Christoph Hellwig wrote: > > > > default_file_splice_write is the last piece of generic code that uses > > > > set_fs to make the uaccess routines operate on kernel pointers. It > > > > implements a "fallback loop" for splicing from files that do not actually > > > > provide a proper splice_read method. The usual file systems and other > > > > high bandwith instances all provide a ->splice_read, so this just removes > > > > support for various device drivers and procfs/debugfs files. If splice > > > > support for any of those turns out to be important it can be added back > > > > by switching them to the iter ops and using generic_file_splice_read. > > > > > > > > Signed-off-by: Christoph Hellwig > > > > > > This seems a bit disruptive? I feel like this is going to make fuzzers > > > really noisy (e.g. trinity likes to splice random stuff out of /sys and > > > /proc). > > > > Noisy in the sence of triggering the pr_debug or because they can't > > handle -EINVAL? > > Well, maybe both? I doubt much _expects_ to be using splice, so I'm fine > with that, but it seems weird not to have a fall-back, especially if > something would like to splice a file out of there. But, I'm not opposed > to the change, it just seems like it might cause pain down the road. The problem is that without pretending a buffer is in user space when it actually isn't, we can't have a generic fallback. So we'll have to have specific support - I wrote generic support for seq_file, and willy did for /proc/sys, but at least the first caused a few problems and a fair amount of churn, so I'd rather see first if we can get away without it. > > -- > Kees Cook ---end quoted text---