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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 C2920C433ED for ; Wed, 14 Apr 2021 07:59:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7EB6761179 for ; Wed, 14 Apr 2021 07:59:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349839AbhDNH7m (ORCPT ); Wed, 14 Apr 2021 03:59:42 -0400 Received: from elvis.franken.de ([193.175.24.41]:49467 "EHLO elvis.franken.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231868AbhDNH7k (ORCPT ); Wed, 14 Apr 2021 03:59:40 -0400 Received: from uucp (helo=alpha) by elvis.franken.de with local-bsmtp (Exim 3.36 #1) id 1lWaQe-0000mp-00; Wed, 14 Apr 2021 09:59:16 +0200 Received: by alpha.franken.de (Postfix, from userid 1000) id D2B0EC0311; Wed, 14 Apr 2021 09:59:00 +0200 (CEST) Date: Wed, 14 Apr 2021 09:59:00 +0200 From: Thomas Bogendoerfer To: David Laight Cc: Jinyang He , Tiezhu Yang , "linux-mips@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] MIPS: Fix strnlen_user access check Message-ID: <20210414075900.GA6073@alpha.franken.de> References: <1618139092-4018-1-git-send-email-hejinyang@loongson.cn> <20210412142730.GA23146@alpha.franken.de> <2fd31420-1f96-9165-23ea-fdccac1b522a@loongson.cn> <20210413111438.GA9472@alpha.franken.de> <069e524dbad2412f9e74fd234f40fff5@AcuMS.aculab.com> <20210413151909.GA13549@alpha.franken.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 13, 2021 at 04:01:13PM +0000, David Laight wrote: > From: Thomas Bogendoerfer > > Sent: 13 April 2021 16:19 > > > > On Tue, Apr 13, 2021 at 12:37:25PM +0000, David Laight wrote: > > > From: Thomas Bogendoerfer > > > > Sent: 13 April 2021 12:15 > > > ... > > > > > The __access_ok() is noted with `Ensure that the range [addr, addr+size) > > > > > is within the process's address space`. Does the range checked by > > > > > __access_ok() on MIPS is [addr, addr+size]. So if we want to use > > > > > access_ok(s, 1), should we modify __access_ok()? Or my misunderstanding? > > > > > > > > you are right, I'm going to apply > > > > > > > > https://patchwork.kernel.org/project/linux-mips/patch/20190209194718.1294-1-paul.burton@mips.com/ > > > > > > > > to fix that. > > > > > > Isn't that still wrong? > > > If an application does: > > > write(fd, (void *)0xffff0000, 0); > > > it should return 0, not -1 and EFAULT/SIGSEGV. > > > > WRITE(2) Linux Programmer's Manual WRITE(2) > > [...] > > If count is zero and fd refers to a regular file, then write() may > > return a failure status if one of the errors below is detected. If no > > errors are detected, or error detection is not performed, 0 will be > > returned without causing any other effect. If count is zero and fd > > refers to a file other than a regular file, the results are not speci- > > fied. > > [...] > > EFAULT buf is outside your accessible address space. > > > > at least it's covered by the man page on my Linux system. > > Something related definitely caused grief in the setsockopt() changes. > > > > There is also the question about why this makes any difference > > > to the original problem of logging in via the graphical interface. > > > > kernel/module.c: mod->args = strndup_user(uargs, ~0UL >> 1); > > > > and strndup_user does a strnlen_user. > > That call is just gross. > Why did it work before the removal of set_fs() etc. strnlen_user just did the equivalent of access_ok(s, 0) and I copy&pasted the wrong access_ok() statement :-( > Or was there another change that affected strndup_user() ? no, just the change in strnlen_user. Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]