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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 EFD0ECA9ECF for ; Thu, 31 Oct 2019 14:27:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C06F92083E for ; Thu, 31 Oct 2019 14:27:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728063AbfJaO1k convert rfc822-to-8bit (ORCPT ); Thu, 31 Oct 2019 10:27:40 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:56480 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727742AbfJaO1k (ORCPT ); Thu, 31 Oct 2019 10:27:40 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-70-YU6WXDc2PrG1nexM6IIzbw-1; Thu, 31 Oct 2019 14:27:31 +0000 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Thu, 31 Oct 2019 14:27:30 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Thu, 31 Oct 2019 14:27:30 +0000 From: David Laight To: 'Christian Brauner' , "linux-kernel@vger.kernel.org" , Florian Weimer , GNU C Library CC: Arnd Bergmann , Kees Cook , "Jann Horn" , David Howells , Ingo Molnar , Oleg Nesterov , Linus Torvalds , Peter Zijlstra , "linux-api@vger.kernel.org" , "stable@vger.kernel.org" Subject: RE: [PATCH] clone3: validate stack arguments Thread-Topic: [PATCH] clone3: validate stack arguments Thread-Index: AQHVj99vS5K32QXnq0iIRbo0zlqhOad0zlFw Date: Thu, 31 Oct 2019 14:27:30 +0000 Message-ID: <7f59e7e573aa40f08cb0e465d8d0150e@AcuMS.aculab.com> References: <20191031113608.20713-1-christian.brauner@ubuntu.com> In-Reply-To: <20191031113608.20713-1-christian.brauner@ubuntu.com> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: YU6WXDc2PrG1nexM6IIzbw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >From Christian Brauner > Sent: 31 October 2019 11:36 > > Validate the stack arguments and setup the stack depening on whether or not > it is growing down or up. > ... > -static bool clone3_args_valid(const struct kernel_clone_args *kargs) > +/** > + * clone3_stack_valid - check and prepare stack > + * @kargs: kernel clone args > + * > + * Verify that the stack arguments userspace gave us are sane. > + * In addition, set the stack direction for userspace since it's easy for us to > + * determine. > + */ > +static inline bool clone3_stack_valid(struct kernel_clone_args *kargs) > +{ > + if (kargs->stack == 0) { > + if (kargs->stack_size > 0) > + return false; > + } else { > + if (kargs->stack_size == 0) > + return false; > + > + if (!access_ok((void __user *)kargs->stack, kargs->stack_size)) > + return false; Does access_ok() do anything useful here? It only verifies that the buffer isn't in kernel space. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)