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=-3.8 required=3.0 tests=BAYES_00, 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 22F98C43465 for ; Mon, 21 Sep 2020 15:11:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E36EE2075E for ; Mon, 21 Sep 2020 15:11:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726417AbgIUPL0 (ORCPT ); Mon, 21 Sep 2020 11:11:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726413AbgIUPL0 (ORCPT ); Mon, 21 Sep 2020 11:11:26 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E5750C061755; Mon, 21 Sep 2020 08:11:25 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kKNTL-003Byz-4d; Mon, 21 Sep 2020 15:11:19 +0000 Date: Mon, 21 Sep 2020 16:11:19 +0100 From: Al Viro To: David Laight Cc: 'Christoph Hellwig' , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-parisc@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-s390@vger.kernel.org" , "sparclinux@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , "netdev@vger.kernel.org" , "keyrings@vger.kernel.org" , "linux-security-module@vger.kernel.org" Subject: Re: [PATCH 04/11] iov_iter: explicitly check for CHECK_IOVEC_ONLY in rw_copy_check_uvector Message-ID: <20200921151119.GU3421308@ZenIV.linux.org.uk> References: <20200921143434.707844-1-hch@lst.de> <20200921143434.707844-5-hch@lst.de> <7336624280b8444fb4cb00407317741b@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7336624280b8444fb4cb00407317741b@AcuMS.aculab.com> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Sep 21, 2020 at 03:05:32PM +0000, David Laight wrote: > I've actually no idea: > 1) Why there is an access_ok() check here. > It will be repeated by the user copy functions. Early sanity check. > 2) Why it isn't done when called from mm/process_vm_access.c. > Ok, the addresses refer to a different process, but they > must still be valid user addresses. > > Is 2 a legacy from when access_ok() actually checked that the > addresses were mapped into the process's address space? It never did. 2 is for the situation when a 32bit process accesses 64bit one; addresses that are perfectly legitimate for 64bit userland (and fitting into the first 4Gb of address space, so they can be represented by 32bit pointers just fine) might be rejected by access_ok() if the caller is 32bit.