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 CB959C43463 for ; Sun, 20 Sep 2020 15:02:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9B01A20870 for ; Sun, 20 Sep 2020 15:02:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726306AbgITPC6 (ORCPT ); Sun, 20 Sep 2020 11:02:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726267AbgITPC6 (ORCPT ); Sun, 20 Sep 2020 11:02:58 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 77085C061755; Sun, 20 Sep 2020 08:02:58 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kK0rT-002VoG-Vd; Sun, 20 Sep 2020 15:02:44 +0000 Date: Sun, 20 Sep 2020 16:02:43 +0100 From: Al Viro To: Arnd Bergmann Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , David Howells , Linux ARM , the arch/x86 maintainers , "linux-kernel@vger.kernel.org" , "open list:BROADCOM NVRAM DRIVER" , Parisc List , linuxppc-dev , linux-s390 , sparclinux , linux-block , linux-scsi , Linux FS-devel Mailing List , linux-aio , io-uring@vger.kernel.org, linux-arch , Linux-MM , Networking , keyrings@vger.kernel.org, LSM List Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag Message-ID: <20200920150243.GM3421308@ZenIV.linux.org.uk> References: <20200918124533.3487701-1-hch@lst.de> <20200918124533.3487701-2-hch@lst.de> <20200918134012.GY3421308@ZenIV.linux.org.uk> <20200918134406.GA17064@lst.de> <20200918135822.GZ3421308@ZenIV.linux.org.uk> <20200918151615.GA23432@lst.de> <20200919220920.GI3421308@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Sun, Sep 20, 2020 at 03:55:47PM +0200, Arnd Bergmann wrote: > On Sun, Sep 20, 2020 at 12:09 AM Al Viro wrote: > > On Fri, Sep 18, 2020 at 05:16:15PM +0200, Christoph Hellwig wrote: > > > On Fri, Sep 18, 2020 at 02:58:22PM +0100, Al Viro wrote: > > > > Said that, why not provide a variant that would take an explicit > > > > "is it compat" argument and use it there? And have the normal > > > > one pass in_compat_syscall() to that... > > > > > > That would help to not introduce a regression with this series yes. > > > But it wouldn't fix existing bugs when io_uring is used to access > > > read or write methods that use in_compat_syscall(). One example that > > > I recently ran into is drivers/scsi/sg.c. > > > > So screw such read/write methods - don't use them with io_uring. > > That, BTW, is one of the reasons I'm sceptical about burying the > > decisions deep into the callchain - we don't _want_ different > > data layouts on read/write depending upon the 32bit vs. 64bit > > caller, let alone the pointer-chasing garbage that is /dev/sg. > > Would it be too late to limit what kind of file descriptors we allow > io_uring to read/write on? > > If io_uring can get changed to return -EINVAL on trying to > read/write something other than S_IFREG file descriptors, > that particular problem space gets a lot simpler, but this > is of course only possible if nobody actually relies on it yet. S_IFREG is almost certainly too heavy as a restriction. Looking through the stuff sensitive to 32bit/64bit, we seem to have * /dev/sg - pointer-chasing horror * sysfs files for efivar - different layouts for compat and native, shitty userland ABI design ( struct efi_variable { efi_char16_t VariableName[EFI_VAR_NAME_LEN/sizeof(efi_char16_t)]; efi_guid_t VendorGuid; unsigned long DataSize; __u8 Data[1024]; efi_status_t Status; __u32 Attributes; } __attribute__((packed)); ) is the piece of crap in question; 'DataSize' is where the headache comes from. Regular files, BTW... * uhid - character device, milder pointer-chasing horror. Trouble comes from this: /* Obsolete! Use UHID_CREATE2. */ struct uhid_create_req { __u8 name[128]; __u8 phys[64]; __u8 uniq[64]; __u8 __user *rd_data; __u16 rd_size; __u16 bus; __u32 vendor; __u32 product; __u32 version; __u32 country; } __attribute__((__packed__)); and suggested replacement doesn't do any pointer-chasing (rd_data is an embedded array in the end of struct uhid_create2_req). * evdev, uinput - bitness-sensitive layout, due to timestamps * /proc/bus/input/devices - weird crap with printing bitmap, different _text_ layouts seen by 32bit and 64bit readers. Binary structures are PITA, but with sufficient effort you can screw the text just as hard... Oh, and it's a regular file. * similar in sysfs analogue And AFAICS, that's it for read/write-related method instances.