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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 347DEC433E0 for ; Thu, 11 Feb 2021 01:05:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EAF3864ECA for ; Thu, 11 Feb 2021 01:05:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230031AbhBKBFK (ORCPT ); Wed, 10 Feb 2021 20:05:10 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:59291 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230149AbhBKBFJ (ORCPT ); Wed, 10 Feb 2021 20:05:09 -0500 Received: from fsav401.sakura.ne.jp (fsav401.sakura.ne.jp [133.242.250.100]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 11B14DhP024244; Thu, 11 Feb 2021 10:04:13 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav401.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav401.sakura.ne.jp); Thu, 11 Feb 2021 10:04:13 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav401.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 11B14CrZ024239 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Thu, 11 Feb 2021 10:04:12 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] usb: usbip: fix error handling of kthread_get_run() To: Shuah Khan , Greg Kroah-Hartman , Valentina Manea , Shuah Khan Cc: Hillf Danton , linux-usb@vger.kernel.org, Arnd Bergmann References: <000000000000414db905b6e9bae8@google.com> <20210205135707.4574-1-penguin-kernel@I-love.SAKURA.ne.jp> <6b2b9f7c-a412-0f52-3373-bc58d1e95ad9@linuxfoundation.org> <1f4b36a1-460e-1154-b46c-32ba72b88205@linuxfoundation.org> <2f922e76-623e-1d87-17a5-c4a87dc8f2fc@linuxfoundation.org> From: Tetsuo Handa Message-ID: Date: Thu, 11 Feb 2021 10:04:07 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On 2021/02/11 5:15, Shuah Khan wrote: > On 2/10/21 11:43 AM, Tetsuo Handa wrote: >> On 2021/02/11 3:20, Shuah Khan wrote: >>> On 2/10/21 11:16 AM, Tetsuo Handa wrote: >>>> On 2021/02/11 3:11, Shuah Khan wrote: >>>>> I would like to see to see a complete fix. This patch changes >>>>> kthread_get_run() to return NULL. Without adding handling for >>>>> NULL in the callers of kthread_get_run(), we will start seeing >>>>> problems. >>>> >>>> What problems are you aware of? >>>> >>> >>> The fact that driver doesn't cleanup after failing to create >>> the thread is a problem. >> >> What are the cleanup functions? >> > > When user-space requests attaching to a device, attach_store() > tries to attach the requested device. When kthread_get_run() > failure is ignored silently, and continue with call to > rh_port_connect(), user-space assumes attach is successful. > User thinks attach is successful. The struct kthread_create_info *create = kmalloc(sizeof(*create), GFP_KERNEL); in __kthread_create_on_node() never fails unless killed by the OOM killer due to the "too small to fail" memory-allocation rule, and wait_for_completion_killable(&done) in __kthread_create_on_node() never fails unless killed. Creating a kernel thread as root user unlikely fails, and memory allocations by that kernel thread also never fails due to the "too small to fail" memory-allocation rule. Therefore, kthread_get_run() effectively fails only when current thread which called attach_store() was killed. And > > When and how will this attach failure gets reported to the > in this scenario? if the current thread was killed, how can the failure get reported to the user-space in this scenario? > > Error handling for this case is no different from other error > paths in attach_store(). > > Please see error handling for other errors in attach_store(). Being "killed" means that user-space can never know the result unlike other error paths in attach_store(). > In this case the right error handling is to rewind the vdev > init and bail out returning error. This would include setting > vdev->ud.status to VDEV_ST_NULL. If the user-space was killed, the kernel is responsible for offering automatic cleanup which includes setting vdev->ud.status to VDEV_ST_NULL. > > I found the following reproducer that tells me how attach > is triggered. > https://syzkaller.appspot.com/text?tag=ReproC&x=128506e4d00000 This reproducer (which is killed after 5 seconds from fork()) uses only /sys/devices/platform/vhci_hcd.0/attach interface and never uses detach interface. Detach and cleanup are up to automatic cleanup offered by the kernel. > > syzbot is helping us harden these paths, which is awesome. > Fixing these have to consider user api. > > I you would like to fix this, please send me a complete fix. If you want to handle the unlikely "__kthread_create_on_node() fails without being killed" case, such change ( the drivers/usb/usbip/vhci_sysfs.c portion in https://syzkaller.appspot.com/x/patch.diff?x=16c3c090d00000 ) should be a separate patch. Since this patch declares "Fixes: 9720b4bc76a83807 ("staging/usbip: convert to kthread")", this patch intends for the minimal change and does not want to do extra things.