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=-2.2 required=3.0 tests=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 946A8C433E1 for ; Sat, 13 Jun 2020 04:23:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 76D50208C3 for ; Sat, 13 Jun 2020 04:23:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726049AbgFMEXz (ORCPT ); Sat, 13 Jun 2020 00:23:55 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:54128 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725272AbgFMEXz (ORCPT ); Sat, 13 Jun 2020 00:23:55 -0400 Received: from fsav301.sakura.ne.jp (fsav301.sakura.ne.jp [153.120.85.132]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 05D4MlgJ014729; Sat, 13 Jun 2020 13:22:47 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav301.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav301.sakura.ne.jp); Sat, 13 Jun 2020 13:22:47 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav301.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 05D4Mg4c014641 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Sat, 13 Jun 2020 13:22:47 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [RFC][PATCH] net/bpfilter: Remove this broken and apparently unmantained To: Alexei Starovoitov Cc: "Eric W. Biederman" , Linus Torvalds , Kees Cook , Andrew Morton , Alexei Starovoitov , David Miller , Al Viro , bpf , linux-fsdevel , Daniel Borkmann , Jakub Kicinski , Masahiro Yamada , Gary Lin , Bruno Meneguele References: <20200606201956.rvfanoqkevjcptfl@ast-mbp> <20200607014935.vhd3scr4qmawq7no@ast-mbp> <33cf7a57-0afa-9bb9-f831-61cca6c19eba@i-love.sakura.ne.jp> <20200608162306.iu35p4xoa2kcp3bu@ast-mbp.dhcp.thefacebook.com> <87r1uo2ejt.fsf@x220.int.ebiederm.org> <20200609235631.ukpm3xngbehfqthz@ast-mbp.dhcp.thefacebook.com> <87d066vd4y.fsf@x220.int.ebiederm.org> <20200611233134.5vofl53dj5wpwp5j@ast-mbp.dhcp.thefacebook.com> <62859212-df69-b913-c1e0-cd2e358d1adf@i-love.sakura.ne.jp> <20200613033821.l62q2ed5ligheyhu@ast-mbp> From: Tetsuo Handa Message-ID: <92011d12-5d73-b0fd-a744-3f99f19922fe@i-love.sakura.ne.jp> Date: Sat, 13 Jun 2020 13:22:39 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200613033821.l62q2ed5ligheyhu@ast-mbp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Archived-At: List-Archive: List-Post: On 2020/06/13 12:38, Alexei Starovoitov wrote: > On Fri, Jun 12, 2020 at 09:57:40AM +0900, Tetsuo Handa wrote: >> >> , the userspace memory can be easily interfered from userspace. The kernel module >> running in kernel space is protected (unless methods like /dev/{mem,kmem} are used) >> but the kernel module running in user space is not protected. > > huh? One user process 'can easily interfere' with memory of other process? It is an execution environment problem. Somebody can send SIGKILL (e.g. OOM-killker, SysRq-i) to kill kernel code running as usermode process, somebody can send SIGSTOP to make kernel code running as usermode process defunctional, somebody can /usr/bin/strace in order to eavesdrop on secret data used by kernel code running as usermode process etc. >> can be interfered) is so painful. I won't be able to trust kernel modules running >> in userspace memory. > > The part that I suspect is still missing is what triggers fork_usermode_blob(). > It's always kernel code == trusted code. How can that part be guaranteed? In future somebody might add a caller that allows sys_execute_anonymously_in_usermode(const char code, const int len) { return fork_usermode_blob(code, len); } or something similar. > The interface between kernel part of .ko and user part of .ko is > specific to that particular kernel module. It's not a typical user space. How can that part be guaranteed? A caller can pass arbitrary code including typical user space program (e.g. /bin/sh). > But when loaded the bpfilter.ko will start its user space side > via fork_usermode_blob() that is specific to that version of .ko. How can we guarantee that its user space side started via fork_usermode_blob() is not disturbed (e.g. SIGKILL, SIGSTOP, /usr/bin/strace) ? I consider that reliability (from "robustness" perspective) of fork_usermode_blob() is same with CONFIG_INITRAMFS_SOURCE or call_usermodehelper() or init= approach.