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=-2.5 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 13CB6C433E0 for ; Mon, 29 Jun 2020 02:21:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EF2E820720 for ; Mon, 29 Jun 2020 02:21:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726345AbgF2CV2 (ORCPT ); Sun, 28 Jun 2020 22:21:28 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:60985 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726204AbgF2CV2 (ORCPT ); Sun, 28 Jun 2020 22:21:28 -0400 Received: from fsav105.sakura.ne.jp (fsav105.sakura.ne.jp [27.133.134.232]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 05T2KJWq076036; Mon, 29 Jun 2020 11:20:19 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav105.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav105.sakura.ne.jp); Mon, 29 Jun 2020 11:20:19 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav105.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 05T2KIxF076032 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 29 Jun 2020 11:20:19 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH 00/14] Make the user mode driver code a better citizen To: Alexei Starovoitov Cc: "Eric W. Biederman" , Linus Torvalds , David Miller , Greg Kroah-Hartman , Kees Cook , Andrew Morton , Alexei Starovoitov , Al Viro , bpf , linux-fsdevel , Daniel Borkmann , Jakub Kicinski , Masahiro Yamada , Gary Lin , Bruno Meneguele , LSM List , Casey Schaufler References: <20200625095725.GA3303921@kroah.com> <778297d2-512a-8361-cf05-42d9379e6977@i-love.sakura.ne.jp> <20200625120725.GA3493334@kroah.com> <20200625.123437.2219826613137938086.davem@davemloft.net> <87pn9mgfc2.fsf_-_@x220.int.ebiederm.org> <40720db5-92f0-4b5b-3d8a-beb78464a57f@i-love.sakura.ne.jp> <87366g8y1e.fsf@x220.int.ebiederm.org> <20200628194440.puzh7nhdnk6i4rqj@ast-mbp.dhcp.thefacebook.com> From: Tetsuo Handa Message-ID: Date: Mon, 29 Jun 2020 11:20:14 +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: <20200628194440.puzh7nhdnk6i4rqj@ast-mbp.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On 2020/06/29 4:44, Alexei Starovoitov wrote: > But all the defensive programming kinda goes against general kernel style. > I wouldn't do it. Especially pr_info() ?! > Though I don't feel strongly about it. Honestly speaking, caller should check for errors and print appropriate messages. info->wd.mnt->mnt_root != info->wd.dentry indicates that something went wrong (maybe memory corruption). But other conditions are not fatal. That is, I consider even pr_info() here should be unnecessary. > > I would like to generalize elf_header_check() a bit and call it > before doing blob_to_mnt() to make sure that all blobs are elf files only. > Supporting '#!/bin/bash' or other things as blobs seems wrong to me. Why? There is no point with forbidding "#!", for users can use a wrapper ELF binary which contains instructions including glibc's execv()/system() functions even if "#!" cannot be used. What is more important is what protection/isolation properties processes started via fork_usermode_driver() should hold, for ELF binary can contain arbitrary instructions, these processes run as daemons (reading request from stdin and writing response to stdout) but hidden from "/usr/bin/pstree -p 1" (because they are forked from kthreadd kernel thread).