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=-5.2 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 BDFC6C61DD8 for ; Mon, 16 Nov 2020 14:15:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6180F22265 for ; Mon, 16 Nov 2020 14:15:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729674AbgKPOPf (ORCPT ); Mon, 16 Nov 2020 09:15:35 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:52558 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728667AbgKPOPf (ORCPT ); Mon, 16 Nov 2020 09:15:35 -0500 Received: from fsav106.sakura.ne.jp (fsav106.sakura.ne.jp [27.133.134.233]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 0AGEFVEN066011; Mon, 16 Nov 2020 23:15:31 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav106.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav106.sakura.ne.jp); Mon, 16 Nov 2020 23:15:31 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav106.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 0AGEFVKB066007 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Mon, 16 Nov 2020 23:15:31 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: Garbage data while reading via usermode driver? To: Al Viro Cc: "Eric W. Biederman" , Alexei Starovoitov , linux-fsdevel References: <0c98ab7f-8483-bb54-7b8f-3d69ed45f1ff@i-love.sakura.ne.jp> <20201116123525.GW3576660@ZenIV.linux.org.uk> From: Tetsuo Handa Message-ID: <69d7648e-2c73-65bb-c2eb-53dd10b9a072@i-love.sakura.ne.jp> Date: Mon, 16 Nov 2020 23:15:31 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.3 MIME-Version: 1.0 In-Reply-To: <20201116123525.GW3576660@ZenIV.linux.org.uk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2020/11/16 21:35, Al Viro wrote: > On Mon, Nov 16, 2020 at 08:11:04PM +0900, Tetsuo Handa wrote: >> Hello. >> >> Below is a loadable kernel module which attempts to read (for example) /proc/interrupts from >> kernel using usermode driver interface. What is strange is that the total bytes obtained by >> doing "wc -c /proc/interrupts" from userspace's shell and trying to insmod this kernel module >> differs; for unknown reason, kernel_read() returns "#!/bin/cat /proc/interrupts\n" (28 bytes) >> at the end of input. > > Because /bin/cat writes it out ;-) You are right. ;-) I have an out of tree kernel module (a loadable kernel version of TOMOYO security module) which needs to read /proc/kallsyms from kernel (in order to find symbols needed by TOMOYO). Now that kernel_read() can no longer read /proc/kallsyms , I had to abuse usermode driver only for reading /proc/kallsyms ( https://osdn.net/projects/akari/scm/svn/commits/662 ).