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=-7.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 A80B1C43603 for ; Wed, 18 Dec 2019 10:31:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 84A36218AC for ; Wed, 18 Dec 2019 10:31:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726726AbfLRKbI (ORCPT ); Wed, 18 Dec 2019 05:31:08 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:56149 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726551AbfLRKbI (ORCPT ); Wed, 18 Dec 2019 05:31:08 -0500 Received: from fsav110.sakura.ne.jp (fsav110.sakura.ne.jp [27.133.134.237]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id xBIATpNC011264; Wed, 18 Dec 2019 19:29:51 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav110.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav110.sakura.ne.jp); Wed, 18 Dec 2019 19:29:51 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav110.sakura.ne.jp) Received: from [192.168.1.9] (softbank126040062084.bbtec.net [126.40.62.84]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id xBIATkm1011020 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Wed, 18 Dec 2019 19:29:51 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] kconfig: Add kernel config option for fuzz testing. To: Dmitry Vyukov Cc: Andi Kleen , "Theodore Y. Ts'o" , Greg Kroah-Hartman , Alexander Viro , Petr Mladek , Sergey Senozhatsky , Arnd Bergmann , Jiri Slaby , Steven Rostedt , Linus Torvalds , LKML References: <20191216095955.9886-1-penguin-kernel@I-love.SAKURA.ne.jp> <20191216114636.GB1515069@kroah.com> <20191216201834.GA785904@mit.edu> <46e8f6b3-46ac-6600-ba40-9545b7e44016@i-love.sakura.ne.jp> From: Tetsuo Handa Message-ID: Date: Wed, 18 Dec 2019 19:29:47 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/12/17 17:36, Dmitry Vyukov wrote: > FWIW we've just disabled sysrq entirely: > https://github.com/google/syzkaller/blob/master/dashboard/config/bits-syzbot.config#L182 > because random packets over usb can trigger a panic sysrq (again > almost impossible to reliably filter these out on fuzzer side). Excuse me, but CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x0 helps only if show_state() etc. are called via the __handle_sysrq() handler in drivers/tty/sysrq.c . static void sysrq_handle_showstate(int key) { show_state(); show_workqueue_state(); } static struct sysrq_key_op sysrq_showstate_op = { .handler = sysrq_handle_showstate, .help_msg = "show-task-states(t)", .action_msg = "Show State", .enable_mask = SYSRQ_ENABLE_DUMP, }; The k_spec() handler in drivers/tty/vt/keyboard.c calls show_state() etc. without evaluating sysrq_enabled value. #define FN_HANDLERS\ fn_null, fn_enter, fn_show_ptregs, fn_show_mem,\ fn_show_state, fn_send_intr, fn_lastcons, fn_caps_toggle,\ fn_num, fn_hold, fn_scroll_forw, fn_scroll_back,\ fn_boot_it, fn_caps_on, fn_compose, fn_SAK,\ fn_dec_console, fn_inc_console, fn_spawn_con, fn_bare_num typedef void (fn_handler_fn)(struct vc_data *vc); static fn_handler_fn FN_HANDLERS; static fn_handler_fn *fn_handler[] = { FN_HANDLERS }; static void fn_show_state(struct vc_data *vc) { show_state(); } static void k_spec(struct vc_data *vc, unsigned char value, char up_flag) { if (up_flag) return; if (value >= ARRAY_SIZE(fn_handler)) return; if ((kbd->kbdmode == VC_RAW || kbd->kbdmode == VC_MEDIUMRAW || kbd->kbdmode == VC_OFF) && value != KVAL(K_SAK)) return; /* SAK is allowed even in raw mode */ fn_handler[value](vc); } Therefore, we need to guard at either callee side (e.g. show_state_filter()) or caller side (e.g. k_spec()) using kernel config (or something equivalent) in order to avoid forever calling show_state() from timer function.