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 E18E1C433E1 for ; Tue, 30 Jun 2020 06:29:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C951420672 for ; Tue, 30 Jun 2020 06:29:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730120AbgF3G3m (ORCPT ); Tue, 30 Jun 2020 02:29:42 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:58740 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730089AbgF3G3l (ORCPT ); Tue, 30 Jun 2020 02:29:41 -0400 Received: from fsav404.sakura.ne.jp (fsav404.sakura.ne.jp [133.242.250.103]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 05U6SrH8086585; Tue, 30 Jun 2020 15:28:53 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav404.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav404.sakura.ne.jp); Tue, 30 Jun 2020 15:28:53 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav404.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 05U6Sr7Q086582 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 30 Jun 2020 15:28:53 +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: "Eric W. Biederman" Cc: Alexei Starovoitov , 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> <874kqt39qo.fsf@x220.int.ebiederm.org> From: Tetsuo Handa Message-ID: <6a9dd8be-333a-fd21-d125-ec20fb7c81df@i-love.sakura.ne.jp> Date: Tue, 30 Jun 2020 15:28:49 +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: <874kqt39qo.fsf@x220.int.ebiederm.org> 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 On 2020/06/30 5:19, Eric W. Biederman wrote: > Tetsuo Handa writes: > >> 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. > > They were all should never happen cases. Which is why my patches do: > if (WARN_ON_ONCE(...)) No. Fuzz testing (which uses panic_on_warn=1) will trivially hit them. This bug was unfortunately not found by syzkaller because this path is not easily reachable via syscall interface. > > That let's the caller know the messed up very clearly while still > providing a change to continue. > > If they were clearly corruption no ones kernel should ever continue > BUG_ON would be appropriate. Please use BUG_ON() (to only corruption case) like I suggested in my updated diff.