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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT 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 D47CFC282CE for ; Wed, 22 May 2019 11:25:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A0D6B217D4 for ; Wed, 22 May 2019 11:25:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="tiq6Kw58" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728882AbfEVLZC (ORCPT ); Wed, 22 May 2019 07:25:02 -0400 Received: from mail-pf1-f193.google.com ([209.85.210.193]:45015 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728447AbfEVLZC (ORCPT ); Wed, 22 May 2019 07:25:02 -0400 Received: by mail-pf1-f193.google.com with SMTP id g9so1161871pfo.11 for ; Wed, 22 May 2019 04:25:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=zHCtr3ee893RWzC1W/JdFH2wk8+X49KQQGHhnWLjYbA=; b=tiq6Kw58v16c0abfIgnJxwi3MeVuRMAaDpqP1hu30YBxtNu2eC/WUc9s2sP8T40H4y 0iHve+UworKGHm0/Mbt0MvbN35ubpc//WF423gTzUTmPaOuHA5MIDmr+ckJpoPhKLGkF uBCfEWM7CCBWFsOFtD684ORXtWn28N2TC1Y0xzXX/zGL2SbOIh5MoRO5GKOkCLu+eDaV oyPwZELyiPZtAVQ/BifaKPKcIjhWdxIegjCwNPtwDYQchvvJJrBVaZ56A5hn+tEogqXM JKXfy2I+RIYnxkzc5AC9qVV6jiy6bsORIyM7g488q6qdcUD5B7ok7VKP+HvPPEFK/fd7 B94g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=zHCtr3ee893RWzC1W/JdFH2wk8+X49KQQGHhnWLjYbA=; b=rDlMt2JtfDVypAfwnkv1bjWz9pvvAmuEJx4WIIfnB3bxLwrD+ITlkX3ttOEKSz0wrf E24RficSLMbuysPhYYy9SGFOlFwMm/I2dYMgMqMOITHt6uAmTN/I1FCEvDgQgfCClWB7 Q2bqsGLN+zbv7XZqJGlOQhj919u5r82lSHdvxP/tI60x5DOxv7Etco63i6vAhJHJz0N0 3dZRDbc4WtrjHtNgfVDHmuxV91RanjPwNGFYHDanJOCJHclY04WaAg33OlI6CASpo/cT rweg578WUGSzVzGf8qW96C2dZpif4meZ/B0U+GTC3oUT+aBjJdLC1cWfQaISfG1pLvPf 9nwg== X-Gm-Message-State: APjAAAXrxMpUR5jvgyg0Obh6vopO7sQWolMxCvEfCvWSQgjyBjTgLlYV WP0z357SWKgPEIe9c3pfXXpt6Ok7AjAlbA== X-Google-Smtp-Source: APXvYqx0QGnTATPGJ3rt836ixiWDcvxDqlghfFIHzST/TjgpjKdboa4Jp7tbQ8YUgco6Uo2GaTrNtw== X-Received: by 2002:a62:4ed8:: with SMTP id c207mr96137226pfb.241.1558524301587; Wed, 22 May 2019 04:25:01 -0700 (PDT) Received: from zhanggen-UX430UQ ([66.42.35.75]) by smtp.gmail.com with ESMTPSA id z4sm29240765pfa.142.2019.05.22.04.24.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 May 2019 04:25:00 -0700 (PDT) Date: Wed, 22 May 2019 19:24:49 +0800 From: Gen Zhang To: Johan Hovold Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] tty_io: Fix a missing-check bug in drivers/tty/tty_io.c Message-ID: <20190522112449.GA6666@zhanggen-UX430UQ> References: <20190522014006.GB4093@zhanggen-UX430UQ> <20190522080656.GA5109@zhanggen-UX430UQ> <3a3db304-9725-6a90-65ac-dff09ef31aae@suse.cz> <20190522102900.GC2200@localhost> <20190522111354.GA5849@zhanggen-UX430UQ> <20190522111949.GB568@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190522111949.GB568@localhost> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 22, 2019 at 01:19:49PM +0200, Johan Hovold wrote: > On Wed, May 22, 2019 at 07:13:54PM +0800, Gen Zhang wrote: > > On Wed, May 22, 2019 at 12:29:00PM +0200, Johan Hovold wrote: > > > Where do you see that the kernel is dereferencing tty->dev without > > > checking for NULL first? If you can find that, then that would indeed be > > > a bug that needs fixing. > > Thanks for your reply, Johan! > > I examined the code but failed to find this situation. > > Ok, so your claim in the commit message was incorrect: > > And tty->dev is dereferenced in the following codes. > > > Anyway, checking return value of tty_get_device() is theoritically > > right. But tty->dev is never dereferenced, so checking is not needed. > > No, sorry, it's not even theoretically correct. Our current code depends > on tty->dev sometimes being NULL. Your patch would specifically break > pseudo terminals. Thanks for your comments. I have to be very proficient in this module to know this. Of course I am not. Anyway, appreciate your replies, Johan. Thanks Gen > > > However, what if in later kernels tty->dev is dereferenced by some > > codes? Is it better to apply this check for this reason? > > So for the above reason, no. > > Johan