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=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 849D0C072A4 for ; Wed, 22 May 2019 08:07:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5103120675 for ; Wed, 22 May 2019 08:07:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="mBSlYA70" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728718AbfEVIHI (ORCPT ); Wed, 22 May 2019 04:07:08 -0400 Received: from mail-pg1-f194.google.com ([209.85.215.194]:40308 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727946AbfEVIHI (ORCPT ); Wed, 22 May 2019 04:07:08 -0400 Received: by mail-pg1-f194.google.com with SMTP id d30so915122pgm.7 for ; Wed, 22 May 2019 01:07:07 -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=R9LcwzmisTS7r+q4SwIHnWG/B1+FQ56zuQk1IuY/Co0=; b=mBSlYA7037o5LdH8eMdLpiuP/Z0aDaIBdqWhlZ1Aw1ZT8Q0ilpxCXWDmHOA94KAy4j FOHOJChPrPKrQDhRVVxSvqgb5u2TH3sYCMxc9vIKl+/LVWRXQkSKIepTRb2fNuUhNwok 5GJaBXVx6qxIkP+yAmN81F5CjXh2AY/HjHNrMcCMuT5rBktHcEu3F0KIBuMrPLqBN4mz 6Im0gi+ueBW0CjxkTIDxaXEneaNuaUJ6T7knsVvc38tOcLSTPNG5Oyrur3gAggIT/UFE ZdKU/mMrGxhRyeeOEUbp7nDUgWL9TTqt2YN1CsX+RcC3u90GjlqqeGMcJ+Zpw2DKQeHy UegQ== 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=R9LcwzmisTS7r+q4SwIHnWG/B1+FQ56zuQk1IuY/Co0=; b=h1ZlNYwknak6QMqOGD9yZHM11+lZNvGG1fY4x33Md67pBWOlHdxSrB5oJqXmo3o+te mbT4qe/ZmnWpDmQqJN8z6sD6eo3xXQY9dZMYP4y6nZ171Vd8CbgzTmZRE0no/iyUtDPT wWf3lba3VO/z/NZymVoOBGRVyg0644vJDgqOKFbHuTFlZCl/BsHWhEZzzLI4rJlZDQIH FMHNYXfz1NgQnJjzBpFtI3wlWx37wCJ8aAyN6jYGylCvj8tBWf10oYtMugHtKPKJ6vSu sS0cru8YsKCTey+ptgJSQczs4OierAU9qC45h7K+QhA7gAFu9QsvnS60E9ThGPgDz0s8 lxjA== X-Gm-Message-State: APjAAAVwvcV+WquNhI55b3kSQw65RaSL8+FOjhpNAi2eaO3ggSFEUAGN YIYyHKWNQ3csDVLmX5PN9Sed6PyOqHQ= X-Google-Smtp-Source: APXvYqzQNy8lcXx0lrcIRiJQ6ZfSoau8hQXBKZ8CDx9/qXMrvEXwAOkhvqcFadJHGimhxun18HFPMA== X-Received: by 2002:aa7:930e:: with SMTP id 14mr36801323pfj.262.1558512427215; Wed, 22 May 2019 01:07:07 -0700 (PDT) Received: from zhanggen-UX430UQ ([66.42.35.75]) by smtp.gmail.com with ESMTPSA id e12sm43143956pfl.122.2019.05.22.01.07.04 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 May 2019 01:07:06 -0700 (PDT) Date: Wed, 22 May 2019 16:06:56 +0800 From: Gen Zhang To: Jiri Slaby Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] tty_io: Fix a missing-check bug in drivers/tty/tty_io.c Message-ID: <20190522080656.GA5109@zhanggen-UX430UQ> References: <20190522014006.GB4093@zhanggen-UX430UQ> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 06:25:36AM +0200, Jiri Slaby wrote: > On 22. 05. 19, 3:40, Gen Zhang wrote: > > In alloc_tty_struct(), tty->dev is assigned by tty_get_device(). And it > > calls class_find_device(). And class_find_device() may return NULL. > > And tty->dev is dereferenced in the following codes. When > > tty_get_device() returns NULL, dereferencing this tty->dev null pointer > > may cause the kernel go wrong. Thus we should check tty->dev. > > Further, if tty_get_device() returns NULL, we should free tty and > > return NULL. > > > > Signed-off-by: Gen Zhang > > > > --- > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > > index 033ac7e..1444b59 100644 > > --- a/drivers/tty/tty_io.c > > +++ b/drivers/tty/tty_io.c > > @@ -3008,6 +3008,10 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) > > tty->index = idx; > > tty_line_name(driver, idx, tty->name); > > tty->dev = tty_get_device(tty); > > + if (!tty->dev) { > > + kfree(tty); > > + return NULL; > > + } > > This is incorrect, you introduced an ldisc reference leak. Thanks for your reply, Jiri! And what do you mean by an ldisc reference leak? I did't get the reason of introducing it. > > And can this happen at all? I think tty_get_device() may happen to return NULL. Because it calls class_find_device() and there's a chance class_find_device() returns NULL. Thanks Gen > > thanks, > -- > js > suse labs