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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 665D8C2BA19 for ; Mon, 6 Apr 2020 11:16:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 394BB206F5 for ; Mon, 6 Apr 2020 11:16:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586171813; bh=DBLgYA2jJe29u2yG1zEKM15bBvyYd8p0FiFATN1DXaE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=17zb8EnSBbfWEbtAVHutrG3N9dmWEMLHSwpX/2EeV3YLWgOY2WeGP6OA4Qxhm6bis gx3AiM3ZLFlRbMOHD6Vi9/kb5q9MNK1nkFWN6xW2Vm2vZTz17CfVUvXVlin3ZFQRtC nMDhgFRVQ96jWX3Jgdl5FhUgwrQhgrcz+iSweRt4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727387AbgDFLQw (ORCPT ); Mon, 6 Apr 2020 07:16:52 -0400 Received: from mail.kernel.org ([198.145.29.99]:49942 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726873AbgDFLQv (ORCPT ); Mon, 6 Apr 2020 07:16:51 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6C521206F5; Mon, 6 Apr 2020 11:16:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586171810; bh=DBLgYA2jJe29u2yG1zEKM15bBvyYd8p0FiFATN1DXaE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MFmK3wx8/lBjaM/xGWW23dhl/t3LtuG5v7nX2lLnNOMp2ISLziWTJ5nFbRCl8H6pz j95wUXBqd5JYWCp1KtJ4j3GCwg1klnSk84Yojezi9AYwuNAkQMSuJPuuR7WX+UEhBK jBuZKNPBn5CqrheEocCA5Y4urLKN8HwbJ2EhnEKg= Date: Mon, 6 Apr 2020 13:16:48 +0200 From: Greg KH To: =?utf-8?B?5a6L54mn5pil?= Cc: Fei Zhang , rafael@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [External] Re: [PATCH] driver core: Fix possible use after free on name Message-ID: <20200406111648.GA1797430@kroah.com> References: <1586102749-3364-1-git-send-email-zhangfeionline@gmail.com> <20200405164006.GA1582475@kroah.com> <20200406054110.GA1638548@kroah.com> <20200406082857.GA1646464@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 06, 2020 at 06:42:46PM +0800, 宋牧春 wrote: > Hi Greg, > > Greg KH 于2020年4月6日周一 下午4:29写道： > > > > A: http://en.wikipedia.org/wiki/Top_post > > Q: Were do I find info about this thing called top-posting? > > A: Because it messes up the order in which people normally read text. > > Q: Why is top-posting such a bad thing? > > A: Top-posting. > > Q: What is the most annoying thing in e-mail? > > > > A: No. > > Q: Should I include quotations after my reply? > > > > http://daringfireball.net/2007/07/on_top > > > > On Mon, Apr 06, 2020 at 03:40:41PM +0800, Fei Zhang wrote: > > > Dear Greg, > > > > > > Mostly, "class_creat" is used in kernel driver module, basically > > > read-only strings, > > > but it is easier to use a local variable string. When writing drive module, > > > it fails to judge the local variable string which cannot be passed in > > > only via interface. > > > I found that someone else may also face the same problem. > > > > An individual driver should NOT be creating a class, that is not what it > > is there for. > > If someone want to create a virtual device, someone can call device_create(). > But the first argument is type of 'struct class *class', so we have to > call class_create() > before create device. So an individual driver may be creating a class, right? Again, they should not be, as classes are not what a driver creates. It is what a subsystem creates, as a class is a type of common devices that all talk to userspace in the same way. > > Class names are very "rare" and should not be dynamically created at > > all. > > I have reviewed the code of the kstrdup_const() which is just below. > > const char *kstrdup_const(const char *s, gfp_t gfp) > { > if (is_kernel_rodata((unsigned long)s)) > return s; > > return kstrdup(s, gfp); > } > > A readonly string which is in the kernel rodata, so we do not need to > dynamically allocate > memory to store the name. So with this patch applied, there is nothing > changed which > means that we did not waste memory. But it can prevent someone from > reading stale name > if an unaware user passes an address to a stack-allocated buffer. > > So I think it is worth fixing, right? Again, there is nothing to "fix" here as there is no code in the kernel tree today calling this api with a class name that is not static. If we have code that does need to do this, and it is submitted for merging, and I agree with how it is creating the class names, I will be glad to take a patch at that time to make this change. Until then, this is just added complexity for no benefit at all. thanks, greg k-h