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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 F1ADEC433E9 for ; Wed, 17 Mar 2021 15:49:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A91D964F21 for ; Wed, 17 Mar 2021 15:49:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232498AbhCQPtR (ORCPT ); Wed, 17 Mar 2021 11:49:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:57902 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232000AbhCQPsn (ORCPT ); Wed, 17 Mar 2021 11:48:43 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2665664F79; Wed, 17 Mar 2021 15:38:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1615995540; bh=dRMFBcsJPQLbRf+F2GnTT8HZD6K7smJG9tJcKpHlzZQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=x0Pslo20SOFOFOQGgLFdw1xmTRR4RzT8vop+FZzT9vNbxyc/rAgf1TQVNQu36NzYB l0+hhrzC1MptmAlnbN8PSoFi47FzX2hlsMiADDGRDOOgwuUS6rNVwru4IkoQrRm2as zNSkF6Vv4gidWLNSHqIgMpXVuIgVWaHddYT6Q2F0= Date: Wed, 17 Mar 2021 16:38:57 +0100 From: Greg Kroah-Hartman To: Michal Hocko Cc: Kees Cook , Andrew Morton , Alexey Dobriyan , Lee Duncan , Chris Leech , Adam Nichols , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org, Uladzislau Rezki Subject: Re: [PATCH v2] seq_file: Unconditionally use vmalloc for buffer Message-ID: References: <20210315174851.622228-1-keescook@chromium.org> <202103161205.B2181BDE38@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 17, 2021 at 04:20:52PM +0100, Michal Hocko wrote: > On Wed 17-03-21 15:56:44, Greg KH wrote: > > On Wed, Mar 17, 2021 at 03:44:16PM +0100, Michal Hocko wrote: > > > On Wed 17-03-21 14:34:27, Greg KH wrote: > > > > On Wed, Mar 17, 2021 at 01:08:21PM +0100, Michal Hocko wrote: > > > > > Btw. I still have problems with the approach. seq_file is intended to > > > > > provide safe way to dump values to the userspace. Sacrificing > > > > > performance just because of some abuser seems like a wrong way to go as > > > > > Al pointed out earlier. Can we simply stop the abuse and disallow to > > > > > manipulate the buffer directly? I do realize this might be more tricky > > > > > for reasons mentioned in other emails but this is definitely worth > > > > > doing. > > > > > > > > We have to provide a buffer to "write into" somehow, so what is the best > > > > way to stop "abuse" like this? > > > > > > What is wrong about using seq_* interface directly? > > > > Right now every show() callback of sysfs would have to be changed :( > > Is this really the case? Would it be too ugly to have an intermediate > buffer and then seq_puts it into the seq file inside sysfs_kf_seq_show. Oh, good idea. > Sure one copy more than necessary but it this shouldn't be a hot path or > even visible on small strings. So that might be worth destroying an > inherently dangerous seq API (seq_get_buf). I'm all for that, let me see if I can carve out some time tomorrow to try this out. But, you don't get rid of the "ability" to have a driver write more than a PAGE_SIZE into the buffer passed to it. I guess I could be paranoid and do some internal checks (allocate a bunch of memory and check for overflow by hand), if this is something to really be concerned about... thanks, greg k-h