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=-5.8 required=3.0 tests=BAYES_00,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 64BC8C43332 for ; Wed, 17 Mar 2021 15:49:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 066D464FA7 for ; Wed, 17 Mar 2021 15:49:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232288AbhCQPsz (ORCPT ); Wed, 17 Mar 2021 11:48:55 -0400 Received: from mx2.suse.de ([195.135.220.15]:58602 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232464AbhCQPsN (ORCPT ); Wed, 17 Mar 2021 11:48:13 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1615994453; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=btiCGAjBA+oTgNvFWaiwkJdxvkvB5M3EHBf3slgWcEs=; b=XSVK/Iiy0jAUmkNHsP4RIvYQjP02KLonGBsFLEgOhG6aqrR2X8maT/j4ZoVaVjnqQ2gXvH wopF8k8fk3AEZrCO4QDIBw+anURxIWREEWxeCY+ig+7rnE65ksqmeQAAP/IyUxFbkaeUZu PeuLwFlpOvU8jyORIiEgk9ADrbDJSN0= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 39B7FAD74; Wed, 17 Mar 2021 15:20:53 +0000 (UTC) Date: Wed, 17 Mar 2021 16:20:52 +0100 From: Michal Hocko To: Greg Kroah-Hartman 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 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. 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). -- Michal Hocko SUSE Labs