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=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=unavailable 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 EFE20C43460 for ; Thu, 1 Apr 2021 05:17:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C19C861055 for ; Thu, 1 Apr 2021 05:17:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232874AbhDAFRR (ORCPT ); Thu, 1 Apr 2021 01:17:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:60856 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230291AbhDAFRA (ORCPT ); Thu, 1 Apr 2021 01:17:00 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 3C54160698; Thu, 1 Apr 2021 05:16:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1617254220; bh=2mRDIp06P0j/bB8232tnYtSW3E01K7ZZc1Nw02ZWyvY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=eANJakmGRxZDb+Xkpg421mz30JzRtYNFWUnykPf8kp/sZKoEOtEErPBGB2HpWyXqx t92s4r9KhaYXa6eTo3TIyafa1BXwR1XenEht3RXQlSQf3csya55JuOiqJclmYP1KVg v/buf82YL6FnQpARpGkTeDBAO96lXob+GzD9MA0Y= Date: Thu, 1 Apr 2021 07:16:56 +0200 From: Greg Kroah-Hartman To: Kees Cook Cc: Andrew Morton , "Rafael J. Wysocki" , Michal Hocko , Alexey Dobriyan , Lee Duncan , Chris Leech , Adam Nichols , linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] sysfs: Unconditionally use vmalloc for buffer Message-ID: References: <20210401022145.2019422-1-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210401022145.2019422-1-keescook@chromium.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 31, 2021 at 07:21:45PM -0700, Kees Cook wrote: > The sysfs interface to seq_file continues to be rather fragile > (seq_get_buf() should not be used outside of seq_file), as seen with > some recent exploits[1]. Move the seq_file buffer to the vmap area > (while retaining the accounting flag), since it has guard pages that > will catch and stop linear overflows. This seems justified given that > sysfs's use of seq_file already uses kvmalloc(), is almost always using > a PAGE_SIZE or larger allocation, has normally short-lived allocations, > and is not normally on a performance critical path. > > Once seq_get_buf() has been removed (and all sysfs callbacks using > seq_file directly), this change can also be removed. > > [1] https://blog.grimm-co.com/2021/03/new-old-bugs-in-linux-kernel.html > > Signed-off-by: Kees Cook > --- > v3: > - Limit to only sysfs (instead of all of seq_file). > v2: https://lore.kernel.org/lkml/20210315174851.622228-1-keescook@chromium.org/ > v1: https://lore.kernel.org/lkml/20210312205558.2947488-1-keescook@chromium.org/ > --- > fs/sysfs/file.c | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c > index 9aefa7779b29..70e7a450e5d1 100644 > --- a/fs/sysfs/file.c > +++ b/fs/sysfs/file.c > @@ -16,6 +16,7 @@ > #include > #include > #include > +#include > > #include "sysfs.h" > > @@ -32,6 +33,25 @@ static const struct sysfs_ops *sysfs_file_ops(struct kernfs_node *kn) > return kobj->ktype ? kobj->ktype->sysfs_ops : NULL; > } > > +/* > + * To be proactively defensive against sysfs show() handlers that do not > + * correctly stay within their PAGE_SIZE buffer, use the vmap area to gain > + * the trailing guard page which will stop linear buffer overflows. > + */ > +static void *sysfs_kf_seq_start(struct seq_file *sf, loff_t *ppos) > +{ > + struct kernfs_open_file *of = sf->private; > + struct kernfs_node *kn = of->kn; > + > + WARN_ON_ONCE(sf->buf); How can buf ever not be NULL? And if it is, we will leak memory in the next line so we shouldn't have _ONCE, we should always know, but not rebooting the machine would be nice. > + sf->buf = __vmalloc(kn->attr.size, GFP_KERNEL_ACCOUNT); > + if (!sf->buf) > + return ERR_PTR(-ENOMEM); > + sf->size = kn->attr.size; > + > + return NULL + !*ppos; > +} Will this also cause the vmalloc fragmentation/abuse that others have mentioned as userspace can trigger this? And what code frees it? thanks, greg k-h