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,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 2A49DC43460 for ; Thu, 1 Apr 2021 07:15:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EDB85610CB for ; Thu, 1 Apr 2021 07:15:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233404AbhDAHOv (ORCPT ); Thu, 1 Apr 2021 03:14:51 -0400 Received: from mx2.suse.de ([195.135.220.15]:35080 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233179AbhDAHO1 (ORCPT ); Thu, 1 Apr 2021 03:14:27 -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=1617261266; 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=EdG19ICQsbKOwlsiDe5wakN2BrS2LIAGNa7VKGcjnVQ=; b=fv8kcptpBLAQc0tJiNubXbf0ugKJ2hvWgVLLMJZ/0LAHZ/H7hmdcW6UwavgsRRuc8UxgRK uVOojLtyIhxNKuBsOGYqMKNXgag1BwBpmIwahMUC+Gy8wFkQmmFCaBhr0G2p/Uf6VRWUZI jXwMtTfR7cz/IFgxCLmpSKRX8t+hfs8= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 61E08AF4F; Thu, 1 Apr 2021 07:14:26 +0000 (UTC) Date: Thu, 1 Apr 2021 09:14:25 +0200 From: Michal Hocko To: Kees Cook Cc: Greg Kroah-Hartman , Andrew Morton , "Rafael J. Wysocki" , 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-fsdevel@vger.kernel.org On Wed 31-03-21 19:21:45, 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. I thought the previous discussion has led to a conclusion that the preferred way is to disallow direct seq_file buffer usage. But this is obviously up to sysfs maintainers. I am happy you do not want to spread this out to all seq_file users anymore. > 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. Let me clarify on this, because this is not quite right. kvmalloc vs vmalloc (both with GFP_KERNEL) on PAGE_SIZE are two different beasts. The first one is almost always going to use kmalloc because the page allocator almost never fails those requests. > 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); > + sf->buf = __vmalloc(kn->attr.size, GFP_KERNEL_ACCOUNT); > + if (!sf->buf) > + return ERR_PTR(-ENOMEM); > + sf->size = kn->attr.size; > + > + return NULL + !*ppos; > +} > + > /* > * Reads on sysfs are handled through seq_file, which takes care of hairy > * details like buffering and seeking. The following function pipes > @@ -206,14 +226,17 @@ static const struct kernfs_ops sysfs_file_kfops_empty = { > }; > > static const struct kernfs_ops sysfs_file_kfops_ro = { > + .seq_start = sysfs_kf_seq_start, > .seq_show = sysfs_kf_seq_show, > }; > > static const struct kernfs_ops sysfs_file_kfops_wo = { > + .seq_start = sysfs_kf_seq_start, > .write = sysfs_kf_write, > }; > > static const struct kernfs_ops sysfs_file_kfops_rw = { > + .seq_start = sysfs_kf_seq_start, > .seq_show = sysfs_kf_seq_show, > .write = sysfs_kf_write, > }; > -- > 2.25.1 -- Michal Hocko SUSE Labs