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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 394FAC433E1 for ; Thu, 23 Jul 2020 14:45:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1E2AD20674 for ; Thu, 23 Jul 2020 14:45:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729291AbgGWOpD (ORCPT ); Thu, 23 Jul 2020 10:45:03 -0400 Received: from verein.lst.de ([213.95.11.211]:60533 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726761AbgGWOpC (ORCPT ); Thu, 23 Jul 2020 10:45:02 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 7138C68AFE; Thu, 23 Jul 2020 16:44:55 +0200 (CEST) Date: Thu, 23 Jul 2020 16:44:55 +0200 From: 'Christoph Hellwig' To: David Laight Cc: 'Christoph Hellwig' , "David S. Miller" , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Alexey Kuznetsov , Hideaki YOSHIFUJI , Eric Dumazet , "linux-crypto@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "bpf@vger.kernel.org" , "netfilter-devel@vger.kernel.org" , "coreteam@netfilter.org" , "linux-sctp@vger.kernel.org" , "linux-hams@vger.kernel.org" , "linux-bluetooth@vger.kernel.org" , "bridge@lists.linux-foundation.org" , "linux-can@vger.kernel.org" , "dccp@vger.kernel.org" , "linux-decnet-user@lists.sourceforge.net" , "linux-wpan@vger.kernel.org" , "linux-s390@vger.kernel.org" , "mptcp@lists.01.org" , "lvs-devel@vger.kernel.org" , "rds-devel@oss.oracle.com" , "linux-afs@lists.infradead.org" , "tipc-discussion@lists.sourceforge.net" , "linux-x25@vger.kernel.org" Subject: Re: [PATCH 03/26] bpfilter: reject kernel addresses Message-ID: <20200723144455.GA12280@lst.de> References: <20200723060908.50081-1-hch@lst.de> <20200723060908.50081-4-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 23, 2020 at 02:42:11PM +0000, David Laight wrote: > From: Christoph Hellwig > > Sent: 23 July 2020 07:09 > > > > The bpfilter user mode helper processes the optval address using > > process_vm_readv. Don't send it kernel addresses fed under > > set_fs(KERNEL_DS) as that won't work. > > What sort of operations is the bpf filter doing on the sockopt buffers? > > Any attempts to reject some requests can be thwarted by a second > application thread modifying the buffer after the bpf filter has > checked that it allowed. > > You can't do security by reading a user buffer twice. I'm not saying that I approve of the design, but the current bpfilter design uses process_vm_readv to access the buffer, which obviously does not work with kernel buffers.