From patchwork Fri Nov 6 18:16:45 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tom Parkin X-Patchwork-Id: 11887723 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=-11.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham 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 C7511C55178 for ; Fri, 6 Nov 2020 18:22:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5E6A4221F8 for ; Fri, 6 Nov 2020 18:22:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=katalix.com header.i=@katalix.com header.b="Bsdz6POK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727811AbgKFSWF (ORCPT ); Fri, 6 Nov 2020 13:22:05 -0500 Received: from mail.katalix.com ([3.9.82.81]:43090 "EHLO mail.katalix.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726075AbgKFSWE (ORCPT ); Fri, 6 Nov 2020 13:22:04 -0500 X-Greylist: delayed 303 seconds by postgrey-1.27 at vger.kernel.org; Fri, 06 Nov 2020 13:22:03 EST Received: from localhost.localdomain (82-69-49-219.dsl.in-addr.zen.co.uk [82.69.49.219]) (Authenticated sender: tom) by mail.katalix.com (Postfix) with ESMTPSA id 45B0B96EE8; Fri, 6 Nov 2020 18:16:59 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=katalix.com; s=mail; t=1604686619; bh=nLZbPVTzgZRSBmlwfL1F972zxXyM6VmRM6S9TF3oBOE=; h=From:To:Cc:Subject:Date:Message-Id:From; z=From:=20Tom=20Parkin=20|To:=20netdev@vger.ke rnel.org|Cc:=20gnault@redhat.com,=0D=0A=09jchapman@katalix.com,=0D =0A=09Tom=20Parkin=20|Subject:=20[RFC=20PATCH =200/2]=20add=20ppp_generic=20ioctl=20to=20bridge=20channels|Date: =20Fri,=20=206=20Nov=202020=2018:16:45=20+0000|Message-Id:=20<2020 1106181647.16358-1-tparkin@katalix.com>; b=Bsdz6POK9GT5xH0ziWrMFTnUZp5iqWMLxeXJUOr4xWptkSiNB6YGKpvdfqCL3KMfT aFMMvv8HBGD7UBcOt6hnV2oAG6V46LaISpkU53y5l9gUQBHFiJuuls6VV1NjjsihP+ Is7Bd8vxQBXbsGGluAJyVt93lpOzDOjrCYulIljmlF1nB5fusUAkyTZGKMo4zpbDGb CE6LMIBVU3mpneyJcXItnL85zZoGVExMm83R3xqVI9EbGy8DgZOlYaGHLf6cBGR8Ay IlqHv24Dg+fL/d1juHhSj0B+5ekM5KULCzY+OMjFLsEYhJV66llIXqkkSZ8n7NnwvJ yBygPlPzSK/vA== From: Tom Parkin To: netdev@vger.kernel.org Cc: gnault@redhat.com, jchapman@katalix.com, Tom Parkin Subject: [RFC PATCH 0/2] add ppp_generic ioctl to bridge channels Date: Fri, 6 Nov 2020 18:16:45 +0000 Message-Id: <20201106181647.16358-1-tparkin@katalix.com> X-Mailer: git-send-email 2.17.1 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-State: RFC This small RFC series implements a suggestion from Guillaume Nault in response to my previous submission to add an ac/pppoe driver to the l2tp subsystem[1]. Following Guillaume's advice, this series adds an ioctl to the ppp code to allow a ppp channel to be bridged to another. Quoting Guillaume: "It's just a matter of extending struct channel (in ppp_generic.c) with a pointer to another channel, then testing this pointer in ppp_input(). If the pointer is NULL, use the classical path, if not, forward the PPP frame using the ->start_xmit function of the peer channel." This allows userspace to easily take PPP frames from e.g. a PPPoE session, and forward them over a PPPoL2TP session; accomplishing the same thing my earlier ac/pppoe driver in l2tp did but in much less code! Since I am not an expert in the ppp code, this patch set is RFC to gather any comments prior to making a proper submission. I have tested this code using go-l2tp[2] and l2tp-ktest[3], but I have some uncertainties about the current implementation: * I believe that the fact we're not explicitly locking anything in the ppp_input path for access to the channel bridge field is OK since: - ppp_input is called from the socket backlog recv - pppox_unbind (which calls ppp_channel_unregister, which unsets the channel bridge field) is called from the socket release As such I think the bridge pointer cannot change in the recv path since as the pppoe.c code says: "Semantics of backlog rcv preclude any code from executing in lock_sock()/release_sock() bounds". * When userspace makes a PPPIOCBRIDGECHAN ioctl call, the channel the ioctl is called on is updated to point to the channel identified using the index passed in the ioctl call. As such, allow PPP frames to pass in both directions from channel A to channel B, userspace must call ioctl twice: once to bridge A to B, and once to bridge B to A. This approach makes the kernel coding easier, because the ioctl handler doesn't need to do anything to lock the channel which is identified by index: it's sufficient to find it in the per-net list (under protection of the list lock) and take a reference on it. The downside is that userspace must make two ioctl calls to fully set up the bridge. Any comments on the design welcome, especially thoughts on the two points above. Thanks :-) [1]. Previous l2tp ac/pppoe patch set: https://lore.kernel.org/netdev/20200930210707.10717-1-tparkin@katalix.com/ [2]. go-l2tp: a Go library for building L2TP applications on Linux systems, support for the PPPIOCBRIDGECHAN ioctl is on a branch: https://github.com/katalix/go-l2tp/tree/tp_002_pppoe_2 [3]. l2tp-ktest: a test suite for the Linux Kernel L2TP subsystem https://github.com/katalix/l2tp-ktest Tom Parkin (2): ppp: add PPPIOCBRIDGECHAN ioctl docs: update ppp_generic.rst to describe ioctl PPPIOCBRIDGECHAN Documentation/networking/ppp_generic.rst | 5 ++++ drivers/net/ppp/ppp_generic.c | 35 +++++++++++++++++++++++- include/uapi/linux/ppp-ioctl.h | 1 + 3 files changed, 40 insertions(+), 1 deletion(-)