From patchwork Thu Nov 26 12:24:25 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tom Parkin X-Patchwork-Id: 334108 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=-18.8 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, 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 CCD00C56202 for ; Thu, 26 Nov 2020 12:24:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6B63F2087C for ; Thu, 26 Nov 2020 12:24:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=katalix.com header.i=@katalix.com header.b="SbVHAG3h" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731237AbgKZMYo (ORCPT ); Thu, 26 Nov 2020 07:24:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46512 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730735AbgKZMYn (ORCPT ); Thu, 26 Nov 2020 07:24:43 -0500 Received: from mail.katalix.com (mail.katalix.com [IPv6:2a05:d01c:827:b342:16d0:7237:f32a:8096]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 23336C0613D4 for ; Thu, 26 Nov 2020 04:24:43 -0800 (PST) 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 DAC9296FB7; Thu, 26 Nov 2020 12:24:40 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=katalix.com; s=mail; t=1606393481; bh=uGUJ+7FYjnVQEw2JXXmc9sRqrLRqU95TJrWxRBh0zm8=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: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[PATCH=20net -next=201/2]=20ppp:=20add=20PPPIOCBRIDGECHAN=20and=20PPPIOCUNBRIDG ECHAN=20ioctls|Date:=20Thu,=2026=20Nov=202020=2012:24:25=20+0000|M essage-Id:=20<20201126122426.25243-2-tparkin@katalix.com>|In-Reply -To:=20<20201126122426.25243-1-tparkin@katalix.com>|References:=20 <20201126122426.25243-1-tparkin@katalix.com>; b=SbVHAG3hGne5REsVJJ9fMmh9gpbfumPAFCb/vb82ZfppzpFnPNQGP9dW7pCN1kfgO dfura8GqyaKvpqSewI9VLt9aTZvYIRC6LfHjKzuxT+67En6kSR9RvzYCVdjWV5JF22 yxq9HAPosb0DVEltOniNRuX59XnmX8zZnMvBp77/3TzjRBc185hFnzQeAB/G0GtGMs FxiZx2b4+kQpG7V338k14uNezGZhC7YV637otC+M69tMSGoMs1vSA/54rA5JrUVrWf 3veTFT7W1bXAvi1L8WIqjMkeOhXG42Qdx208AA6IvvAGEu9s8SSfke5hMufZkov6JL tyyMkLCIgA8KQ== From: Tom Parkin To: netdev@vger.kernel.org Cc: gnault@redhat.com, jchapman@katalix.com, Tom Parkin Subject: [PATCH net-next 1/2] ppp: add PPPIOCBRIDGECHAN and PPPIOCUNBRIDGECHAN ioctls Date: Thu, 26 Nov 2020 12:24:25 +0000 Message-Id: <20201126122426.25243-2-tparkin@katalix.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20201126122426.25243-1-tparkin@katalix.com> References: <20201126122426.25243-1-tparkin@katalix.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org This new ioctl pair allows two ppp channels to be bridged together: frames arriving in one channel are transmitted in the other channel and vice versa. The practical use for this is primarily to support the L2TP Access Concentrator use-case. The end-user session is presented as a ppp channel (typically PPPoE, although it could be e.g. PPPoA, or even PPP over a serial link) and is switched into a PPPoL2TP session for transmission to the LNS. At the LNS the PPP session is terminated in the ISP's network. When a PPP channel is bridged to another it takes a reference on the other's struct ppp_file. This reference is dropped when the channels are unbridged, which can occur either explicitly on userspace calling the PPPIOCUNBRIDGECHAN ioctl, or implicitly when either channel in the bridge is unregistered. In order to implement the channel bridge, struct channel is extended with a new field, 'bridge', which points to the other struct channel making up the bridge. This pointer is RCU protected to avoid adding another lock to the data path. To guard against concurrent writes to the pointer, the existing struct channel lock 'downl' use is extended (rather than adding a new lock). Order of lock acquisition is maintained: i.e. the channel 'upl' lock is always acquired before 'downl' in code paths that need to hold both. Signed-off-by: Tom Parkin --- drivers/net/ppp/ppp_generic.c | 147 ++++++++++++++++++++++++++++++++- include/uapi/linux/ppp-ioctl.h | 2 + 2 files changed, 147 insertions(+), 2 deletions(-) diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index 7d005896a0f9..5e563bfb8e2a 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -170,11 +170,12 @@ struct channel { struct list_head list; /* link in all/new_channels list */ struct ppp_channel *chan; /* public channel data structure */ struct rw_semaphore chan_sem; /* protects `chan' during chan ioctl */ - spinlock_t downl; /* protects `chan', file.xq dequeue */ + spinlock_t downl; /* protects `chan', 'bridge', file.xq dequeue */ struct ppp *ppp; /* ppp unit we're connected to */ struct net *chan_net; /* the net channel belongs to */ struct list_head clist; /* link in list of channels per unit */ rwlock_t upl; /* protects `ppp' */ + struct channel *bridge; /* "bridged" ppp channel */ #ifdef CONFIG_PPP_MULTILINK u8 avail; /* flag used in multilink stuff */ u8 had_frag; /* >= 1 fragments have been sent */ @@ -606,6 +607,95 @@ static struct bpf_prog *compat_ppp_get_filter(struct sock_fprog32 __user *p) #endif #endif +/* Bridge one PPP channel to another. + * When two channels are bridged, ppp_input on one channel is redirected to + * the other's ops->start_xmit handler. + * In order to safely bridge channels we must reject channels which are already + * part of a bridge instance, or which form part of an existing unit. + * Once successfully bridged, each channel holds a reference on the other + * to prevent it being freed while the bridge is extant. + */ +static int ppp_bridge_channels(struct channel *pch, struct channel *pchb) +{ + int ret = -EALREADY; + + /* We need to take each channel upl for access to the 'ppp' field, + * and each channel downl for write access to the 'bridge' field. + */ + + read_lock_bh(&pch->upl); + if (pch->ppp) + goto out0; + + spin_lock(&pch->downl); + + read_lock_bh(&pchb->upl); + if (pchb->ppp) + goto out1; + + spin_lock(&pchb->downl); + + if (pch->bridge || pchb->bridge) + goto out2; + + rcu_assign_pointer(pch->bridge, pchb); + refcount_inc(&pchb->file.refcnt); + + rcu_assign_pointer(pchb->bridge, pch); + refcount_inc(&pch->file.refcnt); + + ret = 0; + +out2: + spin_unlock(&pchb->downl); +out1: + read_unlock_bh(&pchb->upl); + spin_unlock(&pch->downl); +out0: + read_unlock_bh(&pch->upl); + + return ret; +} + +static int ppp_unbridge_channels(struct channel *pch) +{ + struct channel *pchb; + + rcu_read_lock(); + + pchb = rcu_dereference(pch->bridge); + if (!pchb) { + rcu_read_unlock(); + return -ENXIO; + } + + if (pch != rcu_dereference(pchb->bridge)) { + rcu_read_unlock(); + return -ENXIO; + } + + spin_lock(&pch->downl); + spin_lock(&pchb->downl); + + rcu_assign_pointer(pch->bridge, NULL); + rcu_assign_pointer(pchb->bridge, NULL); + + spin_unlock(&pchb->downl); + spin_unlock(&pch->downl); + + rcu_read_unlock(); + + synchronize_rcu(); + + if (refcount_dec_and_test(&pch->file.refcnt)) + ppp_destroy_channel(pch); + + if (refcount_dec_and_test(&pchb->file.refcnt)) + ppp_destroy_channel(pchb); + + return 0; +} + static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { struct ppp_file *pf; @@ -641,8 +731,9 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) } if (pf->kind == CHANNEL) { - struct channel *pch; + struct channel *pch, *pchb; struct ppp_channel *chan; + struct ppp_net *pn; pch = PF_TO_CHANNEL(pf); @@ -657,6 +748,22 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg) err = ppp_disconnect_channel(pch); break; + case PPPIOCBRIDGECHAN: + if (get_user(unit, p)) + break; + err = -ENXIO; + pn = ppp_pernet(current->nsproxy->net_ns); + spin_lock_bh(&pn->all_channels_lock); + pchb = ppp_find_channel(pn, unit); + if (pchb) + err = ppp_bridge_channels(pch, pchb); + spin_unlock_bh(&pn->all_channels_lock); + break; + + case PPPIOCUNBRIDGECHAN: + err = ppp_unbridge_channels(pch); + break; + default: down_read(&pch->chan_sem); chan = pch->chan; @@ -2089,6 +2196,35 @@ static bool ppp_decompress_proto(struct sk_buff *skb) return pskb_may_pull(skb, 2); } +/* Attempt to handle a frame via. a bridged channel, if one exists. + * If the channel is bridged, the frame is consumed by the bridge. + * If not, the caller must handle the frame by normal recv mechanisms. + * Returns true if the frame is consumed, false otherwise. + */ +static bool ppp_channel_bridge_input(struct channel *pch, struct sk_buff *skb) +{ + struct channel *pchb; + + rcu_read_lock(); + pchb = rcu_dereference(pch->bridge); + if (pchb) { + spin_lock(&pchb->downl); + if (pchb->chan) { + skb_scrub_packet(skb, !net_eq(pch->chan_net, pchb->chan_net)); + if (!pchb->chan->ops->start_xmit(pchb->chan, skb)) + kfree_skb(skb); + } else { + /* channel got unregistered */ + kfree_skb(skb); + } + spin_unlock(&pchb->downl); + } + rcu_read_unlock(); + + /* If pchb is set then we've consumed the packet */ + return pchb; +} + void ppp_input(struct ppp_channel *chan, struct sk_buff *skb) { @@ -2100,6 +2236,10 @@ ppp_input(struct ppp_channel *chan, struct sk_buff *skb) return; } + /* If the channel is bridged, transmit via. bridge */ + if (ppp_channel_bridge_input(pch, skb)) + return; + read_lock_bh(&pch->upl); if (!ppp_decompress_proto(skb)) { kfree_skb(skb); @@ -2796,8 +2936,11 @@ ppp_unregister_channel(struct ppp_channel *chan) list_del(&pch->list); spin_unlock_bh(&pn->all_channels_lock); + ppp_unbridge_channels(pch); + pch->file.dead = 1; wake_up_interruptible(&pch->file.rwait); + if (refcount_dec_and_test(&pch->file.refcnt)) ppp_destroy_channel(pch); } diff --git a/include/uapi/linux/ppp-ioctl.h b/include/uapi/linux/ppp-ioctl.h index 7bd2a5a75348..8dbecb3ad036 100644 --- a/include/uapi/linux/ppp-ioctl.h +++ b/include/uapi/linux/ppp-ioctl.h @@ -115,6 +115,8 @@ struct pppol2tp_ioc_stats { #define PPPIOCATTCHAN _IOW('t', 56, int) /* attach to ppp channel */ #define PPPIOCGCHAN _IOR('t', 55, int) /* get ppp channel number */ #define PPPIOCGL2TPSTATS _IOR('t', 54, struct pppol2tp_ioc_stats) +#define PPPIOCBRIDGECHAN _IOW('t', 53, int) /* bridge one channel to another */ +#define PPPIOCUNBRIDGECHAN _IO('t', 54) /* unbridge channel */ #define SIOCGPPPSTATS (SIOCDEVPRIVATE + 0) #define SIOCGPPPVER (SIOCDEVPRIVATE + 1) /* NEVER change this!! */