PPTP: PPP over IPv4 (Point-to-Point Tunneling Protocol)

PPP: introduce "pptp" module which implements point-to-point tunneling protocol using pppox framework
NET: introduce the "gre" module for demultiplexing GRE packets on version criteria
     (required to pptp and ip_gre may coexists)
NET: ip_gre: update to use the "gre" module

This patch introduces then pptp support to the linux kernel which
dramatically speeds up pptp vpn connections and decreases cpu usage in
comparison of existing user-space implementation
(poptop/pptpclient). There is accel-pptp project
(https://sourceforge.net/projects/accel-pptp/) to utilize this module,
it contains plugin for pppd to use pptp in client-mode and modified
pptpd (poptop) to build high-performance pptp NAS.

There was many changes from initial submitted patch, most important are:
1. using rcu instead of read-write locks
2. using static bitmap instead of dynamically allocated
3. using vmalloc for memory allocation instead of BITS_PER_LONG + __get_free_pages
4. fixed many coding style issues
Thanks to Eric Dumazet.
Signed-off-by: Dmitry Kozlov <xeb@mail.ru>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -6528,6 +6528,20 @@ M:	"Maciej W. Rozycki" <macro@linux-mips.org>
 S:	Maintained
 F:	drivers/serial/zs.*
 
+GRE DEMULTIPLEXER DRIVER
+M:	Dmitry Kozlov <xeb@mail.ru>
+L:	netdev@vger.kernel.org
+S:	Maintained
+F:	net/ipv4/gre.c
+F:	include/net/gre.h
+
+PPTP DRIVER
+M:	Dmitry Kozlov <xeb@mail.ru>
+L:	netdev@vger.kernel.org
+S:	Maintained
+F:	drivers/net/pptp.c
+W:	http://sourceforge.net/projects/accel-pptp
+
 THE REST
 M:	Linus Torvalds <torvalds@linux-foundation.org>
 L:	linux-kernel@vger.kernel.org

drivers/net/Kconfig

@@ -3192,6 +3192,17 @@ config PPPOE
 	  which contains instruction on how to use this driver (under 
 	  the heading "Kernel mode PPPoE").
 
+config PPTP
+	tristate "PPP over IPv4 (PPTP) (EXPERIMENTAL)"
+	depends on EXPERIMENTAL && PPP && NET_IPGRE_DEMUX
+	help
+	  Support for PPP over IPv4.(Point-to-Point Tunneling Protocol)
+
+	  This driver requires pppd plugin to work in client mode or
+	  modified pptpd (poptop) to work in server mode.
+	  See http://accel-pptp.sourceforge.net/ for information how to
+	  utilize this module.
+
 config PPPOATM
 	tristate "PPP over ATM"
 	depends on ATM && PPP

drivers/net/Makefile

@@ -162,6 +162,7 @@ obj-$(CONFIG_PPP_BSDCOMP) += bsd_comp.o
 obj-$(CONFIG_PPP_MPPE) += ppp_mppe.o
 obj-$(CONFIG_PPPOE) += pppox.o pppoe.o
 obj-$(CONFIG_PPPOL2TP) += pppox.o
+obj-$(CONFIG_PPTP) += pppox.o pptp.o
 
 obj-$(CONFIG_SLIP) += slip.o
 obj-$(CONFIG_SLHC) += slhc.o

include/linux/if_pppox.h

@@ -40,25 +40,35 @@
  * PPPoE addressing definition 
  */ 
 typedef __be16 sid_t;
-struct pppoe_addr{ 
+struct pppoe_addr {
 	sid_t         sid;                    /* Session identifier */
 	unsigned char remote[ETH_ALEN];       /* Remote address */
 	char          dev[IFNAMSIZ];          /* Local device to use */
 }; 
  
+/************************************************************************ 
+ * PPTP addressing definition
+ */
+struct pptp_addr {
+	u16             call_id;
+	struct in_addr  sin_addr;
+};
+
 /************************************************************************
  * Protocols supported by AF_PPPOX
  */
 #define PX_PROTO_OE    0 /* Currently just PPPoE */
 #define PX_PROTO_OL2TP 1 /* Now L2TP also */
-#define PX_MAX_PROTO   2
+#define PX_PROTO_PPTP  2
+#define PX_MAX_PROTO   3
 
 struct sockaddr_pppox {
 	sa_family_t     sa_family;            /* address family, AF_PPPOX */
 	unsigned int    sa_protocol;          /* protocol identifier */
-       union{ 
+	union {
 		struct pppoe_addr  pppoe;
-       }sa_addr; 
+		struct pptp_addr   pptp;
+	} sa_addr;
 } __packed;
 
 /* The use of the above union isn't viable because the size of this
@@ -101,7 +111,7 @@ struct pppoe_tag {
 	__be16 tag_type;
 	__be16 tag_len;
 	char tag_data[0];
-} __attribute ((packed));
+} __packed;
 
 /* Tag identifiers */
 #define PTT_EOL		__cpu_to_be16(0x0000)
@@ -150,6 +160,13 @@ struct pppoe_opt {
 					     relayed to (PPPoE relaying) */
 };
 
+struct pptp_opt {
+	struct pptp_addr src_addr;
+	struct pptp_addr dst_addr;
+	u32 ack_sent, ack_recv;
+	u32 seq_sent, seq_recv;
+	int ppp_flags;
+};
 #include <net/sock.h>
 
 struct pppox_sock {
@@ -159,6 +176,7 @@ struct pppox_sock {
 	struct pppox_sock	*next;	  /* for hash table */
 	union {
 		struct pppoe_opt pppoe;
+		struct pptp_opt  pptp;
 	} proto;
 	__be16			num;
 };

include/net/gre.h

+#ifndef __LINUX_GRE_H
+#define __LINUX_GRE_H
+
+#include <linux/skbuff.h>
+
+#define GREPROTO_CISCO		0
+#define GREPROTO_PPTP		1
+#define GREPROTO_MAX		2
+
+struct gre_protocol {
+	int  (*handler)(struct sk_buff *skb);
+	void (*err_handler)(struct sk_buff *skb, u32 info);
+};
+
+int gre_add_protocol(const struct gre_protocol *proto, u8 version);
+int gre_del_protocol(const struct gre_protocol *proto, u8 version);
+
+#endif

net/ipv4/Kconfig

@@ -215,8 +215,15 @@ config NET_IPIP
 	  be inserted in and removed from the running kernel whenever you
 	  want). Most people won't need this and can say N.
 
+config NET_IPGRE_DEMUX
+	tristate "IP: GRE demultiplexer"
+	help
+	 This is helper module to demultiplex GRE packets on GRE version field criteria.
+	 Required by ip_gre and pptp modules.
+
 config NET_IPGRE
 	tristate "IP: GRE tunnels over IP"
+	depends on NET_IPGRE_DEMUX
 	help
 	  Tunneling means encapsulating data of one protocol type within
 	  another protocol and sending it over a channel that understands the

net/ipv4/Makefile

@@ -20,6 +20,7 @@ obj-$(CONFIG_PROC_FS) += proc.o
 obj-$(CONFIG_IP_MULTIPLE_TABLES) += fib_rules.o
 obj-$(CONFIG_IP_MROUTE) += ipmr.o
 obj-$(CONFIG_NET_IPIP) += ipip.o
+obj-$(CONFIG_NET_IPGRE_DEMUX) += gre.o
 obj-$(CONFIG_NET_IPGRE) += ip_gre.o
 obj-$(CONFIG_SYN_COOKIES) += syncookies.o
 obj-$(CONFIG_INET_AH) += ah4.o

net/ipv4/gre.c

+/*
+ *	GRE over IPv4 demultiplexer driver
+ *
+ *	Authors: Dmitry Kozlov (xeb@mail.ru)
+ *
+ *	This program is free software; you can redistribute it and/or
+ *	modify it under the terms of the GNU General Public License
+ *	as published by the Free Software Foundation; either version
+ *	2 of the License, or (at your option) any later version.
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/kmod.h>
+#include <linux/skbuff.h>
+#include <linux/in.h>
+#include <linux/netdevice.h>
+#include <linux/version.h>
+#include <linux/spinlock.h>
+#include <net/protocol.h>
+#include <net/gre.h>
+
+
+const struct gre_protocol *gre_proto[GREPROTO_MAX] __read_mostly;
+static DEFINE_SPINLOCK(gre_proto_lock);
+
+int gre_add_protocol(const struct gre_protocol *proto, u8 version)
+{
+	if (version >= GREPROTO_MAX)
+		goto err_out;
+
+	spin_lock(&gre_proto_lock);
+	if (gre_proto[version])
+		goto err_out_unlock;
+
+	rcu_assign_pointer(gre_proto[version], proto);
+	spin_unlock(&gre_proto_lock);
+	return 0;
+
+err_out_unlock:
+	spin_unlock(&gre_proto_lock);
+err_out:
+	return -1;
+}
+EXPORT_SYMBOL_GPL(gre_add_protocol);
+
+int gre_del_protocol(const struct gre_protocol *proto, u8 version)
+{
+	if (version >= GREPROTO_MAX)
+		goto err_out;
+
+	spin_lock(&gre_proto_lock);
+	if (gre_proto[version] != proto)
+		goto err_out_unlock;
+	rcu_assign_pointer(gre_proto[version], NULL);
+	spin_unlock(&gre_proto_lock);
+	synchronize_rcu();
+	return 0;
+
+err_out_unlock:
+	spin_unlock(&gre_proto_lock);
+err_out:
+	return -1;
+}
+EXPORT_SYMBOL_GPL(gre_del_protocol);
+
+static int gre_rcv(struct sk_buff *skb)
+{
+	const struct gre_protocol *proto;
+	u8 ver;
+	int ret;
+
+	if (!pskb_may_pull(skb, 12))
+		goto drop;
+
+	ver = skb->data[1]&0x7f;
+	if (ver >= GREPROTO_MAX)
+		goto drop;
+
+	rcu_read_lock();
+	proto = rcu_dereference(gre_proto[ver]);
+	if (!proto || !proto->handler)
+		goto drop_unlock;
+	ret = proto->handler(skb);
+	rcu_read_unlock();
+	return ret;
+
+drop_unlock:
+	rcu_read_unlock();
+drop:
+	kfree_skb(skb);
+	return NET_RX_DROP;
+}
+
+static void gre_err(struct sk_buff *skb, u32 info)
+{
+	const struct gre_protocol *proto;
+	u8 ver;
+
+	if (!pskb_may_pull(skb, 12))
+		goto drop;
+
+	ver = skb->data[1]&0x7f;
+	if (ver >= GREPROTO_MAX)
+		goto drop;
+
+	rcu_read_lock();
+	proto = rcu_dereference(gre_proto[ver]);
+	if (!proto || !proto->err_handler)
+		goto drop_unlock;
+	proto->err_handler(skb, info);
+	rcu_read_unlock();
+	return;
+
+drop_unlock:
+	rcu_read_unlock();
+drop:
+	kfree_skb(skb);
+}
+
+static const struct net_protocol net_gre_protocol = {
+	.handler     = gre_rcv,
+	.err_handler = gre_err,
+	.netns_ok    = 1,
+};
+
+static int __init gre_init(void)
+{
+	pr_info("GRE over IPv4 demultiplexor driver");
+
+	if (inet_add_protocol(&net_gre_protocol, IPPROTO_GRE) < 0) {
+		pr_err("gre: can't add protocol\n");
+		return -EAGAIN;
+	}
+
+	return 0;
+}
+
+static void __exit gre_exit(void)
+{
+	inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
+}
+
+module_init(gre_init);
+module_exit(gre_exit);
+
+MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
+MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
+MODULE_LICENSE("GPL");
+

net/ipv4/ip_gre.c

@@ -44,6 +44,7 @@
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 #include <net/rtnetlink.h>
+#include <net/gre.h>
 
 #ifdef CONFIG_IPV6
 #include <net/ipv6.h>
@@ -1278,10 +1279,9 @@ static void ipgre_fb_tunnel_init(struct net_device *dev)
 }
 
 
-static const struct net_protocol ipgre_protocol = {
+static const struct gre_protocol ipgre_protocol = {
 	.handler     = ipgre_rcv,
 	.err_handler = ipgre_err,
-	.netns_ok	=	1,
 };
 
 static void ipgre_destroy_tunnels(struct ipgre_net *ign, struct list_head *head)
@@ -1663,7 +1663,7 @@ static int __init ipgre_init(void)
 	if (err < 0)
 		return err;
 
-	err = inet_add_protocol(&ipgre_protocol, IPPROTO_GRE);
+	err = gre_add_protocol(&ipgre_protocol, GREPROTO_CISCO);
 	if (err < 0) {
 		printk(KERN_INFO "ipgre init: can't add protocol\n");
 		goto add_proto_failed;
@@ -1683,7 +1683,7 @@ static int __init ipgre_init(void)
 tap_ops_failed:
 	rtnl_link_unregister(&ipgre_link_ops);
 rtnl_link_failed:
-	inet_del_protocol(&ipgre_protocol, IPPROTO_GRE);
+	gre_del_protocol(&ipgre_protocol, GREPROTO_CISCO);
 add_proto_failed:
 	unregister_pernet_device(&ipgre_net_ops);
 	goto out;
@@ -1693,7 +1693,7 @@ static void __exit ipgre_fini(void)
 {
 	rtnl_link_unregister(&ipgre_tap_ops);
 	rtnl_link_unregister(&ipgre_link_ops);
-	if (inet_del_protocol(&ipgre_protocol, IPPROTO_GRE) < 0)
+	if (gre_del_protocol(&ipgre_protocol, GREPROTO_CISCO) < 0)
 		printk(KERN_INFO "ipgre close: can't remove protocol\n");
 	unregister_pernet_device(&ipgre_net_ops);
 }