net: add PPP on L2TP Access Concentrator (PPPoLAC) driver.

Change-Id: I3ae3ee7520951ae24269db0ef2898c6455cf6bcc
Signed-off-by: Chia-chi Yeh <chiachi@android.com>

1 files changed, 359 insertions, 0 deletions

diff --git a/drivers/net/pppolac.c b/drivers/net/pppolac.c
new file mode 100644
index 000000000000..8843a9d30911
--- /dev/null
+++ b/drivers/net/pppolac.c
@@ -0,0 +1,359 @@
+/* drivers/net/pppolac.c
+ *
+ * Driver for PPP on L2TP Access Concentrator / PPPoLAC Socket (RFC 2661)
+ *
+ * Copyright (C) 2009 Google, Inc.
+ * Author: Chia-chi Yeh <chiachi@android.com>
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+/* This driver handles L2TP data packets between a UDP socket and a PPP channel.
+ * To keep things simple, only one session per socket is permitted. Packets are
+ * sent via the socket, so it must keep connected to the same address. One must
+ * not set sequencing in ICCN but let LNS controll it. Currently this driver
+ * only works on IPv4 due to the lack of UDP encapsulation support in IPv6. */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/file.h>
+#include <linux/net.h>
+#include <linux/udp.h>
+#include <linux/ppp_defs.h>
+#include <linux/if_ppp.h>
+#include <linux/if_pppox.h>
+#include <linux/ppp_channel.h>
+#include <net/tcp_states.h>
+
+#define L2TP_CONTROL_MASK	0x80
+#define L2TP_VERSION_MASK	0x0F
+#define L2TP_VERSION		0x02
+#define L2TP_LENGTH_MASK	0x40
+#define L2TP_OFFSET_MASK	0x02
+#define L2TP_SEQUENCE_MASK	0x08
+
+#define PPP_ADDR	0xFF
+#define PPP_CTRL	0x03
+
+union unaligned {
+	__u32 u32;
+} __attribute__((packed));
+
+static inline union unaligned *unaligned(void *ptr)
+{
+	return (union unaligned *)ptr;
+}
+
+static int pppolac_recv(struct sock *sk_udp, struct sk_buff *skb)
+{
+	struct sock *sk;
+	struct pppolac_opt *opt;
+	__u8 bits;
+	__u8 *ptr;
+
+	/* Drop the packet if it is too short. */
+	if (skb->len < sizeof(struct udphdr) + 6)
+		goto drop;
+
+	/* Put it back if it is a control packet. */
+	if (skb->data[sizeof(struct udphdr)] & L2TP_CONTROL_MASK)
+		return 1;
+
+	/* Now the packet is ours. Skip UDP header. */
+	skb_pull(skb, sizeof(struct udphdr));
+
+	/* Check the version. */
+	if ((skb->data[1] & L2TP_VERSION_MASK) != L2TP_VERSION)
+		goto drop;
+	bits = skb->data[0];
+	ptr = &skb->data[2];
+
+	/* Check the length if it is present. */
+	if (bits & L2TP_LENGTH_MASK) {
+		if ((ptr[0] << 8 | ptr[1]) != skb->len)
+			goto drop;
+		ptr += 2;
+	}
+
+	/* Skip all fields including optional ones. */
+	if (!skb_pull(skb, 6 + (bits & L2TP_SEQUENCE_MASK ? 4 : 0) +
+			(bits & L2TP_LENGTH_MASK ? 2 : 0) +
+			(bits & L2TP_OFFSET_MASK ? 2 : 0)))
+		goto drop;
+
+	/* Skip the offset padding if it is present. */
+	if (bits & L2TP_OFFSET_MASK &&
+			!skb_pull(skb, skb->data[-2] << 8 | skb->data[-1]))
+		goto drop;
+
+	/* Now ptr is pointing to the tunnel and skb is pointing to the payload.
+	 * We have to lock sk_udp to prevent sk from being closed. */
+	lock_sock(sk_udp);
+	sk = sk_udp->sk_user_data;
+	if (!sk) {
+		release_sock(sk_udp);
+		goto drop;
+	}
+	sock_hold(sk);
+	release_sock(sk_udp);
+	opt = &pppox_sk(sk)->proto.lac;
+
+	/* Check the tunnel and the session. */
+	if (unaligned(ptr)->u32 != opt->local) {
+		sock_put(sk);
+		goto drop;
+	}
+
+	/* Check the sequence if it is present. According to RFC 2661 page 10
+	 * and 43, the only thing to do is updating opt->sequencing. */
+	opt->sequencing = bits & L2TP_SEQUENCE_MASK;
+
+	/* Skip PPP address and control if they are present. */
+	if (skb->len >= 2 && skb->data[0] == PPP_ADDR &&
+			skb->data[1] == PPP_CTRL)
+		skb_pull(skb, 2);
+
+	/* Fix PPP protocol if it is compressed. */
+	if (skb->len >= 1 && skb->data[0] & 1)
+		skb_push(skb, 1)[0] = 0;
+
+	/* Finally, deliver the packet to PPP channel. We have to lock sk to
+	 * prevent another thread from calling pppox_unbind_sock(). */
+	skb_orphan(skb);
+	lock_sock(sk);
+	ppp_input(&pppox_sk(sk)->chan, skb);
+	release_sock(sk);
+	sock_put(sk);
+	return 0;
+
+drop:
+	kfree_skb(skb);
+	return 0;
+}
+
+static int pppolac_xmit(struct ppp_channel *chan, struct sk_buff *skb)
+{
+	struct sock *sk_udp = (struct sock *)chan->private;
+	struct pppolac_opt *opt = &pppox_sk(sk_udp->sk_user_data)->proto.lac;
+	struct msghdr msg = {.msg_flags = MSG_NOSIGNAL | MSG_DONTWAIT};
+	struct kvec iov;
+
+	/* Install PPP address and control. */
+	skb_push(skb, 2);
+	skb->data[0] = PPP_ADDR;
+	skb->data[1] = PPP_CTRL;
+
+	/* Install L2TP header. */
+	if (opt->sequencing) {
+		skb_push(skb, 10);
+		skb->data[0] = L2TP_SEQUENCE_MASK;
+		skb->data[6] = opt->sequence >> 8;
+		skb->data[7] = opt->sequence;
+		skb->data[8] = 0;
+		skb->data[9] = 0;
+		opt->sequence++;
+	} else {
+		skb_push(skb, 6);
+		skb->data[0] = 0;
+	}
+	skb->data[1] = L2TP_VERSION;
+	unaligned(&skb->data[2])->u32 = opt->remote;
+
+	/* Now send the packet via UDP socket. */
+	iov.iov_base = skb->data;
+	iov.iov_len = skb->len;
+	kernel_sendmsg(sk_udp->sk_socket, &msg, &iov, 1, skb->len);
+	kfree_skb(skb);
+	return 1;
+}
+
+/******************************************************************************/
+
+static struct ppp_channel_ops pppolac_channel_ops = {
+	.start_xmit = pppolac_xmit,
+};
+
+static int pppolac_connect(struct socket *sock, struct sockaddr *useraddr,
+	int addrlen, int flags)
+{
+	struct sock *sk = sock->sk;
+	struct pppox_sock *po = pppox_sk(sk);
+	struct sockaddr_pppolac *addr = (struct sockaddr_pppolac *)useraddr;
+	struct socket *sock_udp = NULL;
+	struct sock *sk_udp;
+	int error;
+
+	if (addrlen != sizeof(struct sockaddr_pppolac) ||
+			!addr->local.tunnel || !addr->local.session ||
+			!addr->remote.tunnel || !addr->remote.session) {
+		return -EINVAL;
+	}
+
+	lock_sock(sk);
+	error = -EALREADY;
+	if (sk->sk_state != PPPOX_NONE)
+		goto out;
+
+	sock_udp = sockfd_lookup(addr->udp_socket, &error);
+	if (!sock_udp)
+		goto out;
+	sk_udp = sock_udp->sk;
+	lock_sock(sk_udp);
+
+	/* Remove this check when IPv6 supports UDP encapsulation. */
+	error = -EAFNOSUPPORT;
+	if (sk_udp->sk_family != AF_INET)
+		goto out;
+	error = -EPROTONOSUPPORT;
+	if (sk_udp->sk_protocol != IPPROTO_UDP)
+		goto out;
+	error = -EDESTADDRREQ;
+	if (sk_udp->sk_state != TCP_ESTABLISHED)
+		goto out;
+	error = -EBUSY;
+	if (udp_sk(sk_udp)->encap_type || sk_udp->sk_user_data)
+		goto out;
+
+	po->chan.hdrlen = 12;
+	po->chan.private = sk_udp;
+	po->chan.ops = &pppolac_channel_ops;
+	po->chan.mtu = PPP_MTU - 80;
+	po->proto.lac.local = unaligned(&addr->local)->u32;
+	po->proto.lac.remote = unaligned(&addr->remote)->u32;
+
+	error = ppp_register_channel(&po->chan);
+	if (error)
+		goto out;
+
+	sk->sk_state = PPPOX_CONNECTED;
+	udp_sk(sk_udp)->encap_type = UDP_ENCAP_L2TPINUDP;
+	udp_sk(sk_udp)->encap_rcv = pppolac_recv;
+	sk_udp->sk_user_data = sk;
+
+out:
+	if (sock_udp) {
+		release_sock(sk_udp);
+		if (error)
+			sockfd_put(sock_udp);
+	}
+	release_sock(sk);
+	return error;
+}
+
+static int pppolac_release(struct socket *sock)
+{
+	struct sock *sk = sock->sk;
+
+	if (!sk)
+		return 0;
+
+	lock_sock(sk);
+	if (sock_flag(sk, SOCK_DEAD)) {
+		release_sock(sk);
+		return -EBADF;
+	}
+
+	if (sk->sk_state != PPPOX_NONE) {
+		struct sock *sk_udp = (struct sock *)pppox_sk(sk)->chan.private;
+		lock_sock(sk_udp);
+
+		pppox_unbind_sock(sk);
+		sk_udp->sk_user_data = NULL;
+		udp_sk(sk_udp)->encap_type = 0;
+		udp_sk(sk_udp)->encap_rcv = NULL;
+
+		release_sock(sk_udp);
+		sockfd_put(sk_udp->sk_socket);
+	}
+
+	sock_orphan(sk);
+	sock->sk = NULL;
+	release_sock(sk);
+	sock_put(sk);
+	return 0;
+}
+
+/******************************************************************************/
+
+static struct proto pppolac_proto = {
+	.name = "PPPOLAC",
+	.owner = THIS_MODULE,
+	.obj_size = sizeof(struct pppox_sock),
+};
+
+static struct proto_ops pppolac_proto_ops = {
+	.family = PF_PPPOX,
+	.owner = THIS_MODULE,
+	.release = pppolac_release,
+	.bind = sock_no_bind,
+	.connect = pppolac_connect,
+	.socketpair = sock_no_socketpair,
+	.accept = sock_no_accept,
+	.getname = sock_no_getname,
+	.poll = sock_no_poll,
+	.ioctl = pppox_ioctl,
+	.listen = sock_no_listen,
+	.shutdown = sock_no_shutdown,
+	.setsockopt = sock_no_setsockopt,
+	.getsockopt = sock_no_getsockopt,
+	.sendmsg = sock_no_sendmsg,
+	.recvmsg = sock_no_recvmsg,
+	.mmap = sock_no_mmap,
+};
+
+static int pppolac_create(struct net *net, struct socket *sock)
+{
+	struct sock *sk;
+
+	sk = sk_alloc(net, PF_PPPOX, GFP_KERNEL, &pppolac_proto);
+	if (!sk)
+		return -ENOMEM;
+
+	sock_init_data(sock, sk);
+	sock->state = SS_UNCONNECTED;
+	sock->ops = &pppolac_proto_ops;
+	sk->sk_protocol = PX_PROTO_OLAC;
+	sk->sk_state = PPPOX_NONE;
+	return 0;
+}
+
+/******************************************************************************/
+
+static struct pppox_proto pppolac_pppox_proto = {
+	.create = pppolac_create,
+	.owner = THIS_MODULE,
+};
+
+static int __init pppolac_init(void)
+{
+	int error;
+
+	error = proto_register(&pppolac_proto, 0);
+	if (error)
+		return error;
+
+	error = register_pppox_proto(PX_PROTO_OLAC, &pppolac_pppox_proto);
+	if (error)
+		proto_unregister(&pppolac_proto);
+	return error;
+}
+
+static void __exit pppolac_exit(void)
+{
+	unregister_pppox_proto(PX_PROTO_OLAC);
+	proto_unregister(&pppolac_proto);
+}
+
+module_init(pppolac_init);
+module_exit(pppolac_exit);
+
+MODULE_DESCRIPTION("PPP on L2TP Access Concentrator (PPPoLAC)");
+MODULE_AUTHOR("Chia-chi Yeh <chiachi@android.com>");
+MODULE_LICENSE("GPL");