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/*****************************************************************************
 * Linux PPP over L2TP (PPPoX/PPPoL2TP) Sockets
 *
 * PPPoX    --- Generic PPP encapsulation socket family
 * PPPoL2TP --- PPP over L2TP (RFC 2661)
 *
 * Version:	2.0.0
 *
 * Authors:	James Chapman (jchapman@katalix.com)
 *
 * Based on original work by Martijn van Oosterhout <kleptog@svana.org>
 *
 * License:
 *		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.
 *
 */

/* This driver handles only L2TP data frames; control frames are handled by a
 * userspace application.
 *
 * To send data in an L2TP session, userspace opens a PPPoL2TP socket and
 * attaches it to a bound UDP socket with local tunnel_id / session_id and
 * peer tunnel_id / session_id set. Data can then be sent or received using
 * regular socket sendmsg() / recvmsg() calls. Kernel parameters of the socket
 * can be read or modified using ioctl() or [gs]etsockopt() calls.
 *
 * When a PPPoL2TP socket is connected with local and peer session_id values
 * zero, the socket is treated as a special tunnel management socket.
 *
 * Here's example userspace code to create a socket for sending/receiving data
 * over an L2TP session:-
 *
 *	struct sockaddr_pppol2tp sax;
 *	int fd;
 *	int session_fd;
 *
 *	fd = socket(AF_PPPOX, SOCK_DGRAM, PX_PROTO_OL2TP);
 *
 *	sax.sa_family = AF_PPPOX;
 *	sax.sa_protocol = PX_PROTO_OL2TP;
 *	sax.pppol2tp.fd = tunnel_fd;	// bound UDP socket
 *	sax.pppol2tp.addr.sin_addr.s_addr = addr->sin_addr.s_addr;
 *	sax.pppol2tp.addr.sin_port = addr->sin_port;
 *	sax.pppol2tp.addr.sin_family = AF_INET;
 *	sax.pppol2tp.s_tunnel  = tunnel_id;
 *	sax.pppol2tp.s_session = session_id;
 *	sax.pppol2tp.d_tunnel  = peer_tunnel_id;
 *	sax.pppol2tp.d_session = peer_session_id;
 *
 *	session_fd = connect(fd, (struct sockaddr *)&sax, sizeof(sax));
 *
 * A pppd plugin that allows PPP traffic to be carried over L2TP using
 * this driver is available from the OpenL2TP project at
 * http://openl2tp.sourceforge.net.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/string.h>
#include <linux/list.h>
#include <linux/uaccess.h>

#include <linux/kernel.h>
#include <linux/spinlock.h>
#include <linux/kthread.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/jiffies.h>

#include <linux/netdevice.h>
#include <linux/net.h>
#include <linux/inetdevice.h>
#include <linux/skbuff.h>
#include <linux/init.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <linux/if_pppox.h>
#include <linux/if_pppol2tp.h>
#include <net/sock.h>
#include <linux/ppp_channel.h>
#include <linux/ppp_defs.h>
#include <linux/ppp-ioctl.h>
#include <linux/file.h>
#include <linux/hash.h>
#include <linux/sort.h>
#include <linux/proc_fs.h>
#include <linux/l2tp.h>
#include <linux/nsproxy.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <net/dst.h>
#include <net/ip.h>
#include <net/udp.h>
#include <net/xfrm.h>
#include <net/inet_common.h>

#include <asm/byteorder.h>
#include <linux/atomic.h>

#include "l2tp_core.h"

#define PPPOL2TP_DRV_VERSION	"V2.0"

/* Space for UDP, L2TP and PPP headers */
#define PPPOL2TP_HEADER_OVERHEAD	40

/* Number of bytes to build transmit L2TP headers.
 * Unfortunately the size is different depending on whether sequence numbers
 * are enabled.
 */
#define PPPOL2TP_L2TP_HDR_SIZE_SEQ		10
#define PPPOL2TP_L2TP_HDR_SIZE_NOSEQ		6

/* Private data of each session. This data lives at the end of struct
 * l2tp_session, referenced via session->priv[].
 */
struct pppol2tp_session {
	int			owner;		/* pid that opened the socket */

	struct sock		*sock;		/* Pointer to the session
						 * PPPoX socket */
	struct sock		*tunnel_sock;	/* Pointer to the tunnel UDP
						 * socket */
	int			flags;		/* accessed by PPPIOCGFLAGS.
						 * Unused. */
};

static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb);

static const struct ppp_channel_ops pppol2tp_chan_ops = {
	.start_xmit =  pppol2tp_xmit,
};

static const struct proto_ops pppol2tp_ops;

/* Helpers to obtain tunnel/session contexts from sockets.
 */
static inline struct l2tp_session *pppol2tp_sock_to_session(struct sock *sk)
{
	struct l2tp_session *session;

	if (sk == NULL)
		return NULL;

	sock_hold(sk);
	session = (struct l2tp_session *)(sk->sk_user_data);
	if (session == NULL) {
		sock_put(sk);
		goto out;
	}

	BUG_ON(session->magic != L2TP_SESSION_MAGIC);

out:
	return session;
}

/*****************************************************************************
 * Receive data handling
 *****************************************************************************/

static int pppol2tp_recv_payload_hook(struct sk_buff *skb)
{
	/* Skip PPP header, if present.	 In testing, Microsoft L2TP clients
	 * don't send the PPP header (PPP header compression enabled), but
	 * other clients can include the header. So we cope with both cases
	 * here. The PPP header is always FF03 when using L2TP.
	 *
	 * Note that skb->data[] isn't dereferenced from a u16 ptr here since
	 * the field may be unaligned.
	 */
	if (!pskb_may_pull(skb, 2))
		return 1;

	if ((skb->data[0] == 0xff) && (skb->data[1] == 0x03))
		skb_pull(skb, 2);

	return 0;
}

/* Receive message. This is the recvmsg for the PPPoL2TP socket.
 */
static int pppol2tp_recvmsg(struct kiocb *iocb, struct socket *sock,
			    struct msghdr *msg, size_t len,
			    int flags)
{
	int err;
	struct sk_buff *skb;
	struct sock *sk = sock->sk;

	err = -EIO;
	if (sk->sk_state & PPPOX_BOUND)
		goto end;

	msg->msg_namelen = 0;

	err = 0;
	skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT,
				flags & MSG_DONTWAIT, &err);
	if (!skb)
		goto end;

	if (len > skb->len)
		len = skb->len;
	else if (len < skb->len)
		msg->msg_flags |= MSG_TRUNC;

	err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, len);
	if (likely(err == 0))
		err = len;

	kfree_skb(skb);
end:
	return err;
}

static void pppol2tp_recv(struct l2tp_session *session, struct sk_buff *skb, int data_len)
{
	struct pppol2tp_session *ps = l2tp_session_priv(session);
	struct sock *sk = NULL;

	/* If the socket is bound, send it in to PPP's input queue. Otherwise
	 * queue it on the session socket.
	 */
	sk = ps->sock;
	if (sk == NULL)
		goto no_sock;

	if (sk->sk_state & PPPOX_BOUND) {
		struct pppox_sock *po;
		l2tp_dbg(session, PPPOL2TP_MSG_DATA,
			 "%s: recv %d byte data frame, passing to ppp\n",
			 session->name, data_len);

		/* We need to forget all info related to the L2TP packet
		 * gathered in the skb as we are going to reuse the same
		 * skb for the inner packet.
		 * Namely we need to:
		 * - reset xfrm (IPSec) information as it applies to
		 *   the outer L2TP packet and not to the inner one
		 * - release the dst to force a route lookup on the inner
		 *   IP packet since skb->dst currently points to the dst
		 *   of the UDP tunnel
		 * - reset netfilter information as it doesn't apply
		 *   to the inner packet either
		 */
		secpath_reset(skb);
		skb_dst_drop(skb);
		nf_reset(skb);

		po = pppox_sk(sk);
		ppp_input(&po->chan, skb);
	} else {
		l2tp_info(session, PPPOL2TP_MSG_DATA, "%s: socket not bound\n",
			  session->name);

		/* Not bound. Nothing we can do, so discard. */
		atomic_long_inc(&session->stats.rx_errors);
		kfree_skb(skb);
	}

	return;

no_sock:
	l2tp_info(session, PPPOL2TP_MSG_DATA, "%s: no socket\n", session->name);
	kfree_skb(skb);
}

static void pppol2tp_session_sock_hold(struct l2tp_session *session)
{
	struct pppol2tp_session *ps = l2tp_session_priv(session);

	if (ps->sock)
		sock_hold(ps->sock);
}

static void pppol2tp_session_sock_put(struct l2tp_session *session)
{
	struct pppol2tp_session *ps = l2tp_session_priv(session);

	if (ps->sock)
		sock_put(ps->sock);
}

/************************************************************************
 * Transmit handling
 ***********************************************************************/

/* This is the sendmsg for the PPPoL2TP pppol2tp_session socket.  We come here
 * when a user application does a sendmsg() on the session socket. L2TP and
 * PPP headers must be inserted into the user's data.
 */
static int pppol2tp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *m,
			    size_t total_len)
{
	static const unsigned char ppph[2] = { 0xff, 0x03 };
	struct sock *sk = sock->sk;
	struct sk_buff *skb;
	int error;
	struct l2tp_session *session;
	struct l2tp_tunnel *tunnel;
	struct pppol2tp_session *ps;
	int uhlen;

	error = -ENOTCONN;
	if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED))
		goto error;

	/* Get session and tunnel contexts */
	error = -EBADF;
	session = pppol2tp_sock_to_session(sk);
	if (session == NULL)
		goto error;

	ps = l2tp_session_priv(session);
	tunnel = l2tp_sock_to_tunnel(ps->tunnel_sock);
	if (tunnel == NULL)
		goto error_put_sess;

	uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;

	/* Allocate a socket buffer */
	error = -ENOMEM;
	skb = sock_wmalloc(sk, NET_SKB_PAD + sizeof(struct iphdr) +
			   uhlen + session->hdr_len +
			   sizeof(ppph) + total_len,
			   0, GFP_KERNEL);
	if (!skb)
		goto error_put_sess_tun;

	/* Reserve space for headers. */
	skb_reserve(skb, NET_SKB_PAD);
	skb_reset_network_header(skb);
	skb_reserve(skb, sizeof(struct iphdr));
	skb_reset_transport_header(skb);
	skb_reserve(skb, uhlen);

	/* Add PPP header */
	skb->data[0] = ppph[0];
	skb->data[1] = ppph[1];
	skb_put(skb, 2);

	/* Copy user data into skb */
	error = memcpy_fromiovec(skb->data, m->msg_iov, total_len);
	if (error < 0) {
		kfree_skb(skb);
		goto error_put_sess_tun;
	}
	skb_put(skb, total_len);

	l2tp_xmit_skb(session, skb, session->hdr_len);

	sock_put(ps->tunnel_sock);
	sock_put(sk);

	return error;

error_put_sess_tun:
	sock_put(ps->tunnel_sock);
error_put_sess:
	sock_put(sk);
error:
	return error;
}

/* Transmit function called by generic PPP driver.  Sends PPP frame
 * over PPPoL2TP socket.
 *
 * This is almost the same as pppol2tp_sendmsg(), but rather than
 * being called with a msghdr from userspace, it is called with a skb
 * from the kernel.
 *
 * The supplied skb from ppp doesn't have enough headroom for the
 * insertion of L2TP, UDP and IP headers so we need to allocate more
 * headroom in the skb. This will create a cloned skb. But we must be
 * careful in the error case because the caller will expect to free
 * the skb it supplied, not our cloned skb. So we take care to always
 * leave the original skb unfreed if we return an error.
 */
static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
{
	static const u8 ppph[2] = { 0xff, 0x03 };
	struct sock *sk = (struct sock *) chan->private;
	struct sock *sk_tun;
	struct l2tp_session *session;
	struct l2tp_tunnel *tunnel;
	struct pppol2tp_session *ps;
	int uhlen, headroom;

	if (sock_flag(sk, SOCK_DEAD) || !(sk->sk_state & PPPOX_CONNECTED))
		goto abort;

	/* Get session and tunnel contexts from the socket */
	session = pppol2tp_sock_to_session(sk);
	if (session == NULL)
		goto abort;

	ps = l2tp_session_priv(session);
	sk_tun = ps->tunnel_sock;
	if (sk_tun == NULL)
		goto abort_put_sess;
	tunnel = l2tp_sock_to_tunnel(sk_tun);
	if (tunnel == NULL)
		goto abort_put_sess;

	uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(struct udphdr) : 0;
	headroom = NET_SKB_PAD +
		   sizeof(struct iphdr) + /* IP header */
		   uhlen +		/* UDP header (if L2TP_ENCAPTYPE_UDP) */
		   session->hdr_len +	/* L2TP header */
		   sizeof(ppph);	/* PPP header */
	if (skb_cow_head(skb, headroom))
		goto abort_put_sess_tun;

	/* Setup PPP header */
	__skb_push(skb, sizeof(ppph));
	skb->data[0] = ppph[0];
	skb->data[1] = ppph[1];

	l2tp_xmit_skb(session, skb, session->hdr_len);

	sock_put(sk_tun);
	sock_put(sk);
	return 1;

abort_put_sess_tun:
	sock_put(sk_tun);
abort_put_sess:
	sock_put(sk);
abort:
	/* Free the original skb */
	kfree_skb(skb);
	return 1;
}

/*****************************************************************************
 * Session (and tunnel control) socket create/destroy.
 *****************************************************************************/

/* Called by l2tp_core when a session socket is being closed.
 */
static void pppol2tp_session_close(struct l2tp_session *session)
{
	struct pppol2tp_session *ps = l2tp_session_priv(session);
	struct sock *sk = ps->sock;
	struct socket *sock = sk->sk_socket;

	BUG_ON(session->magic != L2TP_SESSION_MAGIC);


	if (sock) {
		inet_shutdown(sock, 2);
		/* Don't let the session go away before our socket does */
		l2tp_session_inc_refcount(session);
	}
	return;
}

/* Really kill the session socket. (Called from sock_put() if
 * refcnt == 0.)
 */
static void pppol2tp_session_destruct(struct sock *sk)
{
	struct l2tp_session *session = sk->sk_user_data;
	if (session) {
		sk->sk_user_data = NULL;
		BUG_ON(session->magic != L2TP_SESSION_MAGIC);
		l2tp_session_dec_refcount(session);
	}
	return;
}

/* Called when the PPPoX socket (session) is closed.
 */
static int pppol2tp_release(struct socket *sock)
{
	struct sock *sk = sock->sk;
	struct l2tp_session *session;
	int error;

	if (!sk)
		return 0;

	error = -EBADF;
	lock_sock(sk);
	if (sock_flag(sk, SOCK_DEAD) != 0)
		goto error;

	pppox_unbind_sock(sk);

	/* Signal the death of the socket. */
	sk->sk_state = PPPOX_DEAD;
	sock_orphan(sk);
	sock->sk = NULL;

	session = pppol2tp_sock_to_session(sk);

	/* Purge any queued data */
	if (session != NULL) {
		__l2tp_session_unhash(session);
		l2tp_session_queue_purge(session);
		sock_put(sk);
	}
	skb_queue_purge(&sk->sk_receive_queue);
	skb_queue_purge(&sk->sk_write_queue);

	release_sock(sk);

	/* This will delete the session context via
	 * pppol2tp_session_destruct() if the socket's refcnt drops to
	 * zero.
	 */
	sock_put(sk);

	return 0;

error:
	release_sock(sk);
	return error;
}

static struct proto pppol2tp_sk_proto = {
	.name	  = "PPPOL2TP",
	.owner	  = THIS_MODULE,
	.obj_size = sizeof(struct pppox_sock),
};

static int pppol2tp_backlog_recv(struct sock *sk, struct sk_buff *skb)
{
	int rc;

	rc = l2tp_udp_encap_recv(sk, skb);
	if (rc)
		kfree_skb(skb);

	return NET_RX_SUCCESS;
}

/* socket() handler. Initialize a new struct sock.
 */
static int pppol2tp_create(struct net *net, struct socket *sock)
{
	int error = -ENOMEM;
	struct sock *sk;

	sk = sk_alloc(net, PF_PPPOX, GFP_KERNEL, &pppol2tp_sk_proto);
	if (!sk)
		goto out;

	sock_init_data(sock, sk);

	sock->state  = SS_UNCONNECTED;
	sock->ops    = &pppol2tp_ops;

	sk->sk_backlog_rcv = pppol2tp_backlog_recv;
	sk->sk_protocol	   = PX_PROTO_OL2TP;
	sk->sk_family	   = PF_PPPOX;
	sk->sk_state	   = PPPOX_NONE;
	sk->sk_type	   = SOCK_STREAM;
	sk->sk_destruct	   = pppol2tp_session_destruct;

	error = 0;

out:
	return error;
}

#if defined(CONFIG_L2TP_DEBUGFS) || defined(CONFIG_L2TP_DEBUGFS_MODULE)
static void pppol2tp_show(struct seq_file *m, void *arg)
{
	struct l2tp_session *session = arg;
	struct pppol2tp_session *ps = l2tp_session_priv(session);

	if (ps) {
		struct pppox_sock *po = pppox_sk(ps->sock);
		if (po)
			seq_printf(m, "   interface %s\n", ppp_dev_name(&po->chan));
	}
}
#endif

/* connect() handler. Attach a PPPoX socket to a tunnel UDP socket
 */
static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
			    int sockaddr_len, int flags)
{
	struct sock *sk = sock->sk;
	struct sockaddr_pppol2tp *sp = (struct sockaddr_pppol2tp *) uservaddr;
	struct pppox_sock *po = pppox_sk(sk);
	struct l2tp_session *session = NULL;
	struct l2tp_tunnel *tunnel;
	struct pppol2tp_session *ps;
	struct dst_entry *dst;
	struct l2tp_session_cfg cfg = { 0, };
	int error = 0;
	u32 tunnel_id, peer_tunnel_id;
	u32 session_id, peer_session_id;
	int ver = 2;
	int fd;

	lock_sock(sk);

	error = -EINVAL;
	if (sp->sa_protocol != PX_PROTO_OL2TP)
		goto end;

	/* Check for already bound sockets */
	error = -EBUSY;
	if (sk->sk_state & PPPOX_CONNECTED)
		goto end;

	/* We don't supporting rebinding anyway */
	error = -EALREADY;
	if (sk->sk_user_data)
		goto end; /* socket is already attached */

	/* Get params from socket address. Handle L2TPv2 and L2TPv3.
	 * This is nasty because there are different sockaddr_pppol2tp
	 * structs for L2TPv2, L2TPv3, over IPv4 and IPv6. We use
	 * the sockaddr size to determine which structure the caller
	 * is using.
	 */
	peer_tunnel_id = 0;
	if (sockaddr_len == sizeof(struct sockaddr_pppol2tp)) {
		fd = sp->pppol2tp.fd;
		tunnel_id = sp->pppol2tp.s_tunnel;
		peer_tunnel_id = sp->pppol2tp.d_tunnel;
		session_id = sp->pppol2tp.s_session;
		peer_session_id = sp->pppol2tp.d_session;
	} else if (sockaddr_len == sizeof(struct sockaddr_pppol2tpv3)) {
		struct sockaddr_pppol2tpv3 *sp3 =
			(struct sockaddr_pppol2tpv3 *) sp;
		ver = 3;
		fd = sp3->pppol2tp.fd;
		tunnel_id = sp3->pppol2tp.s_tunnel;
		peer_tunnel_id = sp3->pppol2tp.d_tunnel;
		session_id = sp3->pppol2tp.s_session;
		peer_session_id = sp3->pppol2tp.d_session;
	} else if (sockaddr_len == sizeof(struct sockaddr_pppol2tpin6)) {
		struct sockaddr_pppol2tpin6 *sp6 =
			(struct sockaddr_pppol2tpin6 *) sp;
		fd = sp6->pppol2tp.fd;
		tunnel_id = sp6->pppol2tp.s_tunnel;
		peer_tunnel_id = sp6->pppol2tp.d_tunnel;
		session_id = sp6->pppol2tp.s_session;
		peer_session_id = sp6->pppol2tp.d_session;
	} else if (sockaddr_len == sizeof(struct sockaddr_pppol2tpv3in6)) {
		struct sockaddr_pppol2tpv3in6 *sp6 =
			(struct sockaddr_pppol2tpv3in6 *) sp;
		ver = 3;
		fd = sp6->pppol2tp.fd;
		tunnel_id = sp6->pppol2tp.s_tunnel;
		peer_tunnel_id = sp6->pppol2tp.d_tunnel;
		session_id = sp6->pppol2tp.s_session;
		peer_session_id = sp6->pppol2tp.d_session;
	} else {
		error = -EINVAL;
		goto end; /* bad socket address */
	}

	/* Don't bind if tunnel_id is 0 */
	error = -EINVAL;
	if (tunnel_id == 0)
		goto end;

	tunnel = l2tp_tunnel_find(sock_net(sk), tunnel_id);

	/* Special case: create tunnel context if session_id and
	 * peer_session_id is 0. Otherwise look up tunnel using supplied
	 * tunnel id.
	 */
	if ((session_id == 0) && (peer_session_id == 0)) {
		if (tunnel == NULL) {
			struct l2tp_tunnel_cfg tcfg = {
				.encap = L2TP_ENCAPTYPE_UDP,
				.debug = 0,
			};
			error = l2tp_tunnel_create(sock_net(sk), fd, ver, tunnel_id, peer_tunnel_id, &tcfg, &tunnel);
			if (error < 0)
				goto end;
		}
	} else {
		/* Error if we can't find the tunnel */
		error = -ENOENT;
		if (tunnel == NULL)
			goto end;

		/* Error if socket is not prepped */
		if (tunnel->sock == NULL)
			goto end;
	}

	if (tunnel->recv_payload_hook == NULL)
		tunnel->recv_payload_hook = pppol2tp_recv_payload_hook;

	if (tunnel->peer_tunnel_id == 0)
		tunnel->peer_tunnel_id = peer_tunnel_id;

	/* Create session if it doesn't already exist. We handle the
	 * case where a session was previously created by the netlink
	 * interface by checking that the session doesn't already have
	 * a socket and its tunnel socket are what we expect. If any
	 * of those checks fail, return EEXIST to the caller.
	 */
	session = l2tp_session_find(sock_net(sk), tunnel, session_id);
	if (session == NULL) {
		/* Default MTU must allow space for UDP/L2TP/PPP
		 * headers.
		 */
		cfg.mtu = cfg.mru = 1500 - PPPOL2TP_HEADER_OVERHEAD;

		/* Allocate and initialize a new session context. */
		session = l2tp_session_create(sizeof(struct pppol2tp_session),
					      tunnel, session_id,
					      peer_session_id, &cfg);
		if (session == NULL) {
			error = -ENOMEM;
			goto end;
		}
	} else {
		ps = l2tp_session_priv(session);
		error = -EEXIST;
		if (ps->sock != NULL)
			goto end;

		/* consistency checks */
		if (ps->tunnel_sock != tunnel->sock)
			goto end;
	}

	/* Associate session with its PPPoL2TP socket */
	ps = l2tp_session_priv(session);
	ps->owner	     = current->pid;
	ps->sock	     = sk;
	ps->tunnel_sock = tunnel->sock;

	session->recv_skb	= pppol2tp_recv;
	session->session_close	= pppol2tp_session_close;
#if defined(CONFIG_L2TP_DEBUGFS) || defined(CONFIG_L2TP_DEBUGFS_MODULE)
	session->show		= pppol2tp_show;
#endif

	/* We need to know each time a skb is dropped from the reorder
	 * queue.
	 */
	session->ref = pppol2tp_session_sock_hold;
	session->deref = pppol2tp_session_sock_put;

	/* If PMTU discovery was enabled, use the MTU that was discovered */
	dst = sk_dst_get(sk);
	if (dst != NULL) {
		u32 pmtu = dst_mtu(__sk_dst_get(sk));
		if (pmtu != 0)
			session->mtu = session->mru = pmtu -
				PPPOL2TP_HEADER_OVERHEAD;
		dst_release(dst);
	}

	/* Special case: if source & dest session_id == 0x0000, this
	 * socket is being created to manage the tunnel. Just set up
	 * the internal context for use by ioctl() and sockopt()
	 * handlers.
	 */
	if ((session->session_id == 0) &&
	    (session->peer_session_id == 0)) {
		error = 0;
		goto out_no_ppp;
	}

	/* The only header we need to worry about is the L2TP
	 * header. This size is different depending on whether
	 * sequence numbers are enabled for the data channel.
	 */
	po->chan.hdrlen = PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;

	po->chan.private = sk;
	po->chan.ops	 = &pppol2tp_chan_ops;
	po->chan.mtu	 = session->mtu;

	error = ppp_register_net_channel(sock_net(sk), &po->chan);
	if (error)
		goto end;

out_no_ppp:
	/* This is how we get the session context from the socket. */
	sk->sk_user_data = session;
	sk->sk_state = PPPOX_CONNECTED;
	l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: created\n",
		  session->name);

end:
	release_sock(sk);

	return error;
}

#ifdef CONFIG_L2TP_V3

/* Called when creating sessions via the netlink interface.
 */
static int pppol2tp_session_create(struct net *net, u32 tunnel_id, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg)
{
	int error;
	struct l2tp_tunnel *tunnel;
	struct l2tp_session *session;
	struct pppol2tp_session *ps;

	tunnel = l2tp_tunnel_find(net, tunnel_id);

	/* Error if we can't find the tunnel */
	error = -ENOENT;
	if (tunnel == NULL)
		goto out;

	/* Error if tunnel socket is not prepped */
	if (tunnel->sock == NULL)
		goto out;

	/* Check that this session doesn't already exist */
	error = -EEXIST;
	session = l2tp_session_find(net, tunnel, session_id);
	if (session != NULL)
		goto out;

	/* Default MTU values. */
	if (cfg->mtu == 0)
		cfg->mtu = 1500 - PPPOL2TP_HEADER_OVERHEAD;
	if (cfg->mru == 0)
		cfg->mru = cfg->mtu;

	/* Allocate and initialize a new session context. */
	error = -ENOMEM;
	session = l2tp_session_create(sizeof(struct pppol2tp_session),
				      tunnel, session_id,
				      peer_session_id, cfg);
	if (session == NULL)
		goto out;

	ps = l2tp_session_priv(session);
	ps->tunnel_sock = tunnel->sock;

	l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: created\n",
		  session->name);

	error = 0;

out:
	return error;
}

#endif /* CONFIG_L2TP_V3 */

/* getname() support.
 */
static int pppol2tp_getname(struct socket *sock, struct sockaddr *uaddr,
			    int *usockaddr_len, int peer)
{
	int len = 0;
	int error = 0;
	struct l2tp_session *session;
	struct l2tp_tunnel *tunnel;
	struct sock *sk = sock->sk;
	struct inet_sock *inet;
	struct pppol2tp_session *pls;

	error = -ENOTCONN;
	if (sk == NULL)
		goto end;
	if (sk->sk_state != PPPOX_CONNECTED)
		goto end;

	error = -EBADF;
	session = pppol2tp_sock_to_session(sk);
	if (session == NULL)
		goto end;

	pls = l2tp_session_priv(session);
	tunnel = l2tp_sock_to_tunnel(pls->tunnel_sock);
	if (tunnel == NULL) {
		error = -EBADF;
		goto end_put_sess;
	}

	inet = inet_sk(tunnel->sock);
	if ((tunnel->version == 2) && (tunnel->sock->sk_family == AF_INET)) {
		struct sockaddr_pppol2tp sp;
		len = sizeof(sp);
		memset(&sp, 0, len);
		sp.sa_family	= AF_PPPOX;
		sp.sa_protocol	= PX_PROTO_OL2TP;
		sp.pppol2tp.fd  = tunnel->fd;
		sp.pppol2tp.pid = pls->owner;
		sp.pppol2tp.s_tunnel = tunnel->tunnel_id;
		sp.pppol2tp.d_tunnel = tunnel->peer_tunnel_id;
		sp.pppol2tp.s_session = session->session_id;
		sp.pppol2tp.d_session = session->peer_session_id;
		sp.pppol2tp.addr.sin_family = AF_INET;
		sp.pppol2tp.addr.sin_port = inet->inet_dport;
		sp.pppol2tp.addr.sin_addr.s_addr = inet->inet_daddr;
		memcpy(uaddr, &sp, len);
#if IS_ENABLED(CONFIG_IPV6)
	} else if ((tunnel->version == 2) &&
		   (tunnel->sock->sk_family == AF_INET6)) {
		struct ipv6_pinfo *np = inet6_sk(tunnel->sock);
		struct sockaddr_pppol2tpin6 sp;
		len = sizeof(sp);
		memset(&sp, 0, len);
		sp.sa_family	= AF_PPPOX;
		sp.sa_protocol	= PX_PROTO_OL2TP;
		sp.pppol2tp.fd  = tunnel->fd;
		sp.pppol2tp.pid = pls->owner;
		sp.pppol2tp.s_tunnel = tunnel->tunnel_id;
		sp.pppol2tp.d_tunnel = tunnel->peer_tunnel_id;
		sp.pppol2tp.s_session = session->session_id;
		sp.pppol2tp.d_session = session->peer_session_id;
		sp.pppol2tp.addr.sin6_family = AF_INET6;
		sp.pppol2tp.addr.sin6_port = inet->inet_dport;
		memcpy(&sp.pppol2tp.addr.sin6_addr, &np->daddr,
		       sizeof(np->daddr));
		memcpy(uaddr, &sp, len);
	} else if ((tunnel->version == 3) &&
		   (tunnel->sock->sk_family == AF_INET6)) {
		struct ipv6_pinfo *np = inet6_sk(tunnel->sock);
		struct sockaddr_pppol2tpv3in6 sp;
		len = sizeof(sp);
		memset(&sp, 0, len);
		sp.sa_family	= AF_PPPOX;
		sp.sa_protocol	= PX_PROTO_OL2TP;
		sp.pppol2tp.fd  = tunnel->fd;
		sp.pppol2tp.pid = pls->owner;
		sp.pppol2tp.s_tunnel = tunnel->tunnel_id;
		sp.pppol2tp.d_tunnel = tunnel->peer_tunnel_id;
		sp.pppol2tp.s_session = session->session_id;
		sp.pppol2tp.d_session = session->peer_session_id;
		sp.pppol2tp.addr.sin6_family = AF_INET6;
		sp.pppol2tp.addr.sin6_port = inet->inet_dport;
		memcpy(&sp.pppol2tp.addr.sin6_addr, &np->daddr,
		       sizeof(np->daddr));
		memcpy(uaddr, &sp, len);
#endif
	} else if (tunnel->version == 3) {
		struct sockaddr_pppol2tpv3 sp;
		len = sizeof(sp);
		memset(&sp, 0, len);
		sp.sa_family	= AF_PPPOX;
		sp.sa_protocol	= PX_PROTO_OL2TP;
		sp.pppol2tp.fd  = tunnel->fd;
		sp.pppol2tp.pid = pls->owner;
		sp.pppol2tp.s_tunnel = tunnel->tunnel_id;
		sp.pppol2tp.d_tunnel = tunnel->peer_tunnel_id;
		sp.pppol2tp.s_session = session->session_id;
		sp.pppol2tp.d_session = session->peer_session_id;
		sp.pppol2tp.addr.sin_family = AF_INET;
		sp.pppol2tp.addr.sin_port = inet->inet_dport;
		sp.pppol2tp.addr.sin_addr.s_addr = inet->inet_daddr;
		memcpy(uaddr, &sp, len);
	}

	*usockaddr_len = len;

	sock_put(pls->tunnel_sock);
end_put_sess:
	sock_put(sk);
	error = 0;

end:
	return error;
}

/****************************************************************************
 * ioctl() handlers.
 *
 * The PPPoX socket is created for L2TP sessions: tunnels have their own UDP
 * sockets. However, in order to control kernel tunnel features, we allow
 * userspace to create a special "tunnel" PPPoX socket which is used for
 * control only.  Tunnel PPPoX sockets have session_id == 0 and simply allow
 * the user application to issue L2TP setsockopt(), getsockopt() and ioctl()
 * calls.
 ****************************************************************************/

static void pppol2tp_copy_stats(struct pppol2tp_ioc_stats *dest,
				struct l2tp_stats *stats)
{
	dest->tx_packets = atomic_long_read(&stats->tx_packets);
	dest->tx_bytes = atomic_long_read(&stats->tx_bytes);
	dest->tx_errors = atomic_long_read(&stats->tx_errors);
	dest->rx_packets = atomic_long_read(&stats->rx_packets);
	dest->rx_bytes = atomic_long_read(&stats->rx_bytes);
	dest->rx_seq_discards = atomic_long_read(&stats->rx_seq_discards);
	dest->rx_oos_packets = atomic_long_read(&stats->rx_oos_packets);
	dest->rx_errors = atomic_long_read(&stats->rx_errors);
}

/* Session ioctl helper.
 */
static int pppol2tp_session_ioctl(struct l2tp_session *session,
				  unsigned int cmd, unsigned long arg)
{
	struct ifreq ifr;
	int err = 0;
	struct sock *sk;
	int val = (int) arg;
	struct pppol2tp_session *ps = l2tp_session_priv(session);
	struct l2tp_tunnel *tunnel = session->tunnel;
	struct pppol2tp_ioc_stats stats;

	l2tp_dbg(session, PPPOL2TP_MSG_CONTROL,
		 "%s: pppol2tp_session_ioctl(cmd=%#x, arg=%#lx)\n",
		 session->name, cmd, arg);

	sk = ps->sock;
	sock_hold(sk);

	switch (cmd) {
	case SIOCGIFMTU:
		err = -ENXIO;
		if (!(sk->sk_state & PPPOX_CONNECTED))
			break;

		err = -EFAULT;
		if (copy_from_user(&ifr, (void __user *) arg, sizeof(struct ifreq)))
			break;
		ifr.ifr_mtu = session->mtu;
		if (copy_to_user((void __user *) arg, &ifr, sizeof(struct ifreq)))
			break;

		l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: get mtu=%d\n",
			  session->name, session->mtu);
		err = 0;
		break;

	case SIOCSIFMTU:
		err = -ENXIO;
		if (!(sk->sk_state & PPPOX_CONNECTED))
			break;

		err = -EFAULT;
		if (copy_from_user(&ifr, (void __user *) arg, sizeof(struct ifreq)))
			break;

		session->mtu = ifr.ifr_mtu;

		l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: set mtu=%d\n",
			  session->name, session->mtu);
		err = 0;
		break;

	case PPPIOCGMRU:
		err = -ENXIO;
		if (!(sk->sk_state & PPPOX_CONNECTED))
			break;

		err = -EFAULT;
		if (put_user(session->mru, (int __user *) arg))
			break;

		l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: get mru=%d\n",
			  session->name, session->mru);
		err = 0;
		break;

	case PPPIOCSMRU:
		err = -ENXIO;
		if (!(sk->sk_state & PPPOX_CONNECTED))
			break;

		err = -EFAULT;
		if (get_user(val, (int __user *) arg))
			break;

		session->mru = val;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: set mru=%d\n",
			  session->name, session->mru);
		err = 0;
		break;

	case PPPIOCGFLAGS:
		err = -EFAULT;
		if (put_user(ps->flags, (int __user *) arg))
			break;

		l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: get flags=%d\n",
			  session->name, ps->flags);
		err = 0;
		break;

	case PPPIOCSFLAGS:
		err = -EFAULT;
		if (get_user(val, (int __user *) arg))
			break;
		ps->flags = val;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: set flags=%d\n",
			  session->name, ps->flags);
		err = 0;
		break;

	case PPPIOCGL2TPSTATS:
		err = -ENXIO;
		if (!(sk->sk_state & PPPOX_CONNECTED))
			break;

		memset(&stats, 0, sizeof(stats));
		stats.tunnel_id = tunnel->tunnel_id;
		stats.session_id = session->session_id;
		pppol2tp_copy_stats(&stats, &session->stats);
		if (copy_to_user((void __user *) arg, &stats,
				 sizeof(stats)))
			break;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: get L2TP stats\n",
			  session->name);
		err = 0;
		break;

	default:
		err = -ENOSYS;
		break;
	}

	sock_put(sk);

	return err;
}

/* Tunnel ioctl helper.
 *
 * Note the special handling for PPPIOCGL2TPSTATS below. If the ioctl data
 * specifies a session_id, the session ioctl handler is called. This allows an
 * application to retrieve session stats via a tunnel socket.
 */
static int pppol2tp_tunnel_ioctl(struct l2tp_tunnel *tunnel,
				 unsigned int cmd, unsigned long arg)
{
	int err = 0;
	struct sock *sk;
	struct pppol2tp_ioc_stats stats;

	l2tp_dbg(tunnel, PPPOL2TP_MSG_CONTROL,
		 "%s: pppol2tp_tunnel_ioctl(cmd=%#x, arg=%#lx)\n",
		 tunnel->name, cmd, arg);

	sk = tunnel->sock;
	sock_hold(sk);

	switch (cmd) {
	case PPPIOCGL2TPSTATS:
		err = -ENXIO;
		if (!(sk->sk_state & PPPOX_CONNECTED))
			break;

		if (copy_from_user(&stats, (void __user *) arg,
				   sizeof(stats))) {
			err = -EFAULT;
			break;
		}
		if (stats.session_id != 0) {
			/* resend to session ioctl handler */
			struct l2tp_session *session =
				l2tp_session_find(sock_net(sk), tunnel, stats.session_id);
			if (session != NULL)
				err = pppol2tp_session_ioctl(session, cmd, arg);
			else
				err = -EBADR;
			break;
		}
#ifdef CONFIG_XFRM
		stats.using_ipsec = (sk->sk_policy[0] || sk->sk_policy[1]) ? 1 : 0;
#endif
		pppol2tp_copy_stats(&stats, &tunnel->stats);
		if (copy_to_user((void __user *) arg, &stats, sizeof(stats))) {
			err = -EFAULT;
			break;
		}
		l2tp_info(tunnel, PPPOL2TP_MSG_CONTROL, "%s: get L2TP stats\n",
			  tunnel->name);
		err = 0;
		break;

	default:
		err = -ENOSYS;
		break;
	}

	sock_put(sk);

	return err;
}

/* Main ioctl() handler.
 * Dispatch to tunnel or session helpers depending on the socket.
 */
static int pppol2tp_ioctl(struct socket *sock, unsigned int cmd,
			  unsigned long arg)
{
	struct sock *sk = sock->sk;
	struct l2tp_session *session;
	struct l2tp_tunnel *tunnel;
	struct pppol2tp_session *ps;
	int err;

	if (!sk)
		return 0;

	err = -EBADF;
	if (sock_flag(sk, SOCK_DEAD) != 0)
		goto end;

	err = -ENOTCONN;
	if ((sk->sk_user_data == NULL) ||
	    (!(sk->sk_state & (PPPOX_CONNECTED | PPPOX_BOUND))))
		goto end;

	/* Get session context from the socket */
	err = -EBADF;
	session = pppol2tp_sock_to_session(sk);
	if (session == NULL)
		goto end;

	/* Special case: if session's session_id is zero, treat ioctl as a
	 * tunnel ioctl
	 */
	ps = l2tp_session_priv(session);
	if ((session->session_id == 0) &&
	    (session->peer_session_id == 0)) {
		err = -EBADF;
		tunnel = l2tp_sock_to_tunnel(ps->tunnel_sock);
		if (tunnel == NULL)
			goto end_put_sess;

		err = pppol2tp_tunnel_ioctl(tunnel, cmd, arg);
		sock_put(ps->tunnel_sock);
		goto end_put_sess;
	}

	err = pppol2tp_session_ioctl(session, cmd, arg);

end_put_sess:
	sock_put(sk);
end:
	return err;
}

/*****************************************************************************
 * setsockopt() / getsockopt() support.
 *
 * The PPPoX socket is created for L2TP sessions: tunnels have their own UDP
 * sockets. In order to control kernel tunnel features, we allow userspace to
 * create a special "tunnel" PPPoX socket which is used for control only.
 * Tunnel PPPoX sockets have session_id == 0 and simply allow the user
 * application to issue L2TP setsockopt(), getsockopt() and ioctl() calls.
 *****************************************************************************/

/* Tunnel setsockopt() helper.
 */
static int pppol2tp_tunnel_setsockopt(struct sock *sk,
				      struct l2tp_tunnel *tunnel,
				      int optname, int val)
{
	int err = 0;

	switch (optname) {
	case PPPOL2TP_SO_DEBUG:
		tunnel->debug = val;
		l2tp_info(tunnel, PPPOL2TP_MSG_CONTROL, "%s: set debug=%x\n",
			  tunnel->name, tunnel->debug);
		break;

	default:
		err = -ENOPROTOOPT;
		break;
	}

	return err;
}

/* Session setsockopt helper.
 */
static int pppol2tp_session_setsockopt(struct sock *sk,
				       struct l2tp_session *session,
				       int optname, int val)
{
	int err = 0;
	struct pppol2tp_session *ps = l2tp_session_priv(session);

	switch (optname) {
	case PPPOL2TP_SO_RECVSEQ:
		if ((val != 0) && (val != 1)) {
			err = -EINVAL;
			break;
		}
		session->recv_seq = val ? -1 : 0;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL,
			  "%s: set recv_seq=%d\n",
			  session->name, session->recv_seq);
		break;

	case PPPOL2TP_SO_SENDSEQ:
		if ((val != 0) && (val != 1)) {
			err = -EINVAL;
			break;
		}
		session->send_seq = val ? -1 : 0;
		{
			struct sock *ssk      = ps->sock;
			struct pppox_sock *po = pppox_sk(ssk);
			po->chan.hdrlen = val ? PPPOL2TP_L2TP_HDR_SIZE_SEQ :
				PPPOL2TP_L2TP_HDR_SIZE_NOSEQ;
		}
		l2tp_info(session, PPPOL2TP_MSG_CONTROL,
			  "%s: set send_seq=%d\n",
			  session->name, session->send_seq);
		break;

	case PPPOL2TP_SO_LNSMODE:
		if ((val != 0) && (val != 1)) {
			err = -EINVAL;
			break;
		}
		session->lns_mode = val ? -1 : 0;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL,
			  "%s: set lns_mode=%d\n",
			  session->name, session->lns_mode);
		break;

	case PPPOL2TP_SO_DEBUG:
		session->debug = val;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: set debug=%x\n",
			  session->name, session->debug);
		break;

	case PPPOL2TP_SO_REORDERTO:
		session->reorder_timeout = msecs_to_jiffies(val);
		l2tp_info(session, PPPOL2TP_MSG_CONTROL,
			  "%s: set reorder_timeout=%d\n",
			  session->name, session->reorder_timeout);
		break;

	default:
		err = -ENOPROTOOPT;
		break;
	}

	return err;
}

/* Main setsockopt() entry point.
 * Does API checks, then calls either the tunnel or session setsockopt
 * handler, according to whether the PPPoL2TP socket is a for a regular
 * session or the special tunnel type.
 */
static int pppol2tp_setsockopt(struct socket *sock, int level, int optname,
			       char __user *optval, unsigned int optlen)
{
	struct sock *sk = sock->sk;
	struct l2tp_session *session;
	struct l2tp_tunnel *tunnel;
	struct pppol2tp_session *ps;
	int val;
	int err;

	if (level != SOL_PPPOL2TP)
		return udp_prot.setsockopt(sk, level, optname, optval, optlen);

	if (optlen < sizeof(int))
		return -EINVAL;

	if (get_user(val, (int __user *)optval))
		return -EFAULT;

	err = -ENOTCONN;
	if (sk->sk_user_data == NULL)
		goto end;

	/* Get session context from the socket */
	err = -EBADF;
	session = pppol2tp_sock_to_session(sk);
	if (session == NULL)
		goto end;

	/* Special case: if session_id == 0x0000, treat as operation on tunnel
	 */
	ps = l2tp_session_priv(session);
	if ((session->session_id == 0) &&
	    (session->peer_session_id == 0)) {
		err = -EBADF;
		tunnel = l2tp_sock_to_tunnel(ps->tunnel_sock);
		if (tunnel == NULL)
			goto end_put_sess;

		err = pppol2tp_tunnel_setsockopt(sk, tunnel, optname, val);
		sock_put(ps->tunnel_sock);
	} else
		err = pppol2tp_session_setsockopt(sk, session, optname, val);

	err = 0;

end_put_sess:
	sock_put(sk);
end:
	return err;
}

/* Tunnel getsockopt helper. Called with sock locked.
 */
static int pppol2tp_tunnel_getsockopt(struct sock *sk,
				      struct l2tp_tunnel *tunnel,
				      int optname, int *val)
{
	int err = 0;

	switch (optname) {
	case PPPOL2TP_SO_DEBUG:
		*val = tunnel->debug;
		l2tp_info(tunnel, PPPOL2TP_MSG_CONTROL, "%s: get debug=%x\n",
			  tunnel->name, tunnel->debug);
		break;

	default:
		err = -ENOPROTOOPT;
		break;
	}

	return err;
}

/* Session getsockopt helper. Called with sock locked.
 */
static int pppol2tp_session_getsockopt(struct sock *sk,
				       struct l2tp_session *session,
				       int optname, int *val)
{
	int err = 0;

	switch (optname) {
	case PPPOL2TP_SO_RECVSEQ:
		*val = session->recv_seq;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL,
			  "%s: get recv_seq=%d\n", session->name, *val);
		break;

	case PPPOL2TP_SO_SENDSEQ:
		*val = session->send_seq;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL,
			  "%s: get send_seq=%d\n", session->name, *val);
		break;

	case PPPOL2TP_SO_LNSMODE:
		*val = session->lns_mode;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL,
			  "%s: get lns_mode=%d\n", session->name, *val);
		break;

	case PPPOL2TP_SO_DEBUG:
		*val = session->debug;
		l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: get debug=%d\n",
			  session->name, *val);
		break;

	case PPPOL2TP_SO_REORDERTO:
		*val = (int) jiffies_to_msecs(session->reorder_timeout);
		l2tp_info(session, PPPOL2TP_MSG_CONTROL,
			  "%s: get reorder_timeout=%d\n", session->name, *val);
		break;

	default:
		err = -ENOPROTOOPT;
	}

	return err;
}

/* Main getsockopt() entry point.
 * Does API checks, then calls either the tunnel or session getsockopt
 * handler, according to whether the PPPoX socket is a for a regular session
 * or the special tunnel type.
 */
static int pppol2tp_getsockopt(struct socket *sock, int level, int optname,
			       char __user *optval, int __user *optlen)
{
	struct sock *sk = sock->sk;
	struct l2tp_session *session;
	struct l2tp_tunnel *tunnel;
	int val, len;
	int err;
	struct pppol2tp_session *ps;

	if (level != SOL_PPPOL2TP)
		return udp_prot.getsockopt(sk, level, optname, optval, optlen);

	if (get_user(len, optlen))
		return -EFAULT;

	len = min_t(unsigned int, len, sizeof(int));

	if (len < 0)
		return -EINVAL;

	err = -ENOTCONN;
	if (sk->sk_user_data == NULL)
		goto end;

	/* Get the session context */
	err = -EBADF;
	session = pppol2tp_sock_to_session(sk);
	if (session == NULL)
		goto end;

	/* Special case: if session_id == 0x0000, treat as operation on tunnel */
	ps = l2tp_session_priv(session);
	if ((session->session_id == 0) &&
	    (session->peer_session_id == 0)) {
		err = -EBADF;
		tunnel = l2tp_sock_to_tunnel(ps->tunnel_sock);
		if (tunnel == NULL)
			goto end_put_sess;

		err = pppol2tp_tunnel_getsockopt(sk, tunnel, optname, &val);
		sock_put(ps->tunnel_sock);
	} else
		err = pppol2tp_session_getsockopt(sk, session, optname, &val);

	err = -EFAULT;
	if (put_user(len, optlen))
		goto end_put_sess;

	if (copy_to_user((void __user *) optval, &val, len))
		goto end_put_sess;

	err = 0;

end_put_sess:
	sock_put(sk);
end:
	return err;
}

/*****************************************************************************
 * /proc filesystem for debug
 * Since the original pppol2tp driver provided /proc/net/pppol2tp for
 * L2TPv2, we dump only L2TPv2 tunnels and sessions here.
 *****************************************************************************/

static unsigned int pppol2tp_net_id;

#ifdef CONFIG_PROC_FS

struct pppol2tp_seq_data {
	struct seq_net_private p;
	int tunnel_idx;			/* current tunnel */
	int session_idx;		/* index of session within current tunnel */
	struct l2tp_tunnel *tunnel;
	struct l2tp_session *session;	/* NULL means get next tunnel */
};

static void pppol2tp_next_tunnel(struct net *net, struct pppol2tp_seq_data *pd)
{
	for (;;) {
		pd->tunnel = l2tp_tunnel_find_nth(net, pd->tunnel_idx);
		pd->tunnel_idx++;

		if (pd->tunnel == NULL)
			break;

		/* Ignore L2TPv3 tunnels */
		if (pd->tunnel->version < 3)
			break;
	}
}

static void pppol2tp_next_session(struct net *net, struct pppol2tp_seq_data *pd)
{
	pd->session = l2tp_session_find_nth(pd->tunnel, pd->session_idx);
	pd->session_idx++;

	if (pd->session == NULL) {
		pd->session_idx = 0;
		pppol2tp_next_tunnel(net, pd);
	}
}

static void *pppol2tp_seq_start(struct seq_file *m, loff_t *offs)
{
	struct pppol2tp_seq_data *pd = SEQ_START_TOKEN;
	loff_t pos = *offs;
	struct net *net;

	if (!pos)
		goto out;

	BUG_ON(m->private == NULL);
	pd = m->private;
	net = seq_file_net(m);

	if (pd->tunnel == NULL)
		pppol2tp_next_tunnel(net, pd);
	else
		pppol2tp_next_session(net, pd);

	/* NULL tunnel and session indicates end of list */
	if ((pd->tunnel == NULL) && (pd->session == NULL))
		pd = NULL;

out:
	return pd;
}

static void *pppol2tp_seq_next(struct seq_file *m, void *v, loff_t *pos)
{
	(*pos)++;
	return NULL;
}

static void pppol2tp_seq_stop(struct seq_file *p, void *v)
{
	/* nothing to do */
}

static void pppol2tp_seq_tunnel_show(struct seq_file *m, void *v)
{
	struct l2tp_tunnel *tunnel = v;

	seq_printf(m, "\nTUNNEL '%s', %c %d\n",
		   tunnel->name,
		   (tunnel == tunnel->sock->sk_user_data) ? 'Y' : 'N',
		   atomic_read(&tunnel->ref_count) - 1);
	seq_printf(m, " %08x %ld/%ld/%ld %ld/%ld/%ld\n",
		   tunnel->debug,
		   atomic_long_read(&tunnel->stats.tx_packets),
		   atomic_long_read(&tunnel->stats.tx_bytes),
		   atomic_long_read(&tunnel->stats.tx_errors),
		   atomic_long_read(&tunnel->stats.rx_packets),
		   atomic_long_read(&tunnel->stats.rx_bytes),
		   atomic_long_read(&tunnel->stats.rx_errors));
}

static void pppol2tp_seq_session_show(struct seq_file *m, void *v)
{
	struct l2tp_session *session = v;
	struct l2tp_tunnel *tunnel = session->tunnel;
	struct pppol2tp_session *ps = l2tp_session_priv(session);
	struct pppox_sock *po = pppox_sk(ps->sock);
	u32 ip = 0;
	u16 port = 0;

	if (tunnel->sock) {
		struct inet_sock *inet = inet_sk(tunnel->sock);
		ip = ntohl(inet->inet_saddr);
		port = ntohs(inet->inet_sport);
	}

	seq_printf(m, "  SESSION '%s' %08X/%d %04X/%04X -> "
		   "%04X/%04X %d %c\n",
		   session->name, ip, port,
		   tunnel->tunnel_id,
		   session->session_id,
		   tunnel->peer_tunnel_id,
		   session->peer_session_id,
		   ps->sock->sk_state,
		   (session == ps->sock->sk_user_data) ?
		   'Y' : 'N');
	seq_printf(m, "   %d/%d/%c/%c/%s %08x %u\n",
		   session->mtu, session->mru,
		   session->recv_seq ? 'R' : '-',
		   session->send_seq ? 'S' : '-',
		   session->lns_mode ? "LNS" : "LAC",
		   session->debug,
		   jiffies_to_msecs(session->reorder_timeout));
	seq_printf(m, "   %hu/%hu %ld/%ld/%ld %ld/%ld/%ld\n",
		   session->nr, session->ns,
		   atomic_long_read(&session->stats.tx_packets),
		   atomic_long_read(&session->stats.tx_bytes),
		   atomic_long_read(&session->stats.tx_errors),
		   atomic_long_read(&session->stats.rx_packets),
		   atomic_long_read(&session->stats.rx_bytes),
		   atomic_long_read(&session->stats.rx_errors));

	if (po)
		seq_printf(m, "   interface %s\n", ppp_dev_name(&po->chan));
}

static int pppol2tp_seq_show(struct seq_file *m, void *v)
{
	struct pppol2tp_seq_data *pd = v;

	/* display header on line 1 */
	if (v == SEQ_START_TOKEN) {
		seq_puts(m, "PPPoL2TP driver info, " PPPOL2TP_DRV_VERSION "\n");
		seq_puts(m, "TUNNEL name, user-data-ok session-count\n");
		seq_puts(m, " debug tx-pkts/bytes/errs rx-pkts/bytes/errs\n");
		seq_puts(m, "  SESSION name, addr/port src-tid/sid "
			 "dest-tid/sid state user-data-ok\n");
		seq_puts(m, "   mtu/mru/rcvseq/sendseq/lns debug reorderto\n");
		seq_puts(m, "   nr/ns tx-pkts/bytes/errs rx-pkts/bytes/errs\n");
		goto out;
	}

	/* Show the tunnel or session context.
	 */
	if (pd->session == NULL)
		pppol2tp_seq_tunnel_show(m, pd->tunnel);
	else
		pppol2tp_seq_session_show(m, pd->session);

out:
	return 0;
}

static const struct seq_operations pppol2tp_seq_ops = {
	.start		= pppol2tp_seq_start,
	.next		= pppol2tp_seq_next,
	.stop		= pppol2tp_seq_stop,
	.show		= pppol2tp_seq_show,
};

/* Called when our /proc file is opened. We allocate data for use when
 * iterating our tunnel / session contexts and store it in the private
 * data of the seq_file.
 */
static int pppol2tp_proc_open(struct inode *inode, struct file *file)
{
	return seq_open_net(inode, file, &pppol2tp_seq_ops,
			    sizeof(struct pppol2tp_seq_data));
}

static const struct file_operations pppol2tp_proc_fops = {
	.owner		= THIS_MODULE,
	.open		= pppol2tp_proc_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= seq_release_net,
};

#endif /* CONFIG_PROC_FS */

/*****************************************************************************
 * Network namespace
 *****************************************************************************/

static __net_init int pppol2tp_init_net(struct net *net)
{
	struct proc_dir_entry *pde;
	int err = 0;

	pde = proc_create("pppol2tp", S_IRUGO, net->proc_net,
			  &pppol2tp_proc_fops);
	if (!pde) {
		err = -ENOMEM;
		goto out;
	}

out:
	return err;
}

static __net_exit void pppol2tp_exit_net(struct net *net)
{
	remove_proc_entry("pppol2tp", net->proc_net);
}

static struct pernet_operations pppol2tp_net_ops = {
	.init = pppol2tp_init_net,
	.exit = pppol2tp_exit_net,
	.id   = &pppol2tp_net_id,
};

/*****************************************************************************
 * Init and cleanup
 *****************************************************************************/

static const struct proto_ops pppol2tp_ops = {
	.family		= AF_PPPOX,
	.owner		= THIS_MODULE,
	.release	= pppol2tp_release,
	.bind		= sock_no_bind,
	.connect	= pppol2tp_connect,
	.socketpair	= sock_no_socketpair,
	.accept		= sock_no_accept,
	.getname	= pppol2tp_getname,
	.poll		= datagram_poll,
	.listen		= sock_no_listen,
	.shutdown	= sock_no_shutdown,
	.setsockopt	= pppol2tp_setsockopt,
	.getsockopt	= pppol2tp_getsockopt,
	.sendmsg	= pppol2tp_sendmsg,
	.recvmsg	= pppol2tp_recvmsg,
	.mmap		= sock_no_mmap,
	.ioctl		= pppox_ioctl,
};

static const struct pppox_proto pppol2tp_proto = {
	.create		= pppol2tp_create,
	.ioctl		= pppol2tp_ioctl
};

#ifdef CONFIG_L2TP_V3

static const struct l2tp_nl_cmd_ops pppol2tp_nl_cmd_ops = {
	.session_create	= pppol2tp_session_create,
	.session_delete	= l2tp_session_delete,
};

#endif /* CONFIG_L2TP_V3 */

static int __init pppol2tp_init(void)
{
	int err;

	err = register_pernet_device(&pppol2tp_net_ops);
	if (err)
		goto out;

	err = proto_register(&pppol2tp_sk_proto, 0);
	if (err)
		goto out_unregister_pppol2tp_pernet;

	err = register_pppox_proto(PX_PROTO_OL2TP, &pppol2tp_proto);
	if (err)
		goto out_unregister_pppol2tp_proto;

#ifdef CONFIG_L2TP_V3
	err = l2tp_nl_register_ops(L2TP_PWTYPE_PPP, &pppol2tp_nl_cmd_ops);
	if (err)
		goto out_unregister_pppox;
#endif

	pr_info("PPPoL2TP kernel driver, %s\n", PPPOL2TP_DRV_VERSION);

out:
	return err;

#ifdef CONFIG_L2TP_V3
out_unregister_pppox:
	unregister_pppox_proto(PX_PROTO_OL2TP);
#endif
out_unregister_pppol2tp_proto:
	proto_unregister(&pppol2tp_sk_proto);
out_unregister_pppol2tp_pernet:
	unregister_pernet_device(&pppol2tp_net_ops);
	goto out;
}

static void __exit pppol2tp_exit(void)
{
#ifdef CONFIG_L2TP_V3
	l2tp_nl_unregister_ops(L2TP_PWTYPE_PPP);
#endif
	unregister_pppox_proto(PX_PROTO_OL2TP);
	proto_unregister(&pppol2tp_sk_proto);
	unregister_pernet_device(&pppol2tp_net_ops);
}

module_init(pppol2tp_init);
module_exit(pppol2tp_exit);

MODULE_AUTHOR("James Chapman <jchapman@katalix.com>");
MODULE_DESCRIPTION("PPP over L2TP over UDP");
MODULE_LICENSE("GPL");
MODULE_VERSION(PPPOL2TP_DRV_VERSION);
MODULE_ALIAS("pppox-proto-" __stringify(PX_PROTO_OL2TP));