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/* SPDX-License-Identifier: GPL-2.0-only */
/* L2TP internal definitions.
* Copyright (c) 2008,2009 Katalix Systems Ltd
#include <linux/refcount.h>
#ifndef _L2TP_CORE_H_
#define _L2TP_CORE_H_
#include <net/dst.h>
#include <net/sock.h>
#include <net/xfrm.h>
/* Random numbers used for internal consistency checks of tunnel and session structures */
#define L2TP_TUNNEL_MAGIC 0x42114DDA
/* Per tunnel session hash table size */
#define L2TP_HASH_BITS 4
/* System-wide session hash table size */
#define L2TP_HASH_BITS_2 8
struct sk_buff;
struct l2tp_stats {
atomic_long_t tx_packets;
atomic_long_t tx_bytes;
atomic_long_t tx_errors;
atomic_long_t rx_packets;
atomic_long_t rx_bytes;
atomic_long_t rx_seq_discards;
atomic_long_t rx_oos_packets;
atomic_long_t rx_errors;
atomic_long_t rx_cookie_discards;
atomic_long_t rx_invalid;
struct l2tp_tunnel;
/* L2TP session configuration */
struct l2tp_session_cfg {
enum l2tp_pwtype pw_type;
unsigned int recv_seq:1; /* expect receive packets with sequence numbers? */
unsigned int send_seq:1; /* send packets with sequence numbers? */
unsigned int lns_mode:1; /* behave as LNS?
* LAC enables sequence numbers under LNS control.
u16 l2specific_type; /* Layer 2 specific type */
u8 cookie[8]; /* optional cookie */
int cookie_len; /* 0, 4 or 8 bytes */
u8 peer_cookie[8]; /* peer's cookie */
int peer_cookie_len; /* 0, 4 or 8 bytes */
int reorder_timeout; /* configured reorder timeout (in jiffies) */
char *ifname;
/* Represents a session (pseudowire) instance.
* Tracks runtime state including cookies, dataplane packet sequencing, and IO statistics.
* Is linked into a per-tunnel session hashlist; and in the case of an L2TPv3 session into
* an additional per-net ("global") hashlist.
struct l2tp_session {
int magic; /* should be L2TP_SESSION_MAGIC */
long dead;
struct l2tp_tunnel *tunnel; /* back pointer to tunnel context */
u32 session_id;
u32 peer_session_id;
u8 cookie[8];
int cookie_len;
u8 peer_cookie[8];
int peer_cookie_len;
u16 l2specific_type;
u16 hdr_len;
u32 nr; /* session NR state (receive) */
u32 ns; /* session NR state (send) */
struct sk_buff_head reorder_q; /* receive reorder queue */
u32 nr_max; /* max NR. Depends on tunnel */
u32 nr_window_size; /* NR window size */
u32 nr_oos; /* NR of last OOS packet */
int nr_oos_count; /* for OOS recovery */
int nr_oos_count_max;
struct hlist_node hlist; /* hash list node */
refcount_t ref_count;
char name[L2TP_SESSION_NAME_MAX]; /* for logging */
char ifname[IFNAMSIZ];
unsigned int recv_seq:1; /* expect receive packets with sequence numbers? */
unsigned int send_seq:1; /* send packets with sequence numbers? */
unsigned int lns_mode:1; /* behave as LNS?
* LAC enables sequence numbers under LNS control.
int reorder_timeout; /* configured reorder timeout (in jiffies) */
int reorder_skip; /* set if skip to next nr */
enum l2tp_pwtype pwtype;
struct l2tp_stats stats;
struct hlist_node global_hlist; /* global hash list node */
/* Session receive handler for data packets.
* Each pseudowire implementation should implement this callback in order to
* handle incoming packets. Packets are passed to the pseudowire handler after
* reordering, if data sequence numbers are enabled for the session.
void (*recv_skb)(struct l2tp_session *session, struct sk_buff *skb, int data_len);
/* Session close handler.
* Each pseudowire implementation may implement this callback in order to carry
* out pseudowire-specific shutdown actions.
* The callback is called by core after unhashing the session and purging its
* reorder queue.
void (*session_close)(struct l2tp_session *session);
/* Session show handler.
* Pseudowire-specific implementation of debugfs session rendering.
* The callback is called by l2tp_debugfs.c after rendering core session
* information.
void (*show)(struct seq_file *m, void *priv);
u8 priv[]; /* private data */
/* L2TP tunnel configuration */
struct l2tp_tunnel_cfg {
enum l2tp_encap_type encap;
/* Used only for kernel-created sockets */
struct in_addr local_ip;
struct in_addr peer_ip;
struct in6_addr *local_ip6;
struct in6_addr *peer_ip6;
u16 local_udp_port;
u16 peer_udp_port;
unsigned int use_udp_checksums:1,
/* Represents a tunnel instance.
* Tracks runtime state including IO statistics.
* Holds the tunnel socket (either passed from userspace or directly created by the kernel).
* Maintains a hashlist of sessions belonging to the tunnel instance.
* Is linked into a per-net list of tunnels.
struct l2tp_tunnel {
int magic; /* Should be L2TP_TUNNEL_MAGIC */
unsigned long dead;
struct rcu_head rcu;
spinlock_t hlist_lock; /* write-protection for session_hlist */
bool acpt_newsess; /* indicates whether this tunnel accepts
* new sessions. Protected by hlist_lock.
struct hlist_head session_hlist[L2TP_HASH_SIZE];
/* hashed list of sessions, hashed by id */
u32 tunnel_id;
u32 peer_tunnel_id;
int version; /* 2=>L2TPv2, 3=>L2TPv3 */
char name[L2TP_TUNNEL_NAME_MAX]; /* for logging */
enum l2tp_encap_type encap;
struct l2tp_stats stats;
struct list_head list; /* list node on per-namespace list of tunnels */
struct net *l2tp_net; /* the net we belong to */
refcount_t ref_count;
void (*old_sk_destruct)(struct sock *sk);
struct sock *sock; /* parent socket */
int fd; /* parent fd, if tunnel socket was created
* by userspace
struct work_struct del_work;
/* Pseudowire ops callbacks for use with the l2tp genetlink interface */
struct l2tp_nl_cmd_ops {
/* The pseudowire session create callback is responsible for creating a session
* instance for a specific pseudowire type.
* It must call l2tp_session_create and l2tp_session_register to register the
* session instance, as well as carry out any pseudowire-specific initialisation.
* It must return >= 0 on success, or an appropriate negative errno value on failure.
int (*session_create)(struct net *net, struct l2tp_tunnel *tunnel,
u32 session_id, u32 peer_session_id,
struct l2tp_session_cfg *cfg);
/* The pseudowire session delete callback is responsible for initiating the deletion
* of a session instance.
* It must call l2tp_session_delete, as well as carry out any pseudowire-specific
* teardown actions.
void (*session_delete)(struct l2tp_session *session);
static inline void *l2tp_session_priv(struct l2tp_session *session)
return &session->priv[0];
/* Tunnel and session refcounts */
void l2tp_tunnel_inc_refcount(struct l2tp_tunnel *tunnel);
void l2tp_tunnel_dec_refcount(struct l2tp_tunnel *tunnel);
void l2tp_session_inc_refcount(struct l2tp_session *session);
void l2tp_session_dec_refcount(struct l2tp_session *session);
/* Tunnel and session lookup.
* These functions take a reference on the instances they return, so
* the caller must ensure that the reference is dropped appropriately.
struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id);
struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth);
struct l2tp_session *l2tp_tunnel_get_session(struct l2tp_tunnel *tunnel,
u32 session_id);
struct l2tp_session *l2tp_session_get(const struct net *net, u32 session_id);
struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth);
struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
const char *ifname);
/* Tunnel and session lifetime management.
* Creation of a new instance is a two-step process: create, then register.
* Destruction is triggered using the *_delete functions, and completes asynchronously.
int l2tp_tunnel_create(int fd, int version, u32 tunnel_id,
u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg,
struct l2tp_tunnel **tunnelp);
int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
struct l2tp_tunnel_cfg *cfg);
void l2tp_tunnel_delete(struct l2tp_tunnel *tunnel);
struct l2tp_session *l2tp_session_create(int priv_size,
struct l2tp_tunnel *tunnel,
u32 session_id, u32 peer_session_id,
struct l2tp_session_cfg *cfg);
int l2tp_session_register(struct l2tp_session *session,
struct l2tp_tunnel *tunnel);
void l2tp_session_delete(struct l2tp_session *session);
/* Receive path helpers. If data sequencing is enabled for the session these
* functions handle queuing and reordering prior to passing packets to the
* pseudowire code to be passed to userspace.
void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
unsigned char *ptr, unsigned char *optr, u16 hdrflags,
int length);
int l2tp_udp_encap_recv(struct sock *sk, struct sk_buff *skb);
/* Transmit path helpers for sending packets over the tunnel socket. */
void l2tp_session_set_header_len(struct l2tp_session *session, int version);
int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb);
/* Pseudowire management.
* Pseudowires should register with l2tp core on module init, and unregister
* on module exit.
int l2tp_nl_register_ops(enum l2tp_pwtype pw_type, const struct l2tp_nl_cmd_ops *ops);
void l2tp_nl_unregister_ops(enum l2tp_pwtype pw_type);
/* IOCTL helper for IP encap modules. */
int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg);
/* Extract the tunnel structure from a socket's sk_user_data pointer,
* validating the tunnel magic feather.
struct l2tp_tunnel *l2tp_sk_to_tunnel(struct sock *sk);
static inline int l2tp_get_l2specific_len(struct l2tp_session *session)
switch (session->l2specific_type) {
return 4;
return 0;
static inline u32 l2tp_tunnel_dst_mtu(const struct l2tp_tunnel *tunnel)
struct dst_entry *dst;
u32 mtu;
dst = sk_dst_get(tunnel->sock);
if (!dst)
return 0;
mtu = dst_mtu(dst);
return mtu;
static inline bool l2tp_tunnel_uses_xfrm(const struct l2tp_tunnel *tunnel)
struct sock *sk = tunnel->sock;
return sk && (rcu_access_pointer(sk->sk_policy[0]) ||
static inline bool l2tp_tunnel_uses_xfrm(const struct l2tp_tunnel *tunnel)
return false;
static inline int l2tp_v3_ensure_opt_in_linear(struct l2tp_session *session, struct sk_buff *skb,
unsigned char **ptr, unsigned char **optr)
int opt_len = session->peer_cookie_len + l2tp_get_l2specific_len(session);
if (opt_len > 0) {
int off = *ptr - *optr;
if (!pskb_may_pull(skb, off + opt_len))
return -1;
if (skb->data != *optr) {
*optr = skb->data;
*ptr = skb->data + off;
return 0;
#define MODULE_ALIAS_L2TP_PWTYPE(type) \
MODULE_ALIAS("net-l2tp-type-" __stringify(type))
#endif /* _L2TP_CORE_H_ */