/* 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>

#ifdef CONFIG_XFRM
#include <net/xfrm.h>
#endif

/* Random numbers used for internal consistency checks of tunnel and session structures */
#define L2TP_TUNNEL_MAGIC       0x42114DDA
#define L2TP_SESSION_MAGIC      0x0C04EB7D

/* Per tunnel session hash table size */
#define L2TP_HASH_BITS  4
#define L2TP_HASH_SIZE  BIT(L2TP_HASH_BITS)

/* System-wide session hash table size */
#define L2TP_HASH_BITS_2        8
#define L2TP_HASH_SIZE_2        BIT(L2TP_HASH_BITS_2)

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.
 */
#define L2TP_SESSION_NAME_MAX 32
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;
#if IS_ENABLED(CONFIG_IPV6)
        struct in6_addr         *local_ip6;
        struct in6_addr         *peer_ip6;
#endif
        u16                     local_udp_port;
        u16                     peer_udp_port;
        unsigned int            use_udp_checksums:1,
                                udp6_zero_tx_checksums:1,
                                udp6_zero_rx_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.
 */
#define L2TP_TUNNEL_NAME_MAX 20
struct l2tp_tunnel {
        int                     magic;          /* Should be L2TP_TUNNEL_MAGIC */

        unsigned long           dead;

        struct rcu_head rcu;
        rwlock_t                hlist_lock;     /* protect 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) {
        case L2TP_L2SPECTYPE_DEFAULT:
                return 4;
        case L2TP_L2SPECTYPE_NONE:
        default:
                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);
        dst_release(dst);

        return mtu;
}

#ifdef CONFIG_XFRM
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]) ||
                      rcu_access_pointer(sk->sk_policy[1]));
}
#else
static inline bool l2tp_tunnel_uses_xfrm(const struct l2tp_tunnel *tunnel)
{
        return false;
}
#endif

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_ */