l2tp_ip.c

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/*
 * L2TPv3 IP encapsulation support
 *
 * Copyright (c) 2008,2009,2010 Katalix Systems Ltd
 *
 *  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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/icmp.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/random.h>
#include <linux/socket.h>
#include <linux/l2tp.h>
#include <linux/in.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/udp.h>
#include <net/inet_common.h>
#include <net/inet_hashtables.h>
#include <net/tcp_states.h>
#include <net/protocol.h>
#include <net/xfrm.h>

#include "l2tp_core.h"

struct l2tp_ip_sock {
    /* inet_sock has to be the first member of l2tp_ip_sock */
    struct inet_sock    inet;

    u32         conn_id;
    u32         peer_conn_id;
};

static DEFINE_RWLOCK(l2tp_ip_lock);
static struct hlist_head l2tp_ip_table;
static struct hlist_head l2tp_ip_bind_table;

static inline struct l2tp_ip_sock *l2tp_ip_sk(const struct sock *sk)
{
    return (struct l2tp_ip_sock *)sk;
}

static struct sock *__l2tp_ip_bind_lookup(struct net *net, __be32 laddr, int dif, u32 tunnel_id)
{
    struct hlist_node *node;
    struct sock *sk;

    sk_for_each_bound(sk, node, &l2tp_ip_bind_table) {
        struct inet_sock *inet = inet_sk(sk);
        struct l2tp_ip_sock *l2tp = l2tp_ip_sk(sk);

        if (l2tp == NULL)
            continue;

        if ((l2tp->conn_id == tunnel_id) &&
            net_eq(sock_net(sk), net) &&
            !(inet->inet_rcv_saddr && inet->inet_rcv_saddr != laddr) &&
            !(sk->sk_bound_dev_if && sk->sk_bound_dev_if != dif))
            goto found;
    }

    sk = NULL;
found:
    return sk;
}

static inline struct sock *l2tp_ip_bind_lookup(struct net *net, __be32 laddr, int dif, u32 tunnel_id)
{
    struct sock *sk = __l2tp_ip_bind_lookup(net, laddr, dif, tunnel_id);
    if (sk)
        sock_hold(sk);

    return sk;
}

/* When processing receive frames, there are two cases to
 * consider. Data frames consist of a non-zero session-id and an
 * optional cookie. Control frames consist of a regular L2TP header
 * preceded by 32-bits of zeros.
 *
 * L2TPv3 Session Header Over IP
 *
 *  0                   1                   2                   3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                           Session ID                          |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |               Cookie (optional, maximum 64 bits)...
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *                                                                 |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 * L2TPv3 Control Message Header Over IP
 *
 *  0                   1                   2                   3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                      (32 bits of zeros)                       |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |T|L|x|x|S|x|x|x|x|x|x|x|  Ver  |             Length            |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                     Control Connection ID                     |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |               Ns              |               Nr              |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 * All control frames are passed to userspace.
 */
static int l2tp_ip_recv(struct sk_buff *skb)
{
    struct sock *sk;
    u32 session_id;
    u32 tunnel_id;
    unsigned char *ptr, *optr;
    struct l2tp_session *session;
    struct l2tp_tunnel *tunnel = NULL;
    int length;

    /* Point to L2TP header */
    optr = ptr = skb->data;

    if (!pskb_may_pull(skb, 4))
        goto discard;

    session_id = ntohl(*((__be32 *) ptr));
    ptr += 4;

    /* RFC3931: L2TP/IP packets have the first 4 bytes containing
     * the session_id. If it is 0, the packet is a L2TP control
     * frame and the session_id value can be discarded.
     */
    if (session_id == 0) {
        __skb_pull(skb, 4);
        goto pass_up;
    }

    /* Ok, this is a data packet. Lookup the session. */
    session = l2tp_session_find(&init_net, NULL, session_id);
    if (session == NULL)
        goto discard;

    tunnel = session->tunnel;
    if (tunnel == NULL)
        goto discard;

    /* Trace packet contents, if enabled */
    if (tunnel->debug & L2TP_MSG_DATA) {
        length = min(32u, skb->len);
        if (!pskb_may_pull(skb, length))
            goto discard;

        pr_debug("%s: ip recv\n", tunnel->name);
        print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, ptr, length);
    }

    l2tp_recv_common(session, skb, ptr, optr, 0, skb->len, tunnel->recv_payload_hook);

    return 0;

pass_up:
    /* Get the tunnel_id from the L2TP header */
    if (!pskb_may_pull(skb, 12))
        goto discard;

    if ((skb->data[0] & 0xc0) != 0xc0)
        goto discard;

    tunnel_id = ntohl(*(__be32 *) &skb->data[4]);
    tunnel = l2tp_tunnel_find(&init_net, tunnel_id);
    if (tunnel != NULL)
        sk = tunnel->sock;
    else {
        struct iphdr *iph = (struct iphdr *) skb_network_header(skb);

        read_lock_bh(&l2tp_ip_lock);
        sk = __l2tp_ip_bind_lookup(&init_net, iph->daddr, 0, tunnel_id);
        read_unlock_bh(&l2tp_ip_lock);
    }

    if (sk == NULL)
        goto discard;

    sock_hold(sk);

    if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
        goto discard_put;

    nf_reset(skb);

    return sk_receive_skb(sk, skb, 1);

discard_put:
    sock_put(sk);

discard:
    kfree_skb(skb);
    return 0;
}

static int l2tp_ip_open(struct sock *sk)
{
    /* Prevent autobind. We don't have ports. */
    inet_sk(sk)->inet_num = IPPROTO_L2TP;

    write_lock_bh(&l2tp_ip_lock);
    sk_add_node(sk, &l2tp_ip_table);
    write_unlock_bh(&l2tp_ip_lock);

    return 0;
}

static void l2tp_ip_close(struct sock *sk, long timeout)
{
    write_lock_bh(&l2tp_ip_lock);
    hlist_del_init(&sk->sk_bind_node);
    sk_del_node_init(sk);
    write_unlock_bh(&l2tp_ip_lock);
    sk_common_release(sk);
}

static void l2tp_ip_destroy_sock(struct sock *sk)
{
    struct sk_buff *skb;

    while ((skb = __skb_dequeue_tail(&sk->sk_write_queue)) != NULL)
        kfree_skb(skb);

    sk_refcnt_debug_dec(sk);
}

static int l2tp_ip_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
{
    struct inet_sock *inet = inet_sk(sk);
    struct sockaddr_l2tpip *addr = (struct sockaddr_l2tpip *) uaddr;
    int ret;
    int chk_addr_ret;

    if (!sock_flag(sk, SOCK_ZAPPED))
        return -EINVAL;
    if (addr_len < sizeof(struct sockaddr_l2tpip))
        return -EINVAL;
    if (addr->l2tp_family != AF_INET)
        return -EINVAL;

    ret = -EADDRINUSE;
    read_lock_bh(&l2tp_ip_lock);
    if (__l2tp_ip_bind_lookup(&init_net, addr->l2tp_addr.s_addr, sk->sk_bound_dev_if, addr->l2tp_conn_id))
        goto out_in_use;

    read_unlock_bh(&l2tp_ip_lock);

    lock_sock(sk);
    if (sk->sk_state != TCP_CLOSE || addr_len < sizeof(struct sockaddr_l2tpip))
        goto out;

    chk_addr_ret = inet_addr_type(&init_net, addr->l2tp_addr.s_addr);
    ret = -EADDRNOTAVAIL;
    if (addr->l2tp_addr.s_addr && chk_addr_ret != RTN_LOCAL &&
        chk_addr_ret != RTN_MULTICAST && chk_addr_ret != RTN_BROADCAST)
        goto out;

    if (addr->l2tp_addr.s_addr)
        inet->inet_rcv_saddr = inet->inet_saddr = addr->l2tp_addr.s_addr;
    if (chk_addr_ret == RTN_MULTICAST || chk_addr_ret == RTN_BROADCAST)
        inet->inet_saddr = 0;  /* Use device */
    sk_dst_reset(sk);

    l2tp_ip_sk(sk)->conn_id = addr->l2tp_conn_id;

    write_lock_bh(&l2tp_ip_lock);
    sk_add_bind_node(sk, &l2tp_ip_bind_table);
    sk_del_node_init(sk);
    write_unlock_bh(&l2tp_ip_lock);
    ret = 0;
    sock_reset_flag(sk, SOCK_ZAPPED);

out:
    release_sock(sk);

    return ret;

out_in_use:
    read_unlock_bh(&l2tp_ip_lock);

    return ret;
}

static int l2tp_ip_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
{
    struct sockaddr_l2tpip *lsa = (struct sockaddr_l2tpip *) uaddr;
    int rc;

    if (sock_flag(sk, SOCK_ZAPPED)) /* Must bind first - autobinding does not work */
        return -EINVAL;

    if (addr_len < sizeof(*lsa))
        return -EINVAL;

    if (ipv4_is_multicast(lsa->l2tp_addr.s_addr))
        return -EINVAL;

    rc = ip4_datagram_connect(sk, uaddr, addr_len);
    if (rc < 0)
        return rc;

    lock_sock(sk);

    l2tp_ip_sk(sk)->peer_conn_id = lsa->l2tp_conn_id;

    write_lock_bh(&l2tp_ip_lock);
    hlist_del_init(&sk->sk_bind_node);
    sk_add_bind_node(sk, &l2tp_ip_bind_table);
    write_unlock_bh(&l2tp_ip_lock);

    release_sock(sk);
    return rc;
}

static int l2tp_ip_disconnect(struct sock *sk, int flags)
{
    if (sock_flag(sk, SOCK_ZAPPED))
        return 0;

    return udp_disconnect(sk, flags);
}

static int l2tp_ip_getname(struct socket *sock, struct sockaddr *uaddr,
               int *uaddr_len, int peer)
{
    struct sock *sk     = sock->sk;
    struct inet_sock *inet  = inet_sk(sk);
    struct l2tp_ip_sock *lsk = l2tp_ip_sk(sk);
    struct sockaddr_l2tpip *lsa = (struct sockaddr_l2tpip *)uaddr;

    memset(lsa, 0, sizeof(*lsa));
    lsa->l2tp_family = AF_INET;
    if (peer) {
        if (!inet->inet_dport)
            return -ENOTCONN;
        lsa->l2tp_conn_id = lsk->peer_conn_id;
        lsa->l2tp_addr.s_addr = inet->inet_daddr;
    } else {
        __be32 addr = inet->inet_rcv_saddr;
        if (!addr)
            addr = inet->inet_saddr;
        lsa->l2tp_conn_id = lsk->conn_id;
        lsa->l2tp_addr.s_addr = addr;
    }
    *uaddr_len = sizeof(*lsa);
    return 0;
}

static int l2tp_ip_backlog_recv(struct sock *sk, struct sk_buff *skb)
{
    int rc;

    /* Charge it to the socket, dropping if the queue is full. */
    rc = sock_queue_rcv_skb(sk, skb);
    if (rc < 0)
        goto drop;

    return 0;

drop:
    IP_INC_STATS(&init_net, IPSTATS_MIB_INDISCARDS);
    kfree_skb(skb);
    return -1;
}

/* Userspace will call sendmsg() on the tunnel socket to send L2TP
 * control frames.
 */
static int l2tp_ip_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, size_t len)
{
    struct sk_buff *skb;
    int rc;
    struct inet_sock *inet = inet_sk(sk);
    struct rtable *rt = NULL;
    struct flowi4 *fl4;
    int connected = 0;
    __be32 daddr;

    lock_sock(sk);

    rc = -ENOTCONN;
    if (sock_flag(sk, SOCK_DEAD))
        goto out;

    /* Get and verify the address. */
    if (msg->msg_name) {
        struct sockaddr_l2tpip *lip = (struct sockaddr_l2tpip *) msg->msg_name;
        rc = -EINVAL;
        if (msg->msg_namelen < sizeof(*lip))
            goto out;

        if (lip->l2tp_family != AF_INET) {
            rc = -EAFNOSUPPORT;
            if (lip->l2tp_family != AF_UNSPEC)
                goto out;
        }

        daddr = lip->l2tp_addr.s_addr;
    } else {
        rc = -EDESTADDRREQ;
        if (sk->sk_state != TCP_ESTABLISHED)
            goto out;

        daddr = inet->inet_daddr;
        connected = 1;
    }

    /* Allocate a socket buffer */
    rc = -ENOMEM;
    skb = sock_wmalloc(sk, 2 + NET_SKB_PAD + sizeof(struct iphdr) +
               4 + len, 0, GFP_KERNEL);
    if (!skb)
        goto error;

    /* Reserve space for headers, putting IP header on 4-byte boundary. */
    skb_reserve(skb, 2 + NET_SKB_PAD);
    skb_reset_network_header(skb);
    skb_reserve(skb, sizeof(struct iphdr));
    skb_reset_transport_header(skb);

    /* Insert 0 session_id */
    *((__be32 *) skb_put(skb, 4)) = 0;

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

    fl4 = &inet->cork.fl.u.ip4;
    if (connected)
        rt = (struct rtable *) __sk_dst_check(sk, 0);

    rcu_read_lock();
    if (rt == NULL) {
        const struct ip_options_rcu *inet_opt;

        inet_opt = rcu_dereference(inet->inet_opt);

        /* Use correct destination address if we have options. */
        if (inet_opt && inet_opt->opt.srr)
            daddr = inet_opt->opt.faddr;

        /* If this fails, retransmit mechanism of transport layer will
         * keep trying until route appears or the connection times
         * itself out.
         */
        rt = ip_route_output_ports(sock_net(sk), fl4, sk,
                       daddr, inet->inet_saddr,
                       inet->inet_dport, inet->inet_sport,
                       sk->sk_protocol, RT_CONN_FLAGS(sk),
                       sk->sk_bound_dev_if);
        if (IS_ERR(rt))
            goto no_route;
        if (connected) {
            sk_setup_caps(sk, &rt->dst);
        } else {
            skb_dst_set(skb, &rt->dst);
            goto xmit;
        }
    }

    /* We dont need to clone dst here, it is guaranteed to not disappear.
     *  __dev_xmit_skb() might force a refcount if needed.
     */
    skb_dst_set_noref(skb, &rt->dst);

xmit:
    /* Queue the packet to IP for output */
    rc = ip_queue_xmit(skb, &inet->cork.fl);
    rcu_read_unlock();

error:
    if (rc >= 0)
        rc = len;

out:
    release_sock(sk);
    return rc;

no_route:
    rcu_read_unlock();
    IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES);
    kfree_skb(skb);
    rc = -EHOSTUNREACH;
    goto out;
}

static int l2tp_ip_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
               size_t len, int noblock, int flags, int *addr_len)
{
    struct inet_sock *inet = inet_sk(sk);
    size_t copied = 0;
    int err = -EOPNOTSUPP;
    struct sockaddr_in *sin = (struct sockaddr_in *)msg->msg_name;
    struct sk_buff *skb;

    if (flags & MSG_OOB)
        goto out;

    if (addr_len)
        *addr_len = sizeof(*sin);

    skb = skb_recv_datagram(sk, flags, noblock, &err);
    if (!skb)
        goto out;

    copied = skb->len;
    if (len < copied) {
        msg->msg_flags |= MSG_TRUNC;
        copied = len;
    }

    err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);
    if (err)
        goto done;

    sock_recv_timestamp(msg, sk, skb);

    /* Copy the address. */
    if (sin) {
        sin->sin_family = AF_INET;
        sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
        sin->sin_port = 0;
        memset(&sin->sin_zero, 0, sizeof(sin->sin_zero));
    }
    if (inet->cmsg_flags)
        ip_cmsg_recv(msg, skb);
    if (flags & MSG_TRUNC)
        copied = skb->len;
done:
    skb_free_datagram(sk, skb);
out:
    return err ? err : copied;
}

static struct proto l2tp_ip_prot = {
    .name          = "L2TP/IP",
    .owner         = THIS_MODULE,
    .init          = l2tp_ip_open,
    .close         = l2tp_ip_close,
    .bind          = l2tp_ip_bind,
    .connect       = l2tp_ip_connect,
    .disconnect    = l2tp_ip_disconnect,
    .ioctl         = udp_ioctl,
    .destroy       = l2tp_ip_destroy_sock,
    .setsockopt    = ip_setsockopt,
    .getsockopt    = ip_getsockopt,
    .sendmsg       = l2tp_ip_sendmsg,
    .recvmsg       = l2tp_ip_recvmsg,
    .backlog_rcv       = l2tp_ip_backlog_recv,
    .hash          = inet_hash,
    .unhash        = inet_unhash,
    .obj_size      = sizeof(struct l2tp_ip_sock),
#ifdef CONFIG_COMPAT
    .compat_setsockopt = compat_ip_setsockopt,
    .compat_getsockopt = compat_ip_getsockopt,
#endif
};

static const struct proto_ops l2tp_ip_ops = {
    .family        = PF_INET,
    .owner         = THIS_MODULE,
    .release       = inet_release,
    .bind          = inet_bind,
    .connect       = inet_dgram_connect,
    .socketpair    = sock_no_socketpair,
    .accept        = sock_no_accept,
    .getname       = l2tp_ip_getname,
    .poll          = datagram_poll,
    .ioctl         = inet_ioctl,
    .listen        = sock_no_listen,
    .shutdown      = inet_shutdown,
    .setsockopt    = sock_common_setsockopt,
    .getsockopt    = sock_common_getsockopt,
    .sendmsg       = inet_sendmsg,
    .recvmsg       = sock_common_recvmsg,
    .mmap          = sock_no_mmap,
    .sendpage      = sock_no_sendpage,
#ifdef CONFIG_COMPAT
    .compat_setsockopt = compat_sock_common_setsockopt,
    .compat_getsockopt = compat_sock_common_getsockopt,
#endif
};

static struct inet_protosw l2tp_ip_protosw = {
    .type       = SOCK_DGRAM,
    .protocol   = IPPROTO_L2TP,
    .prot       = &l2tp_ip_prot,
    .ops        = &l2tp_ip_ops,
    .no_check   = 0,
};

static struct net_protocol l2tp_ip_protocol __read_mostly = {
    .handler    = l2tp_ip_recv,
};

static int __init l2tp_ip_init(void)
{
    int err;

    pr_info("L2TP IP encapsulation support (L2TPv3)\n");

    err = proto_register(&l2tp_ip_prot, 1);
    if (err != 0)
        goto out;

    err = inet_add_protocol(&l2tp_ip_protocol, IPPROTO_L2TP);
    if (err)
        goto out1;

    inet_register_protosw(&l2tp_ip_protosw);
    return 0;

out1:
    proto_unregister(&l2tp_ip_prot);
out:
    return err;
}

static void __exit l2tp_ip_exit(void)
{
    inet_unregister_protosw(&l2tp_ip_protosw);
    inet_del_protocol(&l2tp_ip_protocol, IPPROTO_L2TP);
    proto_unregister(&l2tp_ip_prot);
}

module_init(l2tp_ip_init);
module_exit(l2tp_ip_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("James Chapman <[email protected]>");
MODULE_DESCRIPTION("L2TP over IP");
MODULE_VERSION("1.0");

/* Use the value of SOCK_DGRAM (2) directory, because __stringify doesn't like
 * enums
 */
MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, 2, IPPROTO_L2TP);