/** -*- linux-c -*- ***********************************************************
 * Linux PPP over Ethernet (PPPoX/PPPoE) Sockets
 *
 * PPPoX --- Generic PPP encapsulation socket family
 * PPPoE --- PPP over Ethernet (RFC 2516)
 *
 *
 * Version:     0.7.0
 *
 * 070228 :     Fix to allow multiple sessions with same remote MAC and same
 *              session id by including the local device ifindex in the
 *              tuple identifying a session. This also ensures packets can't
 *              be injected into a session from interfaces other than the one
 *              specified by userspace. Florian Zumbiehl <florz@florz.de>
 *              (Oh, BTW, this one is YYMMDD, in case you were wondering ...)
 * 220102 :     Fix module use count on failure in pppoe_create, pppox_sk -acme
 * 030700 :     Fixed connect logic to allow for disconnect.
 * 270700 :     Fixed potential SMP problems; we must protect against
 *              simultaneous invocation of ppp_input
 *              and ppp_unregister_channel.
 * 040800 :     Respect reference count mechanisms on net-devices.
 * 200800 :     fix kfree(skb) in pppoe_rcv (acme)
 *              Module reference count is decremented in the right spot now,
 *              guards against sock_put not actually freeing the sk
 *              in pppoe_release.
 * 051000 :     Initialization cleanup.
 * 111100 :     Fix recvmsg.
 * 050101 :     Fix PADT procesing.
 * 140501 :     Use pppoe_rcv_core to handle all backlog. (Alexey)
 * 170701 :     Do not lock_sock with rwlock held. (DaveM)
 *              Ignore discovery frames if user has socket
 *              locked. (DaveM)
 *              Ignore return value of dev_queue_xmit in __pppoe_xmit
 *              or else we may kfree an SKB twice. (DaveM)
 * 190701 :     When doing copies of skb's in __pppoe_xmit, always delete
 *              the original skb that was passed in on success, never on
 *              failure.  Delete the copy of the skb on failure to avoid
 *              a memory leak.
 * 081001 :     Misc. cleanup (licence string, non-blocking, prevent
 *              reference of device on close).
 * 121301 :     New ppp channels interface; cannot unregister a channel
 *              from interrupts.  Thus, we mark the socket as a ZOMBIE
 *              and do the unregistration later.
 * 081002 :     seq_file support for proc stuff -acme
 * 111602 :     Merge all 2.4 fixes into 2.5/2.6 tree.  Label 2.5/2.6
 *              as version 0.7.  Spacing cleanup.
 * Author:      Michal Ostrowski <mostrows@speakeasy.net>
 * Contributors:
 *              Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 *              David S. Miller (davem@redhat.com)
 *
 * 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.
 *
 */

#include <linux/string.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/net.h>
#include <linux/inetdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/init.h>
#include <linux/if_ether.h>
#include <linux/if_pppox.h>
#include <linux/ppp_channel.h>
#include <linux/ppp_defs.h>
#include <linux/ppp-ioctl.h>
#include <linux/notifier.h>
#include <linux/file.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>

#include <linux/nsproxy.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <net/sock.h>

#include <asm/uaccess.h>

#define PPPOE_HASH_BITS 4
#define PPPOE_HASH_SIZE (1 << PPPOE_HASH_BITS)
#define PPPOE_HASH_MASK (PPPOE_HASH_SIZE - 1)

static int __pppoe_xmit(struct sock *sk, struct sk_buff *skb);

static const struct proto_ops pppoe_ops;
static const struct ppp_channel_ops pppoe_chan_ops;

/* per-net private data for this module */
static int pppoe_net_id __read_mostly;
struct pppoe_net {
        /*
         * we could use _single_ hash table for all
         * nets by injecting net id into the hash but
         * it would increase hash chains and add
         * a few additional math comparations messy
         * as well, moreover in case of SMP less locking
         * controversy here
         */
        struct pppox_sock *hash_table[PPPOE_HASH_SIZE];
        rwlock_t hash_lock;
};

/*
 * PPPoE could be in the following stages:
 * 1) Discovery stage (to obtain remote MAC and Session ID)
 * 2) Session stage (MAC and SID are known)
 *
 * Ethernet frames have a special tag for this but
 * we use simpler approach based on session id
 */
static inline bool stage_session(__be16 sid)
{
        return sid != 0;
}

static inline struct pppoe_net *pppoe_pernet(struct net *net)
{
        BUG_ON(!net);

        return net_generic(net, pppoe_net_id);
}

static inline int cmp_2_addr(struct pppoe_addr *a, struct pppoe_addr *b)
{
        return a->sid == b->sid && !memcmp(a->remote, b->remote, ETH_ALEN);
}

static inline int cmp_addr(struct pppoe_addr *a, __be16 sid, char *addr)
{
        return a->sid == sid && !memcmp(a->remote, addr, ETH_ALEN);
}

#if 8 % PPPOE_HASH_BITS
#error 8 must be a multiple of PPPOE_HASH_BITS
#endif

static int hash_item(__be16 sid, unsigned char *addr)
{
        unsigned char hash = 0;
        unsigned int i;

        for (i = 0; i < ETH_ALEN; i++)
                hash ^= addr[i];
        for (i = 0; i < sizeof(sid_t) * 8; i += 8)
                hash ^= (__force __u32)sid >> i;
        for (i = 8; (i >>= 1) >= PPPOE_HASH_BITS;)
                hash ^= hash >> i;

        return hash & PPPOE_HASH_MASK;
}

/**********************************************************************
 *
 *  Set/get/delete/rehash items  (internal versions)
 *
 **********************************************************************/
static struct pppox_sock *__get_item(struct pppoe_net *pn, __be16 sid,
                                unsigned char *addr, int ifindex)
{
        int hash = hash_item(sid, addr);
        struct pppox_sock *ret;

        ret = pn->hash_table[hash];
        while (ret) {
                if (cmp_addr(&ret->pppoe_pa, sid, addr) &&
                    ret->pppoe_ifindex == ifindex)
                        return ret;

                ret = ret->next;
        }

        return NULL;
}

static int __set_item(struct pppoe_net *pn, struct pppox_sock *po)
{
        int hash = hash_item(po->pppoe_pa.sid, po->pppoe_pa.remote);
        struct pppox_sock *ret;

        ret = pn->hash_table[hash];
        while (ret) {
                if (cmp_2_addr(&ret->pppoe_pa, &po->pppoe_pa) &&
                    ret->pppoe_ifindex == po->pppoe_ifindex)
                        return -EALREADY;

                ret = ret->next;
        }

        po->next = pn->hash_table[hash];
        pn->hash_table[hash] = po;

        return 0;
}

static void __delete_item(struct pppoe_net *pn, __be16 sid,
                                        char *addr, int ifindex)
{
        int hash = hash_item(sid, addr);
        struct pppox_sock *ret, **src;

        ret = pn->hash_table[hash];
        src = &pn->hash_table[hash];

        while (ret) {
                if (cmp_addr(&ret->pppoe_pa, sid, addr) &&
                    ret->pppoe_ifindex == ifindex) {
                        *src = ret->next;
                        break;
                }

                src = &ret->next;
                ret = ret->next;
        }
}

/**********************************************************************
 *
 *  Set/get/delete/rehash items
 *
 **********************************************************************/
static inline struct pppox_sock *get_item(struct pppoe_net *pn, __be16 sid,
                                        unsigned char *addr, int ifindex)
{
        struct pppox_sock *po;

        read_lock_bh(&pn->hash_lock);
        po = __get_item(pn, sid, addr, ifindex);
        if (po)
                sock_hold(sk_pppox(po));
        read_unlock_bh(&pn->hash_lock);

        return po;
}

static inline struct pppox_sock *get_item_by_addr(struct net *net,
                                                struct sockaddr_pppox *sp)
{
        struct net_device *dev;
        struct pppoe_net *pn;
        struct pppox_sock *pppox_sock = NULL;

        int ifindex;

        rcu_read_lock();
        dev = dev_get_by_name_rcu(net, sp->sa_addr.pppoe.dev);
        if (dev) {
                ifindex = dev->ifindex;
                pn = pppoe_pernet(net);
                pppox_sock = get_item(pn, sp->sa_addr.pppoe.sid,
                                sp->sa_addr.pppoe.remote, ifindex);
        }
        rcu_read_unlock();
        return pppox_sock;
}

static inline void delete_item(struct pppoe_net *pn, __be16 sid,
                                        char *addr, int ifindex)
{
        write_lock_bh(&pn->hash_lock);
        __delete_item(pn, sid, addr, ifindex);
        write_unlock_bh(&pn->hash_lock);
}

/***************************************************************************
 *
 *  Handler for device events.
 *  Certain device events require that sockets be unconnected.
 *
 **************************************************************************/

static void pppoe_flush_dev(struct net_device *dev)
{
        struct pppoe_net *pn;
        int i;

        pn = pppoe_pernet(dev_net(dev));
        write_lock_bh(&pn->hash_lock);
        for (i = 0; i < PPPOE_HASH_SIZE; i++) {
                struct pppox_sock *po = pn->hash_table[i];
                struct sock *sk;

                while (po) {
                        while (po && po->pppoe_dev != dev) {
                                po = po->next;
                        }

                        if (!po)
                                break;

                        sk = sk_pppox(po);

                        /* We always grab the socket lock, followed by the
                         * hash_lock, in that order.  Since we should hold the
                         * sock lock while doing any unbinding, we need to
                         * release the lock we're holding.  Hold a reference to
                         * the sock so it doesn't disappear as we're jumping
                         * between locks.
                         */

                        sock_hold(sk);
                        write_unlock_bh(&pn->hash_lock);
                        lock_sock(sk);

                        if (po->pppoe_dev == dev &&
                            sk->sk_state & (PPPOX_CONNECTED | PPPOX_BOUND | PPPOX_ZOMBIE)) {
                                pppox_unbind_sock(sk);
                                sk->sk_state = PPPOX_ZOMBIE;
                                sk->sk_state_change(sk);
                                po->pppoe_dev = NULL;
                                dev_put(dev);
                        }

                        release_sock(sk);
                        sock_put(sk);

                        /* Restart the process from the start of the current
                         * hash chain. We dropped locks so the world may have
                         * change from underneath us.
                         */

                        BUG_ON(pppoe_pernet(dev_net(dev)) == NULL);
                        write_lock_bh(&pn->hash_lock);
                        po = pn->hash_table[i];
                }
        }
        write_unlock_bh(&pn->hash_lock);
}

static int pppoe_device_event(struct notifier_block *this,
                              unsigned long event, void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);

        /* Only look at sockets that are using this specific device. */
        switch (event) {
        case NETDEV_CHANGEADDR:
        case NETDEV_CHANGEMTU:
                /* A change in mtu or address is a bad thing, requiring
                 * LCP re-negotiation.
                 */

        case NETDEV_GOING_DOWN:
        case NETDEV_DOWN:
                /* Find every socket on this device and kill it. */
                pppoe_flush_dev(dev);
                break;

        default:
                break;
        }

        return NOTIFY_DONE;
}

static struct notifier_block pppoe_notifier = {
        .notifier_call = pppoe_device_event,
};

/************************************************************************
 *
 * Do the real work of receiving a PPPoE Session frame.
 *
 ***********************************************************************/
static int pppoe_rcv_core(struct sock *sk, struct sk_buff *skb)
{
        struct pppox_sock *po = pppox_sk(sk);
        struct pppox_sock *relay_po;

        /* Backlog receive. Semantics of backlog rcv preclude any code from
         * executing in lock_sock()/release_sock() bounds; meaning sk->sk_state
         * can't change.
         */

        if (sk->sk_state & PPPOX_BOUND) {
                ppp_input(&po->chan, skb);
        } else if (sk->sk_state & PPPOX_RELAY) {
                relay_po = get_item_by_addr(sock_net(sk),
                                            &po->pppoe_relay);
                if (relay_po == NULL)
                        goto abort_kfree;

                if ((sk_pppox(relay_po)->sk_state & PPPOX_CONNECTED) == 0)
                        goto abort_put;

                if (!__pppoe_xmit(sk_pppox(relay_po), skb))
                        goto abort_put;
        } else {
                if (sock_queue_rcv_skb(sk, skb))
                        goto abort_kfree;
        }

        return NET_RX_SUCCESS;

abort_put:
        sock_put(sk_pppox(relay_po));

abort_kfree:
        kfree_skb(skb);
        return NET_RX_DROP;
}

/************************************************************************
 *
 * Receive wrapper called in BH context.
 *
 ***********************************************************************/
static int pppoe_rcv(struct sk_buff *skb, struct net_device *dev,
                     struct packet_type *pt, struct net_device *orig_dev)
{
        struct pppoe_hdr *ph;
        struct pppox_sock *po;
        struct pppoe_net *pn;
        int len;

        skb = skb_share_check(skb, GFP_ATOMIC);
        if (!skb)
                goto out;

        if (!pskb_may_pull(skb, sizeof(struct pppoe_hdr)))
                goto drop;

        ph = pppoe_hdr(skb);
        len = ntohs(ph->length);

        skb_pull_rcsum(skb, sizeof(*ph));
        if (skb->len < len)
                goto drop;

        if (pskb_trim_rcsum(skb, len))
                goto drop;

        pn = pppoe_pernet(dev_net(dev));

        /* Note that get_item does a sock_hold(), so sk_pppox(po)
         * is known to be safe.
         */
        po = get_item(pn, ph->sid, eth_hdr(skb)->h_source, dev->ifindex);
        if (!po)
                goto drop;

        return sk_receive_skb(sk_pppox(po), skb, 0);

drop:
        kfree_skb(skb);
out:
        return NET_RX_DROP;
}

/************************************************************************
 *
 * Receive a PPPoE Discovery frame.
 * This is solely for detection of PADT frames
 *
 ***********************************************************************/
static int pppoe_disc_rcv(struct sk_buff *skb, struct net_device *dev,
                          struct packet_type *pt, struct net_device *orig_dev)

{
        struct pppoe_hdr *ph;
        struct pppox_sock *po;
        struct pppoe_net *pn;

        skb = skb_share_check(skb, GFP_ATOMIC);
        if (!skb)
                goto out;

        if (!pskb_may_pull(skb, sizeof(struct pppoe_hdr)))
                goto abort;

        ph = pppoe_hdr(skb);
        if (ph->code != PADT_CODE)
                goto abort;

        pn = pppoe_pernet(dev_net(dev));
        po = get_item(pn, ph->sid, eth_hdr(skb)->h_source, dev->ifindex);
        if (po) {
                struct sock *sk = sk_pppox(po);

                bh_lock_sock(sk);

                /* If the user has locked the socket, just ignore
                 * the packet.  With the way two rcv protocols hook into
                 * one socket family type, we cannot (easily) distinguish
                 * what kind of SKB it is during backlog rcv.
                 */
                if (sock_owned_by_user(sk) == 0) {
                        /* We're no longer connect at the PPPOE layer,
                         * and must wait for ppp channel to disconnect us.
                         */
                        sk->sk_state = PPPOX_ZOMBIE;
                }

                bh_unlock_sock(sk);
                sock_put(sk);
        }

abort:
        kfree_skb(skb);
out:
        return NET_RX_SUCCESS; /* Lies... :-) */
}

static struct packet_type pppoes_ptype __read_mostly = {
        .type   = cpu_to_be16(ETH_P_PPP_SES),
        .func   = pppoe_rcv,
};

static struct packet_type pppoed_ptype __read_mostly = {
        .type   = cpu_to_be16(ETH_P_PPP_DISC),
        .func   = pppoe_disc_rcv,
};

static struct proto pppoe_sk_proto __read_mostly = {
        .name     = "PPPOE",
        .owner    = THIS_MODULE,
        .obj_size = sizeof(struct pppox_sock),
};

/***********************************************************************
 *
 * Initialize a new struct sock.
 *
 **********************************************************************/
static int pppoe_create(struct net *net, struct socket *sock)
{
        struct sock *sk;

        sk = sk_alloc(net, PF_PPPOX, GFP_KERNEL, &pppoe_sk_proto);
        if (!sk)
                return -ENOMEM;

        sock_init_data(sock, sk);

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

        sk->sk_backlog_rcv      = pppoe_rcv_core;
        sk->sk_state            = PPPOX_NONE;
        sk->sk_type             = SOCK_STREAM;
        sk->sk_family           = PF_PPPOX;
        sk->sk_protocol         = PX_PROTO_OE;

        return 0;
}

static int pppoe_release(struct socket *sock)
{
        struct sock *sk = sock->sk;
        struct pppox_sock *po;
        struct pppoe_net *pn;
        struct net *net = NULL;

        if (!sk)
                return 0;

        lock_sock(sk);
        if (sock_flag(sk, SOCK_DEAD)) {
                release_sock(sk);
                return -EBADF;
        }

        po = pppox_sk(sk);

        if (sk->sk_state & (PPPOX_CONNECTED | PPPOX_BOUND | PPPOX_ZOMBIE)) {
                dev_put(po->pppoe_dev);
                po->pppoe_dev = NULL;
        }

        pppox_unbind_sock(sk);

        /* Signal the death of the socket. */
        sk->sk_state = PPPOX_DEAD;

        net = sock_net(sk);
        pn = pppoe_pernet(net);

        /*
         * protect "po" from concurrent updates
         * on pppoe_flush_dev
         */
        delete_item(pn, po->pppoe_pa.sid, po->pppoe_pa.remote,
                    po->pppoe_ifindex);

        sock_orphan(sk);
        sock->sk = NULL;

        skb_queue_purge(&sk->sk_receive_queue);
        release_sock(sk);
        sock_put(sk);

        return 0;
}

static int pppoe_connect(struct socket *sock, struct sockaddr *uservaddr,
                  int sockaddr_len, int flags)
{
        struct sock *sk = sock->sk;
        struct sockaddr_pppox *sp = (struct sockaddr_pppox *)uservaddr;
        struct pppox_sock *po = pppox_sk(sk);
        struct net_device *dev = NULL;
        struct pppoe_net *pn;
        struct net *net = NULL;
        int error;

        lock_sock(sk);

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

        /* Check for already bound sockets */
        error = -EBUSY;
        if ((sk->sk_state & PPPOX_CONNECTED) &&
             stage_session(sp->sa_addr.pppoe.sid))
                goto end;

        /* Check for already disconnected sockets, on attempts to disconnect */
        error = -EALREADY;
        if ((sk->sk_state & PPPOX_DEAD) &&
             !stage_session(sp->sa_addr.pppoe.sid))
                goto end;

        error = 0;

        /* Delete the old binding */
        if (stage_session(po->pppoe_pa.sid)) {
                pppox_unbind_sock(sk);
                pn = pppoe_pernet(sock_net(sk));
                delete_item(pn, po->pppoe_pa.sid,
                            po->pppoe_pa.remote, po->pppoe_ifindex);
                if (po->pppoe_dev) {
                        dev_put(po->pppoe_dev);
                        po->pppoe_dev = NULL;
                }

                memset(sk_pppox(po) + 1, 0,
                       sizeof(struct pppox_sock) - sizeof(struct sock));
                sk->sk_state = PPPOX_NONE;
        }

        /* Re-bind in session stage only */
        if (stage_session(sp->sa_addr.pppoe.sid)) {
                error = -ENODEV;
                net = sock_net(sk);
                dev = dev_get_by_name(net, sp->sa_addr.pppoe.dev);
                if (!dev)
                        goto err_put;

                po->pppoe_dev = dev;
                po->pppoe_ifindex = dev->ifindex;
                pn = pppoe_pernet(net);
                if (!(dev->flags & IFF_UP)) {
                        goto err_put;
                }

                memcpy(&po->pppoe_pa,
                       &sp->sa_addr.pppoe,
                       sizeof(struct pppoe_addr));

                write_lock_bh(&pn->hash_lock);
                error = __set_item(pn, po);
                write_unlock_bh(&pn->hash_lock);
                if (error < 0)
                        goto err_put;

                po->chan.hdrlen = (sizeof(struct pppoe_hdr) +
                                   dev->hard_header_len);

                po->chan.mtu = dev->mtu - sizeof(struct pppoe_hdr);
                po->chan.private = sk;
                po->chan.ops = &pppoe_chan_ops;

                error = ppp_register_net_channel(dev_net(dev), &po->chan);
                if (error) {
                        delete_item(pn, po->pppoe_pa.sid,
                                    po->pppoe_pa.remote, po->pppoe_ifindex);
                        goto err_put;
                }

                sk->sk_state = PPPOX_CONNECTED;
        }

        po->num = sp->sa_addr.pppoe.sid;

end:
        release_sock(sk);
        return error;
err_put:
        if (po->pppoe_dev) {
                dev_put(po->pppoe_dev);
                po->pppoe_dev = NULL;
        }
        goto end;
}

static int pppoe_getname(struct socket *sock, struct sockaddr *uaddr,
                  int *usockaddr_len, int peer)
{
        int len = sizeof(struct sockaddr_pppox);
        struct sockaddr_pppox sp;

        sp.sa_family    = AF_PPPOX;
        sp.sa_protocol  = PX_PROTO_OE;
        memcpy(&sp.sa_addr.pppoe, &pppox_sk(sock->sk)->pppoe_pa,
               sizeof(struct pppoe_addr));

        memcpy(uaddr, &sp, len);

        *usockaddr_len = len;

        return 0;
}

static int pppoe_ioctl(struct socket *sock, unsigned int cmd,
                unsigned long arg)
{
        struct sock *sk = sock->sk;
        struct pppox_sock *po = pppox_sk(sk);
        int val;
        int err;

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

                err = -EFAULT;
                if (put_user(po->pppoe_dev->mtu -
                             sizeof(struct pppoe_hdr) -
                             PPP_HDRLEN,
                             (int __user *)arg))
                        break;
                err = 0;
                break;

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

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

                if (val < (po->pppoe_dev->mtu
                           - sizeof(struct pppoe_hdr)
                           - PPP_HDRLEN))
                        err = 0;
                else
                        err = -EINVAL;
                break;

        case PPPIOCSFLAGS:
                err = -EFAULT;
                if (get_user(val, (int __user *)arg))
                        break;
                err = 0;
                break;

        case PPPOEIOCSFWD:
        {
                struct pppox_sock *relay_po;

                err = -EBUSY;
                if (sk->sk_state & (PPPOX_BOUND | PPPOX_ZOMBIE | PPPOX_DEAD))
                        break;

                err = -ENOTCONN;
                if (!(sk->sk_state & PPPOX_CONNECTED))
                        break;

                /* PPPoE address from the user specifies an outbound
                   PPPoE address which frames are forwarded to */
                err = -EFAULT;
                if (copy_from_user(&po->pppoe_relay,
                                   (void __user *)arg,
                                   sizeof(struct sockaddr_pppox)))
                        break;

                err = -EINVAL;
                if (po->pppoe_relay.sa_family != AF_PPPOX ||
                    po->pppoe_relay.sa_protocol != PX_PROTO_OE)
                        break;

                /* Check that the socket referenced by the address
                   actually exists. */
                relay_po = get_item_by_addr(sock_net(sk), &po->pppoe_relay);
                if (!relay_po)
                        break;

                sock_put(sk_pppox(relay_po));
                sk->sk_state |= PPPOX_RELAY;
                err = 0;
                break;
        }

        case PPPOEIOCDFWD:
                err = -EALREADY;
                if (!(sk->sk_state & PPPOX_RELAY))
                        break;

                sk->sk_state &= ~PPPOX_RELAY;
                err = 0;
                break;

        default:
                err = -ENOTTY;
        }

        return err;
}

static int pppoe_sendmsg(struct kiocb *iocb, struct socket *sock,
                  struct msghdr *m, size_t total_len)
{
        struct sk_buff *skb;
        struct sock *sk = sock->sk;
        struct pppox_sock *po = pppox_sk(sk);
        int error;
        struct pppoe_hdr hdr;
        struct pppoe_hdr *ph;
        struct net_device *dev;
        char *start;

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

        hdr.ver = 1;
        hdr.type = 1;
        hdr.code = 0;
        hdr.sid = po->num;

        dev = po->pppoe_dev;

        error = -EMSGSIZE;
        if (total_len > (dev->mtu + dev->hard_header_len))
                goto end;


        skb = sock_wmalloc(sk, total_len + dev->hard_header_len + 32,
                           0, GFP_KERNEL);
        if (!skb) {
                error = -ENOMEM;
                goto end;
        }

        /* Reserve space for headers. */
        skb_reserve(skb, dev->hard_header_len);
        skb_reset_network_header(skb);

        skb->dev = dev;

        skb->priority = sk->sk_priority;
        skb->protocol = cpu_to_be16(ETH_P_PPP_SES);

        ph = (struct pppoe_hdr *)skb_put(skb, total_len + sizeof(struct pppoe_hdr));
        start = (char *)&ph->tag[0];

        error = memcpy_fromiovec(start, m->msg_iov, total_len);
        if (error < 0) {
                kfree_skb(skb);
                goto end;
        }

        error = total_len;
        dev_hard_header(skb, dev, ETH_P_PPP_SES,
                        po->pppoe_pa.remote, NULL, total_len);

        memcpy(ph, &hdr, sizeof(struct pppoe_hdr));

        ph->length = htons(total_len);

        dev_queue_xmit(skb);

end:
        release_sock(sk);
        return error;
}

/************************************************************************
 *
 * xmit function for internal use.
 *
 ***********************************************************************/
static int __pppoe_xmit(struct sock *sk, struct sk_buff *skb)
{
        struct pppox_sock *po = pppox_sk(sk);
        struct net_device *dev = po->pppoe_dev;
        struct pppoe_hdr *ph;
        int data_len = skb->len;

        /* The higher-level PPP code (ppp_unregister_channel()) ensures the PPP
         * xmit operations conclude prior to an unregistration call.  Thus
         * sk->sk_state cannot change, so we don't need to do lock_sock().
         * But, we also can't do a lock_sock since that introduces a potential
         * deadlock as we'd reverse the lock ordering used when calling
         * ppp_unregister_channel().
         */

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

        if (!dev)
                goto abort;

        /* Copy the data if there is no space for the header or if it's
         * read-only.
         */
        if (skb_cow_head(skb, sizeof(*ph) + dev->hard_header_len))
                goto abort;

        __skb_push(skb, sizeof(*ph));
        skb_reset_network_header(skb);

        ph = pppoe_hdr(skb);
        ph->ver = 1;
        ph->type = 1;
        ph->code = 0;
        ph->sid = po->num;
        ph->length = htons(data_len);

        skb->protocol = cpu_to_be16(ETH_P_PPP_SES);
        skb->dev = dev;

        dev_hard_header(skb, dev, ETH_P_PPP_SES,
                        po->pppoe_pa.remote, NULL, data_len);

        dev_queue_xmit(skb);
        return 1;

abort:
        kfree_skb(skb);
        return 1;
}

/************************************************************************
 *
 * xmit function called by generic PPP driver
 * sends PPP frame over PPPoE socket
 *
 ***********************************************************************/
static int pppoe_xmit(struct ppp_channel *chan, struct sk_buff *skb)
{
        struct sock *sk = (struct sock *)chan->private;
        return __pppoe_xmit(sk, skb);
}

static const struct ppp_channel_ops pppoe_chan_ops = {
        .start_xmit = pppoe_xmit,
};

static int pppoe_recvmsg(struct kiocb *iocb, struct socket *sock,
                  struct msghdr *m, size_t total_len, int flags)
{
        struct sock *sk = sock->sk;
        struct sk_buff *skb;
        int error = 0;

        if (sk->sk_state & PPPOX_BOUND) {
                error = -EIO;
                goto end;
        }

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

        m->msg_namelen = 0;

        if (skb) {
                total_len = min_t(size_t, total_len, skb->len);
                error = skb_copy_datagram_iovec(skb, 0, m->msg_iov, total_len);
                if (error == 0) {
                        consume_skb(skb);
                        return total_len;
                }
        }

        kfree_skb(skb);
end:
        return error;
}

#ifdef CONFIG_PROC_FS
static int pppoe_seq_show(struct seq_file *seq, void *v)
{

        struct pppox_sock *po;
        char *dev_name;

        if (v == SEQ_START_TOKEN) {
                seq_puts(seq, "Id       Address              Device\n");
                goto out;
        }

        po = v;
        dev_name = po->pppoe_pa.dev;

        seq_printf(seq, "%08X %pM %8s\n",
                po->pppoe_pa.sid, po->pppoe_pa.remote, dev_name);
out:
        return 0;
}

static inline struct pppox_sock *pppoe_get_idx(struct pppoe_net *pn, loff_t pos)
{
        struct pppox_sock *po;
        int i;

        for (i = 0; i < PPPOE_HASH_SIZE; i++) {
                po = pn->hash_table[i];
                while (po) {
                        if (!pos--)
                                goto out;
                        po = po->next;
                }
        }

out:
        return po;
}

static void *pppoe_seq_start(struct seq_file *seq, loff_t *pos)
        __acquires(pn->hash_lock)
{
        struct pppoe_net *pn = pppoe_pernet(seq_file_net(seq));
        loff_t l = *pos;

        read_lock_bh(&pn->hash_lock);
        return l ? pppoe_get_idx(pn, --l) : SEQ_START_TOKEN;
}

static void *pppoe_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct pppoe_net *pn = pppoe_pernet(seq_file_net(seq));
        struct pppox_sock *po;

        ++*pos;
        if (v == SEQ_START_TOKEN) {
                po = pppoe_get_idx(pn, 0);
                goto out;
        }
        po = v;
        if (po->next)
                po = po->next;
        else {
                int hash = hash_item(po->pppoe_pa.sid, po->pppoe_pa.remote);

                po = NULL;
                while (++hash < PPPOE_HASH_SIZE) {
                        po = pn->hash_table[hash];
                        if (po)
                                break;
                }
        }

out:
        return po;
}

static void pppoe_seq_stop(struct seq_file *seq, void *v)
        __releases(pn->hash_lock)
{
        struct pppoe_net *pn = pppoe_pernet(seq_file_net(seq));
        read_unlock_bh(&pn->hash_lock);
}

static const struct seq_operations pppoe_seq_ops = {
        .start          = pppoe_seq_start,
        .next           = pppoe_seq_next,
        .stop           = pppoe_seq_stop,
        .show           = pppoe_seq_show,
};

static int pppoe_seq_open(struct inode *inode, struct file *file)
{
        return seq_open_net(inode, file, &pppoe_seq_ops,
                        sizeof(struct seq_net_private));
}

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

#endif /* CONFIG_PROC_FS */

static const struct proto_ops pppoe_ops = {
        .family         = AF_PPPOX,
        .owner          = THIS_MODULE,
        .release        = pppoe_release,
        .bind           = sock_no_bind,
        .connect        = pppoe_connect,
        .socketpair     = sock_no_socketpair,
        .accept         = sock_no_accept,
        .getname        = pppoe_getname,
        .poll           = datagram_poll,
        .listen         = sock_no_listen,
        .shutdown       = sock_no_shutdown,
        .setsockopt     = sock_no_setsockopt,
        .getsockopt     = sock_no_getsockopt,
        .sendmsg        = pppoe_sendmsg,
        .recvmsg        = pppoe_recvmsg,
        .mmap           = sock_no_mmap,
        .ioctl          = pppox_ioctl,
};

static const struct pppox_proto pppoe_proto = {
        .create = pppoe_create,
        .ioctl  = pppoe_ioctl,
        .owner  = THIS_MODULE,
};

static __net_init int pppoe_init_net(struct net *net)
{
        struct pppoe_net *pn = pppoe_pernet(net);
        struct proc_dir_entry *pde;

        rwlock_init(&pn->hash_lock);

        pde = proc_create("pppoe", S_IRUGO, net->proc_net, &pppoe_seq_fops);
#ifdef CONFIG_PROC_FS
        if (!pde)
                return -ENOMEM;
#endif

        return 0;
}

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

static struct pernet_operations pppoe_net_ops = {
        .init = pppoe_init_net,
        .exit = pppoe_exit_net,
        .id   = &pppoe_net_id,
        .size = sizeof(struct pppoe_net),
};

static int __init pppoe_init(void)
{
        int err;

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

        err = proto_register(&pppoe_sk_proto, 0);
        if (err)
                goto out_unregister_net_ops;

        err = register_pppox_proto(PX_PROTO_OE, &pppoe_proto);
        if (err)
                goto out_unregister_pppoe_proto;

        dev_add_pack(&pppoes_ptype);
        dev_add_pack(&pppoed_ptype);
        register_netdevice_notifier(&pppoe_notifier);

        return 0;

out_unregister_pppoe_proto:
        proto_unregister(&pppoe_sk_proto);
out_unregister_net_ops:
        unregister_pernet_device(&pppoe_net_ops);
out:
        return err;
}

static void __exit pppoe_exit(void)
{
        unregister_netdevice_notifier(&pppoe_notifier);
        dev_remove_pack(&pppoed_ptype);
        dev_remove_pack(&pppoes_ptype);
        unregister_pppox_proto(PX_PROTO_OE);
        proto_unregister(&pppoe_sk_proto);
        unregister_pernet_device(&pppoe_net_ops);
}

module_init(pppoe_init);
module_exit(pppoe_exit);

MODULE_AUTHOR("Michal Ostrowski <mostrows@speakeasy.net>");
MODULE_DESCRIPTION("PPP over Ethernet driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_NETPROTO(PF_PPPOX);