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af_netlink.c

/*
 * NETLINK      Kernel-user communication protocol.
 *
 *          Authors:    Alan Cox <alan@redhat.com>
 *                      Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
 *
 *          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.
 *
 * Tue Jun 26 14:36:48 MEST 2001 Herbert "herp" Rosmanith
 *                               added netlink_proto_exit
 * Tue Jan 22 18:32:44 BRST 2002 Arnaldo C. de Melo <acme@conectiva.com.br>
 *                       use nlk_sk, as sk->protinfo is on a diet 8)
 * Fri Jul 22 19:51:12 MEST 2005 Harald Welte <laforge@gnumonks.org>
 *                       - inc module use count of module that owns
 *                         the kernel socket in case userspace opens
 *                         socket of same protocol
 *                       - remove all module support, since netlink is
 *                         mandatory if CONFIG_NET=y these days
 */

#include <linux/module.h>

#include <linux/capability.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/socket.h>
#include <linux/un.h>
#include <linux/fcntl.h>
#include <linux/termios.h>
#include <linux/sockios.h>
#include <linux/net.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <asm/uaccess.h>
#include <linux/skbuff.h>
#include <linux/netdevice.h>
#include <linux/rtnetlink.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/notifier.h>
#include <linux/security.h>
#include <linux/jhash.h>
#include <linux/jiffies.h>
#include <linux/random.h>
#include <linux/bitops.h>
#include <linux/mm.h>
#include <linux/types.h>
#include <linux/audit.h>
#include <linux/selinux.h>
#include <linux/mutex.h>

#include <net/net_namespace.h>
#include <net/sock.h>
#include <net/scm.h>
#include <net/netlink.h>

#define NLGRPSZ(x)      (ALIGN(x, sizeof(unsigned long) * 8) / 8)
#define NLGRPLONGS(x)   (NLGRPSZ(x)/sizeof(unsigned long))

struct netlink_sock {
      /* struct sock has to be the first member of netlink_sock */
      struct sock       sk;
      u32               pid;
      u32               dst_pid;
      u32               dst_group;
      u32               flags;
      u32               subscriptions;
      u32               ngroups;
      unsigned long           *groups;
      unsigned long           state;
      wait_queue_head_t wait;
      struct netlink_callback *cb;
      struct mutex            *cb_mutex;
      struct mutex            cb_def_mutex;
      void              (*netlink_rcv)(struct sk_buff *skb);
      struct module           *module;
};

#define NETLINK_KERNEL_SOCKET 0x1
#define NETLINK_RECV_PKTINFO  0x2

static inline struct netlink_sock *nlk_sk(struct sock *sk)
{
      return container_of(sk, struct netlink_sock, sk);
}

static inline int netlink_is_kernel(struct sock *sk)
{
      return nlk_sk(sk)->flags & NETLINK_KERNEL_SOCKET;
}

struct nl_pid_hash {
      struct hlist_head *table;
      unsigned long rehash_time;

      unsigned int mask;
      unsigned int shift;

      unsigned int entries;
      unsigned int max_shift;

      u32 rnd;
};

struct netlink_table {
      struct nl_pid_hash hash;
      struct hlist_head mc_list;
      unsigned long *listeners;
      unsigned int nl_nonroot;
      unsigned int groups;
      struct mutex *cb_mutex;
      struct module *module;
      int registered;
};

static struct netlink_table *nl_table;

static DECLARE_WAIT_QUEUE_HEAD(nl_table_wait);

static int netlink_dump(struct sock *sk);
static void netlink_destroy_callback(struct netlink_callback *cb);

static DEFINE_RWLOCK(nl_table_lock);
static atomic_t nl_table_users = ATOMIC_INIT(0);

static ATOMIC_NOTIFIER_HEAD(netlink_chain);

static u32 netlink_group_mask(u32 group)
{
      return group ? 1 << (group - 1) : 0;
}

static struct hlist_head *nl_pid_hashfn(struct nl_pid_hash *hash, u32 pid)
{
      return &hash->table[jhash_1word(pid, hash->rnd) & hash->mask];
}

static void netlink_sock_destruct(struct sock *sk)
{
      struct netlink_sock *nlk = nlk_sk(sk);

      if (nlk->cb) {
            if (nlk->cb->done)
                  nlk->cb->done(nlk->cb);
            netlink_destroy_callback(nlk->cb);
      }

      skb_queue_purge(&sk->sk_receive_queue);

      if (!sock_flag(sk, SOCK_DEAD)) {
            printk("Freeing alive netlink socket %p\n", sk);
            return;
      }
      BUG_TRAP(!atomic_read(&sk->sk_rmem_alloc));
      BUG_TRAP(!atomic_read(&sk->sk_wmem_alloc));
      BUG_TRAP(!nlk_sk(sk)->groups);
}

/* This lock without WQ_FLAG_EXCLUSIVE is good on UP and it is _very_ bad on SMP.
 * Look, when several writers sleep and reader wakes them up, all but one
 * immediately hit write lock and grab all the cpus. Exclusive sleep solves
 * this, _but_ remember, it adds useless work on UP machines.
 */

static void netlink_table_grab(void)
{
      write_lock_irq(&nl_table_lock);

      if (atomic_read(&nl_table_users)) {
            DECLARE_WAITQUEUE(wait, current);

            add_wait_queue_exclusive(&nl_table_wait, &wait);
            for(;;) {
                  set_current_state(TASK_UNINTERRUPTIBLE);
                  if (atomic_read(&nl_table_users) == 0)
                        break;
                  write_unlock_irq(&nl_table_lock);
                  schedule();
                  write_lock_irq(&nl_table_lock);
            }

            __set_current_state(TASK_RUNNING);
            remove_wait_queue(&nl_table_wait, &wait);
      }
}

static __inline__ void netlink_table_ungrab(void)
{
      write_unlock_irq(&nl_table_lock);
      wake_up(&nl_table_wait);
}

static __inline__ void
netlink_lock_table(void)
{
      /* read_lock() synchronizes us to netlink_table_grab */

      read_lock(&nl_table_lock);
      atomic_inc(&nl_table_users);
      read_unlock(&nl_table_lock);
}

static __inline__ void
netlink_unlock_table(void)
{
      if (atomic_dec_and_test(&nl_table_users))
            wake_up(&nl_table_wait);
}

static __inline__ struct sock *netlink_lookup(struct net *net, int protocol, u32 pid)
{
      struct nl_pid_hash *hash = &nl_table[protocol].hash;
      struct hlist_head *head;
      struct sock *sk;
      struct hlist_node *node;

      read_lock(&nl_table_lock);
      head = nl_pid_hashfn(hash, pid);
      sk_for_each(sk, node, head) {
            if ((sk->sk_net == net) && (nlk_sk(sk)->pid == pid)) {
                  sock_hold(sk);
                  goto found;
            }
      }
      sk = NULL;
found:
      read_unlock(&nl_table_lock);
      return sk;
}

static inline struct hlist_head *nl_pid_hash_alloc(size_t size)
{
      if (size <= PAGE_SIZE)
            return kmalloc(size, GFP_ATOMIC);
      else
            return (struct hlist_head *)
                  __get_free_pages(GFP_ATOMIC, get_order(size));
}

static inline void nl_pid_hash_free(struct hlist_head *table, size_t size)
{
      if (size <= PAGE_SIZE)
            kfree(table);
      else
            free_pages((unsigned long)table, get_order(size));
}

static int nl_pid_hash_rehash(struct nl_pid_hash *hash, int grow)
{
      unsigned int omask, mask, shift;
      size_t osize, size;
      struct hlist_head *otable, *table;
      int i;

      omask = mask = hash->mask;
      osize = size = (mask + 1) * sizeof(*table);
      shift = hash->shift;

      if (grow) {
            if (++shift > hash->max_shift)
                  return 0;
            mask = mask * 2 + 1;
            size *= 2;
      }

      table = nl_pid_hash_alloc(size);
      if (!table)
            return 0;

      memset(table, 0, size);
      otable = hash->table;
      hash->table = table;
      hash->mask = mask;
      hash->shift = shift;
      get_random_bytes(&hash->rnd, sizeof(hash->rnd));

      for (i = 0; i <= omask; i++) {
            struct sock *sk;
            struct hlist_node *node, *tmp;

            sk_for_each_safe(sk, node, tmp, &otable[i])
                  __sk_add_node(sk, nl_pid_hashfn(hash, nlk_sk(sk)->pid));
      }

      nl_pid_hash_free(otable, osize);
      hash->rehash_time = jiffies + 10 * 60 * HZ;
      return 1;
}

static inline int nl_pid_hash_dilute(struct nl_pid_hash *hash, int len)
{
      int avg = hash->entries >> hash->shift;

      if (unlikely(avg > 1) && nl_pid_hash_rehash(hash, 1))
            return 1;

      if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
            nl_pid_hash_rehash(hash, 0);
            return 1;
      }

      return 0;
}

static const struct proto_ops netlink_ops;

static void
netlink_update_listeners(struct sock *sk)
{
      struct netlink_table *tbl = &nl_table[sk->sk_protocol];
      struct hlist_node *node;
      unsigned long mask;
      unsigned int i;

      for (i = 0; i < NLGRPLONGS(tbl->groups); i++) {
            mask = 0;
            sk_for_each_bound(sk, node, &tbl->mc_list) {
                  if (i < NLGRPLONGS(nlk_sk(sk)->ngroups))
                        mask |= nlk_sk(sk)->groups[i];
            }
            tbl->listeners[i] = mask;
      }
      /* this function is only called with the netlink table "grabbed", which
       * makes sure updates are visible before bind or setsockopt return. */
}

static int netlink_insert(struct sock *sk, struct net *net, u32 pid)
{
      struct nl_pid_hash *hash = &nl_table[sk->sk_protocol].hash;
      struct hlist_head *head;
      int err = -EADDRINUSE;
      struct sock *osk;
      struct hlist_node *node;
      int len;

      netlink_table_grab();
      head = nl_pid_hashfn(hash, pid);
      len = 0;
      sk_for_each(osk, node, head) {
            if ((osk->sk_net == net) && (nlk_sk(osk)->pid == pid))
                  break;
            len++;
      }
      if (node)
            goto err;

      err = -EBUSY;
      if (nlk_sk(sk)->pid)
            goto err;

      err = -ENOMEM;
      if (BITS_PER_LONG > 32 && unlikely(hash->entries >= UINT_MAX))
            goto err;

      if (len && nl_pid_hash_dilute(hash, len))
            head = nl_pid_hashfn(hash, pid);
      hash->entries++;
      nlk_sk(sk)->pid = pid;
      sk_add_node(sk, head);
      err = 0;

err:
      netlink_table_ungrab();
      return err;
}

static void netlink_remove(struct sock *sk)
{
      netlink_table_grab();
      if (sk_del_node_init(sk))
            nl_table[sk->sk_protocol].hash.entries--;
      if (nlk_sk(sk)->subscriptions)
            __sk_del_bind_node(sk);
      netlink_table_ungrab();
}

static struct proto netlink_proto = {
      .name   = "NETLINK",
      .owner        = THIS_MODULE,
      .obj_size = sizeof(struct netlink_sock),
};

static int __netlink_create(struct net *net, struct socket *sock,
                      struct mutex *cb_mutex, int protocol)
{
      struct sock *sk;
      struct netlink_sock *nlk;

      sock->ops = &netlink_ops;

      sk = sk_alloc(net, PF_NETLINK, GFP_KERNEL, &netlink_proto);
      if (!sk)
            return -ENOMEM;

      sock_init_data(sock, sk);

      nlk = nlk_sk(sk);
      if (cb_mutex)
            nlk->cb_mutex = cb_mutex;
      else {
            nlk->cb_mutex = &nlk->cb_def_mutex;
            mutex_init(nlk->cb_mutex);
      }
      init_waitqueue_head(&nlk->wait);

      sk->sk_destruct = netlink_sock_destruct;
      sk->sk_protocol = protocol;
      return 0;
}

static int netlink_create(struct net *net, struct socket *sock, int protocol)
{
      struct module *module = NULL;
      struct mutex *cb_mutex;
      struct netlink_sock *nlk;
      int err = 0;

      sock->state = SS_UNCONNECTED;

      if (sock->type != SOCK_RAW && sock->type != SOCK_DGRAM)
            return -ESOCKTNOSUPPORT;

      if (protocol<0 || protocol >= MAX_LINKS)
            return -EPROTONOSUPPORT;

      netlink_lock_table();
#ifdef CONFIG_KMOD
      if (!nl_table[protocol].registered) {
            netlink_unlock_table();
            request_module("net-pf-%d-proto-%d", PF_NETLINK, protocol);
            netlink_lock_table();
      }
#endif
      if (nl_table[protocol].registered &&
          try_module_get(nl_table[protocol].module))
            module = nl_table[protocol].module;
      cb_mutex = nl_table[protocol].cb_mutex;
      netlink_unlock_table();

      if ((err = __netlink_create(net, sock, cb_mutex, protocol)) < 0)
            goto out_module;

      nlk = nlk_sk(sock->sk);
      nlk->module = module;
out:
      return err;

out_module:
      module_put(module);
      goto out;
}

static int netlink_release(struct socket *sock)
{
      struct sock *sk = sock->sk;
      struct netlink_sock *nlk;

      if (!sk)
            return 0;

      netlink_remove(sk);
      sock_orphan(sk);
      nlk = nlk_sk(sk);

      /*
       * OK. Socket is unlinked, any packets that arrive now
       * will be purged.
       */

      sock->sk = NULL;
      wake_up_interruptible_all(&nlk->wait);

      skb_queue_purge(&sk->sk_write_queue);

      if (nlk->pid && !nlk->subscriptions) {
            struct netlink_notify n = {
                                    .net = sk->sk_net,
                                    .protocol = sk->sk_protocol,
                                    .pid = nlk->pid,
                                };
            atomic_notifier_call_chain(&netlink_chain,
                        NETLINK_URELEASE, &n);
      }

      module_put(nlk->module);

      netlink_table_grab();
      if (netlink_is_kernel(sk)) {
            kfree(nl_table[sk->sk_protocol].listeners);
            nl_table[sk->sk_protocol].module = NULL;
            nl_table[sk->sk_protocol].registered = 0;
      } else if (nlk->subscriptions)
            netlink_update_listeners(sk);
      netlink_table_ungrab();

      kfree(nlk->groups);
      nlk->groups = NULL;

      sock_put(sk);
      return 0;
}

static int netlink_autobind(struct socket *sock)
{
      struct sock *sk = sock->sk;
      struct net *net = sk->sk_net;
      struct nl_pid_hash *hash = &nl_table[sk->sk_protocol].hash;
      struct hlist_head *head;
      struct sock *osk;
      struct hlist_node *node;
      s32 pid = current->tgid;
      int err;
      static s32 rover = -4097;

retry:
      cond_resched();
      netlink_table_grab();
      head = nl_pid_hashfn(hash, pid);
      sk_for_each(osk, node, head) {
            if ((osk->sk_net != net))
                  continue;
            if (nlk_sk(osk)->pid == pid) {
                  /* Bind collision, search negative pid values. */
                  pid = rover--;
                  if (rover > -4097)
                        rover = -4097;
                  netlink_table_ungrab();
                  goto retry;
            }
      }
      netlink_table_ungrab();

      err = netlink_insert(sk, net, pid);
      if (err == -EADDRINUSE)
            goto retry;

      /* If 2 threads race to autobind, that is fine.  */
      if (err == -EBUSY)
            err = 0;

      return err;
}

static inline int netlink_capable(struct socket *sock, unsigned int flag)
{
      return (nl_table[sock->sk->sk_protocol].nl_nonroot & flag) ||
             capable(CAP_NET_ADMIN);
}

static void
netlink_update_subscriptions(struct sock *sk, unsigned int subscriptions)
{
      struct netlink_sock *nlk = nlk_sk(sk);

      if (nlk->subscriptions && !subscriptions)
            __sk_del_bind_node(sk);
      else if (!nlk->subscriptions && subscriptions)
            sk_add_bind_node(sk, &nl_table[sk->sk_protocol].mc_list);
      nlk->subscriptions = subscriptions;
}

static int netlink_realloc_groups(struct sock *sk)
{
      struct netlink_sock *nlk = nlk_sk(sk);
      unsigned int groups;
      unsigned long *new_groups;
      int err = 0;

      netlink_table_grab();

      groups = nl_table[sk->sk_protocol].groups;
      if (!nl_table[sk->sk_protocol].registered) {
            err = -ENOENT;
            goto out_unlock;
      }

      if (nlk->ngroups >= groups)
            goto out_unlock;

      new_groups = krealloc(nlk->groups, NLGRPSZ(groups), GFP_ATOMIC);
      if (new_groups == NULL) {
            err = -ENOMEM;
            goto out_unlock;
      }
      memset((char*)new_groups + NLGRPSZ(nlk->ngroups), 0,
             NLGRPSZ(groups) - NLGRPSZ(nlk->ngroups));

      nlk->groups = new_groups;
      nlk->ngroups = groups;
 out_unlock:
      netlink_table_ungrab();
      return err;
}

static int netlink_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
{
      struct sock *sk = sock->sk;
      struct net *net = sk->sk_net;
      struct netlink_sock *nlk = nlk_sk(sk);
      struct sockaddr_nl *nladdr = (struct sockaddr_nl *)addr;
      int err;

      if (nladdr->nl_family != AF_NETLINK)
            return -EINVAL;

      /* Only superuser is allowed to listen multicasts */
      if (nladdr->nl_groups) {
            if (!netlink_capable(sock, NL_NONROOT_RECV))
                  return -EPERM;
            err = netlink_realloc_groups(sk);
            if (err)
                  return err;
      }

      if (nlk->pid) {
            if (nladdr->nl_pid != nlk->pid)
                  return -EINVAL;
      } else {
            err = nladdr->nl_pid ?
                  netlink_insert(sk, net, nladdr->nl_pid) :
                  netlink_autobind(sock);
            if (err)
                  return err;
      }

      if (!nladdr->nl_groups && (nlk->groups == NULL || !(u32)nlk->groups[0]))
            return 0;

      netlink_table_grab();
      netlink_update_subscriptions(sk, nlk->subscriptions +
                               hweight32(nladdr->nl_groups) -
                               hweight32(nlk->groups[0]));
      nlk->groups[0] = (nlk->groups[0] & ~0xffffffffUL) | nladdr->nl_groups;
      netlink_update_listeners(sk);
      netlink_table_ungrab();

      return 0;
}

static int netlink_connect(struct socket *sock, struct sockaddr *addr,
                     int alen, int flags)
{
      int err = 0;
      struct sock *sk = sock->sk;
      struct netlink_sock *nlk = nlk_sk(sk);
      struct sockaddr_nl *nladdr=(struct sockaddr_nl*)addr;

      if (addr->sa_family == AF_UNSPEC) {
            sk->sk_state      = NETLINK_UNCONNECTED;
            nlk->dst_pid      = 0;
            nlk->dst_group  = 0;
            return 0;
      }
      if (addr->sa_family != AF_NETLINK)
            return -EINVAL;

      /* Only superuser is allowed to send multicasts */
      if (nladdr->nl_groups && !netlink_capable(sock, NL_NONROOT_SEND))
            return -EPERM;

      if (!nlk->pid)
            err = netlink_autobind(sock);

      if (err == 0) {
            sk->sk_state      = NETLINK_CONNECTED;
            nlk->dst_pid      = nladdr->nl_pid;
            nlk->dst_group  = ffs(nladdr->nl_groups);
      }

      return err;
}

static int netlink_getname(struct socket *sock, struct sockaddr *addr, int *addr_len, int peer)
{
      struct sock *sk = sock->sk;
      struct netlink_sock *nlk = nlk_sk(sk);
      struct sockaddr_nl *nladdr=(struct sockaddr_nl *)addr;

      nladdr->nl_family = AF_NETLINK;
      nladdr->nl_pad = 0;
      *addr_len = sizeof(*nladdr);

      if (peer) {
            nladdr->nl_pid = nlk->dst_pid;
            nladdr->nl_groups = netlink_group_mask(nlk->dst_group);
      } else {
            nladdr->nl_pid = nlk->pid;
            nladdr->nl_groups = nlk->groups ? nlk->groups[0] : 0;
      }
      return 0;
}

static void netlink_overrun(struct sock *sk)
{
      if (!test_and_set_bit(0, &nlk_sk(sk)->state)) {
            sk->sk_err = ENOBUFS;
            sk->sk_error_report(sk);
      }
}

static struct sock *netlink_getsockbypid(struct sock *ssk, u32 pid)
{
      struct sock *sock;
      struct netlink_sock *nlk;

      sock = netlink_lookup(ssk->sk_net, ssk->sk_protocol, pid);
      if (!sock)
            return ERR_PTR(-ECONNREFUSED);

      /* Don't bother queuing skb if kernel socket has no input function */
      nlk = nlk_sk(sock);
      if (sock->sk_state == NETLINK_CONNECTED &&
          nlk->dst_pid != nlk_sk(ssk)->pid) {
            sock_put(sock);
            return ERR_PTR(-ECONNREFUSED);
      }
      return sock;
}

struct sock *netlink_getsockbyfilp(struct file *filp)
{
      struct inode *inode = filp->f_path.dentry->d_inode;
      struct sock *sock;

      if (!S_ISSOCK(inode->i_mode))
            return ERR_PTR(-ENOTSOCK);

      sock = SOCKET_I(inode)->sk;
      if (sock->sk_family != AF_NETLINK)
            return ERR_PTR(-EINVAL);

      sock_hold(sock);
      return sock;
}

/*
 * Attach a skb to a netlink socket.
 * The caller must hold a reference to the destination socket. On error, the
 * reference is dropped. The skb is not send to the destination, just all
 * all error checks are performed and memory in the queue is reserved.
 * Return values:
 * < 0: error. skb freed, reference to sock dropped.
 * 0: continue
 * 1: repeat lookup - reference dropped while waiting for socket memory.
 */
int netlink_attachskb(struct sock *sk, struct sk_buff *skb, int nonblock,
                  long *timeo, struct sock *ssk)
{
      struct netlink_sock *nlk;

      nlk = nlk_sk(sk);

      if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
          test_bit(0, &nlk->state)) {
            DECLARE_WAITQUEUE(wait, current);
            if (!*timeo) {
                  if (!ssk || netlink_is_kernel(ssk))
                        netlink_overrun(sk);
                  sock_put(sk);
                  kfree_skb(skb);
                  return -EAGAIN;
            }

            __set_current_state(TASK_INTERRUPTIBLE);
            add_wait_queue(&nlk->wait, &wait);

            if ((atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
                 test_bit(0, &nlk->state)) &&
                !sock_flag(sk, SOCK_DEAD))
                  *timeo = schedule_timeout(*timeo);

            __set_current_state(TASK_RUNNING);
            remove_wait_queue(&nlk->wait, &wait);
            sock_put(sk);

            if (signal_pending(current)) {
                  kfree_skb(skb);
                  return sock_intr_errno(*timeo);
            }
            return 1;
      }
      skb_set_owner_r(skb, sk);
      return 0;
}

int netlink_sendskb(struct sock *sk, struct sk_buff *skb)
{
      int len = skb->len;

      skb_queue_tail(&sk->sk_receive_queue, skb);
      sk->sk_data_ready(sk, len);
      sock_put(sk);
      return len;
}

void netlink_detachskb(struct sock *sk, struct sk_buff *skb)
{
      kfree_skb(skb);
      sock_put(sk);
}

static inline struct sk_buff *netlink_trim(struct sk_buff *skb,
                                 gfp_t allocation)
{
      int delta;

      skb_orphan(skb);

      delta = skb->end - skb->tail;
      if (delta * 2 < skb->truesize)
            return skb;

      if (skb_shared(skb)) {
            struct sk_buff *nskb = skb_clone(skb, allocation);
            if (!nskb)
                  return skb;
            kfree_skb(skb);
            skb = nskb;
      }

      if (!pskb_expand_head(skb, 0, -delta, allocation))
            skb->truesize -= delta;

      return skb;
}

static inline void netlink_rcv_wake(struct sock *sk)
{
      struct netlink_sock *nlk = nlk_sk(sk);

      if (skb_queue_empty(&sk->sk_receive_queue))
            clear_bit(0, &nlk->state);
      if (!test_bit(0, &nlk->state))
            wake_up_interruptible(&nlk->wait);
}

static inline int netlink_unicast_kernel(struct sock *sk, struct sk_buff *skb)
{
      int ret;
      struct netlink_sock *nlk = nlk_sk(sk);

      ret = -ECONNREFUSED;
      if (nlk->netlink_rcv != NULL) {
            ret = skb->len;
            skb_set_owner_r(skb, sk);
            nlk->netlink_rcv(skb);
      }
      kfree_skb(skb);
      sock_put(sk);
      return ret;
}

int netlink_unicast(struct sock *ssk, struct sk_buff *skb,
                u32 pid, int nonblock)
{
      struct sock *sk;
      int err;
      long timeo;

      skb = netlink_trim(skb, gfp_any());

      timeo = sock_sndtimeo(ssk, nonblock);
retry:
      sk = netlink_getsockbypid(ssk, pid);
      if (IS_ERR(sk)) {
            kfree_skb(skb);
            return PTR_ERR(sk);
      }
      if (netlink_is_kernel(sk))
            return netlink_unicast_kernel(sk, skb);

      err = netlink_attachskb(sk, skb, nonblock, &timeo, ssk);
      if (err == 1)
            goto retry;
      if (err)
            return err;

      return netlink_sendskb(sk, skb);
}

int netlink_has_listeners(struct sock *sk, unsigned int group)
{
      int res = 0;
      unsigned long *listeners;

      BUG_ON(!netlink_is_kernel(sk));

      rcu_read_lock();
      listeners = rcu_dereference(nl_table[sk->sk_protocol].listeners);

      if (group - 1 < nl_table[sk->sk_protocol].groups)
            res = test_bit(group - 1, listeners);

      rcu_read_unlock();

      return res;
}
EXPORT_SYMBOL_GPL(netlink_has_listeners);

static __inline__ int netlink_broadcast_deliver(struct sock *sk, struct sk_buff *skb)
{
      struct netlink_sock *nlk = nlk_sk(sk);

      if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
          !test_bit(0, &nlk->state)) {
            skb_set_owner_r(skb, sk);
            skb_queue_tail(&sk->sk_receive_queue, skb);
            sk->sk_data_ready(sk, skb->len);
            return atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf;
      }
      return -1;
}

struct netlink_broadcast_data {
      struct sock *exclude_sk;
      struct net *net;
      u32 pid;
      u32 group;
      int failure;
      int congested;
      int delivered;
      gfp_t allocation;
      struct sk_buff *skb, *skb2;
};

static inline int do_one_broadcast(struct sock *sk,
                           struct netlink_broadcast_data *p)
{
      struct netlink_sock *nlk = nlk_sk(sk);
      int val;

      if (p->exclude_sk == sk)
            goto out;

      if (nlk->pid == p->pid || p->group - 1 >= nlk->ngroups ||
          !test_bit(p->group - 1, nlk->groups))
            goto out;

      if ((sk->sk_net != p->net))
            goto out;

      if (p->failure) {
            netlink_overrun(sk);
            goto out;
      }

      sock_hold(sk);
      if (p->skb2 == NULL) {
            if (skb_shared(p->skb)) {
                  p->skb2 = skb_clone(p->skb, p->allocation);
            } else {
                  p->skb2 = skb_get(p->skb);
                  /*
                   * skb ownership may have been set when
                   * delivered to a previous socket.
                   */
                  skb_orphan(p->skb2);
            }
      }
      if (p->skb2 == NULL) {
            netlink_overrun(sk);
            /* Clone failed. Notify ALL listeners. */
            p->failure = 1;
      } else if ((val = netlink_broadcast_deliver(sk, p->skb2)) < 0) {
            netlink_overrun(sk);
      } else {
            p->congested |= val;
            p->delivered = 1;
            p->skb2 = NULL;
      }
      sock_put(sk);

out:
      return 0;
}

int netlink_broadcast(struct sock *ssk, struct sk_buff *skb, u32 pid,
                  u32 group, gfp_t allocation)
{
      struct net *net = ssk->sk_net;
      struct netlink_broadcast_data info;
      struct hlist_node *node;
      struct sock *sk;

      skb = netlink_trim(skb, allocation);

      info.exclude_sk = ssk;
      info.net = net;
      info.pid = pid;
      info.group = group;
      info.failure = 0;
      info.congested = 0;
      info.delivered = 0;
      info.allocation = allocation;
      info.skb = skb;
      info.skb2 = NULL;

      /* While we sleep in clone, do not allow to change socket list */

      netlink_lock_table();

      sk_for_each_bound(sk, node, &nl_table[ssk->sk_protocol].mc_list)
            do_one_broadcast(sk, &info);

      kfree_skb(skb);

      netlink_unlock_table();

      if (info.skb2)
            kfree_skb(info.skb2);

      if (info.delivered) {
            if (info.congested && (allocation & __GFP_WAIT))
                  yield();
            return 0;
      }
      if (info.failure)
            return -ENOBUFS;
      return -ESRCH;
}

struct netlink_set_err_data {
      struct sock *exclude_sk;
      u32 pid;
      u32 group;
      int code;
};

static inline int do_one_set_err(struct sock *sk,
                         struct netlink_set_err_data *p)
{
      struct netlink_sock *nlk = nlk_sk(sk);

      if (sk == p->exclude_sk)
            goto out;

      if (sk->sk_net != p->exclude_sk->sk_net)
            goto out;

      if (nlk->pid == p->pid || p->group - 1 >= nlk->ngroups ||
          !test_bit(p->group - 1, nlk->groups))
            goto out;

      sk->sk_err = p->code;
      sk->sk_error_report(sk);
out:
      return 0;
}

void netlink_set_err(struct sock *ssk, u32 pid, u32 group, int code)
{
      struct netlink_set_err_data info;
      struct hlist_node *node;
      struct sock *sk;

      info.exclude_sk = ssk;
      info.pid = pid;
      info.group = group;
      info.code = code;

      read_lock(&nl_table_lock);

      sk_for_each_bound(sk, node, &nl_table[ssk->sk_protocol].mc_list)
            do_one_set_err(sk, &info);

      read_unlock(&nl_table_lock);
}

/* must be called with netlink table grabbed */
static void netlink_update_socket_mc(struct netlink_sock *nlk,
                             unsigned int group,
                             int is_new)
{
      int old, new = !!is_new, subscriptions;

      old = test_bit(group - 1, nlk->groups);
      subscriptions = nlk->subscriptions - old + new;
      if (new)
            __set_bit(group - 1, nlk->groups);
      else
            __clear_bit(group - 1, nlk->groups);
      netlink_update_subscriptions(&nlk->sk, subscriptions);
      netlink_update_listeners(&nlk->sk);
}

static int netlink_setsockopt(struct socket *sock, int level, int optname,
                        char __user *optval, int optlen)
{
      struct sock *sk = sock->sk;
      struct netlink_sock *nlk = nlk_sk(sk);
      unsigned int val = 0;
      int err;

      if (level != SOL_NETLINK)
            return -ENOPROTOOPT;

      if (optlen >= sizeof(int) &&
          get_user(val, (unsigned int __user *)optval))
            return -EFAULT;

      switch (optname) {
      case NETLINK_PKTINFO:
            if (val)
                  nlk->flags |= NETLINK_RECV_PKTINFO;
            else
                  nlk->flags &= ~NETLINK_RECV_PKTINFO;
            err = 0;
            break;
      case NETLINK_ADD_MEMBERSHIP:
      case NETLINK_DROP_MEMBERSHIP: {
            if (!netlink_capable(sock, NL_NONROOT_RECV))
                  return -EPERM;
            err = netlink_realloc_groups(sk);
            if (err)
                  return err;
            if (!val || val - 1 >= nlk->ngroups)
                  return -EINVAL;
            netlink_table_grab();
            netlink_update_socket_mc(nlk, val,
                               optname == NETLINK_ADD_MEMBERSHIP);
            netlink_table_ungrab();
            err = 0;
            break;
      }
      default:
            err = -ENOPROTOOPT;
      }
      return err;
}

static int netlink_getsockopt(struct socket *sock, int level, int optname,
                        char __user *optval, int __user *optlen)
{
      struct sock *sk = sock->sk;
      struct netlink_sock *nlk = nlk_sk(sk);
      int len, val, err;

      if (level != SOL_NETLINK)
            return -ENOPROTOOPT;

      if (get_user(len, optlen))
            return -EFAULT;
      if (len < 0)
            return -EINVAL;

      switch (optname) {
      case NETLINK_PKTINFO:
            if (len < sizeof(int))
                  return -EINVAL;
            len = sizeof(int);
            val = nlk->flags & NETLINK_RECV_PKTINFO ? 1 : 0;
            if (put_user(len, optlen) ||
                put_user(val, optval))
                  return -EFAULT;
            err = 0;
            break;
      default:
            err = -ENOPROTOOPT;
      }
      return err;
}

static void netlink_cmsg_recv_pktinfo(struct msghdr *msg, struct sk_buff *skb)
{
      struct nl_pktinfo info;

      info.group = NETLINK_CB(skb).dst_group;
      put_cmsg(msg, SOL_NETLINK, NETLINK_PKTINFO, sizeof(info), &info);
}

static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
                     struct msghdr *msg, size_t len)
{
      struct sock_iocb *siocb = kiocb_to_siocb(kiocb);
      struct sock *sk = sock->sk;
      struct netlink_sock *nlk = nlk_sk(sk);
      struct sockaddr_nl *addr=msg->msg_name;
      u32 dst_pid;
      u32 dst_group;
      struct sk_buff *skb;
      int err;
      struct scm_cookie scm;

      if (msg->msg_flags&MSG_OOB)
            return -EOPNOTSUPP;

      if (NULL == siocb->scm)
            siocb->scm = &scm;
      err = scm_send(sock, msg, siocb->scm);
      if (err < 0)
            return err;

      if (msg->msg_namelen) {
            if (addr->nl_family != AF_NETLINK)
                  return -EINVAL;
            dst_pid = addr->nl_pid;
            dst_group = ffs(addr->nl_groups);
            if (dst_group && !netlink_capable(sock, NL_NONROOT_SEND))
                  return -EPERM;
      } else {
            dst_pid = nlk->dst_pid;
            dst_group = nlk->dst_group;
      }

      if (!nlk->pid) {
            err = netlink_autobind(sock);
            if (err)
                  goto out;
      }

      err = -EMSGSIZE;
      if (len > sk->sk_sndbuf - 32)
            goto out;
      err = -ENOBUFS;
      skb = alloc_skb(len, GFP_KERNEL);
      if (skb==NULL)
            goto out;

      NETLINK_CB(skb).pid     = nlk->pid;
      NETLINK_CB(skb).dst_group = dst_group;
      NETLINK_CB(skb).loginuid = audit_get_loginuid(current->audit_context);
      selinux_get_task_sid(current, &(NETLINK_CB(skb).sid));
      memcpy(NETLINK_CREDS(skb), &siocb->scm->creds, sizeof(struct ucred));

      /* What can I do? Netlink is asynchronous, so that
         we will have to save current capabilities to
         check them, when this message will be delivered
         to corresponding kernel module.   --ANK (980802)
       */

      err = -EFAULT;
      if (memcpy_fromiovec(skb_put(skb,len), msg->msg_iov, len)) {
            kfree_skb(skb);
            goto out;
      }

      err = security_netlink_send(sk, skb);
      if (err) {
            kfree_skb(skb);
            goto out;
      }

      if (dst_group) {
            atomic_inc(&skb->users);
            netlink_broadcast(sk, skb, dst_pid, dst_group, GFP_KERNEL);
      }
      err = netlink_unicast(sk, skb, dst_pid, msg->msg_flags&MSG_DONTWAIT);

out:
      return err;
}

static int netlink_recvmsg(struct kiocb *kiocb, struct socket *sock,
                     struct msghdr *msg, size_t len,
                     int flags)
{
      struct sock_iocb *siocb = kiocb_to_siocb(kiocb);
      struct scm_cookie scm;
      struct sock *sk = sock->sk;
      struct netlink_sock *nlk = nlk_sk(sk);
      int noblock = flags&MSG_DONTWAIT;
      size_t copied;
      struct sk_buff *skb;
      int err;

      if (flags&MSG_OOB)
            return -EOPNOTSUPP;

      copied = 0;

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

      msg->msg_namelen = 0;

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

      skb_reset_transport_header(skb);
      err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);

      if (msg->msg_name) {
            struct sockaddr_nl *addr = (struct sockaddr_nl*)msg->msg_name;
            addr->nl_family = AF_NETLINK;
            addr->nl_pad    = 0;
            addr->nl_pid      = NETLINK_CB(skb).pid;
            addr->nl_groups   = netlink_group_mask(NETLINK_CB(skb).dst_group);
            msg->msg_namelen = sizeof(*addr);
      }

      if (nlk->flags & NETLINK_RECV_PKTINFO)
            netlink_cmsg_recv_pktinfo(msg, skb);

      if (NULL == siocb->scm) {
            memset(&scm, 0, sizeof(scm));
            siocb->scm = &scm;
      }
      siocb->scm->creds = *NETLINK_CREDS(skb);
      if (flags & MSG_TRUNC)
            copied = skb->len;
      skb_free_datagram(sk, skb);

      if (nlk->cb && atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf / 2)
            netlink_dump(sk);

      scm_recv(sock, msg, siocb->scm, flags);
out:
      netlink_rcv_wake(sk);
      return err ? : copied;
}

static void netlink_data_ready(struct sock *sk, int len)
{
      BUG();
}

/*
 *    We export these functions to other modules. They provide a
 *    complete set of kernel non-blocking support for message
 *    queueing.
 */

struct sock *
netlink_kernel_create(struct net *net, int unit, unsigned int groups,
                  void (*input)(struct sk_buff *skb),
                  struct mutex *cb_mutex, struct module *module)
{
      struct socket *sock;
      struct sock *sk;
      struct netlink_sock *nlk;
      unsigned long *listeners = NULL;

      BUG_ON(!nl_table);

      if (unit<0 || unit>=MAX_LINKS)
            return NULL;

      if (sock_create_lite(PF_NETLINK, SOCK_DGRAM, unit, &sock))
            return NULL;

      if (__netlink_create(net, sock, cb_mutex, unit) < 0)
            goto out_sock_release;

      if (groups < 32)
            groups = 32;

      listeners = kzalloc(NLGRPSZ(groups), GFP_KERNEL);
      if (!listeners)
            goto out_sock_release;

      sk = sock->sk;
      sk->sk_data_ready = netlink_data_ready;
      if (input)
            nlk_sk(sk)->netlink_rcv = input;

      if (netlink_insert(sk, net, 0))
            goto out_sock_release;

      nlk = nlk_sk(sk);
      nlk->flags |= NETLINK_KERNEL_SOCKET;

      netlink_table_grab();
      if (!nl_table[unit].registered) {
            nl_table[unit].groups = groups;
            nl_table[unit].listeners = listeners;
            nl_table[unit].cb_mutex = cb_mutex;
            nl_table[unit].module = module;
            nl_table[unit].registered = 1;
      } else {
            kfree(listeners);
      }
      netlink_table_ungrab();

      return sk;

out_sock_release:
      kfree(listeners);
      sock_release(sock);
      return NULL;
}

/**
 * netlink_change_ngroups - change number of multicast groups
 *
 * This changes the number of multicast groups that are available
 * on a certain netlink family. Note that it is not possible to
 * change the number of groups to below 32. Also note that it does
 * not implicitly call netlink_clear_multicast_users() when the
 * number of groups is reduced.
 *
 * @sk: The kernel netlink socket, as returned by netlink_kernel_create().
 * @groups: The new number of groups.
 */
int netlink_change_ngroups(struct sock *sk, unsigned int groups)
{
      unsigned long *listeners, *old = NULL;
      struct netlink_table *tbl = &nl_table[sk->sk_protocol];
      int err = 0;

      if (groups < 32)
            groups = 32;

      netlink_table_grab();
      if (NLGRPSZ(tbl->groups) < NLGRPSZ(groups)) {
            listeners = kzalloc(NLGRPSZ(groups), GFP_ATOMIC);
            if (!listeners) {
                  err = -ENOMEM;
                  goto out_ungrab;
            }
            old = tbl->listeners;
            memcpy(listeners, old, NLGRPSZ(tbl->groups));
            rcu_assign_pointer(tbl->listeners, listeners);
      }
      tbl->groups = groups;

 out_ungrab:
      netlink_table_ungrab();
      synchronize_rcu();
      kfree(old);
      return err;
}
EXPORT_SYMBOL(netlink_change_ngroups);

/**
 * netlink_clear_multicast_users - kick off multicast listeners
 *
 * This function removes all listeners from the given group.
 * @ksk: The kernel netlink socket, as returned by
 *    netlink_kernel_create().
 * @group: The multicast group to clear.
 */
void netlink_clear_multicast_users(struct sock *ksk, unsigned int group)
{
      struct sock *sk;
      struct hlist_node *node;
      struct netlink_table *tbl = &nl_table[ksk->sk_protocol];

      netlink_table_grab();

      sk_for_each_bound(sk, node, &tbl->mc_list)
            netlink_update_socket_mc(nlk_sk(sk), group, 0);

      netlink_table_ungrab();
}
EXPORT_SYMBOL(netlink_clear_multicast_users);

void netlink_set_nonroot(int protocol, unsigned int flags)
{
      if ((unsigned int)protocol < MAX_LINKS)
            nl_table[protocol].nl_nonroot = flags;
}

static void netlink_destroy_callback(struct netlink_callback *cb)
{
      if (cb->skb)
            kfree_skb(cb->skb);
      kfree(cb);
}

/*
 * It looks a bit ugly.
 * It would be better to create kernel thread.
 */

static int netlink_dump(struct sock *sk)
{
      struct netlink_sock *nlk = nlk_sk(sk);
      struct netlink_callback *cb;
      struct sk_buff *skb;
      struct nlmsghdr *nlh;
      int len, err = -ENOBUFS;

      skb = sock_rmalloc(sk, NLMSG_GOODSIZE, 0, GFP_KERNEL);
      if (!skb)
            goto errout;

      mutex_lock(nlk->cb_mutex);

      cb = nlk->cb;
      if (cb == NULL) {
            err = -EINVAL;
            goto errout_skb;
      }

      len = cb->dump(skb, cb);

      if (len > 0) {
            mutex_unlock(nlk->cb_mutex);
            skb_queue_tail(&sk->sk_receive_queue, skb);
            sk->sk_data_ready(sk, len);
            return 0;
      }

      nlh = nlmsg_put_answer(skb, cb, NLMSG_DONE, sizeof(len), NLM_F_MULTI);
      if (!nlh)
            goto errout_skb;

      memcpy(nlmsg_data(nlh), &len, sizeof(len));

      skb_queue_tail(&sk->sk_receive_queue, skb);
      sk->sk_data_ready(sk, skb->len);

      if (cb->done)
            cb->done(cb);
      nlk->cb = NULL;
      mutex_unlock(nlk->cb_mutex);

      netlink_destroy_callback(cb);
      return 0;

errout_skb:
      mutex_unlock(nlk->cb_mutex);
      kfree_skb(skb);
errout:
      return err;
}

int netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
                   struct nlmsghdr *nlh,
                   int (*dump)(struct sk_buff *skb, struct netlink_callback*),
                   int (*done)(struct netlink_callback*))
{
      struct netlink_callback *cb;
      struct sock *sk;
      struct netlink_sock *nlk;

      cb = kzalloc(sizeof(*cb), GFP_KERNEL);
      if (cb == NULL)
            return -ENOBUFS;

      cb->dump = dump;
      cb->done = done;
      cb->nlh = nlh;
      atomic_inc(&skb->users);
      cb->skb = skb;

      sk = netlink_lookup(ssk->sk_net, ssk->sk_protocol, NETLINK_CB(skb).pid);
      if (sk == NULL) {
            netlink_destroy_callback(cb);
            return -ECONNREFUSED;
      }
      nlk = nlk_sk(sk);
      /* A dump is in progress... */
      mutex_lock(nlk->cb_mutex);
      if (nlk->cb) {
            mutex_unlock(nlk->cb_mutex);
            netlink_destroy_callback(cb);
            sock_put(sk);
            return -EBUSY;
      }
      nlk->cb = cb;
      mutex_unlock(nlk->cb_mutex);

      netlink_dump(sk);
      sock_put(sk);

      /* We successfully started a dump, by returning -EINTR we
       * signal not to send ACK even if it was requested.
       */
      return -EINTR;
}

void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err)
{
      struct sk_buff *skb;
      struct nlmsghdr *rep;
      struct nlmsgerr *errmsg;
      size_t payload = sizeof(*errmsg);

      /* error messages get the original request appened */
      if (err)
            payload += nlmsg_len(nlh);

      skb = nlmsg_new(payload, GFP_KERNEL);
      if (!skb) {
            struct sock *sk;

            sk = netlink_lookup(in_skb->sk->sk_net,
                            in_skb->sk->sk_protocol,
                            NETLINK_CB(in_skb).pid);
            if (sk) {
                  sk->sk_err = ENOBUFS;
                  sk->sk_error_report(sk);
                  sock_put(sk);
            }
            return;
      }

      rep = __nlmsg_put(skb, NETLINK_CB(in_skb).pid, nlh->nlmsg_seq,
                    NLMSG_ERROR, sizeof(struct nlmsgerr), 0);
      errmsg = nlmsg_data(rep);
      errmsg->error = err;
      memcpy(&errmsg->msg, nlh, err ? nlh->nlmsg_len : sizeof(*nlh));
      netlink_unicast(in_skb->sk, skb, NETLINK_CB(in_skb).pid, MSG_DONTWAIT);
}

int netlink_rcv_skb(struct sk_buff *skb, int (*cb)(struct sk_buff *,
                                         struct nlmsghdr *))
{
      struct nlmsghdr *nlh;
      int err;

      while (skb->len >= nlmsg_total_size(0)) {
            int msglen;

            nlh = nlmsg_hdr(skb);
            err = 0;

            if (nlh->nlmsg_len < NLMSG_HDRLEN || skb->len < nlh->nlmsg_len)
                  return 0;

            /* Only requests are handled by the kernel */
            if (!(nlh->nlmsg_flags & NLM_F_REQUEST))
                  goto ack;

            /* Skip control messages */
            if (nlh->nlmsg_type < NLMSG_MIN_TYPE)
                  goto ack;

            err = cb(skb, nlh);
            if (err == -EINTR)
                  goto skip;

ack:
            if (nlh->nlmsg_flags & NLM_F_ACK || err)
                  netlink_ack(skb, nlh, err);

skip:
              msglen = NLMSG_ALIGN(nlh->nlmsg_len);
            if (msglen > skb->len)
                  msglen = skb->len;
            skb_pull(skb, msglen);
      }

      return 0;
}

/**
 * nlmsg_notify - send a notification netlink message
 * @sk: netlink socket to use
 * @skb: notification message
 * @pid: destination netlink pid for reports or 0
 * @group: destination multicast group or 0
 * @report: 1 to report back, 0 to disable
 * @flags: allocation flags
 */
int nlmsg_notify(struct sock *sk, struct sk_buff *skb, u32 pid,
             unsigned int group, int report, gfp_t flags)
{
      int err = 0;

      if (group) {
            int exclude_pid = 0;

            if (report) {
                  atomic_inc(&skb->users);
                  exclude_pid = pid;
            }

            /* errors reported via destination sk->sk_err */
            nlmsg_multicast(sk, skb, exclude_pid, group, flags);
      }

      if (report)
            err = nlmsg_unicast(sk, skb, pid);

      return err;
}

#ifdef CONFIG_PROC_FS
struct nl_seq_iter {
      struct net *net;
      int link;
      int hash_idx;
};

static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
{
      struct nl_seq_iter *iter = seq->private;
      int i, j;
      struct sock *s;
      struct hlist_node *node;
      loff_t off = 0;

      for (i=0; i<MAX_LINKS; i++) {
            struct nl_pid_hash *hash = &nl_table[i].hash;

            for (j = 0; j <= hash->mask; j++) {
                  sk_for_each(s, node, &hash->table[j]) {
                        if (iter->net != s->sk_net)
                              continue;
                        if (off == pos) {
                              iter->link = i;
                              iter->hash_idx = j;
                              return s;
                        }
                        ++off;
                  }
            }
      }
      return NULL;
}

static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
{
      read_lock(&nl_table_lock);
      return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
}

static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
      struct sock *s;
      struct nl_seq_iter *iter;
      int i, j;

      ++*pos;

      if (v == SEQ_START_TOKEN)
            return netlink_seq_socket_idx(seq, 0);

      iter = seq->private;
      s = v;
      do {
            s = sk_next(s);
      } while (s && (iter->net != s->sk_net));
      if (s)
            return s;

      i = iter->link;
      j = iter->hash_idx + 1;

      do {
            struct nl_pid_hash *hash = &nl_table[i].hash;

            for (; j <= hash->mask; j++) {
                  s = sk_head(&hash->table[j]);
                  while (s && (iter->net != s->sk_net))
                        s = sk_next(s);
                  if (s) {
                        iter->link = i;
                        iter->hash_idx = j;
                        return s;
                  }
            }

            j = 0;
      } while (++i < MAX_LINKS);

      return NULL;
}

static void netlink_seq_stop(struct seq_file *seq, void *v)
{
      read_unlock(&nl_table_lock);
}


static int netlink_seq_show(struct seq_file *seq, void *v)
{
      if (v == SEQ_START_TOKEN)
            seq_puts(seq,
                   "sk       Eth Pid    Groups   "
                   "Rmem     Wmem     Dump     Locks\n");
      else {
            struct sock *s = v;
            struct netlink_sock *nlk = nlk_sk(s);

            seq_printf(seq, "%p %-3d %-6d %08x %-8d %-8d %p %d\n",
                     s,
                     s->sk_protocol,
                     nlk->pid,
                     nlk->groups ? (u32)nlk->groups[0] : 0,
                     atomic_read(&s->sk_rmem_alloc),
                     atomic_read(&s->sk_wmem_alloc),
                     nlk->cb,
                     atomic_read(&s->sk_refcnt)
                  );

      }
      return 0;
}

static const struct seq_operations netlink_seq_ops = {
      .start  = netlink_seq_start,
      .next   = netlink_seq_next,
      .stop   = netlink_seq_stop,
      .show   = netlink_seq_show,
};


static int netlink_seq_open(struct inode *inode, struct file *file)
{
      struct nl_seq_iter *iter;

      iter = __seq_open_private(file, &netlink_seq_ops, sizeof(*iter));
      if (!iter)
            return -ENOMEM;

      iter->net = get_proc_net(inode);
      if (!iter->net) {
            seq_release_private(inode, file);
            return -ENXIO;
      }

      return 0;
}

static int netlink_seq_release(struct inode *inode, struct file *file)
{
      struct seq_file *seq = file->private_data;
      struct nl_seq_iter *iter = seq->private;
      put_net(iter->net);
      return seq_release_private(inode, file);
}

static const struct file_operations netlink_seq_fops = {
      .owner            = THIS_MODULE,
      .open       = netlink_seq_open,
      .read       = seq_read,
      .llseek           = seq_lseek,
      .release    = netlink_seq_release,
};

#endif

int netlink_register_notifier(struct notifier_block *nb)
{
      return atomic_notifier_chain_register(&netlink_chain, nb);
}

int netlink_unregister_notifier(struct notifier_block *nb)
{
      return atomic_notifier_chain_unregister(&netlink_chain, nb);
}

static const struct proto_ops netlink_ops = {
      .family =   PF_NETLINK,
      .owner =    THIS_MODULE,
      .release =  netlink_release,
      .bind =           netlink_bind,
      .connect =  netlink_connect,
      .socketpair =     sock_no_socketpair,
      .accept =   sock_no_accept,
      .getname =  netlink_getname,
      .poll =           datagram_poll,
      .ioctl =    sock_no_ioctl,
      .listen =   sock_no_listen,
      .shutdown = sock_no_shutdown,
      .setsockopt =     netlink_setsockopt,
      .getsockopt =     netlink_getsockopt,
      .sendmsg =  netlink_sendmsg,
      .recvmsg =  netlink_recvmsg,
      .mmap =           sock_no_mmap,
      .sendpage = sock_no_sendpage,
};

static struct net_proto_family netlink_family_ops = {
      .family = PF_NETLINK,
      .create = netlink_create,
      .owner      = THIS_MODULE,    /* for consistency 8) */
};

static int __net_init netlink_net_init(struct net *net)
{
#ifdef CONFIG_PROC_FS
      if (!proc_net_fops_create(net, "netlink", 0, &netlink_seq_fops))
            return -ENOMEM;
#endif
      return 0;
}

static void __net_exit netlink_net_exit(struct net *net)
{
#ifdef CONFIG_PROC_FS
      proc_net_remove(net, "netlink");
#endif
}

static struct pernet_operations __net_initdata netlink_net_ops = {
      .init = netlink_net_init,
      .exit = netlink_net_exit,
};

static int __init netlink_proto_init(void)
{
      struct sk_buff *dummy_skb;
      int i;
      unsigned long limit;
      unsigned int order;
      int err = proto_register(&netlink_proto, 0);

      if (err != 0)
            goto out;

      BUILD_BUG_ON(sizeof(struct netlink_skb_parms) > sizeof(dummy_skb->cb));

      nl_table = kcalloc(MAX_LINKS, sizeof(*nl_table), GFP_KERNEL);
      if (!nl_table)
            goto panic;

      if (num_physpages >= (128 * 1024))
            limit = num_physpages >> (21 - PAGE_SHIFT);
      else
            limit = num_physpages >> (23 - PAGE_SHIFT);

      order = get_bitmask_order(limit) - 1 + PAGE_SHIFT;
      limit = (1UL << order) / sizeof(struct hlist_head);
      order = get_bitmask_order(min(limit, (unsigned long)UINT_MAX)) - 1;

      for (i = 0; i < MAX_LINKS; i++) {
            struct nl_pid_hash *hash = &nl_table[i].hash;

            hash->table = nl_pid_hash_alloc(1 * sizeof(*hash->table));
            if (!hash->table) {
                  while (i-- > 0)
                        nl_pid_hash_free(nl_table[i].hash.table,
                                     1 * sizeof(*hash->table));
                  kfree(nl_table);
                  goto panic;
            }
            memset(hash->table, 0, 1 * sizeof(*hash->table));
            hash->max_shift = order;
            hash->shift = 0;
            hash->mask = 0;
            hash->rehash_time = jiffies;
      }

      sock_register(&netlink_family_ops);
      register_pernet_subsys(&netlink_net_ops);
      /* The netlink device handler may be needed early. */
      rtnetlink_init();
out:
      return err;
panic:
      panic("netlink_init: Cannot allocate nl_table\n");
}

core_initcall(netlink_proto_init);

EXPORT_SYMBOL(netlink_ack);
EXPORT_SYMBOL(netlink_rcv_skb);
EXPORT_SYMBOL(netlink_broadcast);
EXPORT_SYMBOL(netlink_dump_start);
EXPORT_SYMBOL(netlink_kernel_create);
EXPORT_SYMBOL(netlink_register_notifier);
EXPORT_SYMBOL(netlink_set_nonroot);
EXPORT_SYMBOL(netlink_unicast);
EXPORT_SYMBOL(netlink_unregister_notifier);
EXPORT_SYMBOL(nlmsg_notify);

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