/*
 * NETLINK      Kernel-user communication protocol.
 *
 *              Authors:        Alan Cox <alan@lxorguk.ukuu.org.uk>
 *                              Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
 *                              Patrick McHardy <kaber@trash.net>
 *
 *              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/mutex.h>
#include <linux/vmalloc.h>
#include <linux/if_arp.h>
#include <asm/cacheflush.h>

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

#include "af_netlink.h"

struct listeners {
        struct rcu_head         rcu;
        unsigned long           masks[0];
};

/* state bits */
#define NETLINK_CONGESTED       0x0

/* flags */
#define NETLINK_KERNEL_SOCKET   0x1
#define NETLINK_RECV_PKTINFO    0x2
#define NETLINK_BROADCAST_SEND_ERROR    0x4
#define NETLINK_RECV_NO_ENOBUFS 0x8

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

struct netlink_table *nl_table;
EXPORT_SYMBOL_GPL(nl_table);

static DECLARE_WAIT_QUEUE_HEAD(nl_table_wait);

static int netlink_dump(struct sock *sk);
static void netlink_skb_destructor(struct sk_buff *skb);

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

#define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));

static ATOMIC_NOTIFIER_HEAD(netlink_chain);

static DEFINE_SPINLOCK(netlink_tap_lock);
static struct list_head netlink_tap_all __read_mostly;

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

static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u32 portid)
{
        return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
}

int netlink_add_tap(struct netlink_tap *nt)
{
        if (unlikely(nt->dev->type != ARPHRD_NETLINK))
                return -EINVAL;

        spin_lock(&netlink_tap_lock);
        list_add_rcu(&nt->list, &netlink_tap_all);
        spin_unlock(&netlink_tap_lock);

        if (nt->module)
                __module_get(nt->module);

        return 0;
}
EXPORT_SYMBOL_GPL(netlink_add_tap);

int __netlink_remove_tap(struct netlink_tap *nt)
{
        bool found = false;
        struct netlink_tap *tmp;

        spin_lock(&netlink_tap_lock);

        list_for_each_entry(tmp, &netlink_tap_all, list) {
                if (nt == tmp) {
                        list_del_rcu(&nt->list);
                        found = true;
                        goto out;
                }
        }

        pr_warn("__netlink_remove_tap: %p not found\n", nt);
out:
        spin_unlock(&netlink_tap_lock);

        if (found && nt->module)
                module_put(nt->module);

        return found ? 0 : -ENODEV;
}
EXPORT_SYMBOL_GPL(__netlink_remove_tap);

int netlink_remove_tap(struct netlink_tap *nt)
{
        int ret;

        ret = __netlink_remove_tap(nt);
        synchronize_net();

        return ret;
}
EXPORT_SYMBOL_GPL(netlink_remove_tap);

static bool netlink_filter_tap(const struct sk_buff *skb)
{
        struct sock *sk = skb->sk;
        bool pass = false;

        /* We take the more conservative approach and
         * whitelist socket protocols that may pass.
         */
        switch (sk->sk_protocol) {
        case NETLINK_ROUTE:
        case NETLINK_USERSOCK:
        case NETLINK_SOCK_DIAG:
        case NETLINK_NFLOG:
        case NETLINK_XFRM:
        case NETLINK_FIB_LOOKUP:
        case NETLINK_NETFILTER:
        case NETLINK_GENERIC:
                pass = true;
                break;
        }

        return pass;
}

static int __netlink_deliver_tap_skb(struct sk_buff *skb,
                                     struct net_device *dev)
{
        struct sk_buff *nskb;
        struct sock *sk = skb->sk;
        int ret = -ENOMEM;

        dev_hold(dev);
        nskb = skb_clone(skb, GFP_ATOMIC);
        if (nskb) {
                nskb->dev = dev;
                nskb->protocol = htons((u16) sk->sk_protocol);

                ret = dev_queue_xmit(nskb);
                if (unlikely(ret > 0))
                        ret = net_xmit_errno(ret);
        }

        dev_put(dev);
        return ret;
}

static void __netlink_deliver_tap(struct sk_buff *skb)
{
        int ret;
        struct netlink_tap *tmp;

        if (!netlink_filter_tap(skb))
                return;

        list_for_each_entry_rcu(tmp, &netlink_tap_all, list) {
                ret = __netlink_deliver_tap_skb(skb, tmp->dev);
                if (unlikely(ret))
                        break;
        }
}

static void netlink_deliver_tap(struct sk_buff *skb)
{
        rcu_read_lock();

        if (unlikely(!list_empty(&netlink_tap_all)))
                __netlink_deliver_tap(skb);

        rcu_read_unlock();
}

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

        if (!(nlk->flags & NETLINK_RECV_NO_ENOBUFS)) {
                if (!test_and_set_bit(NETLINK_CONGESTED, &nlk_sk(sk)->state)) {
                        sk->sk_err = ENOBUFS;
                        sk->sk_error_report(sk);
                }
        }
        atomic_inc(&sk->sk_drops);
}

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

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

#ifdef CONFIG_NETLINK_MMAP
static bool netlink_skb_is_mmaped(const struct sk_buff *skb)
{
        return NETLINK_CB(skb).flags & NETLINK_SKB_MMAPED;
}

static bool netlink_rx_is_mmaped(struct sock *sk)
{
        return nlk_sk(sk)->rx_ring.pg_vec != NULL;
}

static bool netlink_tx_is_mmaped(struct sock *sk)
{
        return nlk_sk(sk)->tx_ring.pg_vec != NULL;
}

static __pure struct page *pgvec_to_page(const void *addr)
{
        if (is_vmalloc_addr(addr))
                return vmalloc_to_page(addr);
        else
                return virt_to_page(addr);
}

static void free_pg_vec(void **pg_vec, unsigned int order, unsigned int len)
{
        unsigned int i;

        for (i = 0; i < len; i++) {
                if (pg_vec[i] != NULL) {
                        if (is_vmalloc_addr(pg_vec[i]))
                                vfree(pg_vec[i]);
                        else
                                free_pages((unsigned long)pg_vec[i], order);
                }
        }
        kfree(pg_vec);
}

static void *alloc_one_pg_vec_page(unsigned long order)
{
        void *buffer;
        gfp_t gfp_flags = GFP_KERNEL | __GFP_COMP | __GFP_ZERO |
                          __GFP_NOWARN | __GFP_NORETRY;

        buffer = (void *)__get_free_pages(gfp_flags, order);
        if (buffer != NULL)
                return buffer;

        buffer = vzalloc((1 << order) * PAGE_SIZE);
        if (buffer != NULL)
                return buffer;

        gfp_flags &= ~__GFP_NORETRY;
        return (void *)__get_free_pages(gfp_flags, order);
}

static void **alloc_pg_vec(struct netlink_sock *nlk,
                           struct nl_mmap_req *req, unsigned int order)
{
        unsigned int block_nr = req->nm_block_nr;
        unsigned int i;
        void **pg_vec;

        pg_vec = kcalloc(block_nr, sizeof(void *), GFP_KERNEL);
        if (pg_vec == NULL)
                return NULL;

        for (i = 0; i < block_nr; i++) {
                pg_vec[i] = alloc_one_pg_vec_page(order);
                if (pg_vec[i] == NULL)
                        goto err1;
        }

        return pg_vec;
err1:
        free_pg_vec(pg_vec, order, block_nr);
        return NULL;
}

static int netlink_set_ring(struct sock *sk, struct nl_mmap_req *req,
                            bool closing, bool tx_ring)
{
        struct netlink_sock *nlk = nlk_sk(sk);
        struct netlink_ring *ring;
        struct sk_buff_head *queue;
        void **pg_vec = NULL;
        unsigned int order = 0;
        int err;

        ring  = tx_ring ? &nlk->tx_ring : &nlk->rx_ring;
        queue = tx_ring ? &sk->sk_write_queue : &sk->sk_receive_queue;

        if (!closing) {
                if (atomic_read(&nlk->mapped))
                        return -EBUSY;
                if (atomic_read(&ring->pending))
                        return -EBUSY;
        }

        if (req->nm_block_nr) {
                if (ring->pg_vec != NULL)
                        return -EBUSY;

                if ((int)req->nm_block_size <= 0)
                        return -EINVAL;
                if (!IS_ALIGNED(req->nm_block_size, PAGE_SIZE))
                        return -EINVAL;
                if (req->nm_frame_size < NL_MMAP_HDRLEN)
                        return -EINVAL;
                if (!IS_ALIGNED(req->nm_frame_size, NL_MMAP_MSG_ALIGNMENT))
                        return -EINVAL;

                ring->frames_per_block = req->nm_block_size /
                                         req->nm_frame_size;
                if (ring->frames_per_block == 0)
                        return -EINVAL;
                if (ring->frames_per_block * req->nm_block_nr !=
                    req->nm_frame_nr)
                        return -EINVAL;

                order = get_order(req->nm_block_size);
                pg_vec = alloc_pg_vec(nlk, req, order);
                if (pg_vec == NULL)
                        return -ENOMEM;
        } else {
                if (req->nm_frame_nr)
                        return -EINVAL;
        }

        err = -EBUSY;
        mutex_lock(&nlk->pg_vec_lock);
        if (closing || atomic_read(&nlk->mapped) == 0) {
                err = 0;
                spin_lock_bh(&queue->lock);

                ring->frame_max         = req->nm_frame_nr - 1;
                ring->head              = 0;
                ring->frame_size        = req->nm_frame_size;
                ring->pg_vec_pages      = req->nm_block_size / PAGE_SIZE;

                swap(ring->pg_vec_len, req->nm_block_nr);
                swap(ring->pg_vec_order, order);
                swap(ring->pg_vec, pg_vec);

                __skb_queue_purge(queue);
                spin_unlock_bh(&queue->lock);

                WARN_ON(atomic_read(&nlk->mapped));
        }
        mutex_unlock(&nlk->pg_vec_lock);

        if (pg_vec)
                free_pg_vec(pg_vec, order, req->nm_block_nr);
        return err;
}

static void netlink_mm_open(struct vm_area_struct *vma)
{
        struct file *file = vma->vm_file;
        struct socket *sock = file->private_data;
        struct sock *sk = sock->sk;

        if (sk)
                atomic_inc(&nlk_sk(sk)->mapped);
}

static void netlink_mm_close(struct vm_area_struct *vma)
{
        struct file *file = vma->vm_file;
        struct socket *sock = file->private_data;
        struct sock *sk = sock->sk;

        if (sk)
                atomic_dec(&nlk_sk(sk)->mapped);
}

static const struct vm_operations_struct netlink_mmap_ops = {
        .open   = netlink_mm_open,
        .close  = netlink_mm_close,
};

static int netlink_mmap(struct file *file, struct socket *sock,
                        struct vm_area_struct *vma)
{
        struct sock *sk = sock->sk;
        struct netlink_sock *nlk = nlk_sk(sk);
        struct netlink_ring *ring;
        unsigned long start, size, expected;
        unsigned int i;
        int err = -EINVAL;

        if (vma->vm_pgoff)
                return -EINVAL;

        mutex_lock(&nlk->pg_vec_lock);

        expected = 0;
        for (ring = &nlk->rx_ring; ring <= &nlk->tx_ring; ring++) {
                if (ring->pg_vec == NULL)
                        continue;
                expected += ring->pg_vec_len * ring->pg_vec_pages * PAGE_SIZE;
        }

        if (expected == 0)
                goto out;

        size = vma->vm_end - vma->vm_start;
        if (size != expected)
                goto out;

        start = vma->vm_start;
        for (ring = &nlk->rx_ring; ring <= &nlk->tx_ring; ring++) {
                if (ring->pg_vec == NULL)
                        continue;

                for (i = 0; i < ring->pg_vec_len; i++) {
                        struct page *page;
                        void *kaddr = ring->pg_vec[i];
                        unsigned int pg_num;

                        for (pg_num = 0; pg_num < ring->pg_vec_pages; pg_num++) {
                                page = pgvec_to_page(kaddr);
                                err = vm_insert_page(vma, start, page);
                                if (err < 0)
                                        goto out;
                                start += PAGE_SIZE;
                                kaddr += PAGE_SIZE;
                        }
                }
        }

        atomic_inc(&nlk->mapped);
        vma->vm_ops = &netlink_mmap_ops;
        err = 0;
out:
        mutex_unlock(&nlk->pg_vec_lock);
        return err;
}

static void netlink_frame_flush_dcache(const struct nl_mmap_hdr *hdr)
{
#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE == 1
        struct page *p_start, *p_end;

        /* First page is flushed through netlink_{get,set}_status */
        p_start = pgvec_to_page(hdr + PAGE_SIZE);
        p_end   = pgvec_to_page((void *)hdr + NL_MMAP_HDRLEN + hdr->nm_len - 1);
        while (p_start <= p_end) {
                flush_dcache_page(p_start);
                p_start++;
        }
#endif
}

static enum nl_mmap_status netlink_get_status(const struct nl_mmap_hdr *hdr)
{
        smp_rmb();
        flush_dcache_page(pgvec_to_page(hdr));
        return hdr->nm_status;
}

static void netlink_set_status(struct nl_mmap_hdr *hdr,
                               enum nl_mmap_status status)
{
        hdr->nm_status = status;
        flush_dcache_page(pgvec_to_page(hdr));
        smp_wmb();
}

static struct nl_mmap_hdr *
__netlink_lookup_frame(const struct netlink_ring *ring, unsigned int pos)
{
        unsigned int pg_vec_pos, frame_off;

        pg_vec_pos = pos / ring->frames_per_block;
        frame_off  = pos % ring->frames_per_block;

        return ring->pg_vec[pg_vec_pos] + (frame_off * ring->frame_size);
}

static struct nl_mmap_hdr *
netlink_lookup_frame(const struct netlink_ring *ring, unsigned int pos,
                     enum nl_mmap_status status)
{
        struct nl_mmap_hdr *hdr;

        hdr = __netlink_lookup_frame(ring, pos);
        if (netlink_get_status(hdr) != status)
                return NULL;

        return hdr;
}

static struct nl_mmap_hdr *
netlink_current_frame(const struct netlink_ring *ring,
                      enum nl_mmap_status status)
{
        return netlink_lookup_frame(ring, ring->head, status);
}

static struct nl_mmap_hdr *
netlink_previous_frame(const struct netlink_ring *ring,
                       enum nl_mmap_status status)
{
        unsigned int prev;

        prev = ring->head ? ring->head - 1 : ring->frame_max;
        return netlink_lookup_frame(ring, prev, status);
}

static void netlink_increment_head(struct netlink_ring *ring)
{
        ring->head = ring->head != ring->frame_max ? ring->head + 1 : 0;
}

static void netlink_forward_ring(struct netlink_ring *ring)
{
        unsigned int head = ring->head, pos = head;
        const struct nl_mmap_hdr *hdr;

        do {
                hdr = __netlink_lookup_frame(ring, pos);
                if (hdr->nm_status == NL_MMAP_STATUS_UNUSED)
                        break;
                if (hdr->nm_status != NL_MMAP_STATUS_SKIP)
                        break;
                netlink_increment_head(ring);
        } while (ring->head != head);
}

static bool netlink_dump_space(struct netlink_sock *nlk)
{
        struct netlink_ring *ring = &nlk->rx_ring;
        struct nl_mmap_hdr *hdr;
        unsigned int n;

        hdr = netlink_current_frame(ring, NL_MMAP_STATUS_UNUSED);
        if (hdr == NULL)
                return false;

        n = ring->head + ring->frame_max / 2;
        if (n > ring->frame_max)
                n -= ring->frame_max;

        hdr = __netlink_lookup_frame(ring, n);

        return hdr->nm_status == NL_MMAP_STATUS_UNUSED;
}

static unsigned int netlink_poll(struct file *file, struct socket *sock,
                                 poll_table *wait)
{
        struct sock *sk = sock->sk;
        struct netlink_sock *nlk = nlk_sk(sk);
        unsigned int mask;
        int err;

        if (nlk->rx_ring.pg_vec != NULL) {
                /* Memory mapped sockets don't call recvmsg(), so flow control
                 * for dumps is performed here. A dump is allowed to continue
                 * if at least half the ring is unused.
                 */
                while (nlk->cb_running && netlink_dump_space(nlk)) {
                        err = netlink_dump(sk);
                        if (err < 0) {
                                sk->sk_err = err;
                                sk->sk_error_report(sk);
                                break;
                        }
                }
                netlink_rcv_wake(sk);
        }

        mask = datagram_poll(file, sock, wait);

        spin_lock_bh(&sk->sk_receive_queue.lock);
        if (nlk->rx_ring.pg_vec) {
                netlink_forward_ring(&nlk->rx_ring);
                if (!netlink_previous_frame(&nlk->rx_ring, NL_MMAP_STATUS_UNUSED))
                        mask |= POLLIN | POLLRDNORM;
        }
        spin_unlock_bh(&sk->sk_receive_queue.lock);

        spin_lock_bh(&sk->sk_write_queue.lock);
        if (nlk->tx_ring.pg_vec) {
                if (netlink_current_frame(&nlk->tx_ring, NL_MMAP_STATUS_UNUSED))
                        mask |= POLLOUT | POLLWRNORM;
        }
        spin_unlock_bh(&sk->sk_write_queue.lock);

        return mask;
}

static struct nl_mmap_hdr *netlink_mmap_hdr(struct sk_buff *skb)
{
        return (struct nl_mmap_hdr *)(skb->head - NL_MMAP_HDRLEN);
}

static void netlink_ring_setup_skb(struct sk_buff *skb, struct sock *sk,
                                   struct netlink_ring *ring,
                                   struct nl_mmap_hdr *hdr)
{
        unsigned int size;
        void *data;

        size = ring->frame_size - NL_MMAP_HDRLEN;
        data = (void *)hdr + NL_MMAP_HDRLEN;

        skb->head       = data;
        skb->data       = data;
        skb_reset_tail_pointer(skb);
        skb->end        = skb->tail + size;
        skb->len        = 0;

        skb->destructor = netlink_skb_destructor;
        NETLINK_CB(skb).flags |= NETLINK_SKB_MMAPED;
        NETLINK_CB(skb).sk = sk;
}

static int netlink_mmap_sendmsg(struct sock *sk, struct msghdr *msg,
                                u32 dst_portid, u32 dst_group,
                                struct sock_iocb *siocb)
{
        struct netlink_sock *nlk = nlk_sk(sk);
        struct netlink_ring *ring;
        struct nl_mmap_hdr *hdr;
        struct sk_buff *skb;
        unsigned int maxlen;
        bool excl = true;
        int err = 0, len = 0;

        /* Netlink messages are validated by the receiver before processing.
         * In order to avoid userspace changing the contents of the message
         * after validation, the socket and the ring may only be used by a
         * single process, otherwise we fall back to copying.
         */
        if (atomic_long_read(&sk->sk_socket->file->f_count) > 2 ||
            atomic_read(&nlk->mapped) > 1)
                excl = false;

        mutex_lock(&nlk->pg_vec_lock);

        ring   = &nlk->tx_ring;
        maxlen = ring->frame_size - NL_MMAP_HDRLEN;

        do {
                hdr = netlink_current_frame(ring, NL_MMAP_STATUS_VALID);
                if (hdr == NULL) {
                        if (!(msg->msg_flags & MSG_DONTWAIT) &&
                            atomic_read(&nlk->tx_ring.pending))
                                schedule();
                        continue;
                }
                if (hdr->nm_len > maxlen) {
                        err = -EINVAL;
                        goto out;
                }

                netlink_frame_flush_dcache(hdr);

                if (likely(dst_portid == 0 && dst_group == 0 && excl)) {
                        skb = alloc_skb_head(GFP_KERNEL);
                        if (skb == NULL) {
                                err = -ENOBUFS;
                                goto out;
                        }
                        sock_hold(sk);
                        netlink_ring_setup_skb(skb, sk, ring, hdr);
                        NETLINK_CB(skb).flags |= NETLINK_SKB_TX;
                        __skb_put(skb, hdr->nm_len);
                        netlink_set_status(hdr, NL_MMAP_STATUS_RESERVED);
                        atomic_inc(&ring->pending);
                } else {
                        skb = alloc_skb(hdr->nm_len, GFP_KERNEL);
                        if (skb == NULL) {
                                err = -ENOBUFS;
                                goto out;
                        }
                        __skb_put(skb, hdr->nm_len);
                        memcpy(skb->data, (void *)hdr + NL_MMAP_HDRLEN, hdr->nm_len);
                        netlink_set_status(hdr, NL_MMAP_STATUS_UNUSED);
                }

                netlink_increment_head(ring);

                NETLINK_CB(skb).portid    = nlk->portid;
                NETLINK_CB(skb).dst_group = dst_group;
                NETLINK_CB(skb).creds     = siocb->scm->creds;

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

                if (unlikely(dst_group)) {
                        atomic_inc(&skb->users);
                        netlink_broadcast(sk, skb, dst_portid, dst_group,
                                          GFP_KERNEL);
                }
                err = netlink_unicast(sk, skb, dst_portid,
                                      msg->msg_flags & MSG_DONTWAIT);
                if (err < 0)
                        goto out;
                len += err;

        } while (hdr != NULL ||
                 (!(msg->msg_flags & MSG_DONTWAIT) &&
                  atomic_read(&nlk->tx_ring.pending)));

        if (len > 0)
                err = len;
out:
        mutex_unlock(&nlk->pg_vec_lock);
        return err;
}

static void netlink_queue_mmaped_skb(struct sock *sk, struct sk_buff *skb)
{
        struct nl_mmap_hdr *hdr;

        hdr = netlink_mmap_hdr(skb);
        hdr->nm_len     = skb->len;
        hdr->nm_group   = NETLINK_CB(skb).dst_group;
        hdr->nm_pid     = NETLINK_CB(skb).creds.pid;
        hdr->nm_uid     = from_kuid(sk_user_ns(sk), NETLINK_CB(skb).creds.uid);
        hdr->nm_gid     = from_kgid(sk_user_ns(sk), NETLINK_CB(skb).creds.gid);
        netlink_frame_flush_dcache(hdr);
        netlink_set_status(hdr, NL_MMAP_STATUS_VALID);

        NETLINK_CB(skb).flags |= NETLINK_SKB_DELIVERED;
        kfree_skb(skb);
}

static void netlink_ring_set_copied(struct sock *sk, struct sk_buff *skb)
{
        struct netlink_sock *nlk = nlk_sk(sk);
        struct netlink_ring *ring = &nlk->rx_ring;
        struct nl_mmap_hdr *hdr;

        spin_lock_bh(&sk->sk_receive_queue.lock);
        hdr = netlink_current_frame(ring, NL_MMAP_STATUS_UNUSED);
        if (hdr == NULL) {
                spin_unlock_bh(&sk->sk_receive_queue.lock);
                kfree_skb(skb);
                netlink_overrun(sk);
                return;
        }
        netlink_increment_head(ring);
        __skb_queue_tail(&sk->sk_receive_queue, skb);
        spin_unlock_bh(&sk->sk_receive_queue.lock);

        hdr->nm_len     = skb->len;
        hdr->nm_group   = NETLINK_CB(skb).dst_group;
        hdr->nm_pid     = NETLINK_CB(skb).creds.pid;
        hdr->nm_uid     = from_kuid(sk_user_ns(sk), NETLINK_CB(skb).creds.uid);
        hdr->nm_gid     = from_kgid(sk_user_ns(sk), NETLINK_CB(skb).creds.gid);
        netlink_set_status(hdr, NL_MMAP_STATUS_COPY);
}

#else /* CONFIG_NETLINK_MMAP */
#define netlink_skb_is_mmaped(skb)      false
#define netlink_rx_is_mmaped(sk)        false
#define netlink_tx_is_mmaped(sk)        false
#define netlink_mmap                    sock_no_mmap
#define netlink_poll                    datagram_poll
#define netlink_mmap_sendmsg(sk, msg, dst_portid, dst_group, siocb)     0
#endif /* CONFIG_NETLINK_MMAP */

static void netlink_skb_destructor(struct sk_buff *skb)
{
#ifdef CONFIG_NETLINK_MMAP
        struct nl_mmap_hdr *hdr;
        struct netlink_ring *ring;
        struct sock *sk;

        /* If a packet from the kernel to userspace was freed because of an
         * error without being delivered to userspace, the kernel must reset
         * the status. In the direction userspace to kernel, the status is
         * always reset here after the packet was processed and freed.
         */
        if (netlink_skb_is_mmaped(skb)) {
                hdr = netlink_mmap_hdr(skb);
                sk = NETLINK_CB(skb).sk;

                if (NETLINK_CB(skb).flags & NETLINK_SKB_TX) {
                        netlink_set_status(hdr, NL_MMAP_STATUS_UNUSED);
                        ring = &nlk_sk(sk)->tx_ring;
                } else {
                        if (!(NETLINK_CB(skb).flags & NETLINK_SKB_DELIVERED)) {
                                hdr->nm_len = 0;
                                netlink_set_status(hdr, NL_MMAP_STATUS_VALID);
                        }
                        ring = &nlk_sk(sk)->rx_ring;
                }

                WARN_ON(atomic_read(&ring->pending) == 0);
                atomic_dec(&ring->pending);
                sock_put(sk);

                skb->head = NULL;
        }
#endif
        if (is_vmalloc_addr(skb->head)) {
                if (!skb->cloned ||
                    !atomic_dec_return(&(skb_shinfo(skb)->dataref)))
                        vfree(skb->head);

                skb->head = NULL;
        }
        if (skb->sk != NULL)
                sock_rfree(skb);
}

static void netlink_skb_set_owner_r(struct sk_buff *skb, struct sock *sk)
{
        WARN_ON(skb->sk != NULL);
        skb->sk = sk;
        skb->destructor = netlink_skb_destructor;
        atomic_add(skb->truesize, &sk->sk_rmem_alloc);
        sk_mem_charge(sk, skb->truesize);
}

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

        if (nlk->cb_running) {
                if (nlk->cb.done)
                        nlk->cb.done(&nlk->cb);

                module_put(nlk->cb.module);
                kfree_skb(nlk->cb.skb);
        }

        skb_queue_purge(&sk->sk_receive_queue);
#ifdef CONFIG_NETLINK_MMAP
        if (1) {
                struct nl_mmap_req req;

                memset(&req, 0, sizeof(req));
                if (nlk->rx_ring.pg_vec)
                        netlink_set_ring(sk, &req, true, false);
                memset(&req, 0, sizeof(req));
                if (nlk->tx_ring.pg_vec)
                        netlink_set_ring(sk, &req, true, true);
        }
#endif /* CONFIG_NETLINK_MMAP */

        if (!sock_flag(sk, SOCK_DEAD)) {
                printk(KERN_ERR "Freeing alive netlink socket %p\n", sk);
                return;
        }

        WARN_ON(atomic_read(&sk->sk_rmem_alloc));
        WARN_ON(atomic_read(&sk->sk_wmem_alloc));
        WARN_ON(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.
 */

void netlink_table_grab(void)
        __acquires(nl_table_lock)
{
        might_sleep();

        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);
        }
}

void netlink_table_ungrab(void)
        __releases(nl_table_lock)
{
        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 bool netlink_compare(struct net *net, struct sock *sk)
{
        return net_eq(sock_net(sk), net);
}

static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
{
        struct netlink_table *table = &nl_table[protocol];
        struct nl_portid_hash *hash = &table->hash;
        struct hlist_head *head;
        struct sock *sk;

        read_lock(&nl_table_lock);
        head = nl_portid_hashfn(hash, portid);
        sk_for_each(sk, head) {
                if (table->compare(net, sk) &&
                    (nlk_sk(sk)->portid == portid)) {
                        sock_hold(sk);
                        goto found;
                }
        }

        sk = NULL;
found:
        read_unlock(&nl_table_lock);
        return sk;
}

static struct hlist_head *nl_portid_hash_zalloc(size_t size)
{
        if (size <= PAGE_SIZE)
                return kzalloc(size, GFP_ATOMIC);
        else
                return (struct hlist_head *)
                        __get_free_pages(GFP_ATOMIC | __GFP_ZERO,
                                         get_order(size));
}

static void nl_portid_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_portid_hash_rehash(struct nl_portid_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_portid_hash_zalloc(size);
        if (!table)
                return 0;

        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 *tmp;

                sk_for_each_safe(sk, tmp, &otable[i])
                        __sk_add_node(sk, nl_portid_hashfn(hash, nlk_sk(sk)->portid));
        }

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

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

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

        if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
                nl_portid_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];
        unsigned long mask;
        unsigned int i;
        struct listeners *listeners;

        listeners = nl_deref_protected(tbl->listeners);
        if (!listeners)
                return;

        for (i = 0; i < NLGRPLONGS(tbl->groups); i++) {
                mask = 0;
                sk_for_each_bound(sk, &tbl->mc_list) {
                        if (i < NLGRPLONGS(nlk_sk(sk)->ngroups))
                                mask |= nlk_sk(sk)->groups[i];
                }
                listeners->masks[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 portid)
{
        struct netlink_table *table = &nl_table[sk->sk_protocol];
        struct nl_portid_hash *hash = &table->hash;
        struct hlist_head *head;
        int err = -EADDRINUSE;
        struct sock *osk;
        int len;

        netlink_table_grab();
        head = nl_portid_hashfn(hash, portid);
        len = 0;
        sk_for_each(osk, head) {
                if (table->compare(net, osk) &&
                    (nlk_sk(osk)->portid == portid))
                        break;
                len++;
        }
        if (osk)
                goto err;

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

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

        if (len && nl_portid_hash_dilute(hash, len))
                head = nl_portid_hashfn(hash, portid);
        hash->entries++;
        nlk_sk(sk)->portid = portid;
        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);
#ifdef CONFIG_NETLINK_MMAP
        mutex_init(&nlk->pg_vec_lock);
#endif

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

static int netlink_create(struct net *net, struct socket *sock, int protocol,
                          int kern)
{
        struct module *module = NULL;
        struct mutex *cb_mutex;
        struct netlink_sock *nlk;
        void (*bind)(int group);
        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_MODULES
        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;
        else
                err = -EPROTONOSUPPORT;
        cb_mutex = nl_table[protocol].cb_mutex;
        bind = nl_table[protocol].bind;
        netlink_unlock_table();

        if (err < 0)
                goto out;

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

        local_bh_disable();
        sock_prot_inuse_add(net, &netlink_proto, 1);
        local_bh_enable();

        nlk = nlk_sk(sock->sk);
        nlk->module = module;
        nlk->netlink_bind = bind;
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->portid) {
                struct netlink_notify n = {
                                                .net = sock_net(sk),
                                                .protocol = sk->sk_protocol,
                                                .portid = nlk->portid,
                                          };
                atomic_notifier_call_chain(&netlink_chain,
                                NETLINK_URELEASE, &n);
        }

        module_put(nlk->module);

        netlink_table_grab();
        if (netlink_is_kernel(sk)) {
                BUG_ON(nl_table[sk->sk_protocol].registered == 0);
                if (--nl_table[sk->sk_protocol].registered == 0) {
                        struct listeners *old;

                        old = nl_deref_protected(nl_table[sk->sk_protocol].listeners);
                        RCU_INIT_POINTER(nl_table[sk->sk_protocol].listeners, NULL);
                        kfree_rcu(old, rcu);
                        nl_table[sk->sk_protocol].module = NULL;
                        nl_table[sk->sk_protocol].bind = NULL;
                        nl_table[sk->sk_protocol].flags = 0;
                        nl_table[sk->sk_protocol].registered = 0;
                }
        } else if (nlk->subscriptions) {
                netlink_update_listeners(sk);
        }
        netlink_table_ungrab();

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

        local_bh_disable();
        sock_prot_inuse_add(sock_net(sk), &netlink_proto, -1);
        local_bh_enable();
        sock_put(sk);
        return 0;
}

static int netlink_autobind(struct socket *sock)
{
        struct sock *sk = sock->sk;
        struct net *net = sock_net(sk);
        struct netlink_table *table = &nl_table[sk->sk_protocol];
        struct nl_portid_hash *hash = &table->hash;
        struct hlist_head *head;
        struct sock *osk;
        s32 portid = task_tgid_vnr(current);
        int err;
        static s32 rover = -4097;

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

        err = netlink_insert(sk, net, portid);
        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(const struct socket *sock, unsigned int flag)
{
        return (nl_table[sock->sk->sk_protocol].flags & flag) ||
                ns_capable(sock_net(sock->sk)->user_ns, 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 = sock_net(sk);
        struct netlink_sock *nlk = nlk_sk(sk);
        struct sockaddr_nl *nladdr = (struct sockaddr_nl *)addr;
        int err;

        if (addr_len < sizeof(struct sockaddr_nl))
                return -EINVAL;

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

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

        if (nlk->portid) {
                if (nladdr->nl_pid != nlk->portid)
                        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();

        if (nlk->netlink_bind && nlk->groups[0]) {
                int i;

                for (i=0; i<nlk->ngroups; i++) {
                        if (test_bit(i, nlk->groups))
                                nlk->netlink_bind(i);
                }
        }

        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 (alen < sizeof(addr->sa_family))
                return -EINVAL;

        if (addr->sa_family == AF_UNSPEC) {
                sk->sk_state    = NETLINK_UNCONNECTED;
                nlk->dst_portid = 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_CFG_F_NONROOT_SEND))
                return -EPERM;

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

        if (err == 0) {
                sk->sk_state    = NETLINK_CONNECTED;
                nlk->dst_portid = 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);
        DECLARE_SOCKADDR(struct sockaddr_nl *, nladdr, addr);

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

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

static struct sock *netlink_getsockbyportid(struct sock *ssk, u32 portid)
{
        struct sock *sock;
        struct netlink_sock *nlk;

        sock = netlink_lookup(sock_net(ssk), ssk->sk_protocol, portid);
        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_portid != nlk_sk(ssk)->portid) {
                sock_put(sock);
                return ERR_PTR(-ECONNREFUSED);
        }
        return sock;
}

struct sock *netlink_getsockbyfilp(struct file *filp)
{
        struct inode *inode = file_inode(filp);
        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;
}

static struct sk_buff *netlink_alloc_large_skb(unsigned int size,
                                               int broadcast)
{
        struct sk_buff *skb;
        void *data;

        if (size <= NLMSG_GOODSIZE || broadcast)
                return alloc_skb(size, GFP_KERNEL);

        size = SKB_DATA_ALIGN(size) +
               SKB_DATA_ALIGN(sizeof(struct skb_shared_info));

        data = vmalloc(size);
        if (data == NULL)
                return NULL;

        skb = build_skb(data, size);
        if (skb == NULL)
                vfree(data);
        else {
                skb->head_frag = 0;
                skb->destructor = netlink_skb_destructor;
        }

        return skb;
}

/*
 * 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,
                      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(NETLINK_CONGESTED, &nlk->state)) &&
            !netlink_skb_is_mmaped(skb)) {
                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(NETLINK_CONGESTED, &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;
        }
        netlink_skb_set_owner_r(skb, sk);
        return 0;
}

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

        netlink_deliver_tap(skb);

#ifdef CONFIG_NETLINK_MMAP
        if (netlink_skb_is_mmaped(skb))
                netlink_queue_mmaped_skb(sk, skb);
        else if (netlink_rx_is_mmaped(sk))
                netlink_ring_set_copied(sk, skb);
        else
#endif /* CONFIG_NETLINK_MMAP */
                skb_queue_tail(&sk->sk_receive_queue, skb);
        sk->sk_data_ready(sk, len);
        return len;
}

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

        sock_put(sk);
        return len;
}

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

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

        WARN_ON(skb->sk != NULL);
        if (netlink_skb_is_mmaped(skb))
                return skb;

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

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

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

        return skb;
}

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

        ret = -ECONNREFUSED;
        if (nlk->netlink_rcv != NULL) {
                /* We could do a netlink_deliver_tap(skb) here as well
                 * but since this is intended for the kernel only, we
                 * should rather let it stay under the hood.
                 */

                ret = skb->len;
                netlink_skb_set_owner_r(skb, sk);
                NETLINK_CB(skb).sk = ssk;
                nlk->netlink_rcv(skb);
                consume_skb(skb);
        } else {
                kfree_skb(skb);
        }
        sock_put(sk);
        return ret;
}

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

        skb = netlink_trim(skb, gfp_any());

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

        if (sk_filter(sk, skb)) {
                err = skb->len;
                kfree_skb(skb);
                sock_put(sk);
                return err;
        }

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

        return netlink_sendskb(sk, skb);
}
EXPORT_SYMBOL(netlink_unicast);

struct sk_buff *netlink_alloc_skb(struct sock *ssk, unsigned int size,
                                  u32 dst_portid, gfp_t gfp_mask)
{
#ifdef CONFIG_NETLINK_MMAP
        struct sock *sk = NULL;
        struct sk_buff *skb;
        struct netlink_ring *ring;
        struct nl_mmap_hdr *hdr;
        unsigned int maxlen;

        sk = netlink_getsockbyportid(ssk, dst_portid);
        if (IS_ERR(sk))
                goto out;

        ring = &nlk_sk(sk)->rx_ring;
        /* fast-path without atomic ops for common case: non-mmaped receiver */
        if (ring->pg_vec == NULL)
                goto out_put;

        skb = alloc_skb_head(gfp_mask);
        if (skb == NULL)
                goto err1;

        spin_lock_bh(&sk->sk_receive_queue.lock);
        /* check again under lock */
        if (ring->pg_vec == NULL)
                goto out_free;

        maxlen = ring->frame_size - NL_MMAP_HDRLEN;
        if (maxlen < size)
                goto out_free;

        netlink_forward_ring(ring);
        hdr = netlink_current_frame(ring, NL_MMAP_STATUS_UNUSED);
        if (hdr == NULL)
                goto err2;
        netlink_ring_setup_skb(skb, sk, ring, hdr);
        netlink_set_status(hdr, NL_MMAP_STATUS_RESERVED);
        atomic_inc(&ring->pending);
        netlink_increment_head(ring);

        spin_unlock_bh(&sk->sk_receive_queue.lock);
        return skb;

err2:
        kfree_skb(skb);
        spin_unlock_bh(&sk->sk_receive_queue.lock);
        netlink_overrun(sk);
err1:
        sock_put(sk);
        return NULL;

out_free:
        kfree_skb(skb);
        spin_unlock_bh(&sk->sk_receive_queue.lock);
out_put:
        sock_put(sk);
out:
#endif
        return alloc_skb(size, gfp_mask);
}
EXPORT_SYMBOL_GPL(netlink_alloc_skb);

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

        BUG_ON(!netlink_is_kernel(sk));

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

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

        rcu_read_unlock();

        return res;
}
EXPORT_SYMBOL_GPL(netlink_has_listeners);

static 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(NETLINK_CONGESTED, &nlk->state)) {
                netlink_skb_set_owner_r(skb, sk);
                __netlink_sendskb(sk, skb);
                return atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1);
        }
        return -1;
}

struct netlink_broadcast_data {
        struct sock *exclude_sk;
        struct net *net;
        u32 portid;
        u32 group;
        int failure;
        int delivery_failure;
        int congested;
        int delivered;
        gfp_t allocation;
        struct sk_buff *skb, *skb2;
        int (*tx_filter)(struct sock *dsk, struct sk_buff *skb, void *data);
        void *tx_data;
};

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

        if (!net_eq(sock_net(sk), 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;
                if (nlk->flags & NETLINK_BROADCAST_SEND_ERROR)
                        p->delivery_failure = 1;
        } else if (p->tx_filter && p->tx_filter(sk, p->skb2, p->tx_data)) {
                kfree_skb(p->skb2);
                p->skb2 = NULL;
        } else if (sk_filter(sk, p->skb2)) {
                kfree_skb(p->skb2);
                p->skb2 = NULL;
        } else if ((val = netlink_broadcast_deliver(sk, p->skb2)) < 0) {
                netlink_overrun(sk);
                if (nlk->flags & NETLINK_BROADCAST_SEND_ERROR)
                        p->delivery_failure = 1;
        } else {
                p->congested |= val;
                p->delivered = 1;
                p->skb2 = NULL;
        }
        sock_put(sk);

out:
        return 0;
}

int netlink_broadcast_filtered(struct sock *ssk, struct sk_buff *skb, u32 portid,
        u32 group, gfp_t allocation,
        int (*filter)(struct sock *dsk, struct sk_buff *skb, void *data),
        void *filter_data)
{
        struct net *net = sock_net(ssk);
        struct netlink_broadcast_data info;
        struct sock *sk;

        skb = netlink_trim(skb, allocation);

        info.exclude_sk = ssk;
        info.net = net;
        info.portid = portid;
        info.group = group;
        info.failure = 0;
        info.delivery_failure = 0;
        info.congested = 0;
        info.delivered = 0;
        info.allocation = allocation;
        info.skb = skb;
        info.skb2 = NULL;
        info.tx_filter = filter;
        info.tx_data = filter_data;

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

        netlink_lock_table();

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

        consume_skb(skb);

        netlink_unlock_table();

        if (info.delivery_failure) {
                kfree_skb(info.skb2);
                return -ENOBUFS;
        }
        consume_skb(info.skb2);

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

int netlink_broadcast(struct sock *ssk, struct sk_buff *skb, u32 portid,
                      u32 group, gfp_t allocation)
{
        return netlink_broadcast_filtered(ssk, skb, portid, group, allocation,
                NULL, NULL);
}
EXPORT_SYMBOL(netlink_broadcast);

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

static int do_one_set_err(struct sock *sk, struct netlink_set_err_data *p)
{
        struct netlink_sock *nlk = nlk_sk(sk);
        int ret = 0;

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

        if (!net_eq(sock_net(sk), sock_net(p->exclude_sk)))
                goto out;

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

        if (p->code == ENOBUFS && nlk->flags & NETLINK_RECV_NO_ENOBUFS) {
                ret = 1;
                goto out;
        }

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

/**
 * netlink_set_err - report error to broadcast listeners
 * @ssk: the kernel netlink socket, as returned by netlink_kernel_create()
 * @portid: the PORTID of a process that we want to skip (if any)
 * @groups: the broadcast group that will notice the error
 * @code: error code, must be negative (as usual in kernelspace)
 *
 * This function returns the number of broadcast listeners that have set the
 * NETLINK_RECV_NO_ENOBUFS socket option.
 */
int netlink_set_err(struct sock *ssk, u32 portid, u32 group, int code)
{
        struct netlink_set_err_data info;
        struct sock *sk;
        int ret = 0;

        info.exclude_sk = ssk;
        info.portid = portid;
        info.group = group;
        /* sk->sk_err wants a positive error value */
        info.code = -code;

        read_lock(&nl_table_lock);

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

        read_unlock(&nl_table_lock);
        return ret;
}
EXPORT_SYMBOL(netlink_set_err);

/* 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, unsigned 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 (optname != NETLINK_RX_RING && optname != NETLINK_TX_RING &&
            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_CFG_F_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();

                if (nlk->netlink_bind)
                        nlk->netlink_bind(val);

                err = 0;
                break;
        }
        case NETLINK_BROADCAST_ERROR:
                if (val)
                        nlk->flags |= NETLINK_BROADCAST_SEND_ERROR;
                else
                        nlk->flags &= ~NETLINK_BROADCAST_SEND_ERROR;
                err = 0;
                break;
        case NETLINK_NO_ENOBUFS:
                if (val) {
                        nlk->flags |= NETLINK_RECV_NO_ENOBUFS;
                        clear_bit(NETLINK_CONGESTED, &nlk->state);
                        wake_up_interruptible(&nlk->wait);
                } else {
                        nlk->flags &= ~NETLINK_RECV_NO_ENOBUFS;
                }
                err = 0;
                break;
#ifdef CONFIG_NETLINK_MMAP
        case NETLINK_RX_RING:
        case NETLINK_TX_RING: {
                struct nl_mmap_req req;

                /* Rings might consume more memory than queue limits, require
                 * CAP_NET_ADMIN.
                 */
                if (!capable(CAP_NET_ADMIN))
                        return -EPERM;
                if (optlen < sizeof(req))
                        return -EINVAL;
                if (copy_from_user(&req, optval, sizeof(req)))
                        return -EFAULT;
                err = netlink_set_ring(sk, &req, false,
                                       optname == NETLINK_TX_RING);
                break;
        }
#endif /* CONFIG_NETLINK_MMAP */
        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;
        case NETLINK_BROADCAST_ERROR:
                if (len < sizeof(int))
                        return -EINVAL;
                len = sizeof(int);
                val = nlk->flags & NETLINK_BROADCAST_SEND_ERROR ? 1 : 0;
                if (put_user(len, optlen) ||
                    put_user(val, optval))
                        return -EFAULT;
                err = 0;
                break;
        case NETLINK_NO_ENOBUFS:
                if (len < sizeof(int))
                        return -EINVAL;
                len = sizeof(int);
                val = nlk->flags & NETLINK_RECV_NO_ENOBUFS ? 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_portid;
        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, true);
        if (err < 0)
                return err;

        if (msg->msg_namelen) {
                err = -EINVAL;
                if (addr->nl_family != AF_NETLINK)
                        goto out;
                dst_portid = addr->nl_pid;
                dst_group = ffs(addr->nl_groups);
                err =  -EPERM;
                if ((dst_group || dst_portid) &&
                    !netlink_capable(sock, NL_CFG_F_NONROOT_SEND))
                        goto out;
        } else {
                dst_portid = nlk->dst_portid;
                dst_group = nlk->dst_group;
        }

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

        if (netlink_tx_is_mmaped(sk) &&
            msg->msg_iov->iov_base == NULL) {
                err = netlink_mmap_sendmsg(sk, msg, dst_portid, dst_group,
                                           siocb);
                goto out;
        }

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

        NETLINK_CB(skb).portid  = nlk->portid;
        NETLINK_CB(skb).dst_group = dst_group;
        NETLINK_CB(skb).creds   = siocb->scm->creds;

        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_portid, dst_group, GFP_KERNEL);
        }
        err = netlink_unicast(sk, skb, dst_portid, msg->msg_flags&MSG_DONTWAIT);

out:
        scm_destroy(siocb->scm);
        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, *data_skb;
        int err, ret;

        if (flags&MSG_OOB)
                return -EOPNOTSUPP;

        copied = 0;

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

        data_skb = skb;

#ifdef CONFIG_COMPAT_NETLINK_MESSAGES
        if (unlikely(skb_shinfo(skb)->frag_list)) {
                /*
                 * If this skb has a frag_list, then here that means that we
                 * will have to use the frag_list skb's data for compat tasks
                 * and the regular skb's data for normal (non-compat) tasks.
                 *
                 * If we need to send the compat skb, assign it to the
                 * 'data_skb' variable so that it will be used below for data
                 * copying. We keep 'skb' for everything else, including
                 * freeing both later.
                 */
                if (flags & MSG_CMSG_COMPAT)
                        data_skb = skb_shinfo(skb)->frag_list;
        }
#endif

        msg->msg_namelen = 0;

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

        skb_reset_transport_header(data_skb);
        err = skb_copy_datagram_iovec(data_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).portid;
                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 = data_skb->len;

        skb_free_datagram(sk, skb);

        if (nlk->cb_running &&
            atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf / 2) {
                ret = netlink_dump(sk);
                if (ret) {
                        sk->sk_err = ret;
                        sk->sk_error_report(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, struct module *module,
                        struct netlink_kernel_cfg *cfg)
{
        struct socket *sock;
        struct sock *sk;
        struct netlink_sock *nlk;
        struct listeners *listeners = NULL;
        struct mutex *cb_mutex = cfg ? cfg->cb_mutex : NULL;
        unsigned int groups;

        BUG_ON(!nl_table);

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

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

        /*
         * We have to just have a reference on the net from sk, but don't
         * get_net it. Besides, we cannot get and then put the net here.
         * So we create one inside init_net and the move it to net.
         */

        if (__netlink_create(&init_net, sock, cb_mutex, unit) < 0)
                goto out_sock_release_nosk;

        sk = sock->sk;
        sk_change_net(sk, net);

        if (!cfg || cfg->groups < 32)
                groups = 32;
        else
                groups = cfg->groups;

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

        sk->sk_data_ready = netlink_data_ready;
        if (cfg && cfg->input)
                nlk_sk(sk)->netlink_rcv = cfg->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;
                rcu_assign_pointer(nl_table[unit].listeners, listeners);
                nl_table[unit].cb_mutex = cb_mutex;
                nl_table[unit].module = module;
                if (cfg) {
                        nl_table[unit].bind = cfg->bind;
                        nl_table[unit].flags = cfg->flags;
                        if (cfg->compare)
                                nl_table[unit].compare = cfg->compare;
                }
                nl_table[unit].registered = 1;
        } else {
                kfree(listeners);
                nl_table[unit].registered++;
        }
        netlink_table_ungrab();
        return sk;

out_sock_release:
        kfree(listeners);
        netlink_kernel_release(sk);
        return NULL;

out_sock_release_nosk:
        sock_release(sock);
        return NULL;
}
EXPORT_SYMBOL(__netlink_kernel_create);

void
netlink_kernel_release(struct sock *sk)
{
        sk_release_kernel(sk);
}
EXPORT_SYMBOL(netlink_kernel_release);

int __netlink_change_ngroups(struct sock *sk, unsigned int groups)
{
        struct listeners *new, *old;
        struct netlink_table *tbl = &nl_table[sk->sk_protocol];

        if (groups < 32)
                groups = 32;

        if (NLGRPSZ(tbl->groups) < NLGRPSZ(groups)) {
                new = kzalloc(sizeof(*new) + NLGRPSZ(groups), GFP_ATOMIC);
                if (!new)
                        return -ENOMEM;
                old = nl_deref_protected(tbl->listeners);
                memcpy(new->masks, old->masks, NLGRPSZ(tbl->groups));
                rcu_assign_pointer(tbl->listeners, new);

                kfree_rcu(old, rcu);
        }
        tbl->groups = groups;

        return 0;
}

/**
 * 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)
{
        int err;

        netlink_table_grab();
        err = __netlink_change_ngroups(sk, groups);
        netlink_table_ungrab();

        return err;
}

void __netlink_clear_multicast_users(struct sock *ksk, unsigned int group)
{
        struct sock *sk;
        struct netlink_table *tbl = &nl_table[ksk->sk_protocol];

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

/**
 * 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)
{
        netlink_table_grab();
        __netlink_clear_multicast_users(ksk, group);
        netlink_table_ungrab();
}

struct nlmsghdr *
__nlmsg_put(struct sk_buff *skb, u32 portid, u32 seq, int type, int len, int flags)
{
        struct nlmsghdr *nlh;
        int size = nlmsg_msg_size(len);

        nlh = (struct nlmsghdr*)skb_put(skb, NLMSG_ALIGN(size));
        nlh->nlmsg_type = type;
        nlh->nlmsg_len = size;
        nlh->nlmsg_flags = flags;
        nlh->nlmsg_pid = portid;
        nlh->nlmsg_seq = seq;
        if (!__builtin_constant_p(size) || NLMSG_ALIGN(size) - size != 0)
                memset(nlmsg_data(nlh) + len, 0, NLMSG_ALIGN(size) - size);
        return nlh;
}
EXPORT_SYMBOL(__nlmsg_put);

/*
 * 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 = NULL;
        struct nlmsghdr *nlh;
        int len, err = -ENOBUFS;
        int alloc_size;

        mutex_lock(nlk->cb_mutex);
        if (!nlk->cb_running) {
                err = -EINVAL;
                goto errout_skb;
        }

        cb = &nlk->cb;
        alloc_size = max_t(int, cb->min_dump_alloc, NLMSG_GOODSIZE);

        if (!netlink_rx_is_mmaped(sk) &&
            atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
                goto errout_skb;
        skb = netlink_alloc_skb(sk, alloc_size, nlk->portid, GFP_KERNEL);
        if (!skb)
                goto errout_skb;
        netlink_skb_set_owner_r(skb, sk);

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

        if (len > 0) {
                mutex_unlock(nlk->cb_mutex);

                if (sk_filter(sk, skb))
                        kfree_skb(skb);
                else
                        __netlink_sendskb(sk, skb);
                return 0;
        }

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

        nl_dump_check_consistent(cb, nlh);

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

        if (sk_filter(sk, skb))
                kfree_skb(skb);
        else
                __netlink_sendskb(sk, skb);

        if (cb->done)
                cb->done(cb);

        nlk->cb_running = false;
        mutex_unlock(nlk->cb_mutex);
        module_put(cb->module);
        consume_skb(cb->skb);
        return 0;

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

int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
                         const struct nlmsghdr *nlh,
                         struct netlink_dump_control *control)
{
        struct netlink_callback *cb;
        struct sock *sk;
        struct netlink_sock *nlk;
        int ret;

        /* Memory mapped dump requests need to be copied to avoid looping
         * on the pending state in netlink_mmap_sendmsg() while the CB hold
         * a reference to the skb.
         */
        if (netlink_skb_is_mmaped(skb)) {
                skb = skb_copy(skb, GFP_KERNEL);
                if (skb == NULL)
                        return -ENOBUFS;
        } else
                atomic_inc(&skb->users);

        sk = netlink_lookup(sock_net(ssk), ssk->sk_protocol, NETLINK_CB(skb).portid);
        if (sk == NULL) {
                ret = -ECONNREFUSED;
                goto error_free;
        }

        nlk = nlk_sk(sk);
        mutex_lock(nlk->cb_mutex);
        /* A dump is in progress... */
        if (nlk->cb_running) {
                ret = -EBUSY;
                goto error_unlock;
        }
        /* add reference of module which cb->dump belongs to */
        if (!try_module_get(control->module)) {
                ret = -EPROTONOSUPPORT;
                goto error_unlock;
        }

        cb = &nlk->cb;
        memset(cb, 0, sizeof(*cb));
        cb->dump = control->dump;
        cb->done = control->done;
        cb->nlh = nlh;
        cb->data = control->data;
        cb->module = control->module;
        cb->min_dump_alloc = control->min_dump_alloc;
        cb->skb = skb;

        nlk->cb_running = true;

        mutex_unlock(nlk->cb_mutex);

        ret = netlink_dump(sk);
        sock_put(sk);

        if (ret)
                return ret;

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

error_unlock:
        sock_put(sk);
        mutex_unlock(nlk->cb_mutex);
error_free:
        kfree_skb(skb);
        return ret;
}
EXPORT_SYMBOL(__netlink_dump_start);

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 = netlink_alloc_skb(in_skb->sk, nlmsg_total_size(payload),
                                NETLINK_CB(in_skb).portid, GFP_KERNEL);
        if (!skb) {
                struct sock *sk;

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

        rep = __nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq,
                          NLMSG_ERROR, payload, 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).portid, MSG_DONTWAIT);
}
EXPORT_SYMBOL(netlink_ack);

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;
}
EXPORT_SYMBOL(netlink_rcv_skb);

/**
 * nlmsg_notify - send a notification netlink message
 * @sk: netlink socket to use
 * @skb: notification message
 * @portid: destination netlink portid 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 portid,
                 unsigned int group, int report, gfp_t flags)
{
        int err = 0;

        if (group) {
                int exclude_portid = 0;

                if (report) {
                        atomic_inc(&skb->users);
                        exclude_portid = portid;
                }

                /* errors reported via destination sk->sk_err, but propagate
                 * delivery errors if NETLINK_BROADCAST_ERROR flag is set */
                err = nlmsg_multicast(sk, skb, exclude_portid, group, flags);
        }

        if (report) {
                int err2;

                err2 = nlmsg_unicast(sk, skb, portid);
                if (!err || err == -ESRCH)
                        err = err2;
        }

        return err;
}
EXPORT_SYMBOL(nlmsg_notify);

#ifdef CONFIG_PROC_FS
struct nl_seq_iter {
        struct seq_net_private p;
        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;
        loff_t off = 0;

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

                for (j = 0; j <= hash->mask; j++) {
                        sk_for_each(s, &hash->table[j]) {
                                if (sock_net(s) != seq_file_net(seq))
                                        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)
        __acquires(nl_table_lock)
{
        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;
        struct net *net;
        int i, j;

        ++*pos;

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

        net = seq_file_net(seq);
        iter = seq->private;
        s = v;
        do {
                s = sk_next(s);
        } while (s && !nl_table[s->sk_protocol].compare(net, s));
        if (s)
                return s;

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

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

                for (; j <= hash->mask; j++) {
                        s = sk_head(&hash->table[j]);

                        while (s && !nl_table[s->sk_protocol].compare(net, s))
                                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)
        __releases(nl_table_lock)
{
        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     Drops     Inode\n");
        } else {
                struct sock *s = v;
                struct netlink_sock *nlk = nlk_sk(s);

                seq_printf(seq, "%pK %-3d %-6u %08x %-8d %-8d %d %-8d %-8d %-8lu\n",
                           s,
                           s->sk_protocol,
                           nlk->portid,
                           nlk->groups ? (u32)nlk->groups[0] : 0,
                           sk_rmem_alloc_get(s),
                           sk_wmem_alloc_get(s),
                           nlk->cb_running,
                           atomic_read(&s->sk_refcnt),
                           atomic_read(&s->sk_drops),
                           sock_i_ino(s)
                        );

        }
        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)
{
        return seq_open_net(inode, file, &netlink_seq_ops,
                                sizeof(struct nl_seq_iter));
}

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

#endif

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

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

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 =         netlink_poll,
        .ioctl =        sock_no_ioctl,
        .listen =       sock_no_listen,