thp: fix bad_page to show the real reason the page is bad

[linux/fpc-iii.git] / net / ipv4 / udp.c

/*
 * INET         An implementation of the TCP/IP protocol suite for the LINUX
 *              operating system.  INET is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              The User Datagram Protocol (UDP).
 *
 * Authors:     Ross Biro
 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 *              Alan Cox, <alan@lxorguk.ukuu.org.uk>
 *              Hirokazu Takahashi, <taka@valinux.co.jp>
 *
 * Fixes:
 *              Alan Cox        :       verify_area() calls
 *              Alan Cox        :       stopped close while in use off icmp
 *                                      messages. Not a fix but a botch that
 *                                      for udp at least is 'valid'.
 *              Alan Cox        :       Fixed icmp handling properly
 *              Alan Cox        :       Correct error for oversized datagrams
 *              Alan Cox        :       Tidied select() semantics.
 *              Alan Cox        :       udp_err() fixed properly, also now
 *                                      select and read wake correctly on errors
 *              Alan Cox        :       udp_send verify_area moved to avoid mem leak
 *              Alan Cox        :       UDP can count its memory
 *              Alan Cox        :       send to an unknown connection causes
 *                                      an ECONNREFUSED off the icmp, but
 *                                      does NOT close.
 *              Alan Cox        :       Switched to new sk_buff handlers. No more backlog!
 *              Alan Cox        :       Using generic datagram code. Even smaller and the PEEK
 *                                      bug no longer crashes it.
 *              Fred Van Kempen :       Net2e support for sk->broadcast.
 *              Alan Cox        :       Uses skb_free_datagram
 *              Alan Cox        :       Added get/set sockopt support.
 *              Alan Cox        :       Broadcasting without option set returns EACCES.
 *              Alan Cox        :       No wakeup calls. Instead we now use the callbacks.
 *              Alan Cox        :       Use ip_tos and ip_ttl
 *              Alan Cox        :       SNMP Mibs
 *              Alan Cox        :       MSG_DONTROUTE, and 0.0.0.0 support.
 *              Matt Dillon     :       UDP length checks.
 *              Alan Cox        :       Smarter af_inet used properly.
 *              Alan Cox        :       Use new kernel side addressing.
 *              Alan Cox        :       Incorrect return on truncated datagram receive.
 *      Arnt Gulbrandsen        :       New udp_send and stuff
 *              Alan Cox        :       Cache last socket
 *              Alan Cox        :       Route cache
 *              Jon Peatfield   :       Minor efficiency fix to sendto().
 *              Mike Shaver     :       RFC1122 checks.
 *              Alan Cox        :       Nonblocking error fix.
 *      Willy Konynenberg       :       Transparent proxying support.
 *              Mike McLagan    :       Routing by source
 *              David S. Miller :       New socket lookup architecture.
 *                                      Last socket cache retained as it
 *                                      does have a high hit rate.
 *              Olaf Kirch      :       Don't linearise iovec on sendmsg.
 *              Andi Kleen      :       Some cleanups, cache destination entry
 *                                      for connect.
 *      Vitaly E. Lavrov        :       Transparent proxy revived after year coma.
 *              Melvin Smith    :       Check msg_name not msg_namelen in sendto(),
 *                                      return ENOTCONN for unconnected sockets (POSIX)
 *              Janos Farkas    :       don't deliver multi/broadcasts to a different
 *                                      bound-to-device socket
 *      Hirokazu Takahashi      :       HW checksumming for outgoing UDP
 *                                      datagrams.
 *      Hirokazu Takahashi      :       sendfile() on UDP works now.
 *              Arnaldo C. Melo :       convert /proc/net/udp to seq_file
 *      YOSHIFUJI Hideaki @USAGI and:   Support IPV6_V6ONLY socket option, which
 *      Alexey Kuznetsov:               allow both IPv4 and IPv6 sockets to bind
 *                                      a single port at the same time.
 *      Derek Atkins <derek@ihtfp.com>: Add Encapulation Support
 *      James Chapman           :       Add L2TP encapsulation type.
 *
 *
 *              This program is free software; you can redistribute it and/or
 *              modify it under the terms of the GNU General Public License
 *              as published by the Free Software Foundation; either version
 *              2 of the License, or (at your option) any later version.
 */

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/ioctls.h>
#include <linux/bootmem.h>
#include <linux/highmem.h>
#include <linux/swap.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/module.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/igmp.h>
#include <linux/in.h>
#include <linux/errno.h>
#include <linux/timer.h>
#include <linux/mm.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/slab.h>
#include <net/tcp_states.h>
#include <linux/skbuff.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <net/net_namespace.h>
#include <net/icmp.h>
#include <net/route.h>
#include <net/checksum.h>
#include <net/xfrm.h>
#include "udp_impl.h"

struct udp_table udp_table __read_mostly;
EXPORT_SYMBOL(udp_table);

long sysctl_udp_mem[3] __read_mostly;
EXPORT_SYMBOL(sysctl_udp_mem);

int sysctl_udp_rmem_min __read_mostly;
EXPORT_SYMBOL(sysctl_udp_rmem_min);

int sysctl_udp_wmem_min __read_mostly;
EXPORT_SYMBOL(sysctl_udp_wmem_min);

atomic_long_t udp_memory_allocated;
EXPORT_SYMBOL(udp_memory_allocated);

#define MAX_UDP_PORTS 65536
#define PORTS_PER_CHAIN (MAX_UDP_PORTS / UDP_HTABLE_SIZE_MIN)

static int udp_lib_lport_inuse(struct net *net, __u16 num,
                               const struct udp_hslot *hslot,
                               unsigned long *bitmap,
                               struct sock *sk,
                               int (*saddr_comp)(const struct sock *sk1,
                                                 const struct sock *sk2),
                               unsigned int log)
{
        struct sock *sk2;
        struct hlist_nulls_node *node;

        sk_nulls_for_each(sk2, node, &hslot->head)
                if (net_eq(sock_net(sk2), net) &&
                    sk2 != sk &&
                    (bitmap || udp_sk(sk2)->udp_port_hash == num) &&
                    (!sk2->sk_reuse || !sk->sk_reuse) &&
                    (!sk2->sk_bound_dev_if || !sk->sk_bound_dev_if ||
                     sk2->sk_bound_dev_if == sk->sk_bound_dev_if) &&
                    (*saddr_comp)(sk, sk2)) {
                        if (bitmap)
                                __set_bit(udp_sk(sk2)->udp_port_hash >> log,
                                          bitmap);
                        else
                                return 1;
                }
        return 0;
}

/*
 * Note: we still hold spinlock of primary hash chain, so no other writer
 * can insert/delete a socket with local_port == num
 */
static int udp_lib_lport_inuse2(struct net *net, __u16 num,
                               struct udp_hslot *hslot2,
                               struct sock *sk,
                               int (*saddr_comp)(const struct sock *sk1,
                                                 const struct sock *sk2))
{
        struct sock *sk2;
        struct hlist_nulls_node *node;
        int res = 0;

        spin_lock(&hslot2->lock);
        udp_portaddr_for_each_entry(sk2, node, &hslot2->head)
                if (net_eq(sock_net(sk2), net) &&
                    sk2 != sk &&
                    (udp_sk(sk2)->udp_port_hash == num) &&
                    (!sk2->sk_reuse || !sk->sk_reuse) &&
                    (!sk2->sk_bound_dev_if || !sk->sk_bound_dev_if ||
                     sk2->sk_bound_dev_if == sk->sk_bound_dev_if) &&
                    (*saddr_comp)(sk, sk2)) {
                        res = 1;
                        break;
                }
        spin_unlock(&hslot2->lock);
        return res;
}

/**
 *  udp_lib_get_port  -  UDP/-Lite port lookup for IPv4 and IPv6
 *
 *  @sk:          socket struct in question
 *  @snum:        port number to look up
 *  @saddr_comp:  AF-dependent comparison of bound local IP addresses
 *  @hash2_nulladdr: AF-dependant hash value in secondary hash chains,
 *                   with NULL address
 */
int udp_lib_get_port(struct sock *sk, unsigned short snum,
                       int (*saddr_comp)(const struct sock *sk1,
                                         const struct sock *sk2),
                     unsigned int hash2_nulladdr)
{
        struct udp_hslot *hslot, *hslot2;
        struct udp_table *udptable = sk->sk_prot->h.udp_table;
        int    error = 1;
        struct net *net = sock_net(sk);

        if (!snum) {
                int low, high, remaining;
                unsigned rand;
                unsigned short first, last;
                DECLARE_BITMAP(bitmap, PORTS_PER_CHAIN);

                inet_get_local_port_range(&low, &high);
                remaining = (high - low) + 1;

                rand = net_random();
                first = (((u64)rand * remaining) >> 32) + low;
                /*
                 * force rand to be an odd multiple of UDP_HTABLE_SIZE
                 */
                rand = (rand | 1) * (udptable->mask + 1);
                last = first + udptable->mask + 1;
                do {
                        hslot = udp_hashslot(udptable, net, first);
                        bitmap_zero(bitmap, PORTS_PER_CHAIN);
                        spin_lock_bh(&hslot->lock);
                        udp_lib_lport_inuse(net, snum, hslot, bitmap, sk,
                                            saddr_comp, udptable->log);

                        snum = first;
                        /*
                         * Iterate on all possible values of snum for this hash.
                         * Using steps of an odd multiple of UDP_HTABLE_SIZE
                         * give us randomization and full range coverage.
                         */
                        do {
                                if (low <= snum && snum <= high &&
                                    !test_bit(snum >> udptable->log, bitmap) &&
                                    !inet_is_reserved_local_port(snum))
                                        goto found;
                                snum += rand;
                        } while (snum != first);
                        spin_unlock_bh(&hslot->lock);
                } while (++first != last);
                goto fail;
        } else {
                hslot = udp_hashslot(udptable, net, snum);
                spin_lock_bh(&hslot->lock);
                if (hslot->count > 10) {
                        int exist;
                        unsigned int slot2 = udp_sk(sk)->udp_portaddr_hash ^ snum;

                        slot2          &= udptable->mask;
                        hash2_nulladdr &= udptable->mask;

                        hslot2 = udp_hashslot2(udptable, slot2);
                        if (hslot->count < hslot2->count)
                                goto scan_primary_hash;

                        exist = udp_lib_lport_inuse2(net, snum, hslot2,
                                                     sk, saddr_comp);
                        if (!exist && (hash2_nulladdr != slot2)) {
                                hslot2 = udp_hashslot2(udptable, hash2_nulladdr);
                                exist = udp_lib_lport_inuse2(net, snum, hslot2,
                                                             sk, saddr_comp);
                        }
                        if (exist)
                                goto fail_unlock;
                        else
                                goto found;
                }
scan_primary_hash:
                if (udp_lib_lport_inuse(net, snum, hslot, NULL, sk,
                                        saddr_comp, 0))
                        goto fail_unlock;
        }
found:
        inet_sk(sk)->inet_num = snum;
        udp_sk(sk)->udp_port_hash = snum;
        udp_sk(sk)->udp_portaddr_hash ^= snum;
        if (sk_unhashed(sk)) {
                sk_nulls_add_node_rcu(sk, &hslot->head);
                hslot->count++;
                sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);

                hslot2 = udp_hashslot2(udptable, udp_sk(sk)->udp_portaddr_hash);
                spin_lock(&hslot2->lock);
                hlist_nulls_add_head_rcu(&udp_sk(sk)->udp_portaddr_node,
                                         &hslot2->head);
                hslot2->count++;
                spin_unlock(&hslot2->lock);
        }
        error = 0;
fail_unlock:
        spin_unlock_bh(&hslot->lock);
fail:
        return error;
}
EXPORT_SYMBOL(udp_lib_get_port);

static int ipv4_rcv_saddr_equal(const struct sock *sk1, const struct sock *sk2)
{
        struct inet_sock *inet1 = inet_sk(sk1), *inet2 = inet_sk(sk2);

        return  (!ipv6_only_sock(sk2)  &&
                 (!inet1->inet_rcv_saddr || !inet2->inet_rcv_saddr ||
                   inet1->inet_rcv_saddr == inet2->inet_rcv_saddr));
}

static unsigned int udp4_portaddr_hash(struct net *net, __be32 saddr,
                                       unsigned int port)
{
        return jhash_1word((__force u32)saddr, net_hash_mix(net)) ^ port;
}

int udp_v4_get_port(struct sock *sk, unsigned short snum)
{
        unsigned int hash2_nulladdr =
                udp4_portaddr_hash(sock_net(sk), htonl(INADDR_ANY), snum);
        unsigned int hash2_partial =
                udp4_portaddr_hash(sock_net(sk), inet_sk(sk)->inet_rcv_saddr, 0);

        /* precompute partial secondary hash */
        udp_sk(sk)->udp_portaddr_hash = hash2_partial;
        return udp_lib_get_port(sk, snum, ipv4_rcv_saddr_equal, hash2_nulladdr);
}

static inline int compute_score(struct sock *sk, struct net *net, __be32 saddr,
                         unsigned short hnum,
                         __be16 sport, __be32 daddr, __be16 dport, int dif)
{
        int score = -1;

        if (net_eq(sock_net(sk), net) && udp_sk(sk)->udp_port_hash == hnum &&
                        !ipv6_only_sock(sk)) {
                struct inet_sock *inet = inet_sk(sk);

                score = (sk->sk_family == PF_INET ? 1 : 0);
                if (inet->inet_rcv_saddr) {
                        if (inet->inet_rcv_saddr != daddr)
                                return -1;
                        score += 2;
                }
                if (inet->inet_daddr) {
                        if (inet->inet_daddr != saddr)
                                return -1;
                        score += 2;
                }
                if (inet->inet_dport) {
                        if (inet->inet_dport != sport)
                                return -1;
                        score += 2;
                }
                if (sk->sk_bound_dev_if) {
                        if (sk->sk_bound_dev_if != dif)
                                return -1;
                        score += 2;
                }
        }
        return score;
}

/*
 * In this second variant, we check (daddr, dport) matches (inet_rcv_sadd, inet_num)
 */
#define SCORE2_MAX (1 + 2 + 2 + 2)
static inline int compute_score2(struct sock *sk, struct net *net,
                                 __be32 saddr, __be16 sport,
                                 __be32 daddr, unsigned int hnum, int dif)
{
        int score = -1;

        if (net_eq(sock_net(sk), net) && !ipv6_only_sock(sk)) {
                struct inet_sock *inet = inet_sk(sk);

                if (inet->inet_rcv_saddr != daddr)
                        return -1;
                if (inet->inet_num != hnum)
                        return -1;

                score = (sk->sk_family == PF_INET ? 1 : 0);
                if (inet->inet_daddr) {
                        if (inet->inet_daddr != saddr)
                                return -1;
                        score += 2;
                }
                if (inet->inet_dport) {
                        if (inet->inet_dport != sport)
                                return -1;
                        score += 2;
                }
                if (sk->sk_bound_dev_if) {
                        if (sk->sk_bound_dev_if != dif)
                                return -1;
                        score += 2;
                }
        }
        return score;
}


/* called with read_rcu_lock() */
static struct sock *udp4_lib_lookup2(struct net *net,
                __be32 saddr, __be16 sport,
                __be32 daddr, unsigned int hnum, int dif,
                struct udp_hslot *hslot2, unsigned int slot2)
{
        struct sock *sk, *result;
        struct hlist_nulls_node *node;
        int score, badness;

begin:
        result = NULL;
        badness = -1;
        udp_portaddr_for_each_entry_rcu(sk, node, &hslot2->head) {
                score = compute_score2(sk, net, saddr, sport,
                                      daddr, hnum, dif);
                if (score > badness) {
                        result = sk;
                        badness = score;
                        if (score == SCORE2_MAX)
                                goto exact_match;
                }
        }
        /*
         * if the nulls value we got at the end of this lookup is
         * not the expected one, we must restart lookup.
         * We probably met an item that was moved to another chain.
         */
        if (get_nulls_value(node) != slot2)
                goto begin;

        if (result) {
exact_match:
                if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
                        result = NULL;
                else if (unlikely(compute_score2(result, net, saddr, sport,
                                  daddr, hnum, dif) < badness)) {
                        sock_put(result);
                        goto begin;
                }
        }
        return result;
}

/* UDP is nearly always wildcards out the wazoo, it makes no sense to try
 * harder than this. -DaveM
 */
static struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
                __be16 sport, __be32 daddr, __be16 dport,
                int dif, struct udp_table *udptable)
{
        struct sock *sk, *result;
        struct hlist_nulls_node *node;
        unsigned short hnum = ntohs(dport);
        unsigned int hash2, slot2, slot = udp_hashfn(net, hnum, udptable->mask);
        struct udp_hslot *hslot2, *hslot = &udptable->hash[slot];
        int score, badness;

        rcu_read_lock();
        if (hslot->count > 10) {
                hash2 = udp4_portaddr_hash(net, daddr, hnum);
                slot2 = hash2 & udptable->mask;
                hslot2 = &udptable->hash2[slot2];
                if (hslot->count < hslot2->count)
                        goto begin;

                result = udp4_lib_lookup2(net, saddr, sport,
                                          daddr, hnum, dif,
                                          hslot2, slot2);
                if (!result) {
                        hash2 = udp4_portaddr_hash(net, htonl(INADDR_ANY), hnum);
                        slot2 = hash2 & udptable->mask;
                        hslot2 = &udptable->hash2[slot2];
                        if (hslot->count < hslot2->count)
                                goto begin;

                        result = udp4_lib_lookup2(net, saddr, sport,
                                                  htonl(INADDR_ANY), hnum, dif,
                                                  hslot2, slot2);
                }
                rcu_read_unlock();
                return result;
        }
begin:
        result = NULL;
        badness = -1;
        sk_nulls_for_each_rcu(sk, node, &hslot->head) {
                score = compute_score(sk, net, saddr, hnum, sport,
                                      daddr, dport, dif);
                if (score > badness) {
                        result = sk;
                        badness = score;
                }
        }
        /*
         * if the nulls value we got at the end of this lookup is
         * not the expected one, we must restart lookup.
         * We probably met an item that was moved to another chain.
         */
        if (get_nulls_value(node) != slot)
                goto begin;

        if (result) {
                if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
                        result = NULL;
                else if (unlikely(compute_score(result, net, saddr, hnum, sport,
                                  daddr, dport, dif) < badness)) {
                        sock_put(result);
                        goto begin;
                }
        }
        rcu_read_unlock();
        return result;
}

static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
                                                 __be16 sport, __be16 dport,
                                                 struct udp_table *udptable)
{
        struct sock *sk;
        const struct iphdr *iph = ip_hdr(skb);

        if (unlikely(sk = skb_steal_sock(skb)))
                return sk;
        else
                return __udp4_lib_lookup(dev_net(skb_dst(skb)->dev), iph->saddr, sport,
                                         iph->daddr, dport, inet_iif(skb),
                                         udptable);
}

struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
                             __be32 daddr, __be16 dport, int dif)
{
        return __udp4_lib_lookup(net, saddr, sport, daddr, dport, dif, &udp_table);
}
EXPORT_SYMBOL_GPL(udp4_lib_lookup);

static inline struct sock *udp_v4_mcast_next(struct net *net, struct sock *sk,
                                             __be16 loc_port, __be32 loc_addr,
                                             __be16 rmt_port, __be32 rmt_addr,
                                             int dif)
{
        struct hlist_nulls_node *node;
        struct sock *s = sk;
        unsigned short hnum = ntohs(loc_port);

        sk_nulls_for_each_from(s, node) {
                struct inet_sock *inet = inet_sk(s);

                if (!net_eq(sock_net(s), net) ||
                    udp_sk(s)->udp_port_hash != hnum ||
                    (inet->inet_daddr && inet->inet_daddr != rmt_addr) ||
                    (inet->inet_dport != rmt_port && inet->inet_dport) ||
                    (inet->inet_rcv_saddr &&
                     inet->inet_rcv_saddr != loc_addr) ||
                    ipv6_only_sock(s) ||
                    (s->sk_bound_dev_if && s->sk_bound_dev_if != dif))
                        continue;
                if (!ip_mc_sf_allow(s, loc_addr, rmt_addr, dif))
                        continue;
                goto found;
        }
        s = NULL;
found:
        return s;
}

/*
 * This routine is called by the ICMP module when it gets some
 * sort of error condition.  If err < 0 then the socket should
 * be closed and the error returned to the user.  If err > 0
 * it's just the icmp type << 8 | icmp code.
 * Header points to the ip header of the error packet. We move
 * on past this. Then (as it used to claim before adjustment)
 * header points to the first 8 bytes of the udp header.  We need
 * to find the appropriate port.
 */

void __udp4_lib_err(struct sk_buff *skb, u32 info, struct udp_table *udptable)
{
        struct inet_sock *inet;
        struct iphdr *iph = (struct iphdr *)skb->data;
        struct udphdr *uh = (struct udphdr *)(skb->data+(iph->ihl<<2));
        const int type = icmp_hdr(skb)->type;
        const int code = icmp_hdr(skb)->code;
        struct sock *sk;
        int harderr;
        int err;
        struct net *net = dev_net(skb->dev);

        sk = __udp4_lib_lookup(net, iph->daddr, uh->dest,
                        iph->saddr, uh->source, skb->dev->ifindex, udptable);
        if (sk == NULL) {
                ICMP_INC_STATS_BH(net, ICMP_MIB_INERRORS);
                return; /* No socket for error */
        }

        err = 0;
        harderr = 0;
        inet = inet_sk(sk);

        switch (type) {
        default:
        case ICMP_TIME_EXCEEDED:
                err = EHOSTUNREACH;
                break;
        case ICMP_SOURCE_QUENCH:
                goto out;
        case ICMP_PARAMETERPROB:
                err = EPROTO;
                harderr = 1;
                break;
        case ICMP_DEST_UNREACH:
                if (code == ICMP_FRAG_NEEDED) { /* Path MTU discovery */
                        if (inet->pmtudisc != IP_PMTUDISC_DONT) {
                                err = EMSGSIZE;
                                harderr = 1;
                                break;
                        }
                        goto out;
                }
                err = EHOSTUNREACH;
                if (code <= NR_ICMP_UNREACH) {
                        harderr = icmp_err_convert[code].fatal;
                        err = icmp_err_convert[code].errno;
                }
                break;
        }

        /*
         *      RFC1122: OK.  Passes ICMP errors back to application, as per
         *      4.1.3.3.
         */
        if (!inet->recverr) {
                if (!harderr || sk->sk_state != TCP_ESTABLISHED)
                        goto out;
        } else
                ip_icmp_error(sk, skb, err, uh->dest, info, (u8 *)(uh+1));

        sk->sk_err = err;
        sk->sk_error_report(sk);
out:
        sock_put(sk);
}

void udp_err(struct sk_buff *skb, u32 info)
{
        __udp4_lib_err(skb, info, &udp_table);
}

/*
 * Throw away all pending data and cancel the corking. Socket is locked.
 */
void udp_flush_pending_frames(struct sock *sk)
{
        struct udp_sock *up = udp_sk(sk);

        if (up->pending) {
                up->len = 0;
                up->pending = 0;
                ip_flush_pending_frames(sk);
        }
}
EXPORT_SYMBOL(udp_flush_pending_frames);

/**
 *      udp4_hwcsum_outgoing  -  handle outgoing HW checksumming
 *      @sk:    socket we are sending on
 *      @skb:   sk_buff containing the filled-in UDP header
 *              (checksum field must be zeroed out)
 */
static void udp4_hwcsum_outgoing(struct sock *sk, struct sk_buff *skb,
                                 __be32 src, __be32 dst, int len)
{
        unsigned int offset;
        struct udphdr *uh = udp_hdr(skb);
        __wsum csum = 0;

        if (skb_queue_len(&sk->sk_write_queue) == 1) {
                /*
                 * Only one fragment on the socket.
                 */
                skb->csum_start = skb_transport_header(skb) - skb->head;
                skb->csum_offset = offsetof(struct udphdr, check);
                uh->check = ~csum_tcpudp_magic(src, dst, len, IPPROTO_UDP, 0);
        } else {
                /*
                 * HW-checksum won't work as there are two or more
                 * fragments on the socket so that all csums of sk_buffs
                 * should be together
                 */
                offset = skb_transport_offset(skb);
                skb->csum = skb_checksum(skb, offset, skb->len - offset, 0);

                skb->ip_summed = CHECKSUM_NONE;

                skb_queue_walk(&sk->sk_write_queue, skb) {
                        csum = csum_add(csum, skb->csum);
                }

                uh->check = csum_tcpudp_magic(src, dst, len, IPPROTO_UDP, csum);
                if (uh->check == 0)
                        uh->check = CSUM_MANGLED_0;
        }
}

/*
 * Push out all pending data as one UDP datagram. Socket is locked.
 */
static int udp_push_pending_frames(struct sock *sk)
{
        struct udp_sock  *up = udp_sk(sk);
        struct inet_sock *inet = inet_sk(sk);
        struct flowi *fl = &inet->cork.fl;
        struct sk_buff *skb;
        struct udphdr *uh;
        int err = 0;
        int is_udplite = IS_UDPLITE(sk);
        __wsum csum = 0;

        /* Grab the skbuff where UDP header space exists. */
        if ((skb = skb_peek(&sk->sk_write_queue)) == NULL)
                goto out;

        /*
         * Create a UDP header
         */
        uh = udp_hdr(skb);
        uh->source = fl->fl_ip_sport;
        uh->dest = fl->fl_ip_dport;
        uh->len = htons(up->len);
        uh->check = 0;

        if (is_udplite)                                  /*     UDP-Lite      */
                csum  = udplite_csum_outgoing(sk, skb);

        else if (sk->sk_no_check == UDP_CSUM_NOXMIT) {   /* UDP csum disabled */

                skb->ip_summed = CHECKSUM_NONE;
                goto send;

        } else if (skb->ip_summed == CHECKSUM_PARTIAL) { /* UDP hardware csum */

                udp4_hwcsum_outgoing(sk, skb, fl->fl4_src, fl->fl4_dst, up->len);
                goto send;

        } else                                           /*   `normal' UDP    */
                csum = udp_csum_outgoing(sk, skb);

        /* add protocol-dependent pseudo-header */
        uh->check = csum_tcpudp_magic(fl->fl4_src, fl->fl4_dst, up->len,
                                      sk->sk_protocol, csum);
        if (uh->check == 0)
                uh->check = CSUM_MANGLED_0;

send:
        err = ip_push_pending_frames(sk);
        if (err) {
                if (err == -ENOBUFS && !inet->recverr) {
                        UDP_INC_STATS_USER(sock_net(sk),
                                           UDP_MIB_SNDBUFERRORS, is_udplite);
                        err = 0;
                }
        } else
                UDP_INC_STATS_USER(sock_net(sk),
                                   UDP_MIB_OUTDATAGRAMS, is_udplite);
out:
        up->len = 0;
        up->pending = 0;
        return err;
}

int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
                size_t len)
{
        struct inet_sock *inet = inet_sk(sk);
        struct udp_sock *up = udp_sk(sk);
        int ulen = len;
        struct ipcm_cookie ipc;
        struct rtable *rt = NULL;
        int free = 0;
        int connected = 0;
        __be32 daddr, faddr, saddr;
        __be16 dport;
        u8  tos;
        int err, is_udplite = IS_UDPLITE(sk);
        int corkreq = up->corkflag || msg->msg_flags&MSG_MORE;
        int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);

        if (len > 0xFFFF)
                return -EMSGSIZE;

        /*
         *      Check the flags.
         */

        if (msg->msg_flags & MSG_OOB) /* Mirror BSD error message compatibility */
                return -EOPNOTSUPP;

        ipc.opt = NULL;
        ipc.tx_flags = 0;

        if (up->pending) {
                /*
                 * There are pending frames.
                 * The socket lock must be held while it's corked.
                 */
                lock_sock(sk);
                if (likely(up->pending)) {
                        if (unlikely(up->pending != AF_INET)) {
                                release_sock(sk);
                                return -EINVAL;
                        }
                        goto do_append_data;
                }
                release_sock(sk);
        }
        ulen += sizeof(struct udphdr);

        /*
         *      Get and verify the address.
         */
        if (msg->msg_name) {
                struct sockaddr_in * usin = (struct sockaddr_in *)msg->msg_name;
                if (msg->msg_namelen < sizeof(*usin))
                        return -EINVAL;
                if (usin->sin_family != AF_INET) {
                        if (usin->sin_family != AF_UNSPEC)
                                return -EAFNOSUPPORT;
                }

                daddr = usin->sin_addr.s_addr;
                dport = usin->sin_port;
                if (dport == 0)
                        return -EINVAL;
        } else {
                if (sk->sk_state != TCP_ESTABLISHED)
                        return -EDESTADDRREQ;
                daddr = inet->inet_daddr;
                dport = inet->inet_dport;
                /* Open fast path for connected socket.
                   Route will not be used, if at least one option is set.
                 */
                connected = 1;
        }
        ipc.addr = inet->inet_saddr;

        ipc.oif = sk->sk_bound_dev_if;
        err = sock_tx_timestamp(sk, &ipc.tx_flags);
        if (err)
                return err;
        if (msg->msg_controllen) {
                err = ip_cmsg_send(sock_net(sk), msg, &ipc);
                if (err)
                        return err;
                if (ipc.opt)
                        free = 1;
                connected = 0;
        }
        if (!ipc.opt)
                ipc.opt = inet->opt;

        saddr = ipc.addr;
        ipc.addr = faddr = daddr;

        if (ipc.opt && ipc.opt->srr) {
                if (!daddr)
                        return -EINVAL;
                faddr = ipc.opt->faddr;
                connected = 0;
        }
        tos = RT_TOS(inet->tos);
        if (sock_flag(sk, SOCK_LOCALROUTE) ||
            (msg->msg_flags & MSG_DONTROUTE) ||
            (ipc.opt && ipc.opt->is_strictroute)) {
                tos |= RTO_ONLINK;
                connected = 0;
        }

        if (ipv4_is_multicast(daddr)) {
                if (!ipc.oif)
                        ipc.oif = inet->mc_index;
                if (!saddr)
                        saddr = inet->mc_addr;
                connected = 0;
        }

        if (connected)
                rt = (struct rtable *)sk_dst_check(sk, 0);

        if (rt == NULL) {
                struct flowi fl = { .oif = ipc.oif,
                                    .mark = sk->sk_mark,
                                    .fl4_dst = faddr,
                                    .fl4_src = saddr,
                                    .fl4_tos = tos,
                                    .proto = sk->sk_protocol,
                                    .flags = inet_sk_flowi_flags(sk),
                                    .fl_ip_sport = inet->inet_sport,
                                    .fl_ip_dport = dport };
                struct net *net = sock_net(sk);

                security_sk_classify_flow(sk, &fl);
                err = ip_route_output_flow(net, &rt, &fl, sk, 1);
                if (err) {
                        if (err == -ENETUNREACH)
                                IP_INC_STATS_BH(net, IPSTATS_MIB_OUTNOROUTES);
                        goto out;
                }

                err = -EACCES;
                if ((rt->rt_flags & RTCF_BROADCAST) &&
                    !sock_flag(sk, SOCK_BROADCAST))
                        goto out;
                if (connected)
                        sk_dst_set(sk, dst_clone(&rt->dst));
        }

        if (msg->msg_flags&MSG_CONFIRM)
                goto do_confirm;
back_from_confirm:

        saddr = rt->rt_src;
        if (!ipc.addr)
                daddr = ipc.addr = rt->rt_dst;

        lock_sock(sk);
        if (unlikely(up->pending)) {
                /* The socket is already corked while preparing it. */
                /* ... which is an evident application bug. --ANK */
                release_sock(sk);

                LIMIT_NETDEBUG(KERN_DEBUG "udp cork app bug 2\n");
                err = -EINVAL;
                goto out;
        }
        /*
         *      Now cork the socket to pend data.
         */
        inet->cork.fl.fl4_dst = daddr;
        inet->cork.fl.fl_ip_dport = dport;
        inet->cork.fl.fl4_src = saddr;
        inet->cork.fl.fl_ip_sport = inet->inet_sport;
        up->pending = AF_INET;

do_append_data:
        up->len += ulen;
        getfrag  =  is_udplite ?  udplite_getfrag : ip_generic_getfrag;
        err = ip_append_data(sk, getfrag, msg->msg_iov, ulen,
                        sizeof(struct udphdr), &ipc, &rt,
                        corkreq ? msg->msg_flags|MSG_MORE : msg->msg_flags);
        if (err)
                udp_flush_pending_frames(sk);
        else if (!corkreq)
                err = udp_push_pending_frames(sk);
        else if (unlikely(skb_queue_empty(&sk->sk_write_queue)))
                up->pending = 0;
        release_sock(sk);

out:
        ip_rt_put(rt);
        if (free)
                kfree(ipc.opt);
        if (!err)
                return len;
        /*
         * ENOBUFS = no kernel mem, SOCK_NOSPACE = no sndbuf space.  Reporting
         * ENOBUFS might not be good (it's not tunable per se), but otherwise
         * we don't have a good statistic (IpOutDiscards but it can be too many
         * things).  We could add another new stat but at least for now that
         * seems like overkill.
         */
        if (err == -ENOBUFS || test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
                UDP_INC_STATS_USER(sock_net(sk),
                                UDP_MIB_SNDBUFERRORS, is_udplite);
        }
        return err;

do_confirm:
        dst_confirm(&rt->dst);
        if (!(msg->msg_flags&MSG_PROBE) || len)
                goto back_from_confirm;
        err = 0;
        goto out;
}
EXPORT_SYMBOL(udp_sendmsg);

int udp_sendpage(struct sock *sk, struct page *page, int offset,
                 size_t size, int flags)
{
        struct udp_sock *up = udp_sk(sk);
        int ret;

        if (!up->pending) {
                struct msghdr msg = {   .msg_flags = flags|MSG_MORE };

                /* Call udp_sendmsg to specify destination address which
                 * sendpage interface can't pass.
                 * This will succeed only when the socket is connected.
                 */
                ret = udp_sendmsg(NULL, sk, &msg, 0);
                if (ret < 0)
                        return ret;
        }

        lock_sock(sk);

        if (unlikely(!up->pending)) {
                release_sock(sk);

                LIMIT_NETDEBUG(KERN_DEBUG "udp cork app bug 3\n");
                return -EINVAL;
        }

        ret = ip_append_page(sk, page, offset, size, flags);
        if (ret == -EOPNOTSUPP) {
                release_sock(sk);
                return sock_no_sendpage(sk->sk_socket, page, offset,
                                        size, flags);
        }
        if (ret < 0) {
                udp_flush_pending_frames(sk);
                goto out;
        }

        up->len += size;
        if (!(up->corkflag || (flags&MSG_MORE)))
                ret = udp_push_pending_frames(sk);
        if (!ret)
                ret = size;
out:
        release_sock(sk);
        return ret;
}


/**
 *      first_packet_length     - return length of first packet in receive queue
 *      @sk: socket
 *
 *      Drops all bad checksum frames, until a valid one is found.
 *      Returns the length of found skb, or 0 if none is found.
 */
static unsigned int first_packet_length(struct sock *sk)
{
        struct sk_buff_head list_kill, *rcvq = &sk->sk_receive_queue;
        struct sk_buff *skb;
        unsigned int res;

        __skb_queue_head_init(&list_kill);

        spin_lock_bh(&rcvq->lock);
        while ((skb = skb_peek(rcvq)) != NULL &&
                udp_lib_checksum_complete(skb)) {
                UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_INERRORS,
                                 IS_UDPLITE(sk));
                atomic_inc(&sk->sk_drops);
                __skb_unlink(skb, rcvq);
                __skb_queue_tail(&list_kill, skb);
        }
        res = skb ? skb->len : 0;
        spin_unlock_bh(&rcvq->lock);

        if (!skb_queue_empty(&list_kill)) {
                bool slow = lock_sock_fast(sk);

                __skb_queue_purge(&list_kill);
                sk_mem_reclaim_partial(sk);
                unlock_sock_fast(sk, slow);
        }
        return res;
}

/*
 *      IOCTL requests applicable to the UDP protocol
 */

int udp_ioctl(struct sock *sk, int cmd, unsigned long arg)
{
        switch (cmd) {
        case SIOCOUTQ:
        {
                int amount = sk_wmem_alloc_get(sk);

                return put_user(amount, (int __user *)arg);
        }

        case SIOCINQ:
        {
                unsigned int amount = first_packet_length(sk);

                if (amount)
                        /*
                         * We will only return the amount
                         * of this packet since that is all
                         * that will be read.
                         */
                        amount -= sizeof(struct udphdr);

                return put_user(amount, (int __user *)arg);
        }

        default:
                return -ENOIOCTLCMD;
        }

        return 0;
}
EXPORT_SYMBOL(udp_ioctl);

/*
 *      This should be easy, if there is something there we
 *      return it, otherwise we block.
 */

int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
                size_t len, int noblock, int flags, int *addr_len)
{
        struct inet_sock *inet = inet_sk(sk);
        struct sockaddr_in *sin = (struct sockaddr_in *)msg->msg_name;
        struct sk_buff *skb;
        unsigned int ulen;
        int peeked;
        int err;
        int is_udplite = IS_UDPLITE(sk);
        bool slow;

        /*
         *      Check any passed addresses
         */
        if (addr_len)
                *addr_len = sizeof(*sin);

        if (flags & MSG_ERRQUEUE)
                return ip_recv_error(sk, msg, len);

try_again:
        skb = __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0),
                                  &peeked, &err);
        if (!skb)
                goto out;

        ulen = skb->len - sizeof(struct udphdr);
        if (len > ulen)
                len = ulen;
        else if (len < ulen)
                msg->msg_flags |= MSG_TRUNC;

        /*
         * If checksum is needed at all, try to do it while copying the
         * data.  If the data is truncated, or if we only want a partial
         * coverage checksum (UDP-Lite), do it before the copy.
         */

        if (len < ulen || UDP_SKB_CB(skb)->partial_cov) {
                if (udp_lib_checksum_complete(skb))
                        goto csum_copy_err;
        }

        if (skb_csum_unnecessary(skb))
                err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
                                              msg->msg_iov, len);
        else {
                err = skb_copy_and_csum_datagram_iovec(skb,
                                                       sizeof(struct udphdr),
                                                       msg->msg_iov);

                if (err == -EINVAL)
                        goto csum_copy_err;
        }

        if (err)
                goto out_free;

        if (!peeked)
                UDP_INC_STATS_USER(sock_net(sk),
                                UDP_MIB_INDATAGRAMS, is_udplite);

        sock_recv_ts_and_drops(msg, sk, skb);

        /* Copy the address. */
        if (sin) {
                sin->sin_family = AF_INET;
                sin->sin_port = udp_hdr(skb)->source;
                sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
                memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
        }
        if (inet->cmsg_flags)
                ip_cmsg_recv(msg, skb);

        err = len;
        if (flags & MSG_TRUNC)
                err = ulen;

out_free:
        skb_free_datagram_locked(sk, skb);
out:
        return err;

csum_copy_err:
        slow = lock_sock_fast(sk);
        if (!skb_kill_datagram(sk, skb, flags))
                UDP_INC_STATS_USER(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
        unlock_sock_fast(sk, slow);

        if (noblock)
                return -EAGAIN;
        goto try_again;
}


int udp_disconnect(struct sock *sk, int flags)
{
        struct inet_sock *inet = inet_sk(sk);
        /*
         *      1003.1g - break association.
         */

        sk->sk_state = TCP_CLOSE;
        inet->inet_daddr = 0;
        inet->inet_dport = 0;
        sock_rps_save_rxhash(sk, 0);
        sk->sk_bound_dev_if = 0;
        if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
                inet_reset_saddr(sk);

        if (!(sk->sk_userlocks & SOCK_BINDPORT_LOCK)) {
                sk->sk_prot->unhash(sk);
                inet->inet_sport = 0;
        }
        sk_dst_reset(sk);
        return 0;
}
EXPORT_SYMBOL(udp_disconnect);

void udp_lib_unhash(struct sock *sk)
{
        if (sk_hashed(sk)) {
                struct udp_table *udptable = sk->sk_prot->h.udp_table;
                struct udp_hslot *hslot, *hslot2;

                hslot  = udp_hashslot(udptable, sock_net(sk),
                                      udp_sk(sk)->udp_port_hash);
                hslot2 = udp_hashslot2(udptable, udp_sk(sk)->udp_portaddr_hash);

                spin_lock_bh(&hslot->lock);
                if (sk_nulls_del_node_init_rcu(sk)) {
                        hslot->count--;
                        inet_sk(sk)->inet_num = 0;
                        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);

                        spin_lock(&hslot2->lock);
                        hlist_nulls_del_init_rcu(&udp_sk(sk)->udp_portaddr_node);
                        hslot2->count--;
                        spin_unlock(&hslot2->lock);
                }
                spin_unlock_bh(&hslot->lock);
        }
}
EXPORT_SYMBOL(udp_lib_unhash);

/*
 * inet_rcv_saddr was changed, we must rehash secondary hash
 */
void udp_lib_rehash(struct sock *sk, u16 newhash)
{
        if (sk_hashed(sk)) {
                struct udp_table *udptable = sk->sk_prot->h.udp_table;
                struct udp_hslot *hslot, *hslot2, *nhslot2;

                hslot2 = udp_hashslot2(udptable, udp_sk(sk)->udp_portaddr_hash);
                nhslot2 = udp_hashslot2(udptable, newhash);
                udp_sk(sk)->udp_portaddr_hash = newhash;
                if (hslot2 != nhslot2) {
                        hslot = udp_hashslot(udptable, sock_net(sk),
                                             udp_sk(sk)->udp_port_hash);
                        /* we must lock primary chain too */
                        spin_lock_bh(&hslot->lock);

                        spin_lock(&hslot2->lock);
                        hlist_nulls_del_init_rcu(&udp_sk(sk)->udp_portaddr_node);
                        hslot2->count--;
                        spin_unlock(&hslot2->lock);

                        spin_lock(&nhslot2->lock);
                        hlist_nulls_add_head_rcu(&udp_sk(sk)->udp_portaddr_node,
                                                 &nhslot2->head);
                        nhslot2->count++;
                        spin_unlock(&nhslot2->lock);

                        spin_unlock_bh(&hslot->lock);
                }
        }
}
EXPORT_SYMBOL(udp_lib_rehash);

static void udp_v4_rehash(struct sock *sk)
{
        u16 new_hash = udp4_portaddr_hash(sock_net(sk),
                                          inet_sk(sk)->inet_rcv_saddr,
                                          inet_sk(sk)->inet_num);
        udp_lib_rehash(sk, new_hash);
}

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

        if (inet_sk(sk)->inet_daddr)
                sock_rps_save_rxhash(sk, skb->rxhash);

        rc = ip_queue_rcv_skb(sk, skb);
        if (rc < 0) {
                int is_udplite = IS_UDPLITE(sk);

                /* Note that an ENOMEM error is charged twice */
                if (rc == -ENOMEM)
                        UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_RCVBUFERRORS,
                                         is_udplite);
                UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
                kfree_skb(skb);
                return -1;
        }

        return 0;

}

/* returns:
 *  -1: error
 *   0: success
 *  >0: "udp encap" protocol resubmission
 *
 * Note that in the success and error cases, the skb is assumed to
 * have either been requeued or freed.
 */
int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
{
        struct udp_sock *up = udp_sk(sk);
        int rc;
        int is_udplite = IS_UDPLITE(sk);

        /*
         *      Charge it to the socket, dropping if the queue is full.
         */
        if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
                goto drop;
        nf_reset(skb);

        if (up->encap_type) {
                /*
                 * This is an encapsulation socket so pass the skb to
                 * the socket's udp_encap_rcv() hook. Otherwise, just
                 * fall through and pass this up the UDP socket.
                 * up->encap_rcv() returns the following value:
                 * =0 if skb was successfully passed to the encap
                 *    handler or was discarded by it.
                 * >0 if skb should be passed on to UDP.
                 * <0 if skb should be resubmitted as proto -N
                 */

                /* if we're overly short, let UDP handle it */
                if (skb->len > sizeof(struct udphdr) &&
                    up->encap_rcv != NULL) {
                        int ret;

                        ret = (*up->encap_rcv)(sk, skb);
                        if (ret <= 0) {
                                UDP_INC_STATS_BH(sock_net(sk),
                                                 UDP_MIB_INDATAGRAMS,
                                                 is_udplite);
                                return -ret;
                        }
                }

                /* FALLTHROUGH -- it's a UDP Packet */
        }

        /*
         *      UDP-Lite specific tests, ignored on UDP sockets
         */
        if ((is_udplite & UDPLITE_RECV_CC)  &&  UDP_SKB_CB(skb)->partial_cov) {

                /*
                 * MIB statistics other than incrementing the error count are
                 * disabled for the following two types of errors: these depend
                 * on the application settings, not on the functioning of the
                 * protocol stack as such.
                 *
                 * RFC 3828 here recommends (sec 3.3): "There should also be a
                 * way ... to ... at least let the receiving application block
                 * delivery of packets with coverage values less than a value
                 * provided by the application."
                 */
                if (up->pcrlen == 0) {          /* full coverage was set  */
                        LIMIT_NETDEBUG(KERN_WARNING "UDPLITE: partial coverage "
                                "%d while full coverage %d requested\n",
                                UDP_SKB_CB(skb)->cscov, skb->len);
                        goto drop;
                }
                /* The next case involves violating the min. coverage requested
                 * by the receiver. This is subtle: if receiver wants x and x is
                 * greater than the buffersize/MTU then receiver will complain
                 * that it wants x while sender emits packets of smaller size y.
                 * Therefore the above ...()->partial_cov statement is essential.
                 */
                if (UDP_SKB_CB(skb)->cscov  <  up->pcrlen) {
                        LIMIT_NETDEBUG(KERN_WARNING
                                "UDPLITE: coverage %d too small, need min %d\n",
                                UDP_SKB_CB(skb)->cscov, up->pcrlen);
                        goto drop;
                }
        }

        if (rcu_dereference_raw(sk->sk_filter)) {
                if (udp_lib_checksum_complete(skb))
                        goto drop;
        }


        if (sk_rcvqueues_full(sk, skb))
                goto drop;

        rc = 0;

        bh_lock_sock(sk);
        if (!sock_owned_by_user(sk))
                rc = __udp_queue_rcv_skb(sk, skb);
        else if (sk_add_backlog(sk, skb)) {
                bh_unlock_sock(sk);
                goto drop;
        }
        bh_unlock_sock(sk);

        return rc;

drop:
        UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
        atomic_inc(&sk->sk_drops);
        kfree_skb(skb);
        return -1;
}


static void flush_stack(struct sock **stack, unsigned int count,
                        struct sk_buff *skb, unsigned int final)
{
        unsigned int i;
        struct sk_buff *skb1 = NULL;
        struct sock *sk;

        for (i = 0; i < count; i++) {
                sk = stack[i];
                if (likely(skb1 == NULL))
                        skb1 = (i == final) ? skb : skb_clone(skb, GFP_ATOMIC);

                if (!skb1) {
                        atomic_inc(&sk->sk_drops);
                        UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_RCVBUFERRORS,
                                         IS_UDPLITE(sk));
                        UDP_INC_STATS_BH(sock_net(sk), UDP_MIB_INERRORS,
                                         IS_UDPLITE(sk));
                }

                if (skb1 && udp_queue_rcv_skb(sk, skb1) <= 0)
                        skb1 = NULL;
        }
        if (unlikely(skb1))
                kfree_skb(skb1);
}

/*
 *      Multicasts and broadcasts go to each listener.
 *
 *      Note: called only from the BH handler context.
 */
static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
                                    struct udphdr  *uh,
                                    __be32 saddr, __be32 daddr,
                                    struct udp_table *udptable)
{
        struct sock *sk, *stack[256 / sizeof(struct sock *)];
        struct udp_hslot *hslot = udp_hashslot(udptable, net, ntohs(uh->dest));
        int dif;
        unsigned int i, count = 0;

        spin_lock(&hslot->lock);
        sk = sk_nulls_head(&hslot->head);
        dif = skb->dev->ifindex;
        sk = udp_v4_mcast_next(net, sk, uh->dest, daddr, uh->source, saddr, dif);
        while (sk) {
                stack[count++] = sk;
                sk = udp_v4_mcast_next(net, sk_nulls_next(sk), uh->dest,
                                       daddr, uh->source, saddr, dif);
                if (unlikely(count == ARRAY_SIZE(stack))) {
                        if (!sk)
                                break;
                        flush_stack(stack, count, skb, ~0);
                        count = 0;
                }
        }
        /*
         * before releasing chain lock, we must take a reference on sockets
         */
        for (i = 0; i < count; i++)
                sock_hold(stack[i]);

        spin_unlock(&hslot->lock);

        /*
         * do the slow work with no lock held
         */
        if (count) {
                flush_stack(stack, count, skb, count - 1);

                for (i = 0; i < count; i++)
                        sock_put(stack[i]);
        } else {
                kfree_skb(skb);
        }
        return 0;
}

/* Initialize UDP checksum. If exited with zero value (success),
 * CHECKSUM_UNNECESSARY means, that no more checks are required.
 * Otherwise, csum completion requires chacksumming packet body,
 * including udp header and folding it to skb->csum.
 */
static inline int udp4_csum_init(struct sk_buff *skb, struct udphdr *uh,
                                 int proto)
{
        const struct iphdr *iph;
        int err;

        UDP_SKB_CB(skb)->partial_cov = 0;
        UDP_SKB_CB(skb)->cscov = skb->len;

        if (proto == IPPROTO_UDPLITE) {
                err = udplite_checksum_init(skb, uh);
                if (err)
                        return err;
        }

        iph = ip_hdr(skb);
        if (uh->check == 0) {
                skb->ip_summed = CHECKSUM_UNNECESSARY;
        } else if (skb->ip_summed == CHECKSUM_COMPLETE) {
                if (!csum_tcpudp_magic(iph->saddr, iph->daddr, skb->len,
                                      proto, skb->csum))
                        skb->ip_summed = CHECKSUM_UNNECESSARY;
        }
        if (!skb_csum_unnecessary(skb))
                skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
                                               skb->len, proto, 0);
        /* Probably, we should checksum udp header (it should be in cache
         * in any case) and data in tiny packets (< rx copybreak).
         */

        return 0;
}

/*
 *      All we need to do is get the socket, and then do a checksum.
 */

int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
                   int proto)
{
        struct sock *sk;
        struct udphdr *uh;
        unsigned short ulen;
        struct rtable *rt = skb_rtable(skb);
        __be32 saddr, daddr;
        struct net *net = dev_net(skb->dev);

        /*
         *  Validate the packet.
         */
        if (!pskb_may_pull(skb, sizeof(struct udphdr)))
                goto drop;              /* No space for header. */

        uh   = udp_hdr(skb);
        ulen = ntohs(uh->len);
        saddr = ip_hdr(skb)->saddr;
        daddr = ip_hdr(skb)->daddr;

        if (ulen > skb->len)
                goto short_packet;

        if (proto == IPPROTO_UDP) {
                /* UDP validates ulen. */
                if (ulen < sizeof(*uh) || pskb_trim_rcsum(skb, ulen))
                        goto short_packet;
                uh = udp_hdr(skb);
        }

        if (udp4_csum_init(skb, uh, proto))
                goto csum_error;

        if (rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
                return __udp4_lib_mcast_deliver(net, skb, uh,
                                saddr, daddr, udptable);

        sk = __udp4_lib_lookup_skb(skb, uh->source, uh->dest, udptable);

        if (sk != NULL) {
                int ret = udp_queue_rcv_skb(sk, skb);
                sock_put(sk);

                /* a return value > 0 means to resubmit the input, but
                 * it wants the return to be -protocol, or 0
                 */
                if (ret > 0)
                        return -ret;
                return 0;
        }

        if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
                goto drop;
        nf_reset(skb);

        /* No socket. Drop packet silently, if checksum is wrong */
        if (udp_lib_checksum_complete(skb))
                goto csum_error;

        UDP_INC_STATS_BH(net, UDP_MIB_NOPORTS, proto == IPPROTO_UDPLITE);
        icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);

        /*
         * Hmm.  We got an UDP packet to a port to which we
         * don't wanna listen.  Ignore it.
         */
        kfree_skb(skb);
        return 0;

short_packet:
        LIMIT_NETDEBUG(KERN_DEBUG "UDP%s: short packet: From %pI4:%u %d/%d to %pI4:%u\n",
                       proto == IPPROTO_UDPLITE ? "-Lite" : "",
                       &saddr,
                       ntohs(uh->source),
                       ulen,
                       skb->len,
                       &daddr,
                       ntohs(uh->dest));
        goto drop;

csum_error:
        /*
         * RFC1122: OK.  Discards the bad packet silently (as far as
         * the network is concerned, anyway) as per 4.1.3.4 (MUST).
         */
        LIMIT_NETDEBUG(KERN_DEBUG "UDP%s: bad checksum. From %pI4:%u to %pI4:%u ulen %d\n",
                       proto == IPPROTO_UDPLITE ? "-Lite" : "",
                       &saddr,
                       ntohs(uh->source),
                       &daddr,
                       ntohs(uh->dest),
                       ulen);
drop:
        UDP_INC_STATS_BH(net, UDP_MIB_INERRORS, proto == IPPROTO_UDPLITE);
        kfree_skb(skb);
        return 0;
}

int udp_rcv(struct sk_buff *skb)
{
        return __udp4_lib_rcv(skb, &udp_table, IPPROTO_UDP);
}

void udp_destroy_sock(struct sock *sk)
{
        bool slow = lock_sock_fast(sk);
        udp_flush_pending_frames(sk);
        unlock_sock_fast(sk, slow);
}

/*
 *      Socket option code for UDP
 */
int udp_lib_setsockopt(struct sock *sk, int level, int optname,
                       char __user *optval, unsigned int optlen,
                       int (*push_pending_frames)(struct sock *))
{
        struct udp_sock *up = udp_sk(sk);
        int val;
        int err = 0;
        int is_udplite = IS_UDPLITE(sk);

        if (optlen < sizeof(int))
                return -EINVAL;

        if (get_user(val, (int __user *)optval))
                return -EFAULT;

        switch (optname) {
        case UDP_CORK:
                if (val != 0) {
                        up->corkflag = 1;
                } else {
                        up->corkflag = 0;
                        lock_sock(sk);
                        (*push_pending_frames)(sk);
                        release_sock(sk);
                }
                break;

        case UDP_ENCAP:
                switch (val) {
                case 0:
                case UDP_ENCAP_ESPINUDP:
                case UDP_ENCAP_ESPINUDP_NON_IKE:
                        up->encap_rcv = xfrm4_udp_encap_rcv;
                        /* FALLTHROUGH */
                case UDP_ENCAP_L2TPINUDP:
                        up->encap_type = val;
                        break;
                default:
                        err = -ENOPROTOOPT;
                        break;
                }
                break;

        /*
         *      UDP-Lite's partial checksum coverage (RFC 3828).
         */
        /* The sender sets actual checksum coverage length via this option.
         * The case coverage > packet length is handled by send module. */
        case UDPLITE_SEND_CSCOV:
                if (!is_udplite)         /* Disable the option on UDP sockets */
                        return -ENOPROTOOPT;
                if (val != 0 && val < 8) /* Illegal coverage: use default (8) */
                        val = 8;
                else if (val > USHRT_MAX)
                        val = USHRT_MAX;
                up->pcslen = val;
                up->pcflag |= UDPLITE_SEND_CC;
                break;

        /* The receiver specifies a minimum checksum coverage value. To make
         * sense, this should be set to at least 8 (as done below). If zero is
         * used, this again means full checksum coverage.                     */
        case UDPLITE_RECV_CSCOV:
                if (!is_udplite)         /* Disable the option on UDP sockets */
                        return -ENOPROTOOPT;
                if (val != 0 && val < 8) /* Avoid silly minimal values.       */
                        val = 8;
                else if (val > USHRT_MAX)
                        val = USHRT_MAX;
                up->pcrlen = val;
                up->pcflag |= UDPLITE_RECV_CC;
                break;

        default:
                err = -ENOPROTOOPT;
                break;
        }

        return err;
}
EXPORT_SYMBOL(udp_lib_setsockopt);

int udp_setsockopt(struct sock *sk, int level, int optname,
                   char __user *optval, unsigned int optlen)
{
        if (level == SOL_UDP  ||  level == SOL_UDPLITE)
                return udp_lib_setsockopt(sk, level, optname, optval, optlen,
                                          udp_push_pending_frames);
        return ip_setsockopt(sk, level, optname, optval, optlen);
}

#ifdef CONFIG_COMPAT
int compat_udp_setsockopt(struct sock *sk, int level, int optname,
                          char __user *optval, unsigned int optlen)
{
        if (level == SOL_UDP  ||  level == SOL_UDPLITE)
                return udp_lib_setsockopt(sk, level, optname, optval, optlen,
                                          udp_push_pending_frames);
        return compat_ip_setsockopt(sk, level, optname, optval, optlen);
}
#endif

int udp_lib_getsockopt(struct sock *sk, int level, int optname,
                       char __user *optval, int __user *optlen)
{
        struct udp_sock *up = udp_sk(sk);
        int val, len;

        if (get_user(len, optlen))
                return -EFAULT;

        len = min_t(unsigned int, len, sizeof(int));

        if (len < 0)
                return -EINVAL;

        switch (optname) {
        case UDP_CORK:
                val = up->corkflag;
                break;

        case UDP_ENCAP:
                val = up->encap_type;
                break;

        /* The following two cannot be changed on UDP sockets, the return is
         * always 0 (which corresponds to the full checksum coverage of UDP). */
        case UDPLITE_SEND_CSCOV:
                val = up->pcslen;
                break;

        case UDPLITE_RECV_CSCOV:
                val = up->pcrlen;
                break;

        default:
                return -ENOPROTOOPT;
        }

        if (put_user(len, optlen))
                return -EFAULT;
        if (copy_to_user(optval, &val, len))
                return -EFAULT;
        return 0;
}
EXPORT_SYMBOL(udp_lib_getsockopt);

int udp_getsockopt(struct sock *sk, int level, int optname,
                   char __user *optval, int __user *optlen)
{
        if (level == SOL_UDP  ||  level == SOL_UDPLITE)
                return udp_lib_getsockopt(sk, level, optname, optval, optlen);
        return ip_getsockopt(sk, level, optname, optval, optlen);
}

#ifdef CONFIG_COMPAT
int compat_udp_getsockopt(struct sock *sk, int level, int optname,
                                 char __user *optval, int __user *optlen)
{
        if (level == SOL_UDP  ||  level == SOL_UDPLITE)
                return udp_lib_getsockopt(sk, level, optname, optval, optlen);
        return compat_ip_getsockopt(sk, level, optname, optval, optlen);
}
#endif
/**
 *      udp_poll - wait for a UDP event.
 *      @file - file struct
 *      @sock - socket
 *      @wait - poll table
 *
 *      This is same as datagram poll, except for the special case of
 *      blocking sockets. If application is using a blocking fd
 *      and a packet with checksum error is in the queue;
 *      then it could get return from select indicating data available
 *      but then block when reading it. Add special case code
 *      to work around these arguably broken applications.
 */
unsigned int udp_poll(struct file *file, struct socket *sock, poll_table *wait)
{
        unsigned int mask = datagram_poll(file, sock, wait);
        struct sock *sk = sock->sk;

        /* Check for false positives due to checksum errors */
        if ((mask & POLLRDNORM) && !(file->f_flags & O_NONBLOCK) &&
            !(sk->sk_shutdown & RCV_SHUTDOWN) && !first_packet_length(sk))
                mask &= ~(POLLIN | POLLRDNORM);

        return mask;

}
EXPORT_SYMBOL(udp_poll);

struct proto udp_prot = {
        .name              = "UDP",
        .owner             = THIS_MODULE,
        .close             = udp_lib_close,
        .connect           = ip4_datagram_connect,
        .disconnect        = udp_disconnect,
        .ioctl             = udp_ioctl,
        .destroy           = udp_destroy_sock,
        .setsockopt        = udp_setsockopt,
        .getsockopt        = udp_getsockopt,
        .sendmsg           = udp_sendmsg,
        .recvmsg           = udp_recvmsg,
        .sendpage          = udp_sendpage,
        .backlog_rcv       = __udp_queue_rcv_skb,
        .hash              = udp_lib_hash,
        .unhash            = udp_lib_unhash,
        .rehash            = udp_v4_rehash,
        .get_port          = udp_v4_get_port,
        .memory_allocated  = &udp_memory_allocated,
        .sysctl_mem        = sysctl_udp_mem,
        .sysctl_wmem       = &sysctl_udp_wmem_min,
        .sysctl_rmem       = &sysctl_udp_rmem_min,
        .obj_size          = sizeof(struct udp_sock),
        .slab_flags        = SLAB_DESTROY_BY_RCU,
        .h.udp_table       = &udp_table,
#ifdef CONFIG_COMPAT
        .compat_setsockopt = compat_udp_setsockopt,
        .compat_getsockopt = compat_udp_getsockopt,
#endif
        .clear_sk          = sk_prot_clear_portaddr_nulls,
};
EXPORT_SYMBOL(udp_prot);

/* ------------------------------------------------------------------------ */
#ifdef CONFIG_PROC_FS

static struct sock *udp_get_first(struct seq_file *seq, int start)
{
        struct sock *sk;
        struct udp_iter_state *state = seq->private;
        struct net *net = seq_file_net(seq);

        for (state->bucket = start; state->bucket <= state->udp_table->mask;
             ++state->bucket) {
                struct hlist_nulls_node *node;
                struct udp_hslot *hslot = &state->udp_table->hash[state->bucket];

                if (hlist_nulls_empty(&hslot->head))
                        continue;

                spin_lock_bh(&hslot->lock);
                sk_nulls_for_each(sk, node, &hslot->head) {
                        if (!net_eq(sock_net(sk), net))
                                continue;
                        if (sk->sk_family == state->family)
                                goto found;
                }
                spin_unlock_bh(&hslot->lock);
        }
        sk = NULL;
found:
        return sk;
}

static struct sock *udp_get_next(struct seq_file *seq, struct sock *sk)
{
        struct udp_iter_state *state = seq->private;
        struct net *net = seq_file_net(seq);

        do {
                sk = sk_nulls_next(sk);
        } while (sk && (!net_eq(sock_net(sk), net) || sk->sk_family != state->family));

        if (!sk) {
                if (state->bucket <= state->udp_table->mask)
                        spin_unlock_bh(&state->udp_table->hash[state->bucket].lock);
                return udp_get_first(seq, state->bucket + 1);
        }
        return sk;
}

static struct sock *udp_get_idx(struct seq_file *seq, loff_t pos)
{
        struct sock *sk = udp_get_first(seq, 0);

        if (sk)
                while (pos && (sk = udp_get_next(seq, sk)) != NULL)
                        --pos;
        return pos ? NULL : sk;
}

static void *udp_seq_start(struct seq_file *seq, loff_t *pos)
{
        struct udp_iter_state *state = seq->private;
        state->bucket = MAX_UDP_PORTS;

        return *pos ? udp_get_idx(seq, *pos-1) : SEQ_START_TOKEN;
}

static void *udp_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct sock *sk;

        if (v == SEQ_START_TOKEN)
                sk = udp_get_idx(seq, 0);
        else
                sk = udp_get_next(seq, v);

        ++*pos;
        return sk;
}

static void udp_seq_stop(struct seq_file *seq, void *v)
{
        struct udp_iter_state *state = seq->private;

        if (state->bucket <= state->udp_table->mask)
                spin_unlock_bh(&state->udp_table->hash[state->bucket].lock);
}

static int udp_seq_open(struct inode *inode, struct file *file)
{
        struct udp_seq_afinfo *afinfo = PDE(inode)->data;
        struct udp_iter_state *s;
        int err;

        err = seq_open_net(inode, file, &afinfo->seq_ops,
                           sizeof(struct udp_iter_state));
        if (err < 0)
                return err;

        s = ((struct seq_file *)file->private_data)->private;
        s->family               = afinfo->family;
        s->udp_table            = afinfo->udp_table;
        return err;
}

/* ------------------------------------------------------------------------ */
int udp_proc_register(struct net *net, struct udp_seq_afinfo *afinfo)
{
        struct proc_dir_entry *p;
        int rc = 0;

        afinfo->seq_fops.open           = udp_seq_open;
        afinfo->seq_fops.read           = seq_read;
        afinfo->seq_fops.llseek         = seq_lseek;
        afinfo->seq_fops.release        = seq_release_net;

        afinfo->seq_ops.start           = udp_seq_start;
        afinfo->seq_ops.next            = udp_seq_next;
        afinfo->seq_ops.stop            = udp_seq_stop;

        p = proc_create_data(afinfo->name, S_IRUGO, net->proc_net,
                             &afinfo->seq_fops, afinfo);
        if (!p)
                rc = -ENOMEM;
        return rc;
}
EXPORT_SYMBOL(udp_proc_register);

void udp_proc_unregister(struct net *net, struct udp_seq_afinfo *afinfo)
{
        proc_net_remove(net, afinfo->name);
}
EXPORT_SYMBOL(udp_proc_unregister);

/* ------------------------------------------------------------------------ */
static void udp4_format_sock(struct sock *sp, struct seq_file *f,
                int bucket, int *len)
{
        struct inet_sock *inet = inet_sk(sp);
        __be32 dest = inet->inet_daddr;
        __be32 src  = inet->inet_rcv_saddr;
        __u16 destp       = ntohs(inet->inet_dport);
        __u16 srcp        = ntohs(inet->inet_sport);

        seq_printf(f, "%5d: %08X:%04X %08X:%04X"
                " %02X %08X:%08X %02X:%08lX %08X %5d %8d %lu %d %p %d%n",
                bucket, src, srcp, dest, destp, sp->sk_state,
                sk_wmem_alloc_get(sp),
                sk_rmem_alloc_get(sp),
                0, 0L, 0, sock_i_uid(sp), 0, sock_i_ino(sp),
                atomic_read(&sp->sk_refcnt), sp,
                atomic_read(&sp->sk_drops), len);
}

int udp4_seq_show(struct seq_file *seq, void *v)
{
        if (v == SEQ_START_TOKEN)
                seq_printf(seq, "%-127s\n",
                           "  sl  local_address rem_address   st tx_queue "
                           "rx_queue tr tm->when retrnsmt   uid  timeout "
                           "inode ref pointer drops");
        else {
                struct udp_iter_state *state = seq->private;
                int len;

                udp4_format_sock(v, seq, state->bucket, &len);
                seq_printf(seq, "%*s\n", 127 - len, "");
        }
        return 0;
}

/* ------------------------------------------------------------------------ */
static struct udp_seq_afinfo udp4_seq_afinfo = {
        .name           = "udp",
        .family         = AF_INET,
        .udp_table      = &udp_table,
        .seq_fops       = {
                .owner  =       THIS_MODULE,
        },
        .seq_ops        = {
                .show           = udp4_seq_show,
        },
};

static int __net_init udp4_proc_init_net(struct net *net)
{
        return udp_proc_register(net, &udp4_seq_afinfo);
}

static void __net_exit udp4_proc_exit_net(struct net *net)
{
        udp_proc_unregister(net, &udp4_seq_afinfo);
}

static struct pernet_operations udp4_net_ops = {
        .init = udp4_proc_init_net,
        .exit = udp4_proc_exit_net,
};

int __init udp4_proc_init(void)
{
        return register_pernet_subsys(&udp4_net_ops);
}

void udp4_proc_exit(void)
{
        unregister_pernet_subsys(&udp4_net_ops);
}
#endif /* CONFIG_PROC_FS */

static __initdata unsigned long uhash_entries;
static int __init set_uhash_entries(char *str)
{
        if (!str)
                return 0;
        uhash_entries = simple_strtoul(str, &str, 0);
        if (uhash_entries && uhash_entries < UDP_HTABLE_SIZE_MIN)
                uhash_entries = UDP_HTABLE_SIZE_MIN;
        return 1;
}
__setup("uhash_entries=", set_uhash_entries);

void __init udp_table_init(struct udp_table *table, const char *name)
{
        unsigned int i;

        if (!CONFIG_BASE_SMALL)
                table->hash = alloc_large_system_hash(name,
                        2 * sizeof(struct udp_hslot),
                        uhash_entries,
                        21, /* one slot per 2 MB */
                        0,
                        &table->log,
                        &table->mask,
                        64 * 1024);
        /*
         * Make sure hash table has the minimum size
         */
        if (CONFIG_BASE_SMALL || table->mask < UDP_HTABLE_SIZE_MIN - 1) {
                table->hash = kmalloc(UDP_HTABLE_SIZE_MIN *
                                      2 * sizeof(struct udp_hslot), GFP_KERNEL);
                if (!table->hash)
                        panic(name);
                table->log = ilog2(UDP_HTABLE_SIZE_MIN);
                table->mask = UDP_HTABLE_SIZE_MIN - 1;
        }
        table->hash2 = table->hash + (table->mask + 1);
        for (i = 0; i <= table->mask; i++) {
                INIT_HLIST_NULLS_HEAD(&table->hash[i].head, i);
                table->hash[i].count = 0;
                spin_lock_init(&table->hash[i].lock);
        }
        for (i = 0; i <= table->mask; i++) {
                INIT_HLIST_NULLS_HEAD(&table->hash2[i].head, i);
                table->hash2[i].count = 0;
                spin_lock_init(&table->hash2[i].lock);
        }
}

void __init udp_init(void)
{
        unsigned long nr_pages, limit;

        udp_table_init(&udp_table, "UDP");
        /* Set the pressure threshold up by the same strategy of TCP. It is a
         * fraction of global memory that is up to 1/2 at 256 MB, decreasing
         * toward zero with the amount of memory, with a floor of 128 pages.
         */
        nr_pages = totalram_pages - totalhigh_pages;
        limit = min(nr_pages, 1UL<<(28-PAGE_SHIFT)) >> (20-PAGE_SHIFT);
        limit = (limit * (nr_pages >> (20-PAGE_SHIFT))) >> (PAGE_SHIFT-11);
        limit = max(limit, 128UL);
        sysctl_udp_mem[0] = limit / 4 * 3;
        sysctl_udp_mem[1] = limit;
        sysctl_udp_mem[2] = sysctl_udp_mem[0] * 2;

        sysctl_udp_rmem_min = SK_MEM_QUANTUM;
        sysctl_udp_wmem_min = SK_MEM_QUANTUM;
}

int udp4_ufo_send_check(struct sk_buff *skb)
{
        const struct iphdr *iph;
        struct udphdr *uh;

        if (!pskb_may_pull(skb, sizeof(*uh)))
                return -EINVAL;

        iph = ip_hdr(skb);
        uh = udp_hdr(skb);

        uh->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr, skb->len,
                                       IPPROTO_UDP, 0);
        skb->csum_start = skb_transport_header(skb) - skb->head;
        skb->csum_offset = offsetof(struct udphdr, check);
        skb->ip_summed = CHECKSUM_PARTIAL;
        return 0;
}

struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb, int features)
{
        struct sk_buff *segs = ERR_PTR(-EINVAL);
        unsigned int mss;
        int offset;
        __wsum csum;

        mss = skb_shinfo(skb)->gso_size;
        if (unlikely(skb->len <= mss))
                goto out;

        if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST)) {
                /* Packet is from an untrusted source, reset gso_segs. */
                int type = skb_shinfo(skb)->gso_type;

                if (unlikely(type & ~(SKB_GSO_UDP | SKB_GSO_DODGY) ||
                             !(type & (SKB_GSO_UDP))))
                        goto out;

                skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss);

                segs = NULL;
                goto out;
        }

        /* Do software UFO. Complete and fill in the UDP checksum as HW cannot
         * do checksum of UDP packets sent as multiple IP fragments.
         */
        offset = skb_checksum_start_offset(skb);
        csum = skb_checksum(skb, offset, skb->len - offset, 0);
        offset += skb->csum_offset;
        *(__sum16 *)(skb->data + offset) = csum_fold(csum);
        skb->ip_summed = CHECKSUM_NONE;

        /* Fragment the skb. IP headers of the fragments are updated in
         * inet_gso_segment()
         */
        segs = skb_segment(skb, features);
out:
        return segs;
}