udp.c

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/*
 * 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).
 *
 * Version:     $Id: udp.c,v 1.100.2.4 2002/03/05 12:47:34 davem Exp $
 *
 * Authors:     Ross Biro, <bir7@leland.Stanford.Edu>
 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 *              Alan Cox, <Alan.Cox@linux.org>
 *
 * 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
 *      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.
 *
 *
 *              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/types.h>
#include <linux/fcntl.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/in.h>
#include <linux/errno.h>
#include <linux/timer.h>
#include <linux/mm.h>
#include <linux/config.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <net/snmp.h>
#include <net/ip.h>
#include <net/ipv6.h>
#include <net/protocol.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <net/udp.h>
#include <net/icmp.h>
#include <net/route.h>
#include <net/inet_common.h>
#include <net/checksum.h>

/*
 *      Snmp MIB for the UDP layer
 */

struct udp_mib          udp_statistics[NR_CPUS*2];

struct sock *udp_hash[UDP_HTABLE_SIZE];
rwlock_t udp_hash_lock = RW_LOCK_UNLOCKED;

/* Shared by v4/v6 udp. */
int udp_port_rover;

static int udp_v4_get_port(struct sock *sk, unsigned short snum)
{
        write_lock_bh(&udp_hash_lock);
        if (snum == 0) {
                int best_size_so_far, best, result, i;

                if (udp_port_rover > sysctl_local_port_range[1] ||
                    udp_port_rover < sysctl_local_port_range[0])
                        udp_port_rover = sysctl_local_port_range[0];
                best_size_so_far = 32767;
                best = result = udp_port_rover;
                for (i = 0; i < UDP_HTABLE_SIZE; i++, result++) {
                        struct sock *sk;
                        int size;

                        sk = udp_hash[result & (UDP_HTABLE_SIZE - 1)];
                        if (!sk) {
                                if (result > sysctl_local_port_range[1])
                                        result = sysctl_local_port_range[0] +
                                                ((result - sysctl_local_port_range[0]) &
                                                 (UDP_HTABLE_SIZE - 1));
                                goto gotit;
                        }
                        size = 0;
                        do {
                                if (++size >= best_size_so_far)
                                        goto next;
                        } while ((sk = sk->next) != NULL);
                        best_size_so_far = size;
                        best = result;
                next:;
                }
                result = best;
                for(i = 0; i < (1 << 16) / UDP_HTABLE_SIZE; i++, result += UDP_HTABLE_SIZE) {
                        if (result > sysctl_local_port_range[1])
                                result = sysctl_local_port_range[0]
                                        + ((result - sysctl_local_port_range[0]) &
                                           (UDP_HTABLE_SIZE - 1));
                        if (!udp_lport_inuse(result))
                                break;
                }
                if (i >= (1 << 16) / UDP_HTABLE_SIZE)
                        goto fail;
gotit:
                udp_port_rover = snum = result;
        } else {
                struct sock *sk2;

                for (sk2 = udp_hash[snum & (UDP_HTABLE_SIZE - 1)];
                     sk2 != NULL;
                     sk2 = sk2->next) {
                        if (sk2->num == snum &&
                            sk2 != sk &&
                            !ipv6_only_sock(sk2) &&
                            (!sk2->bound_dev_if ||
                             !sk->bound_dev_if ||
                             sk2->bound_dev_if == sk->bound_dev_if) &&
                            (!sk2->rcv_saddr ||
                             !sk->rcv_saddr ||
                             sk2->rcv_saddr == sk->rcv_saddr) &&
                            (!sk2->reuse || !sk->reuse))
                                goto fail;
                }
        }
        sk->num = snum;
        if (sk->pprev == NULL) {
                struct sock **skp = &udp_hash[snum & (UDP_HTABLE_SIZE - 1)];
                if ((sk->next = *skp) != NULL)
                        (*skp)->pprev = &sk->next;
                *skp = sk;
                sk->pprev = skp;
                sock_prot_inc_use(sk->prot);
                sock_hold(sk);
        }
        write_unlock_bh(&udp_hash_lock);
        return 0;

fail:
        write_unlock_bh(&udp_hash_lock);
        return 1;
}

static void udp_v4_hash(struct sock *sk)
{
        BUG();
}

static void udp_v4_unhash(struct sock *sk)
{
        write_lock_bh(&udp_hash_lock);
        if (sk->pprev) {
                if (sk->next)
                        sk->next->pprev = sk->pprev;
                *sk->pprev = sk->next;
                sk->pprev = NULL;
                sk->num = 0;
                sock_prot_dec_use(sk->prot);
                __sock_put(sk);
        }
        write_unlock_bh(&udp_hash_lock);
}

/* UDP is nearly always wildcards out the wazoo, it makes no sense to try
 * harder than this. -DaveM
 */
struct sock *udp_v4_lookup_longway(u32 saddr, u16 sport, u32 daddr, u16 dport, int dif)
{
        struct sock *sk, *result = NULL;
        unsigned short hnum = ntohs(dport);
        int badness = -1;

        for(sk = udp_hash[hnum & (UDP_HTABLE_SIZE - 1)]; sk != NULL; sk = sk->next) {
                if(sk->num == hnum && !ipv6_only_sock(sk)) {
                        int score;
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
                        score = sk->family == PF_INET ? 1 : 0;
#else
                        score = 1;
#endif
                        if(sk->rcv_saddr) {
                                if(sk->rcv_saddr != daddr)
                                        continue;
                                score+=2;
                        }
                        if(sk->daddr) {
                                if(sk->daddr != saddr)
                                        continue;
                                score+=2;
                        }
                        if(sk->dport) {
                                if(sk->dport != sport)
                                        continue;
                                score+=2;
                        }
                        if(sk->bound_dev_if) {
                                if(sk->bound_dev_if != dif)
                                        continue;
                                score+=2;
                        }
                        if(score == 9) {
                                result = sk;
                                break;
                        } else if(score > badness) {
                                result = sk;
                                badness = score;
                        }
                }
        }
        return result;
}

__inline__ struct sock *udp_v4_lookup(u32 saddr, u16 sport, u32 daddr, u16 dport, int dif)
{
        struct sock *sk;

        read_lock(&udp_hash_lock);
        sk = udp_v4_lookup_longway(saddr, sport, daddr, dport, dif);
        if (sk)
                sock_hold(sk);
        read_unlock(&udp_hash_lock);
        return sk;
}

extern int ip_mc_sf_allow(struct sock *sk, u32 local, u32 rmt, int dif);

static inline struct sock *udp_v4_mcast_next(struct sock *sk,
                                             u16 loc_port, u32 loc_addr,
                                             u16 rmt_port, u32 rmt_addr,
                                             int dif)
{
        struct sock *s = sk;
        unsigned short hnum = ntohs(loc_port);
        for(; s; s = s->next) {
                if ((s->num != hnum)                                    ||
                    (s->daddr && s->daddr!=rmt_addr)                    ||
                    (s->dport != rmt_port && s->dport != 0)                     ||
                    (s->rcv_saddr  && s->rcv_saddr != loc_addr)         ||
                    ipv6_only_sock(s)                                   ||
                    (s->bound_dev_if && s->bound_dev_if != dif))
                        continue;
                if (!ip_mc_sf_allow(sk, loc_addr, rmt_addr, dif))
                        continue;
                break;
        }
        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 udp_err(struct sk_buff *skb, u32 info)
{
        struct iphdr *iph = (struct iphdr*)skb->data;
        struct udphdr *uh = (struct udphdr*)(skb->data+(iph->ihl<<2));
        int type = skb->h.icmph->type;
        int code = skb->h.icmph->code;
        struct sock *sk;
        int harderr;
        int err;

        sk = udp_v4_lookup(iph->daddr, uh->dest, iph->saddr, uh->source, skb->dev->ifindex);
        if (sk == NULL) {
                ICMP_INC_STATS_BH(IcmpInErrors);
                return; /* No socket for error */
        }

        err = 0;
        harderr = 0;

        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 (sk->protinfo.af_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 (!sk->protinfo.af_inet.recverr) {
                if (!harderr || sk->state != TCP_ESTABLISHED)
                        goto out;
        } else {
                ip_icmp_error(sk, skb, err, uh->dest, info, (u8*)(uh+1));
        }
        sk->err = err;
        sk->error_report(sk);
out:
        sock_put(sk);
}


static unsigned short udp_check(struct udphdr *uh, int len, unsigned long saddr, unsigned long daddr, unsigned long base)
{
        return(csum_tcpudp_magic(saddr, daddr, len, IPPROTO_UDP, base));
}

struct udpfakehdr 
{
        struct udphdr uh;
        u32 saddr;
        u32 daddr;
        struct iovec *iov;
        u32 wcheck;
};

/*
 *      Copy and checksum a UDP packet from user space into a buffer.
 */
 
static int udp_getfrag(const void *p, char * to, unsigned int offset, unsigned int fraglen) 
{
        struct udpfakehdr *ufh = (struct udpfakehdr *)p;
        if (offset==0) {
                if (csum_partial_copy_fromiovecend(to+sizeof(struct udphdr), ufh->iov, offset,
                                                   fraglen-sizeof(struct udphdr), &ufh->wcheck))
                        return -EFAULT;
                ufh->wcheck = csum_partial((char *)ufh, sizeof(struct udphdr),
                                           ufh->wcheck);
                ufh->uh.check = csum_tcpudp_magic(ufh->saddr, ufh->daddr, 
                                          ntohs(ufh->uh.len),
                                          IPPROTO_UDP, ufh->wcheck);
                if (ufh->uh.check == 0)
                        ufh->uh.check = -1;
                memcpy(to, ufh, sizeof(struct udphdr));
                return 0;
        }
        if (csum_partial_copy_fromiovecend(to, ufh->iov, offset-sizeof(struct udphdr),
                                           fraglen, &ufh->wcheck))
                return -EFAULT;
        return 0;
}

/*
 *      Copy a UDP packet from user space into a buffer without checksumming.
 */
 
static int udp_getfrag_nosum(const void *p, char * to, unsigned int offset, unsigned int fraglen) 
{
        struct udpfakehdr *ufh = (struct udpfakehdr *)p;

        if (offset==0) {
                memcpy(to, ufh, sizeof(struct udphdr));
                return memcpy_fromiovecend(to+sizeof(struct udphdr), ufh->iov, offset,
                                           fraglen-sizeof(struct udphdr));
        }
        return memcpy_fromiovecend(to, ufh->iov, offset-sizeof(struct udphdr),
                                   fraglen);
}

int udp_sendmsg(struct sock *sk, struct msghdr *msg, int len)
{
        int ulen = len + sizeof(struct udphdr);
        struct ipcm_cookie ipc;
        struct udpfakehdr ufh;
        struct rtable *rt = NULL;
        int free = 0;
        int connected = 0;
        u32 daddr;
        u8  tos;
        int err;

        /* This check is ONLY to check for arithmetic overflow
           on integer(!) len. Not more! Real check will be made
           in ip_build_xmit --ANK

           BTW socket.c -> af_*.c -> ... make multiple
           invalid conversions size_t -> int. We MUST repair it f.e.
           by replacing all of them with size_t and revise all
           the places sort of len += sizeof(struct iphdr)
           If len was ULONG_MAX-10 it would be cathastrophe  --ANK
         */

        if (len < 0 || len > 0xFFFF)
                return -EMSGSIZE;

        /* 
         *      Check the flags.
         */

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

        /*
         *      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 -EINVAL;
                }

                ufh.daddr = usin->sin_addr.s_addr;
                ufh.uh.dest = usin->sin_port;
                if (ufh.uh.dest == 0)
                        return -EINVAL;
        } else {
                if (sk->state != TCP_ESTABLISHED)
                        return -EDESTADDRREQ;
                ufh.daddr = sk->daddr;
                ufh.uh.dest = sk->dport;
                /* Open fast path for connected socket.
                   Route will not be used, if at least one option is set.
                 */
                connected = 1;
        }
        ipc.addr = sk->saddr;
        ufh.uh.source = sk->sport;

        ipc.opt = NULL;
        ipc.oif = sk->bound_dev_if;
        if (msg->msg_controllen) {
                err = ip_cmsg_send(msg, &ipc);
                if (err)
                        return err;
                if (ipc.opt)
                        free = 1;
                connected = 0;
        }
        if (!ipc.opt)
                ipc.opt = sk->protinfo.af_inet.opt;

        ufh.saddr = ipc.addr;
        ipc.addr = daddr = ufh.daddr;

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

        if (MULTICAST(daddr)) {
                if (!ipc.oif)
                        ipc.oif = sk->protinfo.af_inet.mc_index;
                if (!ufh.saddr)
                        ufh.saddr = sk->protinfo.af_inet.mc_addr;
                connected = 0;
        }

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

        if (rt == NULL) {
                err = ip_route_output(&rt, daddr, ufh.saddr, tos, ipc.oif);
                if (err)
                        goto out;

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

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

        ufh.saddr = rt->rt_src;
        if (!ipc.addr)
                ufh.daddr = ipc.addr = rt->rt_dst;
        ufh.uh.len = htons(ulen);
        ufh.uh.check = 0;
        ufh.iov = msg->msg_iov;
        ufh.wcheck = 0;

        /* RFC1122: OK.  Provides the checksumming facility (MUST) as per */
        /* 4.1.3.4. It's configurable by the application via setsockopt() */
        /* (MAY) and it defaults to on (MUST). */

        err = ip_build_xmit(sk,
                            (sk->no_check == UDP_CSUM_NOXMIT ?
                             udp_getfrag_nosum :
                             udp_getfrag),
                            &ufh, ulen, &ipc, rt, msg->msg_flags);

out:
        ip_rt_put(rt);
        if (free)
                kfree(ipc.opt);
        if (!err) {
                UDP_INC_STATS_USER(UdpOutDatagrams);
                return len;
        }
        return err;

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

/*
 *      IOCTL requests applicable to the UDP protocol
 */
 
int udp_ioctl(struct sock *sk, int cmd, unsigned long arg)
{
        switch(cmd) 
        {
                case SIOCOUTQ:
                {
                        int amount = atomic_read(&sk->wmem_alloc);
                        return put_user(amount, (int *)arg);
                }

                case SIOCINQ:
                {
                        struct sk_buff *skb;
                        unsigned long amount;

                        amount = 0;
                        spin_lock_irq(&sk->receive_queue.lock);
                        skb = skb_peek(&sk->receive_queue);
                        if (skb != NULL) {
                                /*
                                 * We will only return the amount
                                 * of this packet since that is all
                                 * that will be read.
                                 */
                                amount = skb->len - sizeof(struct udphdr);
                        }
                        spin_unlock_irq(&sk->receive_queue.lock);
                        return put_user(amount, (int *)arg);
                }

                default:
                        return -ENOIOCTLCMD;
        }
        return(0);
}

static __inline__ int __udp_checksum_complete(struct sk_buff *skb)
{
        return (unsigned short)csum_fold(skb_checksum(skb, 0, skb->len, skb->csum));
}

static __inline__ int udp_checksum_complete(struct sk_buff *skb)
{
        return skb->ip_summed != CHECKSUM_UNNECESSARY &&
                __udp_checksum_complete(skb);
}

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

int udp_recvmsg(struct sock *sk, struct msghdr *msg, int len,
                int noblock, int flags, int *addr_len)
{
        struct sockaddr_in *sin = (struct sockaddr_in *)msg->msg_name;
        struct sk_buff *skb;
        int copied, err;

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

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

        skb = skb_recv_datagram(sk, flags, noblock, &err);
        if (!skb)
                goto out;
  
        copied = skb->len - sizeof(struct udphdr);
        if (copied > len) {
                copied = len;
                msg->msg_flags |= MSG_TRUNC;
        }

        if (skb->ip_summed==CHECKSUM_UNNECESSARY) {
                err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr), msg->msg_iov,
                                              copied);
        } else if (msg->msg_flags&MSG_TRUNC) {
                if (__udp_checksum_complete(skb))
                        goto csum_copy_err;
                err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr), msg->msg_iov,
                                              copied);
        } 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;

        sock_recv_timestamp(msg, sk, skb);

        /* Copy the address. */
        if (sin)
        {
                sin->sin_family = AF_INET;
                sin->sin_port = skb->h.uh->source;
                sin->sin_addr.s_addr = skb->nh.iph->saddr;
                memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
        }
        if (sk->protinfo.af_inet.cmsg_flags)
                ip_cmsg_recv(msg, skb);
        err = copied;
  
out_free:
        skb_free_datagram(sk, skb);
out:
        return err;

csum_copy_err:
        UDP_INC_STATS_BH(UdpInErrors);

        /* Clear queue. */
        if (flags&MSG_PEEK) {
                int clear = 0;
                spin_lock_irq(&sk->receive_queue.lock);
                if (skb == skb_peek(&sk->receive_queue)) {
                        __skb_unlink(skb, &sk->receive_queue);
                        clear = 1;
                }
                spin_unlock_irq(&sk->receive_queue.lock);
                if (clear)
                        kfree_skb(skb);
        }

        skb_free_datagram(sk, skb);

        return -EAGAIN; 
}

int udp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
{
        struct sockaddr_in *usin = (struct sockaddr_in *) uaddr;
        struct rtable *rt;
        u32 saddr;
        int oif;
        int err;

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

        if (usin->sin_family != AF_INET) 
                return -EAFNOSUPPORT;

        sk_dst_reset(sk);

        oif = sk->bound_dev_if;
        saddr = sk->saddr;
        if (MULTICAST(usin->sin_addr.s_addr)) {
                if (!oif)
                        oif = sk->protinfo.af_inet.mc_index;
                if (!saddr)
                        saddr = sk->protinfo.af_inet.mc_addr;
        }
        err = ip_route_connect(&rt, usin->sin_addr.s_addr, saddr,
                               RT_CONN_FLAGS(sk), oif);
        if (err)
                return err;
        if ((rt->rt_flags&RTCF_BROADCAST) && !sk->broadcast) {
                ip_rt_put(rt);
                return -EACCES;
        }
        if(!sk->saddr)
                sk->saddr = rt->rt_src;         /* Update source address */
        if(!sk->rcv_saddr)
                sk->rcv_saddr = rt->rt_src;
        sk->daddr = rt->rt_dst;
        sk->dport = usin->sin_port;
        sk->state = TCP_ESTABLISHED;
        sk->protinfo.af_inet.id = jiffies;

        sk_dst_set(sk, &rt->u.dst);
        return(0);
}

int udp_disconnect(struct sock *sk, int flags)
{
        /*
         *      1003.1g - break association.
         */
         
        sk->state = TCP_CLOSE;
        sk->daddr = 0;
        sk->dport = 0;
        sk->bound_dev_if = 0;
        if (!(sk->userlocks&SOCK_BINDADDR_LOCK)) {
                sk->rcv_saddr = 0;
                sk->saddr = 0;
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
                memset(&sk->net_pinfo.af_inet6.saddr, 0, 16);
                memset(&sk->net_pinfo.af_inet6.rcv_saddr, 0, 16);
#endif
        }
        if (!(sk->userlocks&SOCK_BINDPORT_LOCK)) {
                sk->prot->unhash(sk);
                sk->sport = 0;
        }
        sk_dst_reset(sk);
        return 0;
}

static void udp_close(struct sock *sk, long timeout)
{
        inet_sock_release(sk);
}

static int udp_queue_rcv_skb(struct sock * sk, struct sk_buff *skb)
{
        /*
         *      Charge it to the socket, dropping if the queue is full.
         */

#if defined(CONFIG_FILTER)
        if (sk->filter && skb->ip_summed != CHECKSUM_UNNECESSARY) {
                if (__udp_checksum_complete(skb)) {
                        UDP_INC_STATS_BH(UdpInErrors);
                        IP_INC_STATS_BH(IpInDiscards);
                        ip_statistics[smp_processor_id()*2].IpInDelivers--;
                        kfree_skb(skb);
                        return -1;
                }
                skb->ip_summed = CHECKSUM_UNNECESSARY;
        }
#endif

        if (sock_queue_rcv_skb(sk,skb)<0) {
                UDP_INC_STATS_BH(UdpInErrors);
                IP_INC_STATS_BH(IpInDiscards);
                ip_statistics[smp_processor_id()*2].IpInDelivers--;
                kfree_skb(skb);
                return -1;
        }
        UDP_INC_STATS_BH(UdpInDatagrams);
        return 0;
}

/*
 *      Multicasts and broadcasts go to each listener.
 *
 *      Note: called only from the BH handler context,
 *      so we don't need to lock the hashes.
 */
static int udp_v4_mcast_deliver(struct sk_buff *skb, struct udphdr *uh,
                                 u32 saddr, u32 daddr)
{
        struct sock *sk;
        int dif;

        read_lock(&udp_hash_lock);
        sk = udp_hash[ntohs(uh->dest) & (UDP_HTABLE_SIZE - 1)];
        dif = skb->dev->ifindex;
        sk = udp_v4_mcast_next(sk, uh->dest, daddr, uh->source, saddr, dif);
        if (sk) {
                struct sock *sknext = NULL;

                do {
                        struct sk_buff *skb1 = skb;

                        sknext = udp_v4_mcast_next(sk->next, uh->dest, daddr,
                                                   uh->source, saddr, dif);
                        if(sknext)
                                skb1 = skb_clone(skb, GFP_ATOMIC);

                        if(skb1)
                                udp_queue_rcv_skb(sk, skb1);
                        sk = sknext;
                } while(sknext);
        } else
                kfree_skb(skb);
        read_unlock(&udp_hash_lock);
        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 int udp_checksum_init(struct sk_buff *skb, struct udphdr *uh,
                             unsigned short ulen, u32 saddr, u32 daddr)
{
        if (uh->check == 0) {
                skb->ip_summed = CHECKSUM_UNNECESSARY;
        } else if (skb->ip_summed == CHECKSUM_HW) {
                skb->ip_summed = CHECKSUM_UNNECESSARY;
                if (!udp_check(uh, ulen, saddr, daddr, skb->csum))
                        return 0;
                NETDEBUG(if (net_ratelimit()) printk(KERN_DEBUG "udp v4 hw csum failure.\n"));
                skb->ip_summed = CHECKSUM_NONE;
        }
        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                skb->csum = csum_tcpudp_nofold(saddr, daddr, ulen, IPPROTO_UDP, 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 udp_rcv(struct sk_buff *skb)
{
        struct sock *sk;
        struct udphdr *uh;
        unsigned short ulen;
        struct rtable *rt = (struct rtable*)skb->dst;
        u32 saddr = skb->nh.iph->saddr;
        u32 daddr = skb->nh.iph->daddr;
        int len = skb->len;

        IP_INC_STATS_BH(IpInDelivers);

        /*
         *      Validate the packet and the UDP length.
         */
        if (!pskb_may_pull(skb, sizeof(struct udphdr)))
                goto no_header;

        uh = skb->h.uh;

        ulen = ntohs(uh->len);

        if (ulen > len || ulen < sizeof(*uh))
                goto short_packet;

        if (pskb_trim(skb, ulen))
                goto short_packet;

        if (udp_checksum_init(skb, uh, ulen, saddr, daddr) < 0)
                goto csum_error;

        if(rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
                return udp_v4_mcast_deliver(skb, uh, saddr, daddr);

        sk = udp_v4_lookup(saddr, uh->source, daddr, uh->dest, skb->dev->ifindex);

        if (sk != NULL) {
                udp_queue_rcv_skb(sk, skb);
                sock_put(sk);
                return 0;
        }

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

        UDP_INC_STATS_BH(UdpNoPorts);
        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:
        NETDEBUG(if (net_ratelimit())
                 printk(KERN_DEBUG "UDP: short packet: %u.%u.%u.%u:%u %d/%d to %u.%u.%u.%u:%u\n",
                        NIPQUAD(saddr),
                        ntohs(uh->source),
                        ulen,
                        len,
                        NIPQUAD(daddr),
                        ntohs(uh->dest)));
no_header:
        UDP_INC_STATS_BH(UdpInErrors);
        kfree_skb(skb);
        return(0);

csum_error:
        /* 
         * RFC1122: OK.  Discards the bad packet silently (as far as 
         * the network is concerned, anyway) as per 4.1.3.4 (MUST). 
         */
        NETDEBUG(if (net_ratelimit())
                 printk(KERN_DEBUG "UDP: bad checksum. From %d.%d.%d.%d:%d to %d.%d.%d.%d:%d ulen %d\n",
                        NIPQUAD(saddr),
                        ntohs(uh->source),
                        NIPQUAD(daddr),
                        ntohs(uh->dest),
                        ulen));
        UDP_INC_STATS_BH(UdpInErrors);
        kfree_skb(skb);
        return(0);
}

static void get_udp_sock(struct sock *sp, char *tmpbuf, int i)
{
        unsigned int dest, src;
        __u16 destp, srcp;

        dest  = sp->daddr;
        src   = sp->rcv_saddr;
        destp = ntohs(sp->dport);
        srcp  = ntohs(sp->sport);
        sprintf(tmpbuf, "%4d: %08X:%04X %08X:%04X"
                " %02X %08X:%08X %02X:%08lX %08X %5d %8d %lu %d %p",
                i, src, srcp, dest, destp, sp->state, 
                atomic_read(&sp->wmem_alloc), atomic_read(&sp->rmem_alloc),
                0, 0L, 0,
                sock_i_uid(sp), 0,
                sock_i_ino(sp),
                atomic_read(&sp->refcnt), sp);
}

int udp_get_info(char *buffer, char **start, off_t offset, int length)
{
        int len = 0, num = 0, i;
        off_t pos = 0;
        off_t begin;
        char tmpbuf[129];

        if (offset < 128) 
                len += sprintf(buffer, "%-127s\n",
                               "  sl  local_address rem_address   st tx_queue "
                               "rx_queue tr tm->when retrnsmt   uid  timeout inode");
        pos = 128;
        read_lock(&udp_hash_lock);
        for (i = 0; i < UDP_HTABLE_SIZE; i++) {
                struct sock *sk;

                for (sk = udp_hash[i]; sk; sk = sk->next, num++) {
                        if (sk->family != PF_INET)
                                continue;
                        pos += 128;
                        if (pos <= offset)
                                continue;
                        get_udp_sock(sk, tmpbuf, i);
                        len += sprintf(buffer+len, "%-127s\n", tmpbuf);
                        if(len >= length)
                                goto out;
                }
        }
out:
        read_unlock(&udp_hash_lock);
        begin = len - (pos - offset);
        *start = buffer + begin;
        len -= begin;
        if(len > length)
                len = length;
        if (len < 0)
                len = 0; 
        return len;
}

struct proto udp_prot = {
        name:           "UDP",
        close:          udp_close,
        connect:        udp_connect,
        disconnect:     udp_disconnect,
        ioctl:          udp_ioctl,
        setsockopt:     ip_setsockopt,
        getsockopt:     ip_getsockopt,
        sendmsg:        udp_sendmsg,
        recvmsg:        udp_recvmsg,
        backlog_rcv:    udp_queue_rcv_skb,
        hash:           udp_v4_hash,
        unhash:         udp_v4_unhash,
        get_port:       udp_v4_get_port,
};

---