ip_vs_core.c

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/*
 * IPVS         An implementation of the IP virtual server support for the
 *              LINUX operating system.  IPVS is now implemented as a module
 *              over the Netfilter framework. IPVS can be used to build a
 *              high-performance and highly available server based on a
 *              cluster of servers.
 *
 * Version:     $Id: ip_vs_core.c,v 1.31.2.5 2003/07/29 14:37:12 wensong Exp $
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *              Peter Kese <peter.kese@ijs.si>
 *              Julian Anastasov <ja@ssi.bg>
 *
 *              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.
 *
 * The IPVS code for kernel 2.2 was done by Wensong Zhang and Peter Kese,
 * with changes/fixes from Julian Anastasov, Lars Marowsky-Bree, Horms
 * and others.
 *
 * Changes:
 *
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/icmp.h>

#include <net/ip.h>
#include <net/tcp.h>
#include <net/udp.h>
#include <net/icmp.h>                   /* for icmp_send */
#include <net/route.h>

#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>

#include <net/ip_vs.h>


EXPORT_SYMBOL(register_ip_vs_scheduler);
EXPORT_SYMBOL(unregister_ip_vs_scheduler);
EXPORT_SYMBOL(ip_vs_skb_replace);
EXPORT_SYMBOL(ip_vs_proto_name);
EXPORT_SYMBOL(ip_vs_conn_new);
EXPORT_SYMBOL(ip_vs_conn_in_get);
EXPORT_SYMBOL(ip_vs_conn_out_get);
EXPORT_SYMBOL(ip_vs_conn_listen);
EXPORT_SYMBOL(ip_vs_conn_put);
#ifdef CONFIG_IP_VS_DEBUG
EXPORT_SYMBOL(ip_vs_get_debug_level);
#endif
EXPORT_SYMBOL(check_for_ip_vs_out);


/* ID used in ICMP lookups */
#define icmp_id(icmph)          ((icmph->un).echo.id)

const char *ip_vs_proto_name(unsigned proto)
{
        static char buf[20];

        switch (proto) {
        case IPPROTO_IP:
                return "IP";
        case IPPROTO_UDP:
                return "UDP";
        case IPPROTO_TCP:
                return "TCP";
        case IPPROTO_ICMP:
                return "ICMP";
        default:
                sprintf(buf, "IP_%d", proto);
                return buf;
        }
}


static inline void
ip_vs_in_stats(struct ip_vs_conn *cp, struct sk_buff *skb)
{
        struct ip_vs_dest *dest = cp->dest;
        if (dest && (dest->flags & IP_VS_DEST_F_AVAILABLE)) {
                spin_lock(&dest->stats.lock);
                dest->stats.inpkts++;
                dest->stats.inbytes += skb->len;
                spin_unlock(&dest->stats.lock);

                spin_lock(&dest->svc->stats.lock);
                dest->svc->stats.inpkts++;
                dest->svc->stats.inbytes += skb->len;
                spin_unlock(&dest->svc->stats.lock);

                spin_lock(&ip_vs_stats.lock);
                ip_vs_stats.inpkts++;
                ip_vs_stats.inbytes += skb->len;
                spin_unlock(&ip_vs_stats.lock);
        }
}


static inline void
ip_vs_out_stats(struct ip_vs_conn *cp, struct sk_buff *skb)
{
        struct ip_vs_dest *dest = cp->dest;
        if (dest && (dest->flags & IP_VS_DEST_F_AVAILABLE)) {
                spin_lock(&dest->stats.lock);
                dest->stats.outpkts++;
                dest->stats.outbytes += skb->len;
                spin_unlock(&dest->stats.lock);

                spin_lock(&dest->svc->stats.lock);
                dest->svc->stats.outpkts++;
                dest->svc->stats.outbytes += skb->len;
                spin_unlock(&dest->svc->stats.lock);

                spin_lock(&ip_vs_stats.lock);
                ip_vs_stats.outpkts++;
                ip_vs_stats.outbytes += skb->len;
                spin_unlock(&ip_vs_stats.lock);
        }
}


static inline void
ip_vs_conn_stats(struct ip_vs_conn *cp, struct ip_vs_service *svc)
{
        spin_lock(&cp->dest->stats.lock);
        cp->dest->stats.conns++;
        spin_unlock(&cp->dest->stats.lock);

        spin_lock(&svc->stats.lock);
        svc->stats.conns++;
        spin_unlock(&svc->stats.lock);

        spin_lock(&ip_vs_stats.lock);
        ip_vs_stats.conns++;
        spin_unlock(&ip_vs_stats.lock);
}

/*
 *  IPVS persistent scheduling function
 *  It creates a connection entry according to its template if exists,
 *  or selects a server and creates a connection entry plus a template.
 *  Locking: we are svc user (svc->refcnt), so we hold all dests too
 */
static struct ip_vs_conn *
ip_vs_sched_persist(struct ip_vs_service *svc, struct iphdr *iph)
{
        struct ip_vs_conn *cp = NULL;
        struct ip_vs_dest *dest;
        const __u16 *portp;
        struct ip_vs_conn *ct;
        __u16  dport;    /* destination port to forward */
        __u32  snet;     /* source network of the client, after masking */

        portp = (__u16 *)&(((char *)iph)[iph->ihl*4]);

        /* Mask saddr with the netmask to adjust template granularity */
        snet = iph->saddr & svc->netmask;

        IP_VS_DBG(6, "P-schedule: src %u.%u.%u.%u:%u dest %u.%u.%u.%u:%u "
                  "mnet %u.%u.%u.%u\n",
                  NIPQUAD(iph->saddr), ntohs(portp[0]),
                  NIPQUAD(iph->daddr), ntohs(portp[1]),
                  NIPQUAD(snet));

        /*
         * As far as we know, FTP is a very complicated network protocol, and
         * it uses control connection and data connections. For active FTP,
         * FTP server initialize data connection to the client, its source port
         * is often 20. For passive FTP, FTP server tells the clients the port
         * that it passively listens to,  and the client issues the data
         * connection. In the tunneling or direct routing mode, the load
         * balancer is on the client-to-server half of connection, the port
         * number is unknown to the load balancer. So, a conn template like
         * <caddr, 0, vaddr, 0, daddr, 0> is created for persistent FTP
         * service, and a template like <caddr, 0, vaddr, vport, daddr, dport>
         * is created for other persistent services.
         */
        if (portp[1] == svc->port) {
                /* Check if a template already exists */
                if (svc->port != FTPPORT)
                        ct = ip_vs_conn_in_get(iph->protocol, snet, 0,
                                               iph->daddr, portp[1]);
                else
                        ct = ip_vs_conn_in_get(iph->protocol, snet, 0,
                                               iph->daddr, 0);

                if (!ct || !ip_vs_check_template(ct)) {
                        /*
                         * No template found or the dest of the connection
                         * template is not available.
                         */
                        dest = svc->scheduler->schedule(svc, iph);
                        if (dest == NULL) {
                                IP_VS_DBG(1, "P-schedule: no dest found.\n");
                                return NULL;
                        }

                        /*
                         * Create a template like <protocol,caddr,0,
                         * vaddr,vport,daddr,dport> for non-ftp service,
                         * and <protocol,caddr,0,vaddr,0,daddr,0>
                         * for ftp service.
                         */
                        if (svc->port != FTPPORT)
                                ct = ip_vs_conn_new(iph->protocol,
                                                    snet, 0,
                                                    iph->daddr, portp[1],
                                                    dest->addr, dest->port,
                                                    0,
                                                    dest);
                        else
                                ct = ip_vs_conn_new(iph->protocol,
                                                    snet, 0,
                                                    iph->daddr, 0,
                                                    dest->addr, 0,
                                                    0,
                                                    dest);
                        if (ct == NULL)
                                return NULL;

                        ct->timeout = svc->timeout;
                } else {
                        /* set destination with the found template */
                        dest = ct->dest;
                }
                dport = dest->port;
        } else {
                /*
                 * Note: persistent fwmark-based services and persistent
                 * port zero service are handled here.
                 * fwmark template: <IPPROTO_IP,caddr,0,fwmark,0,daddr,0>
                 * port zero template: <protocol,caddr,0,vaddr,0,daddr,0>
                 */
                if (svc->fwmark)
                        ct = ip_vs_conn_in_get(IPPROTO_IP, snet, 0,
                                               htonl(svc->fwmark), 0);
                else
                        ct = ip_vs_conn_in_get(iph->protocol, snet, 0,
                                               iph->daddr, 0);

                if (!ct || !ip_vs_check_template(ct)) {
                        /*
                         * If it is not persistent port zero, return NULL,
                         * otherwise create a connection template.
                         */
                        if (svc->port)
                                return NULL;

                        dest = svc->scheduler->schedule(svc, iph);
                        if (dest == NULL) {
                                IP_VS_DBG(1, "P-schedule: no dest found.\n");
                                return NULL;
                        }

                        /*
                         * Create a template according to the service
                         */
                        if (svc->fwmark)
                                ct = ip_vs_conn_new(IPPROTO_IP,
                                                    snet, 0,
                                                    htonl(svc->fwmark), 0,
                                                    dest->addr, 0,
                                                    0,
                                                    dest);
                        else
                                ct = ip_vs_conn_new(iph->protocol,
                                                    snet, 0,
                                                    iph->daddr, 0,
                                                    dest->addr, 0,
                                                    0,
                                                    dest);
                        if (ct == NULL)
                                return NULL;

                        ct->timeout = svc->timeout;
                } else {
                        /* set destination with the found template */
                        dest = ct->dest;
                }
                dport = portp[1];
        }

        /*
         *    Create a new connection according to the template
         */
        cp = ip_vs_conn_new(iph->protocol,
                            iph->saddr, portp[0],
                            iph->daddr, portp[1],
                            dest->addr, dport,
                            0,
                            dest);
        if (cp == NULL) {
                ip_vs_conn_put(ct);
                return NULL;
        }

        /*
         *    Increase the inactive connection counter
         *    because it is in Syn-Received
         *    state (inactive) when the connection is created.
         */
        atomic_inc(&dest->inactconns);

        /*
         *    Add its control
         */
        ip_vs_control_add(cp, ct);

        ip_vs_conn_put(ct);
        return cp;
}


/*
 *  IPVS main scheduling function
 *  It selects a server according to the virtual service, and
 *  creates a connection entry.
 */
static struct ip_vs_conn *
ip_vs_schedule(struct ip_vs_service *svc, struct iphdr *iph)
{
        struct ip_vs_conn *cp = NULL;
        struct ip_vs_dest *dest;
        const __u16 *portp;

        /*
         *    Persistent service
         */
        if (svc->flags & IP_VS_SVC_F_PERSISTENT)
                return ip_vs_sched_persist(svc, iph);

        /*
         *    Non-persistent service
         */
        portp = (__u16 *)&(((char *)iph)[iph->ihl*4]);
        if (!svc->fwmark && portp[1] != svc->port) {
                if (!svc->port)
                        IP_VS_ERR("Schedule: port zero only supported "
                                  "in persistent services, "
                                  "check your ipvs configuration\n");
                return NULL;
        }

        dest = svc->scheduler->schedule(svc, iph);
        if (dest == NULL) {
                IP_VS_DBG(1, "Schedule: no dest found.\n");
                return NULL;
        }

        /*
         *    Create a connection entry.
         */
        cp = ip_vs_conn_new(iph->protocol,
                            iph->saddr, portp[0],
                            iph->daddr, portp[1],
                            dest->addr, dest->port?dest->port:portp[1],
                            0,
                            dest);
        if (cp == NULL)
                return NULL;

        /*
         *    Increase the inactive connection counter because it is in
         *    Syn-Received state (inactive) when the connection is created.
         */
        atomic_inc(&dest->inactconns);

        IP_VS_DBG(6, "Schedule fwd:%c s:%s c:%u.%u.%u.%u:%u v:%u.%u.%u.%u:%u "
                  "d:%u.%u.%u.%u:%u flg:%X cnt:%d\n",
                  ip_vs_fwd_tag(cp), ip_vs_state_name(cp->state),
                  NIPQUAD(cp->caddr), ntohs(cp->cport),
                  NIPQUAD(cp->vaddr), ntohs(cp->vport),
                  NIPQUAD(cp->daddr), ntohs(cp->dport),
                  cp->flags, atomic_read(&cp->refcnt));

        return cp;
}


/*
 *  Pass or drop the packet.
 *  Called by ip_vs_in, when the virtual service is available but
 *  no destination is available for a new connection.
 */
static int ip_vs_leave(struct ip_vs_service *svc, struct sk_buff *skb)
{
        struct iphdr *iph = skb->nh.iph;
        __u16 *portp = (__u16 *)&(((char *)iph)[iph->ihl*4]);

        /* if it is fwmark-based service, the cache_bypass sysctl is up
           and the destination is RTN_UNICAST (and not local), then create
           a cache_bypass connection entry */
        if (sysctl_ip_vs_cache_bypass && svc->fwmark
            && (inet_addr_type(iph->daddr) == RTN_UNICAST)) {
                int ret;
                struct ip_vs_conn *cp;

                ip_vs_service_put(svc);

                /* create a new connection entry */
                IP_VS_DBG(6, "ip_vs_leave: create a cache_bypass entry\n");
                cp = ip_vs_conn_new(iph->protocol,
                                    iph->saddr, portp[0],
                                    iph->daddr, portp[1],
                                    0, 0,
                                    IP_VS_CONN_F_BYPASS,
                                    NULL);
                if (cp == NULL) {
                        kfree_skb(skb);
                        return NF_STOLEN;
                }

                /* statistics */
                ip_vs_in_stats(cp, skb);

                /* set state */
                ip_vs_set_state(cp, VS_STATE_INPUT, iph, portp);

                /* transmit the first SYN packet */
                ret = cp->packet_xmit(skb, cp);

                atomic_inc(&cp->in_pkts);
                ip_vs_conn_put(cp);
                return ret;
        }

        /*
         * When the virtual ftp service is presented, packets destined
         * for other services on the VIP may get here (except services
         * listed in the ipvs table), pass the packets, because it is
         * not ipvs job to decide to drop the packets.
         */
        if ((svc->port == FTPPORT) && (portp[1] != FTPPORT)) {
                ip_vs_service_put(svc);
                return NF_ACCEPT;
        }

        ip_vs_service_put(svc);

        /*
         * Notify the client that the destination is unreachable, and
         * release the socket buffer.
         * Since it is in IP layer, the TCP socket is not actually
         * created, the TCP RST packet cannot be sent, instead that
         * ICMP_PORT_UNREACH is sent here no matter it is TCP/UDP. --WZ
         */
        icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
        kfree_skb(skb);
        return NF_STOLEN;
}


/*
 *      It is hooked before NF_IP_PRI_NAT_SRC at the NF_IP_POST_ROUTING
 *      chain, and is used for VS/NAT.
 *      It detects packets for VS/NAT connections and sends the packets
 *      immediately. This can avoid that iptable_nat mangles the packets
 *      for VS/NAT.
 */
static unsigned int ip_vs_post_routing(unsigned int hooknum,
                                       struct sk_buff **skb_p,
                                       const struct net_device *in,
                                       const struct net_device *out,
                                       int (*okfn)(struct sk_buff *))
{
        struct sk_buff  *skb = *skb_p;

        if (!(skb->nfcache & NFC_IPVS_PROPERTY))
                return NF_ACCEPT;

        /* The packet was sent from IPVS, exit this chain */
        (*okfn)(skb);

        return NF_STOLEN;
}


/*
 *      Handle ICMP messages in the inside-to-outside direction (outgoing).
 *      Find any that might be relevant, check against existing connections,
 *      forward to the right destination host if relevant.
 *      Currently handles error types - unreachable, quench, ttl exceeded.
 *      (Only used in VS/NAT)
 */
static int ip_vs_out_icmp(struct sk_buff **skb_p)
{
        struct sk_buff  *skb   = *skb_p;
        struct iphdr    *iph;
        struct icmphdr  *icmph;
        struct iphdr    *ciph;  /* The ip header contained within the ICMP */
        __u16           *pptr;  /* port numbers from TCP/UDP contained header */
        unsigned short  ihl;
        unsigned short  len;
        unsigned short  clen, csize;
        struct ip_vs_conn *cp;

        /* reassemble IP fragments, but will it happen in ICMP packets?? */
        if (skb->nh.iph->frag_off & __constant_htons(IP_MF|IP_OFFSET)) {
                skb = ip_defrag(skb);
                if (!skb)
                        return NF_STOLEN;
                *skb_p = skb;
        }

        if (skb_is_nonlinear(skb)) {
                if (skb_linearize(skb, GFP_ATOMIC) != 0)
                        return NF_DROP;
                ip_send_check(skb->nh.iph);
        }

        iph = skb->nh.iph;
        ihl = iph->ihl << 2;
        icmph = (struct icmphdr *)((char *)iph + ihl);
        len   = ntohs(iph->tot_len) - ihl;
        if (len < sizeof(struct icmphdr))
                return NF_DROP;

        IP_VS_DBG(12, "outgoing ICMP (%d,%d) %u.%u.%u.%u->%u.%u.%u.%u\n",
                  icmph->type, ntohs(icmp_id(icmph)),
                  NIPQUAD(iph->saddr), NIPQUAD(iph->daddr));

        /*
         * Work through seeing if this is for us.
         * These checks are supposed to be in an order that means easy
         * things are checked first to speed up processing.... however
         * this means that some packets will manage to get a long way
         * down this stack and then be rejected, but that's life.
         */
        if ((icmph->type != ICMP_DEST_UNREACH) &&
            (icmph->type != ICMP_SOURCE_QUENCH) &&
            (icmph->type != ICMP_TIME_EXCEEDED))
                return NF_ACCEPT;

        /* Now find the contained IP header */
        clen = len - sizeof(struct icmphdr);
        if (clen < sizeof(struct iphdr))
                return NF_DROP;
        ciph = (struct iphdr *) (icmph + 1);
        csize = ciph->ihl << 2;
        if (clen < csize)
                return NF_DROP;

        /* We are only interested ICMPs generated from TCP or UDP packets */
        if (ciph->protocol != IPPROTO_UDP && ciph->protocol != IPPROTO_TCP)
                return NF_ACCEPT;

        /* Skip non-first embedded TCP/UDP fragments */
        if (ciph->frag_off & __constant_htons(IP_OFFSET))
                return NF_ACCEPT;

        /* We need at least TCP/UDP ports here */
        if (clen < csize + sizeof(struct udphdr))
                return NF_DROP;

        /*
         * Find the ports involved - this packet was
         * incoming so the ports are right way round
         * (but reversed relative to outer IP header!)
         */
        pptr = (__u16 *)&(((char *)ciph)[csize]);

        /* Ensure the checksum is correct */
        if (ip_compute_csum((unsigned char *) icmph, len)) {
                /* Failed checksum! */
                IP_VS_DBG(1, "forward ICMP: failed checksum from %d.%d.%d.%d!\n",
                          NIPQUAD(iph->saddr));
                return NF_DROP;
        }

        IP_VS_DBG(11, "Handling outgoing ICMP for "
                  "%u.%u.%u.%u:%d -> %u.%u.%u.%u:%d\n",
                  NIPQUAD(ciph->saddr), ntohs(pptr[0]),
                  NIPQUAD(ciph->daddr), ntohs(pptr[1]));

        /* ciph content is actually <protocol, caddr, cport, daddr, dport> */
        cp = ip_vs_conn_out_get(ciph->protocol, ciph->daddr, pptr[1],
                                ciph->saddr, pptr[0]);
        if (!cp)
                return NF_ACCEPT;

        if (IP_VS_FWD_METHOD(cp) != 0) {
                IP_VS_ERR("shouldn't reach here, because the box is on the"
                          "half connection in the tun/dr module.\n");
        }

        /* Now we do real damage to this packet...! */
        /* First change the source IP address, and recalc checksum */
        iph->saddr = cp->vaddr;
        ip_send_check(iph);

        /* Now change the *dest* address in the contained IP */
        ciph->daddr = cp->vaddr;
        ip_send_check(ciph);

        /* the TCP/UDP dest port - cannot redo check */
        pptr[1] = cp->vport;

        /* And finally the ICMP checksum */
        icmph->checksum = 0;
        icmph->checksum = ip_compute_csum((unsigned char *) icmph, len);
        skb->ip_summed = CHECKSUM_UNNECESSARY;

        /* do the statistics and put it back */
        ip_vs_out_stats(cp, skb);
        ip_vs_conn_put(cp);

        IP_VS_DBG(11, "Forwarding correct outgoing ICMP to "
                  "%u.%u.%u.%u:%d -> %u.%u.%u.%u:%d\n",
                  NIPQUAD(ciph->saddr), ntohs(pptr[0]),
                  NIPQUAD(ciph->daddr), ntohs(pptr[1]));

        skb->nfcache |= NFC_IPVS_PROPERTY;

        return NF_ACCEPT;
}


/*
 *      It is hooked at the NF_IP_FORWARD chain, used only for VS/NAT.
 *      Check if outgoing packet belongs to the established ip_vs_conn,
 *      rewrite addresses of the packet and send it on its way...
 */
static unsigned int ip_vs_out(unsigned int hooknum,
                              struct sk_buff **skb_p,
                              const struct net_device *in,
                              const struct net_device *out,
                              int (*okfn)(struct sk_buff *))
{
        struct sk_buff  *skb = *skb_p;
        struct iphdr    *iph;
        union ip_vs_tphdr h;
        struct ip_vs_conn *cp;
        int size;
        int ihl;

        EnterFunction(11);

        if (skb->nfcache & NFC_IPVS_PROPERTY)
                return NF_ACCEPT;

        iph = skb->nh.iph;
        if (iph->protocol == IPPROTO_ICMP)
                return ip_vs_out_icmp(skb_p);

        /* let it go if other IP protocols */
        if (iph->protocol != IPPROTO_TCP && iph->protocol != IPPROTO_UDP)
                return NF_ACCEPT;

        /* reassemble IP fragments */
        if (iph->frag_off & __constant_htons(IP_MF|IP_OFFSET)) {
                skb = ip_defrag(skb);
                if (!skb)
                        return NF_STOLEN;
                iph = skb->nh.iph;
                *skb_p = skb;
        }

        /* make sure that protocol header available in skb data area,
           note that skb data area may be reallocated. */
        ihl = iph->ihl << 2;
        if (ip_vs_header_check(skb, iph->protocol, ihl) == -1)
                return NF_DROP;

        iph = skb->nh.iph;
        h.raw = (char*) iph + ihl;

        /*
         *      Check if the packet belongs to an old entry
         */
        cp = ip_vs_conn_out_get(iph->protocol, iph->saddr, h.portp[0],
                                iph->daddr, h.portp[1]);
        if (!cp) {
                if (sysctl_ip_vs_nat_icmp_send &&
                    ip_vs_lookup_real_service(iph->protocol,
                                              iph->saddr, h.portp[0])) {
                        /*
                         * Notify the real server: there is no existing
                         * entry if it is not RST packet or not TCP packet.
                         */
                        if (!h.th->rst || iph->protocol != IPPROTO_TCP) {
                                icmp_send(skb, ICMP_DEST_UNREACH,
                                          ICMP_PORT_UNREACH, 0);
                                kfree_skb(skb);
                                return NF_STOLEN;
                        }
                }
                IP_VS_DBG(12, "packet for %s %d.%d.%d.%d:%d "
                          "continue traversal as normal.\n",
                          ip_vs_proto_name(iph->protocol),
                          NIPQUAD(iph->daddr),
                          ntohs(h.portp[1]));
                if (skb_is_nonlinear(skb))
                        ip_send_check(iph);
                return NF_ACCEPT;
        }

        /*
         * If it has ip_vs_app helper, the helper may change the payload,
         * so it needs full checksum checking and checksum calculation.
         * If not, only the header (addr/port) is changed, so it is fast
         * to do incremental checksum update, and let the destination host
         * do final checksum checking.
         */

        if (cp->app && skb_is_nonlinear(skb)) {
                if (skb_linearize(skb, GFP_ATOMIC) != 0) {
                        ip_vs_conn_put(cp);
                        return NF_DROP;
                }
                iph = skb->nh.iph;
                h.raw = (char*) iph + ihl;
        }

        size = skb->len - ihl;
        IP_VS_DBG(11, "O-pkt: %s size=%d\n",
                  ip_vs_proto_name(iph->protocol), size);

        /* do TCP/UDP checksum checking if it has application helper */
        if (cp->app && (iph->protocol != IPPROTO_UDP || h.uh->check != 0)) {
                switch (skb->ip_summed) {
                case CHECKSUM_NONE:
                        skb->csum = csum_partial(h.raw, size, 0);
                case CHECKSUM_HW:
                        if (csum_tcpudp_magic(iph->saddr, iph->daddr, size,
                                              iph->protocol, skb->csum)) {
                                ip_vs_conn_put(cp);
                                IP_VS_DBG_RL("Outgoing failed %s checksum "
                                             "from %d.%d.%d.%d (size=%d)!\n",
                                             ip_vs_proto_name(iph->protocol),
                                             NIPQUAD(iph->saddr),
                                             size);
                                return NF_DROP;
                        }
                        break;
                default:
                        /* CHECKSUM_UNNECESSARY */
                        break;
                }
        }

        IP_VS_DBG(11, "Outgoing %s %u.%u.%u.%u:%d->%u.%u.%u.%u:%d\n",
                  ip_vs_proto_name(iph->protocol),
                  NIPQUAD(iph->saddr), ntohs(h.portp[0]),
                  NIPQUAD(iph->daddr), ntohs(h.portp[1]));

        /* mangle the packet */
        iph->saddr = cp->vaddr;
        h.portp[0] = cp->vport;

        /*
         *      Call application helper if needed
         */
        if (ip_vs_app_pkt_out(cp, skb) != 0) {
                /* skb data has probably changed, update pointers */
                iph = skb->nh.iph;
                h.raw = (char*)iph + ihl;
                size = skb->len - ihl;
        }

        /*
         *      Adjust TCP/UDP checksums
         */
        if (!cp->app && (iph->protocol != IPPROTO_UDP || h.uh->check != 0)) {
                /* Only port and addr are changed, do fast csum update */
                ip_vs_fast_check_update(&h, cp->daddr, cp->vaddr,
                                        cp->dport, cp->vport, iph->protocol);
                if (skb->ip_summed == CHECKSUM_HW)
                        skb->ip_summed = CHECKSUM_NONE;
        } else {
                /* full checksum calculation */
                switch (iph->protocol) {
                case IPPROTO_TCP:
                        h.th->check = 0;
                        skb->csum = csum_partial(h.raw, size, 0);
                        h.th->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
                                                        size, iph->protocol,
                                                        skb->csum);
                        IP_VS_DBG(11, "O-pkt: %s O-csum=%d (+%d)\n",
                                  ip_vs_proto_name(iph->protocol), h.th->check,
                                  (char*)&(h.th->check) - (char*)h.raw);
                        break;
                case IPPROTO_UDP:
                        h.uh->check = 0;
                        skb->csum = csum_partial(h.raw, size, 0);
                        h.uh->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
                                                        size, iph->protocol,
                                                        skb->csum);
                        if (h.uh->check == 0)
                                h.uh->check = 0xFFFF;
                        IP_VS_DBG(11, "O-pkt: %s O-csum=%d (+%d)\n",
                                  ip_vs_proto_name(iph->protocol), h.uh->check,
                                  (char*)&(h.uh->check) - (char*)h.raw);
                        break;
                }
        }
        ip_send_check(iph);

        ip_vs_out_stats(cp, skb);
        ip_vs_set_state(cp, VS_STATE_OUTPUT, iph, h.portp);
        ip_vs_conn_put(cp);

        skb->nfcache |= NFC_IPVS_PROPERTY;

        LeaveFunction(11);
        return NF_ACCEPT;
}


/*
 *      Check if the packet is for VS/NAT connections, then send it
 *      immediately.
 *      Called by ip_fw_compact to detect packets for VS/NAT before
 *      they are changed by ipchains masquerading code.
 */
unsigned int check_for_ip_vs_out(struct sk_buff **skb_p,
                                 int (*okfn)(struct sk_buff *))
{
        unsigned int ret;

        ret = ip_vs_out(NF_IP_FORWARD, skb_p, NULL, NULL, NULL);
        if (ret != NF_ACCEPT) {
                return ret;
        } else {
                /* send the packet immediately if it is already mangled
                   by ip_vs_out */
                if ((*skb_p)->nfcache & NFC_IPVS_PROPERTY) {
                        (*okfn)(*skb_p);
                        return NF_STOLEN;
                }
        }
        return NF_ACCEPT;
}


/*
 *      Handle ICMP messages in the outside-to-inside direction (incoming)
 *      and sometimes in outgoing direction from ip_vs_forward_icmp.
 *      Find any that might be relevant, check against existing connections,
 *      forward to the right destination host if relevant.
 *      Currently handles error types - unreachable, quench, ttl exceeded.
 */
static int ip_vs_in_icmp(struct sk_buff **skb_p)
{
        struct sk_buff  *skb   = *skb_p;
        struct iphdr    *iph;
        struct icmphdr  *icmph;
        struct iphdr    *ciph;  /* The ip header contained within the ICMP */
        __u16           *pptr;  /* port numbers from TCP/UDP contained header */
        unsigned short   len;
        unsigned short  clen, csize;
        struct ip_vs_conn *cp;
        struct rtable *rt;                      /* Route to the other host */
        int    mtu;

        if (skb_is_nonlinear(skb)) {
                if (skb_linearize(skb, GFP_ATOMIC) != 0)
                        return NF_DROP;
        }

        iph = skb->nh.iph;
        ip_send_check(iph);
        icmph = (struct icmphdr *)((char *)iph + (iph->ihl << 2));
        len = ntohs(iph->tot_len) - (iph->ihl<<2);
        if (len < sizeof(struct icmphdr))
                return NF_DROP;

        IP_VS_DBG(12, "icmp in (%d,%d) %u.%u.%u.%u -> %u.%u.%u.%u\n",
                  icmph->type, ntohs(icmp_id(icmph)),
                  NIPQUAD(iph->saddr), NIPQUAD(iph->daddr));

        if ((icmph->type != ICMP_DEST_UNREACH) &&
            (icmph->type != ICMP_SOURCE_QUENCH) &&
            (icmph->type != ICMP_TIME_EXCEEDED))
                return NF_ACCEPT;

        /*
         * If we get here we have an ICMP error of one of the above 3 types
         * Now find the contained IP header
         */
        clen = len - sizeof(struct icmphdr);
        if (clen < sizeof(struct iphdr))
                return NF_DROP;
        ciph = (struct iphdr *) (icmph + 1);
        csize = ciph->ihl << 2;
        if (clen < csize)
                return NF_DROP;

        /* We are only interested ICMPs generated from TCP or UDP packets */
        if (ciph->protocol != IPPROTO_UDP && ciph->protocol != IPPROTO_TCP)
                return NF_ACCEPT;

        /* Skip non-first embedded TCP/UDP fragments */
        if (ciph->frag_off & __constant_htons(IP_OFFSET))
                return NF_ACCEPT;

        /* We need at least TCP/UDP ports here */
        if (clen < csize + sizeof(struct udphdr))
                return NF_DROP;

        /* Ensure the checksum is correct */
        if (ip_compute_csum((unsigned char *) icmph, len)) {
                /* Failed checksum! */
                IP_VS_ERR_RL("incoming ICMP: failed checksum from "
                             "%d.%d.%d.%d!\n", NIPQUAD(iph->saddr));
                return NF_DROP;
        }

        pptr = (__u16 *)&(((char *)ciph)[csize]);

        IP_VS_DBG(11, "Handling incoming ICMP for "
                  "%u.%u.%u.%u:%d -> %u.%u.%u.%u:%d\n",
                  NIPQUAD(ciph->saddr), ntohs(pptr[0]),
                  NIPQUAD(ciph->daddr), ntohs(pptr[1]));

        /* This is pretty much what ip_vs_conn_in_get() does,
           except parameters are in the reverse order */
        cp = ip_vs_conn_in_get(ciph->protocol,
                               ciph->daddr, pptr[1],
                               ciph->saddr, pptr[0]);
        if (cp == NULL)
                return NF_ACCEPT;

        ip_vs_in_stats(cp, skb);

        /* The ICMP packet for VS/TUN, VS/DR and LOCALNODE will be
           forwarded directly here, because there is no need to
           translate address/port back */
        if (IP_VS_FWD_METHOD(cp) != IP_VS_CONN_F_MASQ) {
                int ret;
                if (cp->packet_xmit)
                        ret = cp->packet_xmit(skb, cp);
                else
                        ret = NF_ACCEPT;
                atomic_inc(&cp->in_pkts);
                ip_vs_conn_put(cp);
                return ret;
        }

        /*
         * mangle and send the packet here
         */
        if (!(rt = __ip_vs_get_out_rt(cp, RT_TOS(iph->tos))))
                goto tx_error_icmp;

        /* MTU checking */
        mtu = rt->u.dst.pmtu;
        if ((skb->len > mtu) && (iph->frag_off&__constant_htons(IP_DF))) {
                ip_rt_put(rt);
                icmp_send(skb, ICMP_DEST_UNREACH,ICMP_FRAG_NEEDED, htonl(mtu));
                IP_VS_DBG_RL("ip_vs_in_icmp(): frag needed\n");
                goto tx_error;
        }

        /* drop old route */
        dst_release(skb->dst);
        skb->dst = &rt->u.dst;

        /* copy-on-write the packet before mangling it */
        if (ip_vs_skb_cow(skb, rt->u.dst.dev->hard_header_len,
                          &iph, (unsigned char**)&icmph)) {
                ip_vs_conn_put(cp);
                return NF_DROP;
        }
        ciph = (struct iphdr *) (icmph + 1);
        pptr = (__u16 *)&(((char *)ciph)[csize]);

        /* The ICMP packet for VS/NAT must be written to correct addresses
           before being forwarded to the right server */

        /* First change the dest IP address, and recalc checksum */
        iph->daddr = cp->daddr;
        ip_send_check(iph);

        /* Now change the *source* address in the contained IP */
        ciph->saddr = cp->daddr;
        ip_send_check(ciph);

        /* the TCP/UDP source port - cannot redo check */
        pptr[0] = cp->dport;

        /* And finally the ICMP checksum */
        icmph->checksum = 0;
        icmph->checksum = ip_compute_csum((unsigned char *) icmph, len);
        skb->ip_summed = CHECKSUM_UNNECESSARY;

        IP_VS_DBG(11, "Forwarding incoming ICMP to "
                  "%u.%u.%u.%u:%d -> %u.%u.%u.%u:%d\n",
                  NIPQUAD(ciph->saddr), ntohs(pptr[0]),
                  NIPQUAD(ciph->daddr), ntohs(pptr[1]));

#ifdef CONFIG_NETFILTER_DEBUG
        skb->nf_debug = 1 << NF_IP_LOCAL_OUT;
#endif /* CONFIG_NETFILTER_DEBUG */
        ip_send(skb);
        ip_vs_conn_put(cp);
        return NF_STOLEN;

  tx_error_icmp:
        dst_link_failure(skb);
  tx_error:
        dev_kfree_skb(skb);
        ip_vs_conn_put(cp);
        return NF_STOLEN;
}


/*
 *      Check if it's for virtual services, look it up,
 *      and send it on its way...
 */
static unsigned int ip_vs_in(unsigned int hooknum,
                             struct sk_buff **skb_p,
                             const struct net_device *in,
                             const struct net_device *out,
                             int (*okfn)(struct sk_buff *))
{
        struct sk_buff  *skb = *skb_p;
        struct iphdr    *iph = skb->nh.iph;
        union ip_vs_tphdr h;
        struct ip_vs_conn *cp;
        struct ip_vs_service *svc;
        int ihl;
        int ret;

        /*
         *      Big tappo: only PACKET_HOST (nor loopback neither mcasts)
         *      ... don't know why 1st test DOES NOT include 2nd (?)
         */
        if (skb->pkt_type != PACKET_HOST || skb->dev == &loopback_dev) {
                IP_VS_DBG(12, "packet type=%d proto=%d daddr=%d.%d.%d.%d ignored\n",
                          skb->pkt_type,
                          iph->protocol,
                          NIPQUAD(iph->daddr));
                return NF_ACCEPT;
        }

        if (iph->protocol == IPPROTO_ICMP)
                return ip_vs_in_icmp(skb_p);

        /* let it go if other IP protocols */
        if (iph->protocol != IPPROTO_TCP && iph->protocol != IPPROTO_UDP)
                return NF_ACCEPT;

        /* make sure that protocol header available in skb data area,
           note that skb data area may be reallocated. */
        ihl = iph->ihl << 2;
        if (ip_vs_header_check(skb, iph->protocol, ihl) == -1)
                return NF_DROP;
        iph = skb->nh.iph;
        h.raw = (char*) iph + ihl;

        /*
         * Check if the packet belongs to an existing connection entry
         */
        cp = ip_vs_conn_in_get(iph->protocol, iph->saddr, h.portp[0],
                               iph->daddr, h.portp[1]);

        if (!cp &&
            (h.th->syn || (iph->protocol!=IPPROTO_TCP)) &&
            (svc = ip_vs_service_get(skb->nfmark, iph->protocol,
                                     iph->daddr, h.portp[1]))) {
                if (ip_vs_todrop()) {
                        /*
                         * It seems that we are very loaded.
                         * We have to drop this packet :(
                         */
                        ip_vs_service_put(svc);
                        return NF_DROP;
                }

                /*
                 * Let the virtual server select a real server for the
                 * incoming connection, and create a connection entry.
                 */
                cp = ip_vs_schedule(svc, iph);
                if (!cp)
                        return ip_vs_leave(svc, skb);
                ip_vs_conn_stats(cp, svc);
                ip_vs_service_put(svc);
        }

        if (!cp) {
                /* sorry, all this trouble for a no-hit :) */
                IP_VS_DBG(12, "packet for %s %d.%d.%d.%d:%d continue "
                          "traversal as normal.\n",
                          ip_vs_proto_name(iph->protocol),
                          NIPQUAD(iph->daddr),
                          ntohs(h.portp[1]));
                return NF_ACCEPT;
        }

        IP_VS_DBG(11, "Incoming %s %u.%u.%u.%u:%d->%u.%u.%u.%u:%d\n",
                  ip_vs_proto_name(iph->protocol),
                  NIPQUAD(iph->saddr), ntohs(h.portp[0]),
                  NIPQUAD(iph->daddr), ntohs(h.portp[1]));

        /* Check the server status */
        if (cp->dest && !(cp->dest->flags & IP_VS_DEST_F_AVAILABLE)) {
                /* the destination server is not availabe */

                if (sysctl_ip_vs_expire_nodest_conn) {
                        /* try to expire the connection immediately */
                        ip_vs_conn_expire_now(cp);
                } else {
                        /* don't restart its timer, and silently
                           drop the packet. */
                        __ip_vs_conn_put(cp);
                }
                return NF_DROP;
        }

        ip_vs_in_stats(cp, skb);
        ip_vs_set_state(cp, VS_STATE_INPUT, iph, h.portp);
        if (cp->packet_xmit)
                ret = cp->packet_xmit(skb, cp);
        else {
                IP_VS_DBG_RL("warning: packet_xmit is null");
                ret = NF_ACCEPT;
        }

        /* increase its packet counter and check if it is needed
           to be synchronized */
        atomic_inc(&cp->in_pkts);
        if (ip_vs_sync_state == IP_VS_STATE_MASTER &&
            (cp->protocol != IPPROTO_TCP ||
             cp->state == IP_VS_S_ESTABLISHED) &&
            (atomic_read(&cp->in_pkts) % 50 == sysctl_ip_vs_sync_threshold))
                ip_vs_sync_conn(cp);

        ip_vs_conn_put(cp);
        return ret;
}


/*
 *      It is hooked at the NF_IP_FORWARD chain, in order to catch ICMP
 *      packets destined for 0.0.0.0/0.
 *      When fwmark-based virtual service is used, such as transparent
 *      cache cluster, TCP packets can be marked and routed to ip_vs_in,
 *      but ICMP destined for 0.0.0.0/0 cannot not be easily marked and
 *      sent to ip_vs_in_icmp. So, catch them at the NF_IP_FORWARD chain
 *      and send them to ip_vs_in_icmp.
 */
static unsigned int ip_vs_forward_icmp(unsigned int hooknum,
                                       struct sk_buff **skb_p,
                                       const struct net_device *in,
                                       const struct net_device *out,
                                       int (*okfn)(struct sk_buff *))
{
        struct sk_buff  *skb = *skb_p;
        struct iphdr    *iph = skb->nh.iph;

        if (iph->protocol != IPPROTO_ICMP)
                return NF_ACCEPT;

        if (iph->frag_off & __constant_htons(IP_MF|IP_OFFSET)) {
                skb = ip_defrag(skb);
                if (!skb)
                        return NF_STOLEN;
                *skb_p = skb;
        }

        return ip_vs_in_icmp(skb_p);
}


/* After packet filtering, forward packet through VS/DR, VS/TUN,
   or VS/NAT(change destination), so that filtering rules can be
   applied to IPVS. */
static struct nf_hook_ops ip_vs_in_ops = {
        { NULL, NULL },
        ip_vs_in, PF_INET, NF_IP_LOCAL_IN, 100
};

/* After packet filtering, change source only for VS/NAT */
static struct nf_hook_ops ip_vs_out_ops = {
        { NULL, NULL },
        ip_vs_out, PF_INET, NF_IP_FORWARD, 100
};

/* After packet filtering (but before ip_vs_out_icmp), catch icmp
   destined for 0.0.0.0/0, which is for incoming IPVS connections */
static struct nf_hook_ops ip_vs_forward_icmp_ops = {
        { NULL, NULL },
        ip_vs_forward_icmp, PF_INET, NF_IP_FORWARD, 99
};

/* Before the netfilter connection tracking, exit from POST_ROUTING */
static struct nf_hook_ops ip_vs_post_routing_ops = {
        { NULL, NULL },
        ip_vs_post_routing, PF_INET, NF_IP_POST_ROUTING, NF_IP_PRI_NAT_SRC-1
};


/*
 *      Initialize IP Virtual Server
 */
static int __init ip_vs_init(void)
{
        int ret;

        ret = ip_vs_control_init();
        if (ret < 0) {
                IP_VS_ERR("can't setup control.\n");
                goto cleanup_nothing;
        }

        ret = ip_vs_conn_init();
        if (ret < 0) {
                IP_VS_ERR("can't setup connection table.\n");
                goto cleanup_control;
        }

        ret = ip_vs_app_init();
        if (ret < 0) {
                IP_VS_ERR("can't setup application helper.\n");
                goto cleanup_conn;
        }

        ret = nf_register_hook(&ip_vs_in_ops);
        if (ret < 0) {
                IP_VS_ERR("can't register in hook.\n");
                goto cleanup_app;
        }
        ret = nf_register_hook(&ip_vs_out_ops);
        if (ret < 0) {
                IP_VS_ERR("can't register out hook.\n");
                goto cleanup_inops;
        }
        ret = nf_register_hook(&ip_vs_post_routing_ops);
        if (ret < 0) {
                IP_VS_ERR("can't register post_routing hook.\n");
                goto cleanup_outops;
        }
        ret = nf_register_hook(&ip_vs_forward_icmp_ops);
        if (ret < 0) {
                IP_VS_ERR("can't register forward_icmp hook.\n");
                goto cleanup_postroutingops;
        }

        IP_VS_INFO("ipvs loaded.\n");
        return ret;

  cleanup_postroutingops:
        nf_unregister_hook(&ip_vs_post_routing_ops);
  cleanup_outops:
        nf_unregister_hook(&ip_vs_out_ops);
  cleanup_inops:
        nf_unregister_hook(&ip_vs_in_ops);
  cleanup_app:
        ip_vs_app_cleanup();
  cleanup_conn:
        ip_vs_conn_cleanup();
  cleanup_control:
        ip_vs_control_cleanup();
  cleanup_nothing:
        return ret;
}

static void __exit ip_vs_cleanup(void)
{
        nf_unregister_hook(&ip_vs_forward_icmp_ops);
        nf_unregister_hook(&ip_vs_post_routing_ops);
        nf_unregister_hook(&ip_vs_out_ops);
        nf_unregister_hook(&ip_vs_in_ops);
        ip_vs_app_cleanup();
        ip_vs_conn_cleanup();
        ip_vs_control_cleanup();
        IP_VS_INFO("ipvs unloaded.\n");
}

module_init(ip_vs_init);
module_exit(ip_vs_cleanup);
MODULE_LICENSE("GPL");

---