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ip_vs_core.c

/*
 * 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 1.34 2003/05/10 03:05:23 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:
 *    Paul `Rusty' Russell          properly handle non-linear skbs
 *    Harald Welte                  don't use nfcache
 *
 */

#include <linux/module.h>
#include <linux/kernel.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);
#ifdef CONFIG_IP_VS_PROTO_TCP
EXPORT_SYMBOL(ip_vs_tcp_conn_listen);
#endif
EXPORT_SYMBOL(ip_vs_conn_put);
#ifdef CONFIG_IP_VS_DEBUG
EXPORT_SYMBOL(ip_vs_get_debug_level);
#endif


/* 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;
      }
}

void ip_vs_init_hash_table(struct list_head *table, int rows)
{
      while (--rows >= 0)
            INIT_LIST_HEAD(&table[rows]);
}

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);
}


static inline int
ip_vs_set_state(struct ip_vs_conn *cp, int direction,
            const struct sk_buff *skb,
            struct ip_vs_protocol *pp)
{
      if (unlikely(!pp->state_transition))
            return 0;
      return pp->state_transition(cp, direction, skb, pp);
}


/*
 *  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
 *  Protocols supported: TCP, UDP
 */
static struct ip_vs_conn *
ip_vs_sched_persist(struct ip_vs_service *svc,
                const struct sk_buff *skb,
                __be16 ports[2])
{
      struct ip_vs_conn *cp = NULL;
      struct iphdr *iph = ip_hdr(skb);
      struct ip_vs_dest *dest;
      struct ip_vs_conn *ct;
      __be16  dport;     /* destination port to forward */
      __be32  snet;      /* source network of the client, after masking */

      /* 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(ports[0]),
              NIPQUAD(iph->daddr), ntohs(ports[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 (ports[1] == svc->port) {
            /* Check if a template already exists */
            if (svc->port != FTPPORT)
                  ct = ip_vs_ct_in_get(iph->protocol, snet, 0,
                                     iph->daddr, ports[1]);
            else
                  ct = ip_vs_ct_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, skb);
                  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,
                                        ports[1],
                                        dest->addr, dest->port,
                                        IP_VS_CONN_F_TEMPLATE,
                                        dest);
                  else
                        ct = ip_vs_conn_new(iph->protocol,
                                        snet, 0,
                                        iph->daddr, 0,
                                        dest->addr, 0,
                                        IP_VS_CONN_F_TEMPLATE,
                                        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_ct_in_get(IPPROTO_IP, snet, 0,
                                     htonl(svc->fwmark), 0);
            else
                  ct = ip_vs_ct_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, skb);
                  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,
                                        IP_VS_CONN_F_TEMPLATE,
                                        dest);
                  else
                        ct = ip_vs_conn_new(iph->protocol,
                                        snet, 0,
                                        iph->daddr, 0,
                                        dest->addr, 0,
                                        IP_VS_CONN_F_TEMPLATE,
                                        dest);
                  if (ct == NULL)
                        return NULL;

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

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

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

      ip_vs_conn_stats(cp, svc);
      return cp;
}


/*
 *  IPVS main scheduling function
 *  It selects a server according to the virtual service, and
 *  creates a connection entry.
 *  Protocols supported: TCP, UDP
 */
struct ip_vs_conn *
ip_vs_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
{
      struct ip_vs_conn *cp = NULL;
      struct iphdr *iph = ip_hdr(skb);
      struct ip_vs_dest *dest;
      __be16 _ports[2], *pptr;

      pptr = skb_header_pointer(skb, iph->ihl*4,
                          sizeof(_ports), _ports);
      if (pptr == NULL)
            return NULL;

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

      /*
       *    Non-persistent service
       */
      if (!svc->fwmark && pptr[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, skb);
      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, pptr[0],
                      iph->daddr, pptr[1],
                      dest->addr, dest->port?dest->port:pptr[1],
                      0,
                      dest);
      if (cp == NULL)
            return NULL;

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

      ip_vs_conn_stats(cp, svc);
      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.
 */
int ip_vs_leave(struct ip_vs_service *svc, struct sk_buff *skb,
            struct ip_vs_protocol *pp)
{
      __be16 _ports[2], *pptr;
      struct iphdr *iph = ip_hdr(skb);

      pptr = skb_header_pointer(skb, iph->ihl*4,
                          sizeof(_ports), _ports);
      if (pptr == NULL) {
            ip_vs_service_put(svc);
            return NF_DROP;
      }

      /* 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, cs;
            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, pptr[0],
                            iph->daddr, pptr[1],
                            0, 0,
                            IP_VS_CONN_F_BYPASS,
                            NULL);
            if (cp == NULL)
                  return NF_DROP;

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

            /* set state */
            cs = ip_vs_set_state(cp, IP_VS_DIR_INPUT, skb, pp);

            /* transmit the first SYN packet */
            ret = cp->packet_xmit(skb, cp, pp);
            /* do not touch skb anymore */

            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) && (pptr[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);
      return NF_DROP;
}


/*
 *      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,
                               const struct net_device *in,
                               const struct net_device *out,
                               int (*okfn)(struct sk_buff *))
{
      if (!skb->ipvs_property)
            return NF_ACCEPT;
      /* The packet was sent from IPVS, exit this chain */
      return NF_STOP;
}

__sum16 ip_vs_checksum_complete(struct sk_buff *skb, int offset)
{
      return csum_fold(skb_checksum(skb, offset, skb->len - offset, 0));
}

static inline int ip_vs_gather_frags(struct sk_buff *skb, u_int32_t user)
{
      int err = ip_defrag(skb, user);

      if (!err)
            ip_send_check(ip_hdr(skb));

      return err;
}

/*
 * Packet has been made sufficiently writable in caller
 * - inout: 1=in->out, 0=out->in
 */
void ip_vs_nat_icmp(struct sk_buff *skb, struct ip_vs_protocol *pp,
                struct ip_vs_conn *cp, int inout)
{
      struct iphdr *iph  = ip_hdr(skb);
      unsigned int icmp_offset = iph->ihl*4;
      struct icmphdr *icmph    = (struct icmphdr *)(skb_network_header(skb) +
                                          icmp_offset);
      struct iphdr *ciph       = (struct iphdr *)(icmph + 1);

      if (inout) {
            iph->saddr = cp->vaddr;
            ip_send_check(iph);
            ciph->daddr = cp->vaddr;
            ip_send_check(ciph);
      } else {
            iph->daddr = cp->daddr;
            ip_send_check(iph);
            ciph->saddr = cp->daddr;
            ip_send_check(ciph);
      }

      /* the TCP/UDP port */
      if (IPPROTO_TCP == ciph->protocol || IPPROTO_UDP == ciph->protocol) {
            __be16 *ports = (void *)ciph + ciph->ihl*4;

            if (inout)
                  ports[1] = cp->vport;
            else
                  ports[0] = cp->dport;
      }

      /* And finally the ICMP checksum */
      icmph->checksum = 0;
      icmph->checksum = ip_vs_checksum_complete(skb, icmp_offset);
      skb->ip_summed = CHECKSUM_UNNECESSARY;

      if (inout)
            IP_VS_DBG_PKT(11, pp, skb, (void *)ciph - (void *)iph,
                  "Forwarding altered outgoing ICMP");
      else
            IP_VS_DBG_PKT(11, pp, skb, (void *)ciph - (void *)iph,
                  "Forwarding altered incoming ICMP");
}

/*
 *    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, int *related)
{
      struct iphdr *iph;
      struct icmphdr    _icmph, *ic;
      struct iphdr      _ciph, *cih;      /* The ip header contained within the ICMP */
      struct ip_vs_conn *cp;
      struct ip_vs_protocol *pp;
      unsigned int offset, ihl, verdict;

      *related = 1;

      /* reassemble IP fragments */
      if (ip_hdr(skb)->frag_off & htons(IP_MF | IP_OFFSET)) {
            if (ip_vs_gather_frags(skb, IP_DEFRAG_VS_OUT))
                  return NF_STOLEN;
      }

      iph = ip_hdr(skb);
      offset = ihl = iph->ihl * 4;
      ic = skb_header_pointer(skb, offset, sizeof(_icmph), &_icmph);
      if (ic == NULL)
            return NF_DROP;

      IP_VS_DBG(12, "Outgoing ICMP (%d,%d) %u.%u.%u.%u->%u.%u.%u.%u\n",
              ic->type, ntohs(icmp_id(ic)),
              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 ((ic->type != ICMP_DEST_UNREACH) &&
          (ic->type != ICMP_SOURCE_QUENCH) &&
          (ic->type != ICMP_TIME_EXCEEDED)) {
            *related = 0;
            return NF_ACCEPT;
      }

      /* Now find the contained IP header */
      offset += sizeof(_icmph);
      cih = skb_header_pointer(skb, offset, sizeof(_ciph), &_ciph);
      if (cih == NULL)
            return NF_ACCEPT; /* The packet looks wrong, ignore */

      pp = ip_vs_proto_get(cih->protocol);
      if (!pp)
            return NF_ACCEPT;

      /* Is the embedded protocol header present? */
      if (unlikely(cih->frag_off & htons(IP_OFFSET) &&
                 pp->dont_defrag))
            return NF_ACCEPT;

      IP_VS_DBG_PKT(11, pp, skb, offset, "Checking outgoing ICMP for");

      offset += cih->ihl * 4;

      /* The embedded headers contain source and dest in reverse order */
      cp = pp->conn_out_get(skb, pp, cih, offset, 1);
      if (!cp)
            return NF_ACCEPT;

      verdict = NF_DROP;

      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");
      }

      /* Ensure the checksum is correct */
      if (!skb_csum_unnecessary(skb) && ip_vs_checksum_complete(skb, ihl)) {
            /* Failed checksum! */
            IP_VS_DBG(1, "Forward ICMP: failed checksum from %d.%d.%d.%d!\n",
                    NIPQUAD(iph->saddr));
            goto out;
      }

      if (IPPROTO_TCP == cih->protocol || IPPROTO_UDP == cih->protocol)
            offset += 2 * sizeof(__u16);
      if (!skb_make_writable(skb, offset))
            goto out;

      ip_vs_nat_icmp(skb, pp, cp, 1);

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

      skb->ipvs_property = 1;
      verdict = NF_ACCEPT;

  out:
      __ip_vs_conn_put(cp);

      return verdict;
}

static inline int is_tcp_reset(const struct sk_buff *skb)
{
      struct tcphdr _tcph, *th;

      th = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
      if (th == NULL)
            return 0;
      return th->rst;
}

/*
 *    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,
        const struct net_device *in, const struct net_device *out,
        int (*okfn)(struct sk_buff *))
{
      struct iphdr      *iph;
      struct ip_vs_protocol *pp;
      struct ip_vs_conn *cp;
      int ihl;

      EnterFunction(11);

      if (skb->ipvs_property)
            return NF_ACCEPT;

      iph = ip_hdr(skb);
      if (unlikely(iph->protocol == IPPROTO_ICMP)) {
            int related, verdict = ip_vs_out_icmp(skb, &related);

            if (related)
                  return verdict;
            iph = ip_hdr(skb);
      }

      pp = ip_vs_proto_get(iph->protocol);
      if (unlikely(!pp))
            return NF_ACCEPT;

      /* reassemble IP fragments */
      if (unlikely(iph->frag_off & htons(IP_MF|IP_OFFSET) &&
                 !pp->dont_defrag)) {
            if (ip_vs_gather_frags(skb, IP_DEFRAG_VS_OUT))
                  return NF_STOLEN;
            iph = ip_hdr(skb);
      }

      ihl = iph->ihl << 2;

      /*
       * Check if the packet belongs to an existing entry
       */
      cp = pp->conn_out_get(skb, pp, iph, ihl, 0);

      if (unlikely(!cp)) {
            if (sysctl_ip_vs_nat_icmp_send &&
                (pp->protocol == IPPROTO_TCP ||
                 pp->protocol == IPPROTO_UDP)) {
                  __be16 _ports[2], *pptr;

                  pptr = skb_header_pointer(skb, ihl,
                                      sizeof(_ports), _ports);
                  if (pptr == NULL)
                        return NF_ACCEPT; /* Not for me */
                  if (ip_vs_lookup_real_service(iph->protocol,
                                          iph->saddr, pptr[0])) {
                        /*
                         * Notify the real server: there is no
                         * existing entry if it is not RST
                         * packet or not TCP packet.
                         */
                        if (iph->protocol != IPPROTO_TCP
                            || !is_tcp_reset(skb)) {
                              icmp_send(skb,ICMP_DEST_UNREACH,
                                      ICMP_PORT_UNREACH, 0);
                              return NF_DROP;
                        }
                  }
            }
            IP_VS_DBG_PKT(12, pp, skb, 0,
                        "packet continues traversal as normal");
            return NF_ACCEPT;
      }

      IP_VS_DBG_PKT(11, pp, skb, 0, "Outgoing packet");

      if (!skb_make_writable(skb, ihl))
            goto drop;

      /* mangle the packet */
      if (pp->snat_handler && !pp->snat_handler(skb, pp, cp))
            goto drop;
      ip_hdr(skb)->saddr = cp->vaddr;
      ip_send_check(ip_hdr(skb));

      /* For policy routing, packets originating from this
       * machine itself may be routed differently to packets
       * passing through.  We want this packet to be routed as
       * if it came from this machine itself.  So re-compute
       * the routing information.
       */
      if (ip_route_me_harder(skb, RTN_LOCAL) != 0)
            goto drop;

      IP_VS_DBG_PKT(10, pp, skb, 0, "After SNAT");

      ip_vs_out_stats(cp, skb);
      ip_vs_set_state(cp, IP_VS_DIR_OUTPUT, skb, pp);
      ip_vs_conn_put(cp);

      skb->ipvs_property = 1;

      LeaveFunction(11);
      return NF_ACCEPT;

  drop:
      ip_vs_conn_put(cp);
      kfree_skb(skb);
      return NF_STOLEN;
}


/*
 *    Handle ICMP messages in the outside-to-inside direction (incoming).
 *    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, int *related, unsigned int hooknum)
{
      struct iphdr *iph;
      struct icmphdr    _icmph, *ic;
      struct iphdr      _ciph, *cih;      /* The ip header contained within the ICMP */
      struct ip_vs_conn *cp;
      struct ip_vs_protocol *pp;
      unsigned int offset, ihl, verdict;

      *related = 1;

      /* reassemble IP fragments */
      if (ip_hdr(skb)->frag_off & htons(IP_MF | IP_OFFSET)) {
            if (ip_vs_gather_frags(skb, hooknum == NF_IP_LOCAL_IN ?
                                  IP_DEFRAG_VS_IN : IP_DEFRAG_VS_FWD))
                  return NF_STOLEN;
      }

      iph = ip_hdr(skb);
      offset = ihl = iph->ihl * 4;
      ic = skb_header_pointer(skb, offset, sizeof(_icmph), &_icmph);
      if (ic == NULL)
            return NF_DROP;

      IP_VS_DBG(12, "Incoming ICMP (%d,%d) %u.%u.%u.%u->%u.%u.%u.%u\n",
              ic->type, ntohs(icmp_id(ic)),
              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 ((ic->type != ICMP_DEST_UNREACH) &&
          (ic->type != ICMP_SOURCE_QUENCH) &&
          (ic->type != ICMP_TIME_EXCEEDED)) {
            *related = 0;
            return NF_ACCEPT;
      }

      /* Now find the contained IP header */
      offset += sizeof(_icmph);
      cih = skb_header_pointer(skb, offset, sizeof(_ciph), &_ciph);
      if (cih == NULL)
            return NF_ACCEPT; /* The packet looks wrong, ignore */

      pp = ip_vs_proto_get(cih->protocol);
      if (!pp)
            return NF_ACCEPT;

      /* Is the embedded protocol header present? */
      if (unlikely(cih->frag_off & htons(IP_OFFSET) &&
                 pp->dont_defrag))
            return NF_ACCEPT;

      IP_VS_DBG_PKT(11, pp, skb, offset, "Checking incoming ICMP for");

      offset += cih->ihl * 4;

      /* The embedded headers contain source and dest in reverse order */
      cp = pp->conn_in_get(skb, pp, cih, offset, 1);
      if (!cp)
            return NF_ACCEPT;

      verdict = NF_DROP;

      /* Ensure the checksum is correct */
      if (!skb_csum_unnecessary(skb) && ip_vs_checksum_complete(skb, ihl)) {
            /* Failed checksum! */
            IP_VS_DBG(1, "Incoming ICMP: failed checksum from %d.%d.%d.%d!\n",
                    NIPQUAD(iph->saddr));
            goto out;
      }

      /* do the statistics and put it back */
      ip_vs_in_stats(cp, skb);
      if (IPPROTO_TCP == cih->protocol || IPPROTO_UDP == cih->protocol)
            offset += 2 * sizeof(__u16);
      verdict = ip_vs_icmp_xmit(skb, cp, pp, offset);
      /* do not touch skb anymore */

  out:
      __ip_vs_conn_put(cp);

      return verdict;
}

/*
 *    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,
       const struct net_device *in, const struct net_device *out,
       int (*okfn)(struct sk_buff *))
{
      struct iphdr      *iph;
      struct ip_vs_protocol *pp;
      struct ip_vs_conn *cp;
      int ret, restart;
      int ihl;

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

      iph = ip_hdr(skb);
      if (unlikely(iph->protocol == IPPROTO_ICMP)) {
            int related, verdict = ip_vs_in_icmp(skb, &related, hooknum);

            if (related)
                  return verdict;
            iph = ip_hdr(skb);
      }

      /* Protocol supported? */
      pp = ip_vs_proto_get(iph->protocol);
      if (unlikely(!pp))
            return NF_ACCEPT;

      ihl = iph->ihl << 2;

      /*
       * Check if the packet belongs to an existing connection entry
       */
      cp = pp->conn_in_get(skb, pp, iph, ihl, 0);

      if (unlikely(!cp)) {
            int v;

            if (!pp->conn_schedule(skb, pp, &v, &cp))
                  return v;
      }

      if (unlikely(!cp)) {
            /* sorry, all this trouble for a no-hit :) */
            IP_VS_DBG_PKT(12, pp, skb, 0,
                        "packet continues traversal as normal");
            return NF_ACCEPT;
      }

      IP_VS_DBG_PKT(11, pp, skb, 0, "Incoming packet");

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

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

      ip_vs_in_stats(cp, skb);
      restart = ip_vs_set_state(cp, IP_VS_DIR_INPUT, skb, pp);
      if (cp->packet_xmit)
            ret = cp->packet_xmit(skb, cp, pp);
            /* do not touch skb anymore */
      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
       *
       * Sync connection if it is about to close to
       * encorage the standby servers to update the connections timeout
       */
      atomic_inc(&cp->in_pkts);
      if ((ip_vs_sync_state & IP_VS_STATE_MASTER) &&
          (((cp->protocol != IPPROTO_TCP ||
             cp->state == IP_VS_TCP_S_ESTABLISHED) &&
            (atomic_read(&cp->in_pkts) % sysctl_ip_vs_sync_threshold[1]
             == sysctl_ip_vs_sync_threshold[0])) ||
           ((cp->protocol == IPPROTO_TCP) && (cp->old_state != cp->state) &&
            ((cp->state == IP_VS_TCP_S_FIN_WAIT) ||
             (cp->state == IP_VS_TCP_S_CLOSE)))))
            ip_vs_sync_conn(cp);
      cp->old_state = cp->state;

      ip_vs_conn_put(cp);
      return ret;
}


/*
 *    It is hooked at the NF_IP_FORWARD chain, in order to catch ICMP
 *      related 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,
               const struct net_device *in, const struct net_device *out,
               int (*okfn)(struct sk_buff *))
{
      int r;

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

      return ip_vs_in_icmp(skb, &r, hooknum);
}


/* 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 = {
      .hook       = ip_vs_in,
      .owner            = THIS_MODULE,
      .pf         = PF_INET,
      .hooknum        = NF_IP_LOCAL_IN,
      .priority       = 100,
};

/* After packet filtering, change source only for VS/NAT */
static struct nf_hook_ops ip_vs_out_ops = {
      .hook       = ip_vs_out,
      .owner            = THIS_MODULE,
      .pf         = PF_INET,
      .hooknum        = NF_IP_FORWARD,
      .priority       = 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 = {
      .hook       = ip_vs_forward_icmp,
      .owner            = THIS_MODULE,
      .pf         = PF_INET,
      .hooknum        = NF_IP_FORWARD,
      .priority       = 99,
};

/* Before the netfilter connection tracking, exit from POST_ROUTING */
static struct nf_hook_ops ip_vs_post_routing_ops = {
      .hook       = ip_vs_post_routing,
      .owner            = THIS_MODULE,
      .pf         = PF_INET,
      .hooknum        = NF_IP_POST_ROUTING,
      .priority       = 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;
      }

      ip_vs_protocol_init();

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

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

      ret = nf_register_hook(&ip_vs_in_ops);
      if (ret < 0) {
            IP_VS_ERR("can't register in hook.\n");
            goto cleanup_conn;
      }

      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_conn:
      ip_vs_conn_cleanup();
  cleanup_app:
      ip_vs_app_cleanup();
  cleanup_protocol:
      ip_vs_protocol_cleanup();
      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_conn_cleanup();
      ip_vs_app_cleanup();
      ip_vs_protocol_cleanup();
      ip_vs_control_cleanup();
      IP_VS_INFO("ipvs unloaded.\n");
}

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

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