net/ipv4/netfilter/ipt_SAME.c

   1 /* Same.  Just like SNAT, only try to make the connections
   2  *        between client A and server B always have the same source ip.
   3  *
   4  * (C) 2000 Paul `Rusty' Russell
   5  * (C) 2001 Martin Josefsson
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11 #include <linux/types.h>
  12 #include <linux/ip.h>
  13 #include <linux/timer.h>
  14 #include <linux/module.h>
  15 #include <linux/netfilter.h>
  16 #include <linux/netdevice.h>
  17 #include <linux/if.h>
  18 #include <linux/inetdevice.h>
  19 #include <net/protocol.h>
  20 #include <net/checksum.h>
  21 #include <linux/netfilter_ipv4.h>
  22 #include <linux/netfilter/x_tables.h>
  23 #include <net/netfilter/nf_nat_rule.h>
  24 #include <linux/netfilter_ipv4/ipt_SAME.h>
  25
  26 MODULE_LICENSE("GPL");
  27 MODULE_AUTHOR("Martin Josefsson <gandalf@wlug.westbo.se>");
  28 MODULE_DESCRIPTION("iptables special SNAT module for consistent sourceip");
  29
  30 static bool
  31 same_check(const char *tablename,
  32               const void *e,
  33               const struct xt_target *target,
  34               void *targinfo,
  35               unsigned int hook_mask)
  36 {
  37         unsigned int count, countess, rangeip, index = 0;
  38         struct ipt_same_info *mr = targinfo;
  39
  40         mr->ipnum = 0;
  41
  42         if (mr->rangesize < 1) {
  43                 pr_debug("same_check: need at least one dest range.\n");
  44                 return false;
  45         }
  46         if (mr->rangesize > IPT_SAME_MAX_RANGE) {
  47                 pr_debug("same_check: too many ranges specified, maximum "
  48                          "is %u ranges\n", IPT_SAME_MAX_RANGE);
  49                 return false;
  50         }
  51         for (count = 0; count < mr->rangesize; count++) {
  52                 if (ntohl(mr->range[count].min_ip) >
  53                                 ntohl(mr->range[count].max_ip)) {
  54                         pr_debug("same_check: min_ip is larger than max_ip in "
  55                                  "range `%u.%u.%u.%u-%u.%u.%u.%u'.\n",
  56                                  NIPQUAD(mr->range[count].min_ip),
  57                                  NIPQUAD(mr->range[count].max_ip));
  58                         return false;
  59                 }
  60                 if (!(mr->range[count].flags & IP_NAT_RANGE_MAP_IPS)) {
  61                         pr_debug("same_check: bad MAP_IPS.\n");
  62                         return false;
  63                 }
  64                 rangeip = (ntohl(mr->range[count].max_ip) -
  65                                         ntohl(mr->range[count].min_ip) + 1);
  66                 mr->ipnum += rangeip;
  67
  68                 pr_debug("same_check: range %u, ipnum = %u\n", count, rangeip);
  69         }
  70         pr_debug("same_check: total ipaddresses = %u\n", mr->ipnum);
  71
  72         mr->iparray = kmalloc((sizeof(u_int32_t) * mr->ipnum), GFP_KERNEL);
  73         if (!mr->iparray) {
  74                 pr_debug("same_check: Couldn't allocate %Zu bytes "
  75                          "for %u ipaddresses!\n",
  76                          (sizeof(u_int32_t) * mr->ipnum), mr->ipnum);
  77                 return false;
  78         }
  79         pr_debug("same_check: Allocated %Zu bytes for %u ipaddresses.\n",
  80                  (sizeof(u_int32_t) * mr->ipnum), mr->ipnum);
  81
  82         for (count = 0; count < mr->rangesize; count++) {
  83                 for (countess = ntohl(mr->range[count].min_ip);
  84                                 countess <= ntohl(mr->range[count].max_ip);
  85                                         countess++) {
  86                         mr->iparray[index] = countess;
  87                         pr_debug("same_check: Added ipaddress `%u.%u.%u.%u' "
  88                                  "in index %u.\n", HIPQUAD(countess), index);
  89                         index++;
  90                 }
  91         }
  92         return true;
  93 }
  94
  95 static void
  96 same_destroy(const struct xt_target *target, void *targinfo)
  97 {
  98         struct ipt_same_info *mr = targinfo;
  99
 100         kfree(mr->iparray);
 101
 102         pr_debug("same_destroy: Deallocated %Zu bytes for %u ipaddresses.\n",
 103                  (sizeof(u_int32_t) * mr->ipnum), mr->ipnum);
 104 }
 105
 106 static unsigned int
 107 same_target(struct sk_buff *skb,
 108                 const struct net_device *in,
 109                 const struct net_device *out,
 110                 unsigned int hooknum,
 111                 const struct xt_target *target,
 112                 const void *targinfo)
 113 {
 114         struct nf_conn *ct;
 115         enum ip_conntrack_info ctinfo;
 116         u_int32_t tmpip, aindex;
 117         __be32 new_ip;
 118         const struct ipt_same_info *same = targinfo;
 119         struct nf_nat_range newrange;
 120         const struct nf_conntrack_tuple *t;
 121
 122         NF_CT_ASSERT(hooknum == NF_IP_PRE_ROUTING ||
 123                         hooknum == NF_IP_POST_ROUTING);
 124         ct = nf_ct_get(skb, &ctinfo);
 125
 126         t = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 127
 128         /* Base new source on real src ip and optionally dst ip,
 129            giving some hope for consistency across reboots.
 130            Here we calculate the index in same->iparray which
 131            holds the ipaddress we should use */
 132
 133         tmpip = ntohl(t->src.u3.ip);
 134
 135         if (!(same->info & IPT_SAME_NODST))
 136                 tmpip += ntohl(t->dst.u3.ip);
 137         aindex = tmpip % same->ipnum;
 138
 139         new_ip = htonl(same->iparray[aindex]);
 140
 141         pr_debug("ipt_SAME: src=%u.%u.%u.%u dst=%u.%u.%u.%u, "
 142                  "new src=%u.%u.%u.%u\n",
 143                  NIPQUAD(t->src.u3.ip), NIPQUAD(t->dst.u3.ip), NIPQUAD(new_ip));
 144
 145         /* Transfer from original range. */
 146         newrange = ((struct nf_nat_range)
 147                 { same->range[0].flags, new_ip, new_ip,
 148                   /* FIXME: Use ports from correct range! */
 149                   same->range[0].min, same->range[0].max });
 150
 151         /* Hand modified range to generic setup. */
 152         return nf_nat_setup_info(ct, &newrange, hooknum);
 153 }
 154
 155 static struct xt_target same_reg __read_mostly = {
 156         .name           = "SAME",
 157         .family         = AF_INET,
 158         .target         = same_target,
 159         .targetsize     = sizeof(struct ipt_same_info),
 160         .table          = "nat",
 161         .hooks          = (1 << NF_IP_PRE_ROUTING | 1 << NF_IP_POST_ROUTING),
 162         .checkentry     = same_check,
 163         .destroy        = same_destroy,
 164         .me             = THIS_MODULE,
 165 };
 166
 167 static int __init ipt_same_init(void)
 168 {
 169         return xt_register_target(&same_reg);
 170 }
 171
 172 static void __exit ipt_same_fini(void)
 173 {
 174         xt_unregister_target(&same_reg);
 175 }
 176
 177 module_init(ipt_same_init);
 178 module_exit(ipt_same_fini);
 179