net/ipv4/netfilter/ip_nat_proto_udp.c

   1 /* (C) 1999-2001 Paul `Rusty' Russell
   2  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8
   9 #include <linux/types.h>
  10 #include <linux/init.h>
  11 #include <linux/netfilter.h>
  12 #include <linux/ip.h>
  13 #include <linux/udp.h>
  14 #include <linux/if.h>
  15
  16 #include <linux/netfilter_ipv4/ip_nat.h>
  17 #include <linux/netfilter_ipv4/ip_nat_core.h>
  18 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  19 #include <linux/netfilter_ipv4/ip_nat_protocol.h>
  20
  21 static int
  22 udp_in_range(const struct ip_conntrack_tuple *tuple,
  23              enum ip_nat_manip_type maniptype,
  24              const union ip_conntrack_manip_proto *min,
  25              const union ip_conntrack_manip_proto *max)
  26 {
  27         u_int16_t port;
  28
  29         if (maniptype == IP_NAT_MANIP_SRC)
  30                 port = tuple->src.u.udp.port;
  31         else
  32                 port = tuple->dst.u.udp.port;
  33
  34         return ntohs(port) >= ntohs(min->udp.port)
  35                 && ntohs(port) <= ntohs(max->udp.port);
  36 }
  37
  38 static int
  39 udp_unique_tuple(struct ip_conntrack_tuple *tuple,
  40                  const struct ip_nat_range *range,
  41                  enum ip_nat_manip_type maniptype,
  42                  const struct ip_conntrack *conntrack)
  43 {
  44         static u_int16_t port, *portptr;
  45         unsigned int range_size, min, i;
  46
  47         if (maniptype == IP_NAT_MANIP_SRC)
  48                 portptr = &tuple->src.u.udp.port;
  49         else
  50                 portptr = &tuple->dst.u.udp.port;
  51
  52         /* If no range specified... */
  53         if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
  54                 /* If it's dst rewrite, can't change port */
  55                 if (maniptype == IP_NAT_MANIP_DST)
  56                         return 0;
  57
  58                 if (ntohs(*portptr) < 1024) {
  59                         /* Loose convention: >> 512 is credential passing */
  60                         if (ntohs(*portptr)<512) {
  61                                 min = 1;
  62                                 range_size = 511 - min + 1;
  63                         } else {
  64                                 min = 600;
  65                                 range_size = 1023 - min + 1;
  66                         }
  67                 } else {
  68                         min = 1024;
  69                         range_size = 65535 - 1024 + 1;
  70                 }
  71         } else {
  72                 min = ntohs(range->min.udp.port);
  73                 range_size = ntohs(range->max.udp.port) - min + 1;
  74         }
  75
  76         for (i = 0; i < range_size; i++, port++) {
  77                 *portptr = htons(min + port % range_size);
  78                 if (!ip_nat_used_tuple(tuple, conntrack))
  79                         return 1;
  80         }
  81         return 0;
  82 }
  83
  84 static int
  85 udp_manip_pkt(struct sk_buff **pskb,
  86               unsigned int iphdroff,
  87               const struct ip_conntrack_tuple *tuple,
  88               enum ip_nat_manip_type maniptype)
  89 {
  90         struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff);
  91         struct udphdr *hdr;
  92         unsigned int hdroff = iphdroff + iph->ihl*4;
  93         u32 oldip, newip;
  94         u16 *portptr, newport;
  95
  96         if (!skb_ip_make_writable(pskb, hdroff + sizeof(*hdr)))
  97                 return 0;
  98
  99         iph = (struct iphdr *)((*pskb)->data + iphdroff);
 100         hdr = (struct udphdr *)((*pskb)->data + hdroff);
 101
 102         if (maniptype == IP_NAT_MANIP_SRC) {
 103                 /* Get rid of src ip and src pt */
 104                 oldip = iph->saddr;
 105                 newip = tuple->src.ip;
 106                 newport = tuple->src.u.udp.port;
 107                 portptr = &hdr->source;
 108         } else {
 109                 /* Get rid of dst ip and dst pt */
 110                 oldip = iph->daddr;
 111                 newip = tuple->dst.ip;
 112                 newport = tuple->dst.u.udp.port;
 113                 portptr = &hdr->dest;
 114         }
 115         if (hdr->check) /* 0 is a special case meaning no checksum */
 116                 hdr->check = ip_nat_cheat_check(~oldip, newip,
 117                                         ip_nat_cheat_check(*portptr ^ 0xFFFF,
 118                                                            newport,
 119                                                            hdr->check));
 120         *portptr = newport;
 121         return 1;
 122 }
 123
 124 static unsigned int
 125 udp_print(char *buffer,
 126           const struct ip_conntrack_tuple *match,
 127           const struct ip_conntrack_tuple *mask)
 128 {
 129         unsigned int len = 0;
 130
 131         if (mask->src.u.udp.port)
 132                 len += sprintf(buffer + len, "srcpt=%u ",
 133                                ntohs(match->src.u.udp.port));
 134
 135
 136         if (mask->dst.u.udp.port)
 137                 len += sprintf(buffer + len, "dstpt=%u ",
 138                                ntohs(match->dst.u.udp.port));
 139
 140         return len;
 141 }
 142
 143 static unsigned int
 144 udp_print_range(char *buffer, const struct ip_nat_range *range)
 145 {
 146         if (range->min.udp.port != 0 || range->max.udp.port != 0xFFFF) {
 147                 if (range->min.udp.port == range->max.udp.port)
 148                         return sprintf(buffer, "port %u ",
 149                                        ntohs(range->min.udp.port));
 150                 else
 151                         return sprintf(buffer, "ports %u-%u ",
 152                                        ntohs(range->min.udp.port),
 153                                        ntohs(range->max.udp.port));
 154         }
 155         else return 0;
 156 }
 157
 158 struct ip_nat_protocol ip_nat_protocol_udp
 159 = { "UDP", IPPROTO_UDP,
 160     udp_manip_pkt,
 161     udp_in_range,
 162     udp_unique_tuple,
 163     udp_print,
 164     udp_print_range
 165 };