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;
  45         u_int16_t *portptr;
  46         unsigned int range_size, min, i;
  47
  48         if (maniptype == IP_NAT_MANIP_SRC)
  49                 portptr = &tuple->src.u.udp.port;
  50         else
  51                 portptr = &tuple->dst.u.udp.port;
  52
  53         /* If no range specified... */
  54         if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
  55                 /* If it's dst rewrite, can't change port */
  56                 if (maniptype == IP_NAT_MANIP_DST)
  57                         return 0;
  58
  59                 if (ntohs(*portptr) < 1024) {
  60                         /* Loose convention: >> 512 is credential passing */
  61                         if (ntohs(*portptr)<512) {
  62                                 min = 1;
  63                                 range_size = 511 - min + 1;
  64                         } else {
  65                                 min = 600;
  66                                 range_size = 1023 - min + 1;
  67                         }
  68                 } else {
  69                         min = 1024;
  70                         range_size = 65535 - 1024 + 1;
  71                 }
  72         } else {
  73                 min = ntohs(range->min.udp.port);
  74                 range_size = ntohs(range->max.udp.port) - min + 1;
  75         }
  76
  77         for (i = 0; i < range_size; i++, port++) {
  78                 *portptr = htons(min + port % range_size);
  79                 if (!ip_nat_used_tuple(tuple, conntrack))
  80                         return 1;
  81         }
  82         return 0;
  83 }
  84
  85 static int
  86 udp_manip_pkt(struct sk_buff **pskb,
  87               unsigned int iphdroff,
  88               const struct ip_conntrack_tuple *tuple,
  89               enum ip_nat_manip_type maniptype)
  90 {
  91         struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff);
  92         struct udphdr *hdr;
  93         unsigned int hdroff = iphdroff + iph->ihl*4;
  94         u32 oldip, newip;
  95         u16 *portptr, newport;
  96
  97         if (!skb_make_writable(pskb, hdroff + sizeof(*hdr)))
  98                 return 0;
  99
 100         iph = (struct iphdr *)((*pskb)->data + iphdroff);
 101         hdr = (struct udphdr *)((*pskb)->data + hdroff);
 102
 103         if (maniptype == IP_NAT_MANIP_SRC) {
 104                 /* Get rid of src ip and src pt */
 105                 oldip = iph->saddr;
 106                 newip = tuple->src.ip;
 107                 newport = tuple->src.u.udp.port;
 108                 portptr = &hdr->source;
 109         } else {
 110                 /* Get rid of dst ip and dst pt */
 111                 oldip = iph->daddr;
 112                 newip = tuple->dst.ip;
 113                 newport = tuple->dst.u.udp.port;
 114                 portptr = &hdr->dest;
 115         }
 116         if (hdr->check) /* 0 is a special case meaning no checksum */
 117                 hdr->check = ip_nat_cheat_check(~oldip, newip,
 118                                         ip_nat_cheat_check(*portptr ^ 0xFFFF,
 119                                                            newport,
 120                                                            hdr->check));
 121         *portptr = newport;
 122         return 1;
 123 }
 124
 125 struct ip_nat_protocol ip_nat_protocol_udp = {
 126         .name                   = "UDP",
 127         .protonum               = IPPROTO_UDP,
 128         .me                     = THIS_MODULE,
 129         .manip_pkt              = udp_manip_pkt,
 130         .in_range               = udp_in_range,
 131         .unique_tuple           = udp_unique_tuple,
 132 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 133     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 134         .range_to_nfattr        = ip_nat_port_range_to_nfattr,
 135         .nfattr_to_range        = ip_nat_port_nfattr_to_range,
 136 #endif
 137 };