net/ipv4/netfilter/nf_nat_proto_udp.c

   1 /* (C) 1999-2001 Paul `Rusty' Russell
   2  * (C) 2002-2006 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/ip.h>
  12 #include <linux/udp.h>
  13
  14 #include <linux/netfilter.h>
  15 #include <net/netfilter/nf_nat.h>
  16 #include <net/netfilter/nf_nat_core.h>
  17 #include <net/netfilter/nf_nat_rule.h>
  18 #include <net/netfilter/nf_nat_protocol.h>
  19
  20 static int
  21 udp_in_range(const struct nf_conntrack_tuple *tuple,
  22              enum nf_nat_manip_type maniptype,
  23              const union nf_conntrack_man_proto *min,
  24              const union nf_conntrack_man_proto *max)
  25 {
  26         __be16 port;
  27
  28         if (maniptype == IP_NAT_MANIP_SRC)
  29                 port = tuple->src.u.udp.port;
  30         else
  31                 port = tuple->dst.u.udp.port;
  32
  33         return ntohs(port) >= ntohs(min->udp.port) &&
  34                ntohs(port) <= ntohs(max->udp.port);
  35 }
  36
  37 static int
  38 udp_unique_tuple(struct nf_conntrack_tuple *tuple,
  39                  const struct nf_nat_range *range,
  40                  enum nf_nat_manip_type maniptype,
  41                  const struct nf_conn *ct)
  42 {
  43         static u_int16_t port;
  44         __be16 *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 (!nf_nat_used_tuple(tuple, ct))
  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 nf_conntrack_tuple *tuple,
  88               enum nf_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         __be32 oldip, newip;
  94         __be16 *portptr, newport;
  95
  96         if (!skb_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.u3.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.u3.ip;
 112                 newport = tuple->dst.u.udp.port;
 113                 portptr = &hdr->dest;
 114         }
 115         if (hdr->check || (*pskb)->ip_summed == CHECKSUM_PARTIAL) {
 116                 nf_proto_csum_replace4(&hdr->check, *pskb, oldip, newip, 1);
 117                 nf_proto_csum_replace2(&hdr->check, *pskb, *portptr, newport,
 118                                        0);
 119                 if (!hdr->check)
 120                         hdr->check = CSUM_MANGLED_0;
 121         }
 122         *portptr = newport;
 123         return 1;
 124 }
 125
 126 struct nf_nat_protocol nf_nat_protocol_udp = {
 127         .name                   = "UDP",
 128         .protonum               = IPPROTO_UDP,
 129         .me                     = THIS_MODULE,
 130         .manip_pkt              = udp_manip_pkt,
 131         .in_range               = udp_in_range,
 132         .unique_tuple           = udp_unique_tuple,
 133 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 134     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 135         .range_to_nfattr        = nf_nat_port_range_to_nfattr,
 136         .nfattr_to_range        = nf_nat_port_nfattr_to_range,
 137 #endif
 138 };