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/random.h>
  12 #include <linux/ip.h>
  13 #include <linux/udp.h>
  14
  15 #include <linux/netfilter.h>
  16 #include <net/netfilter/nf_nat.h>
  17 #include <net/netfilter/nf_nat_core.h>
  18 #include <net/netfilter/nf_nat_rule.h>
  19 #include <net/netfilter/nf_nat_protocol.h>
  20
  21 static int
  22 udp_in_range(const struct nf_conntrack_tuple *tuple,
  23              enum nf_nat_manip_type maniptype,
  24              const union nf_conntrack_man_proto *min,
  25              const union nf_conntrack_man_proto *max)
  26 {
  27         __be16 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 nf_conntrack_tuple *tuple,
  40                  const struct nf_nat_range *range,
  41                  enum nf_nat_manip_type maniptype,
  42                  const struct nf_conn *ct)
  43 {
  44         static u_int16_t port;
  45         __be16 *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         if (range->flags & IP_NAT_RANGE_PROTO_RANDOM)
  78                 port = net_random();
  79
  80         for (i = 0; i < range_size; i++, port++) {
  81                 *portptr = htons(min + port % range_size);
  82                 if (!nf_nat_used_tuple(tuple, ct))
  83                         return 1;
  84         }
  85         return 0;
  86 }
  87
  88 static int
  89 udp_manip_pkt(struct sk_buff **pskb,
  90               unsigned int iphdroff,
  91               const struct nf_conntrack_tuple *tuple,
  92               enum nf_nat_manip_type maniptype)
  93 {
  94         struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff);
  95         struct udphdr *hdr;
  96         unsigned int hdroff = iphdroff + iph->ihl*4;
  97         __be32 oldip, newip;
  98         __be16 *portptr, newport;
  99
 100         if (!skb_make_writable(pskb, hdroff + sizeof(*hdr)))
 101                 return 0;
 102
 103         iph = (struct iphdr *)((*pskb)->data + iphdroff);
 104         hdr = (struct udphdr *)((*pskb)->data + hdroff);
 105
 106         if (maniptype == IP_NAT_MANIP_SRC) {
 107                 /* Get rid of src ip and src pt */
 108                 oldip = iph->saddr;
 109                 newip = tuple->src.u3.ip;
 110                 newport = tuple->src.u.udp.port;
 111                 portptr = &hdr->source;
 112         } else {
 113                 /* Get rid of dst ip and dst pt */
 114                 oldip = iph->daddr;
 115                 newip = tuple->dst.u3.ip;
 116                 newport = tuple->dst.u.udp.port;
 117                 portptr = &hdr->dest;
 118         }
 119         if (hdr->check || (*pskb)->ip_summed == CHECKSUM_PARTIAL) {
 120                 nf_proto_csum_replace4(&hdr->check, *pskb, oldip, newip, 1);
 121                 nf_proto_csum_replace2(&hdr->check, *pskb, *portptr, newport,
 122                                        0);
 123                 if (!hdr->check)
 124                         hdr->check = CSUM_MANGLED_0;
 125         }
 126         *portptr = newport;
 127         return 1;
 128 }
 129
 130 struct nf_nat_protocol nf_nat_protocol_udp = {
 131         .name                   = "UDP",
 132         .protonum               = IPPROTO_UDP,
 133         .me                     = THIS_MODULE,
 134         .manip_pkt              = udp_manip_pkt,
 135         .in_range               = udp_in_range,
 136         .unique_tuple           = udp_unique_tuple,
 137 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 138     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 139         .range_to_nfattr        = nf_nat_port_range_to_nfattr,
 140         .nfattr_to_range        = nf_nat_port_nfattr_to_range,
 141 #endif
 142 };