net/ipv4/netfilter/ip_nat_proto_tcp.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/tcp.h>
  14 #include <linux/if.h>
  15 #include <linux/netfilter_ipv4/ip_nat.h>
  16 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  17 #include <linux/netfilter_ipv4/ip_nat_protocol.h>
  18 #include <linux/netfilter_ipv4/ip_nat_core.h>
  19
  20 static int
  21 tcp_in_range(const struct ip_conntrack_tuple *tuple,
  22              enum ip_nat_manip_type maniptype,
  23              const union ip_conntrack_manip_proto *min,
  24              const union ip_conntrack_manip_proto *max)
  25 {
  26         u_int16_t port;
  27
  28         if (maniptype == IP_NAT_MANIP_SRC)
  29                 port = tuple->src.u.tcp.port;
  30         else
  31                 port = tuple->dst.u.tcp.port;
  32
  33         return ntohs(port) >= ntohs(min->tcp.port)
  34                 && ntohs(port) <= ntohs(max->tcp.port);
  35 }
  36
  37 static int
  38 tcp_unique_tuple(struct ip_conntrack_tuple *tuple,
  39                  const struct ip_nat_range *range,
  40                  enum ip_nat_manip_type maniptype,
  41                  const struct ip_conntrack *conntrack)
  42 {
  43         static u_int16_t port;
  44         u_int16_t *portptr;
  45         unsigned int range_size, min, i;
  46
  47         if (maniptype == IP_NAT_MANIP_SRC)
  48                 portptr = &tuple->src.u.tcp.port;
  49         else
  50                 portptr = &tuple->dst.u.tcp.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                 /* Map privileged onto privileged. */
  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.tcp.port);
  74                 range_size = ntohs(range->max.tcp.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         }
  83         return 0;
  84 }
  85
  86 static int
  87 tcp_manip_pkt(struct sk_buff **pskb,
  88               unsigned int iphdroff,
  89               const struct ip_conntrack_tuple *tuple,
  90               enum ip_nat_manip_type maniptype)
  91 {
  92         struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff);
  93         struct tcphdr *hdr;
  94         unsigned int hdroff = iphdroff + iph->ihl*4;
  95         u32 oldip, newip;
  96         u16 *portptr, newport, oldport;
  97         int hdrsize = 8; /* TCP connection tracking guarantees this much */
  98
  99         /* this could be a inner header returned in icmp packet; in such
 100            cases we cannot update the checksum field since it is outside of
 101            the 8 bytes of transport layer headers we are guaranteed */
 102         if ((*pskb)->len >= hdroff + sizeof(struct tcphdr))
 103                 hdrsize = sizeof(struct tcphdr);
 104
 105         if (!skb_ip_make_writable(pskb, hdroff + hdrsize))
 106                 return 0;
 107
 108         iph = (struct iphdr *)((*pskb)->data + iphdroff);
 109         hdr = (struct tcphdr *)((*pskb)->data + hdroff);
 110
 111         if (maniptype == IP_NAT_MANIP_SRC) {
 112                 /* Get rid of src ip and src pt */
 113                 oldip = iph->saddr;
 114                 newip = tuple->src.ip;
 115                 newport = tuple->src.u.tcp.port;
 116                 portptr = &hdr->source;
 117         } else {
 118                 /* Get rid of dst ip and dst pt */
 119                 oldip = iph->daddr;
 120                 newip = tuple->dst.ip;
 121                 newport = tuple->dst.u.tcp.port;
 122                 portptr = &hdr->dest;
 123         }
 124
 125         oldport = *portptr;
 126         *portptr = newport;
 127
 128         if (hdrsize < sizeof(*hdr))
 129                 return 1;
 130
 131         hdr->check = ip_nat_cheat_check(~oldip, newip,
 132                                         ip_nat_cheat_check(oldport ^ 0xFFFF,
 133                                                            newport,
 134                                                            hdr->check));
 135         return 1;
 136 }
 137
 138 static unsigned int
 139 tcp_print(char *buffer,
 140           const struct ip_conntrack_tuple *match,
 141           const struct ip_conntrack_tuple *mask)
 142 {
 143         unsigned int len = 0;
 144
 145         if (mask->src.u.tcp.port)
 146                 len += sprintf(buffer + len, "srcpt=%u ",
 147                                ntohs(match->src.u.tcp.port));
 148
 149
 150         if (mask->dst.u.tcp.port)
 151                 len += sprintf(buffer + len, "dstpt=%u ",
 152                                ntohs(match->dst.u.tcp.port));
 153
 154         return len;
 155 }
 156
 157 static unsigned int
 158 tcp_print_range(char *buffer, const struct ip_nat_range *range)
 159 {
 160         if (range->min.tcp.port != 0 || range->max.tcp.port != 0xFFFF) {
 161                 if (range->min.tcp.port == range->max.tcp.port)
 162                         return sprintf(buffer, "port %u ",
 163                                        ntohs(range->min.tcp.port));
 164                 else
 165                         return sprintf(buffer, "ports %u-%u ",
 166                                        ntohs(range->min.tcp.port),
 167                                        ntohs(range->max.tcp.port));
 168         }
 169         else return 0;
 170 }
 171
 172 struct ip_nat_protocol ip_nat_protocol_tcp
 173 = { "TCP", IPPROTO_TCP,
 174     tcp_manip_pkt,
 175     tcp_in_range,
 176     tcp_unique_tuple,
 177     tcp_print,
 178     tcp_print_range
 179 };