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, *portptr;
  44         unsigned int range_size, min, i;
  45
  46         if (maniptype == IP_NAT_MANIP_SRC)
  47                 portptr = &tuple->src.u.tcp.port;
  48         else
  49                 portptr = &tuple->dst.u.tcp.port;
  50
  51         /* If no range specified... */
  52         if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
  53                 /* If it's dst rewrite, can't change port */
  54                 if (maniptype == IP_NAT_MANIP_DST)
  55                         return 0;
  56
  57                 /* Map privileged onto privileged. */
  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.tcp.port);
  73                 range_size = ntohs(range->max.tcp.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         }
  82         return 0;
  83 }
  84
  85 static int
  86 tcp_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 tcphdr *hdr;
  93         unsigned int hdroff = iphdroff + iph->ihl*4;
  94         u32 oldip, newip;
  95         u16 *portptr, newport, oldport;
  96         int hdrsize = 8; /* TCP connection tracking guarantees this much */
  97
  98         /* this could be a inner header returned in icmp packet; in such
  99            cases we cannot update the checksum field since it is outside of
 100            the 8 bytes of transport layer headers we are guaranteed */
 101         if ((*pskb)->len >= hdroff + sizeof(struct tcphdr))
 102                 hdrsize = sizeof(struct tcphdr);
 103
 104         if (!skb_ip_make_writable(pskb, hdroff + hdrsize))
 105                 return 0;
 106
 107         iph = (struct iphdr *)((*pskb)->data + iphdroff);
 108         hdr = (struct tcphdr *)((*pskb)->data + hdroff);
 109
 110         if (maniptype == IP_NAT_MANIP_SRC) {
 111                 /* Get rid of src ip and src pt */
 112                 oldip = iph->saddr;
 113                 newip = tuple->src.ip;
 114                 newport = tuple->src.u.tcp.port;
 115                 portptr = &hdr->source;
 116         } else {
 117                 /* Get rid of dst ip and dst pt */
 118                 oldip = iph->daddr;
 119                 newip = tuple->dst.ip;
 120                 newport = tuple->dst.u.tcp.port;
 121                 portptr = &hdr->dest;
 122         }
 123
 124         oldport = *portptr;
 125         *portptr = newport;
 126
 127         if (hdrsize < sizeof(*hdr))
 128                 return 1;
 129
 130         hdr->check = ip_nat_cheat_check(~oldip, newip,
 131                                         ip_nat_cheat_check(oldport ^ 0xFFFF,
 132                                                            newport,
 133                                                            hdr->check));
 134         return 1;
 135 }
 136
 137 static unsigned int
 138 tcp_print(char *buffer,
 139           const struct ip_conntrack_tuple *match,
 140           const struct ip_conntrack_tuple *mask)
 141 {
 142         unsigned int len = 0;
 143
 144         if (mask->src.u.tcp.port)
 145                 len += sprintf(buffer + len, "srcpt=%u ",
 146                                ntohs(match->src.u.tcp.port));
 147
 148
 149         if (mask->dst.u.tcp.port)
 150                 len += sprintf(buffer + len, "dstpt=%u ",
 151                                ntohs(match->dst.u.tcp.port));
 152
 153         return len;
 154 }
 155
 156 static unsigned int
 157 tcp_print_range(char *buffer, const struct ip_nat_range *range)
 158 {
 159         if (range->min.tcp.port != 0 || range->max.tcp.port != 0xFFFF) {
 160                 if (range->min.tcp.port == range->max.tcp.port)
 161                         return sprintf(buffer, "port %u ",
 162                                        ntohs(range->min.tcp.port));
 163                 else
 164                         return sprintf(buffer, "ports %u-%u ",
 165                                        ntohs(range->min.tcp.port),
 166                                        ntohs(range->max.tcp.port));
 167         }
 168         else return 0;
 169 }
 170
 171 struct ip_nat_protocol ip_nat_protocol_tcp
 172 = { "TCP", IPPROTO_TCP,
 173     tcp_manip_pkt,
 174     tcp_in_range,
 175     tcp_unique_tuple,
 176     tcp_print,
 177     tcp_print_range
 178 };