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/nfnetlink_conntrack.h>
  16 #include <linux/netfilter_ipv4/ip_nat.h>
  17 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  18 #include <linux/netfilter_ipv4/ip_nat_protocol.h>
  19 #include <linux/netfilter_ipv4/ip_nat_core.h>
  20
  21 static int
  22 tcp_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.tcp.port;
  31         else
  32                 port = tuple->dst.u.tcp.port;
  33
  34         return ntohs(port) >= ntohs(min->tcp.port)
  35                 && ntohs(port) <= ntohs(max->tcp.port);
  36 }
  37
  38 static int
  39 tcp_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.tcp.port;
  50         else
  51                 portptr = &tuple->dst.u.tcp.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                 /* Map privileged onto privileged. */
  60                 if (ntohs(*portptr) < 1024) {
  61                         /* Loose convention: >> 512 is credential passing */
  62                         if (ntohs(*portptr)<512) {
  63                                 min = 1;
  64                                 range_size = 511 - min + 1;
  65                         } else {
  66                                 min = 600;
  67                                 range_size = 1023 - min + 1;
  68                         }
  69                 } else {
  70                         min = 1024;
  71                         range_size = 65535 - 1024 + 1;
  72                 }
  73         } else {
  74                 min = ntohs(range->min.tcp.port);
  75                 range_size = ntohs(range->max.tcp.port) - min + 1;
  76         }
  77
  78         for (i = 0; i < range_size; i++, port++) {
  79                 *portptr = htons(min + port % range_size);
  80                 if (!ip_nat_used_tuple(tuple, conntrack)) {
  81                         return 1;
  82                 }
  83         }
  84         return 0;
  85 }
  86
  87 static int
  88 tcp_manip_pkt(struct sk_buff **pskb,
  89               unsigned int iphdroff,
  90               const struct ip_conntrack_tuple *tuple,
  91               enum ip_nat_manip_type maniptype)
  92 {
  93         struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff);
  94         struct tcphdr *hdr;
  95         unsigned int hdroff = iphdroff + iph->ihl*4;
  96         u32 oldip, newip;
  97         u16 *portptr, newport, oldport;
  98         int hdrsize = 8; /* TCP connection tracking guarantees this much */
  99
 100         /* this could be a inner header returned in icmp packet; in such
 101            cases we cannot update the checksum field since it is outside of
 102            the 8 bytes of transport layer headers we are guaranteed */
 103         if ((*pskb)->len >= hdroff + sizeof(struct tcphdr))
 104                 hdrsize = sizeof(struct tcphdr);
 105
 106         if (!skb_ip_make_writable(pskb, hdroff + hdrsize))
 107                 return 0;
 108
 109         iph = (struct iphdr *)((*pskb)->data + iphdroff);
 110         hdr = (struct tcphdr *)((*pskb)->data + hdroff);
 111
 112         if (maniptype == IP_NAT_MANIP_SRC) {
 113                 /* Get rid of src ip and src pt */
 114                 oldip = iph->saddr;
 115                 newip = tuple->src.ip;
 116                 newport = tuple->src.u.tcp.port;
 117                 portptr = &hdr->source;
 118         } else {
 119                 /* Get rid of dst ip and dst pt */
 120                 oldip = iph->daddr;
 121                 newip = tuple->dst.ip;
 122                 newport = tuple->dst.u.tcp.port;
 123                 portptr = &hdr->dest;
 124         }
 125
 126         oldport = *portptr;
 127         *portptr = newport;
 128
 129         if (hdrsize < sizeof(*hdr))
 130                 return 1;
 131
 132         hdr->check = ip_nat_cheat_check(~oldip, newip,
 133                                         ip_nat_cheat_check(oldport ^ 0xFFFF,
 134                                                            newport,
 135                                                            hdr->check));
 136         return 1;
 137 }
 138
 139 static unsigned int
 140 tcp_print(char *buffer,
 141           const struct ip_conntrack_tuple *match,
 142           const struct ip_conntrack_tuple *mask)
 143 {
 144         unsigned int len = 0;
 145
 146         if (mask->src.u.tcp.port)
 147                 len += sprintf(buffer + len, "srcpt=%u ",
 148                                ntohs(match->src.u.tcp.port));
 149
 150
 151         if (mask->dst.u.tcp.port)
 152                 len += sprintf(buffer + len, "dstpt=%u ",
 153                                ntohs(match->dst.u.tcp.port));
 154
 155         return len;
 156 }
 157
 158 static unsigned int
 159 tcp_print_range(char *buffer, const struct ip_nat_range *range)
 160 {
 161         if (range->min.tcp.port != 0 || range->max.tcp.port != 0xFFFF) {
 162                 if (range->min.tcp.port == range->max.tcp.port)
 163                         return sprintf(buffer, "port %u ",
 164                                        ntohs(range->min.tcp.port));
 165                 else
 166                         return sprintf(buffer, "ports %u-%u ",
 167                                        ntohs(range->min.tcp.port),
 168                                        ntohs(range->max.tcp.port));
 169         }
 170         else return 0;
 171 }
 172
 173 struct ip_nat_protocol ip_nat_protocol_tcp
 174 = { "TCP", IPPROTO_TCP, THIS_MODULE,
 175     tcp_manip_pkt,
 176     tcp_in_range,
 177     tcp_unique_tuple,
 178     tcp_print,
 179     tcp_print_range,
 180 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 181     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 182     ip_nat_port_range_to_nfattr,
 183     ip_nat_port_nfattr_to_range,
 184 #endif
 185 };