release/src-rt/linux/linux-2.6/net/ipv4/netfilter/nf_nat_proto_tcp.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/tcp.h>
  14
  15 #include <linux/netfilter.h>
  16 #include <linux/netfilter/nfnetlink_conntrack.h>
  17 #include <net/netfilter/nf_nat.h>
  18 #include <net/netfilter/nf_nat_rule.h>
  19 #include <net/netfilter/nf_nat_protocol.h>
  20 #include <net/netfilter/nf_nat_core.h>
  21
  22 static int
  23 tcp_in_range(const struct nf_conntrack_tuple *tuple,
  24              enum nf_nat_manip_type maniptype,
  25              const union nf_conntrack_man_proto *min,
  26              const union nf_conntrack_man_proto *max)
  27 {
  28         __be16 port;
  29
  30         if (maniptype == IP_NAT_MANIP_SRC)
  31                 port = tuple->src.u.tcp.port;
  32         else
  33                 port = tuple->dst.u.tcp.port;
  34
  35         return ntohs(port) >= ntohs(min->tcp.port) &&
  36                ntohs(port) <= ntohs(max->tcp.port);
  37 }
  38
  39 static int
  40 tcp_unique_tuple(struct nf_conntrack_tuple *tuple,
  41                  const struct nf_nat_range *range,
  42                  enum nf_nat_manip_type maniptype,
  43                  const struct nf_conn *ct)
  44 {
  45         static u_int16_t port;
  46         __be16 *portptr;
  47         unsigned int range_size, min, i;
  48
  49         if (maniptype == IP_NAT_MANIP_SRC)
  50                 portptr = &tuple->src.u.tcp.port;
  51         else
  52                 portptr = &tuple->dst.u.tcp.port;
  53
  54         /* If no range specified... */
  55         if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
  56                 /* If it's dst rewrite, can't change port */
  57                 if (maniptype == IP_NAT_MANIP_DST)
  58                         return 0;
  59
  60                 /* Map privileged onto privileged. */
  61                 if (ntohs(*portptr) < 1024) {
  62                         /* Loose convention: >> 512 is credential passing */
  63                         if (ntohs(*portptr)<512) {
  64                                 min = 1;
  65                                 range_size = 511 - min + 1;
  66                         } else {
  67                                 min = 600;
  68                                 range_size = 1023 - min + 1;
  69                         }
  70                 } else {
  71                         min = 1024;
  72                         range_size = 65535 - 1024 + 1;
  73                 }
  74         } else {
  75                 min = ntohs(range->min.tcp.port);
  76                 range_size = ntohs(range->max.tcp.port) - min + 1;
  77         }
  78
  79         if (range->flags & IP_NAT_RANGE_PROTO_RANDOM)
  80                 port =  net_random();
  81
  82         for (i = 0; ; ++port) {
  83                 *portptr = htons(min + port % range_size);
  84                 if (++i == range_size || !nf_nat_used_tuple(tuple, ct))
  85                         return 1;
  86         }
  87         return 0;
  88 }
  89
  90 static int
  91 tcp_manip_pkt(struct sk_buff *skb,
  92               unsigned int iphdroff,
  93               const struct nf_conntrack_tuple *tuple,
  94               enum nf_nat_manip_type maniptype)
  95 {
  96         struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
  97         struct tcphdr *hdr;
  98         unsigned int hdroff = iphdroff + iph->ihl*4;
  99         __be32 oldip, newip;
 100         __be16 *portptr, newport, oldport;
 101         int hdrsize = 8; /* TCP connection tracking guarantees this much */
 102
 103         /* this could be a inner header returned in icmp packet; in such
 104            cases we cannot update the checksum field since it is outside of
 105            the 8 bytes of transport layer headers we are guaranteed */
 106         if (skb->len >= hdroff + sizeof(struct tcphdr))
 107                 hdrsize = sizeof(struct tcphdr);
 108
 109         if (!skb_make_writable(skb, hdroff + hdrsize))
 110                 return 0;
 111
 112         iph = (struct iphdr *)(skb->data + iphdroff);
 113         hdr = (struct tcphdr *)(skb->data + hdroff);
 114
 115         if (maniptype == IP_NAT_MANIP_SRC) {
 116                 /* Get rid of src ip and src pt */
 117                 oldip = iph->saddr;
 118                 newip = tuple->src.u3.ip;
 119                 newport = tuple->src.u.tcp.port;
 120                 portptr = &hdr->source;
 121         } else {
 122                 /* Get rid of dst ip and dst pt */
 123                 oldip = iph->daddr;
 124                 newip = tuple->dst.u3.ip;
 125                 newport = tuple->dst.u.tcp.port;
 126                 portptr = &hdr->dest;
 127         }
 128
 129         oldport = *portptr;
 130         *portptr = newport;
 131
 132         if (hdrsize < sizeof(*hdr))
 133                 return 1;
 134
 135         nf_proto_csum_replace4(&hdr->check, skb, oldip, newip, 1);
 136         nf_proto_csum_replace2(&hdr->check, skb, oldport, newport, 0);
 137         return 1;
 138 }
 139
 140 struct nf_nat_protocol nf_nat_protocol_tcp = {
 141         .name                   = "TCP",
 142         .protonum               = IPPROTO_TCP,
 143         .me                     = THIS_MODULE,
 144         .manip_pkt              = tcp_manip_pkt,
 145         .in_range               = tcp_in_range,
 146         .unique_tuple           = tcp_unique_tuple,
 147 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 148         .range_to_nfattr        = nf_nat_port_range_to_nfattr,
 149         .nfattr_to_range        = nf_nat_port_nfattr_to_range,
 150 #endif
 151 };