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/ip.h>
  12 #include <linux/tcp.h>
  13
  14 #include <linux/netfilter.h>
  15 #include <linux/netfilter/nfnetlink_conntrack.h>
  16 #include <net/netfilter/nf_nat.h>
  17 #include <net/netfilter/nf_nat_rule.h>
  18 #include <net/netfilter/nf_nat_protocol.h>
  19 #include <net/netfilter/nf_nat_core.h>
  20
  21 static int
  22 tcp_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.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 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.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 (!nf_nat_used_tuple(tuple, ct))
  81                         return 1;
  82         }
  83         return 0;
  84 }
  85
  86 static int
  87 tcp_manip_pkt(struct sk_buff **pskb,
  88               unsigned int iphdroff,
  89               const struct nf_conntrack_tuple *tuple,
  90               enum nf_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         __be32 oldip, newip;
  96         __be16 *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_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.u3.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.u3.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         nf_proto_csum_replace4(&hdr->check, *pskb, oldip, newip, 1);
 132         nf_proto_csum_replace2(&hdr->check, *pskb, oldport, newport, 0);
 133         return 1;
 134 }
 135
 136 struct nf_nat_protocol nf_nat_protocol_tcp = {
 137         .name                   = "TCP",
 138         .protonum               = IPPROTO_TCP,
 139         .me                     = THIS_MODULE,
 140         .manip_pkt              = tcp_manip_pkt,
 141         .in_range               = tcp_in_range,
 142         .unique_tuple           = tcp_unique_tuple,
 143 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 144     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 145         .range_to_nfattr        = nf_nat_port_range_to_nfattr,
 146         .nfattr_to_range        = nf_nat_port_nfattr_to_range,
 147 #endif
 148 };