nf_nat_proto_tcp.c
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/* (C) 1999-2001 Paul `Rusty' Russell
* (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/types.h>
#include <linux/init.h>
#include <linux/random.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nfnetlink_conntrack.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_rule.h>
#include <net/netfilter/nf_nat_protocol.h>
#include <net/netfilter/nf_nat_core.h>
static int
tcp_in_range(const struct nf_conntrack_tuple *tuple,
enum nf_nat_manip_type maniptype,
const union nf_conntrack_man_proto *min,
const union nf_conntrack_man_proto *max)
{
__be16 port;
if (maniptype == IP_NAT_MANIP_SRC)
port = tuple->src.u.tcp.port;
else
port = tuple->dst.u.tcp.port;
return ntohs(port) >= ntohs(min->tcp.port) &&
ntohs(port) <= ntohs(max->tcp.port);
}
static int
tcp_unique_tuple(struct nf_conntrack_tuple *tuple,
const struct nf_nat_range *range,
enum nf_nat_manip_type maniptype,
const struct nf_conn *ct)
{
static u_int16_t port;
__be16 *portptr;
unsigned int range_size, min, i;
if (maniptype == IP_NAT_MANIP_SRC)
portptr = &tuple->src.u.tcp.port;
else
portptr = &tuple->dst.u.tcp.port;
/* If no range specified... */
if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
/* If it's dst rewrite, can't change port */
if (maniptype == IP_NAT_MANIP_DST)
return 0;
/* Map privileged onto privileged. */
if (ntohs(*portptr) < 1024) {
/* Loose convention: >> 512 is credential passing */
if (ntohs(*portptr)<512) {
min = 1;
range_size = 511 - min + 1;
} else {
min = 600;
range_size = 1023 - min + 1;
}
} else {
min = 1024;
range_size = 65535 - 1024 + 1;
}
} else {
min = ntohs(range->min.tcp.port);
range_size = ntohs(range->max.tcp.port) - min + 1;
}
if (range->flags & IP_NAT_RANGE_PROTO_RANDOM)
port = net_random();
for (i = 0; i < range_size; i++, port++) {
*portptr = htons(min + port % range_size);
if (!nf_nat_used_tuple(tuple, ct))
return 1;
}
return 0;
}
static int
tcp_manip_pkt(struct sk_buff *skb,
unsigned int iphdroff,
const struct nf_conntrack_tuple *tuple,
enum nf_nat_manip_type maniptype)
{
struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
struct tcphdr *hdr;
unsigned int hdroff = iphdroff + iph->ihl*4;
__be32 oldip, newip;
__be16 *portptr, newport, oldport;
int hdrsize = 8; /* TCP connection tracking guarantees this much */
/* this could be a inner header returned in icmp packet; in such
cases we cannot update the checksum field since it is outside of
the 8 bytes of transport layer headers we are guaranteed */
if (skb->len >= hdroff + sizeof(struct tcphdr))
hdrsize = sizeof(struct tcphdr);
if (!skb_make_writable(skb, hdroff + hdrsize))
return 0;
iph = (struct iphdr *)(skb->data + iphdroff);
hdr = (struct tcphdr *)(skb->data + hdroff);
if (maniptype == IP_NAT_MANIP_SRC) {
/* Get rid of src ip and src pt */
oldip = iph->saddr;
newip = tuple->src.u3.ip;
newport = tuple->src.u.tcp.port;
portptr = &hdr->source;
} else {
/* Get rid of dst ip and dst pt */
oldip = iph->daddr;
newip = tuple->dst.u3.ip;
newport = tuple->dst.u.tcp.port;
portptr = &hdr->dest;
}
oldport = *portptr;
*portptr = newport;
if (hdrsize < sizeof(*hdr))
return 1;
nf_proto_csum_replace4(&hdr->check, skb, oldip, newip, 1);
nf_proto_csum_replace2(&hdr->check, skb, oldport, newport, 0);
return 1;
}
struct nf_nat_protocol nf_nat_protocol_tcp = {
.name = "TCP",
.protonum = IPPROTO_TCP,
.me = THIS_MODULE,
.manip_pkt = tcp_manip_pkt,
.in_range = tcp_in_range,
.unique_tuple = tcp_unique_tuple,
#if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
.range_to_nlattr = nf_nat_port_range_to_nlattr,
.nlattr_to_range = nf_nat_port_nlattr_to_range,
#endif
};