1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
|
/*
* INET An implementation of the TCP/IP protocol suite for the LINUX
* operating system. INET is implemented using the BSD Socket
* interface as the means of communication with the user level.
*
* Dumb Network Address Translation.
*
* Version: $Id: ip_nat_dumb.c,v 1.8 1999/03/21 05:22:40 davem Exp $
*
* Authors: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
* Fixes:
* Rani Assaf : A zero checksum is a special case
* only in UDP
* Rani Assaf : Added ICMP messages rewriting
* Rani Assaf : Repaired wrong changes, made by ANK.
*
*
* NOTE: It is just working model of real NAT.
*/
#include <linux/config.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <linux/netdevice.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/firewall.h>
#include <linux/ip_fw.h>
#include <net/checksum.h>
#include <linux/route.h>
#include <net/route.h>
#include <net/ip_fib.h>
int
ip_do_nat(struct sk_buff *skb)
{
struct rtable *rt = (struct rtable*)skb->dst;
struct iphdr *iph = skb->nh.iph;
u32 odaddr = iph->daddr;
u32 osaddr = iph->saddr;
u16 check;
IPCB(skb)->flags |= IPSKB_TRANSLATED;
/* Rewrite IP header */
iph->daddr = rt->rt_dst_map;
iph->saddr = rt->rt_src_map;
iph->check = 0;
iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
/* If it is the first fragment, rewrite protocol headers */
if (!(iph->frag_off & htons(IP_OFFSET))) {
u16 *cksum;
switch(iph->protocol) {
case IPPROTO_TCP:
cksum = (u16*)&((struct tcphdr*)(((char*)iph) + (iph->ihl<<2)))->check;
if ((u8*)(cksum+1) > skb->tail)
goto truncated;
check = csum_tcpudp_magic(iph->saddr, iph->daddr, 0, 0, ~(*cksum));
*cksum = csum_tcpudp_magic(~osaddr, ~odaddr, 0, 0, ~check);
break;
case IPPROTO_UDP:
cksum = (u16*)&((struct udphdr*)(((char*)iph) + (iph->ihl<<2)))->check;
if ((u8*)(cksum+1) > skb->tail)
goto truncated;
if ((check = *cksum) != 0) {
check = csum_tcpudp_magic(iph->saddr, iph->daddr, 0, 0, ~check);
check = csum_tcpudp_magic(~osaddr, ~odaddr, 0, 0, ~check);
*cksum = check ? : 0xFFFF;
}
break;
case IPPROTO_ICMP:
{
struct icmphdr *icmph = (struct icmphdr*)((char*)iph + (iph->ihl<<2));
struct iphdr *ciph;
u32 idaddr, isaddr;
int updated;
if ((icmph->type != ICMP_DEST_UNREACH) &&
(icmph->type != ICMP_TIME_EXCEEDED) &&
(icmph->type != ICMP_PARAMETERPROB))
break;
ciph = (struct iphdr *) (icmph + 1);
if ((u8*)(ciph+1) > skb->tail)
goto truncated;
isaddr = ciph->saddr;
idaddr = ciph->daddr;
updated = 0;
if (rt->rt_flags&RTCF_DNAT && ciph->saddr == odaddr) {
ciph->saddr = iph->daddr;
updated = 1;
}
if (rt->rt_flags&RTCF_SNAT) {
if (ciph->daddr != osaddr) {
struct fib_result res;
struct rt_key key;
unsigned flags = 0;
key.src = ciph->daddr;
key.dst = ciph->saddr;
key.iif = skb->dev->ifindex;
key.oif = 0;
#ifdef CONFIG_IP_ROUTE_TOS
key.tos = RT_TOS(ciph->tos);
#endif
#ifdef CONFIG_IP_ROUTE_FWMARK
key.fwmark = 0;
#endif
/* Use fib_lookup() until we get our own
* hash table of NATed hosts -- Rani
*/
if (fib_lookup(&key, &res) == 0 && res.r) {
ciph->daddr = fib_rules_policy(ciph->daddr, &res, &flags);
if (ciph->daddr != idaddr)
updated = 1;
}
} else {
ciph->daddr = iph->saddr;
updated = 1;
}
}
if (updated) {
cksum = &icmph->checksum;
/* Using tcpudp primitive. Why not? */
check = csum_tcpudp_magic(ciph->saddr, ciph->daddr, 0, 0, ~(*cksum));
*cksum = csum_tcpudp_magic(~isaddr, ~idaddr, 0, 0, ~check);
}
break;
}
default:
break;
}
}
return 0;
truncated:
return -EINVAL;
}
|
