/
icmp.c
129 lines (111 loc) · 2.65 KB
/
icmp.c
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
/*
* natd - Network Address Translation Daemon for FreeBSD.
*
* This software is provided free of charge, with no
* warranty of any kind, either expressed or implied.
* Use at your own risk.
*
* You may copy, modify and distribute this software (icmp.c) freely.
*
* Ari Suutari <suutari@iki.fi>
*
* $FreeBSD: src/sbin/natd/icmp.c,v 1.6 1999/08/28 00:13:45 peter Exp $
* $DragonFly: src/sbin/natd/icmp.c,v 1.5 2005/06/07 20:21:23 swildner Exp $
*/
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <errno.h>
#include <signal.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <alias.h>
#include "natd.h"
int
SendNeedFragIcmp(int sock, struct ip *failedDgram, int mtu)
{
char icmpBuf[IP_MAXPACKET];
struct ip* ip;
struct icmp* icmp;
int icmpLen;
int failBytes;
int failHdrLen;
struct sockaddr_in addr;
int wrote;
struct in_addr swap;
/*
* Don't send error if packet is
* not the first fragment.
*/
if (ntohs(failedDgram->ip_off) & ~(IP_MF | IP_DF))
return 0;
/*
* Dont respond if failed datagram is ICMP.
*/
if (failedDgram->ip_p == IPPROTO_ICMP)
return 0;
/*
* Start building the message.
*/
ip = (struct ip *)icmpBuf;
icmp = (struct icmp *)(icmpBuf + sizeof(struct ip));
/*
* Complete ICMP part.
*/
icmp->icmp_type = ICMP_UNREACH;
icmp->icmp_code = ICMP_UNREACH_NEEDFRAG;
icmp->icmp_cksum = 0;
icmp->icmp_void = 0;
icmp->icmp_nextmtu = htons(mtu);
/*
* Copy header + 64 bits of original datagram.
*/
failHdrLen = (failedDgram->ip_hl << 2);
failBytes = failedDgram->ip_len - failHdrLen;
if (failBytes > 8)
failBytes = 8;
failBytes += failHdrLen;
icmpLen = ICMP_MINLEN + failBytes;
memcpy(&icmp->icmp_ip, failedDgram, failBytes);
/*
* Calculate checksum.
*/
icmp->icmp_cksum = PacketAliasInternetChecksum((u_short *)icmp,
icmpLen);
/*
* Add IP header using old IP header as template.
*/
memcpy(ip, failedDgram, sizeof(struct ip));
ip->ip_v = 4;
ip->ip_hl = 5;
ip->ip_len = htons(sizeof(struct ip) + icmpLen);
ip->ip_p = IPPROTO_ICMP;
ip->ip_tos = 0;
swap = ip->ip_dst;
ip->ip_dst = ip->ip_src;
ip->ip_src = swap;
PacketAliasIn((char *)ip, IP_MAXPACKET);
addr.sin_family = AF_INET;
addr.sin_addr = ip->ip_dst;
addr.sin_port = 0;
/*
* Put packet into processing queue.
*/
wrote = sendto(sock,
icmp,
icmpLen,
0,
(struct sockaddr *)&addr,
sizeof addr);
if (wrote != icmpLen)
Warn("Cannot send ICMP message.");
return 1;
}