xref: /freebsd/sbin/natd/icmp.c (revision 8aac90f18aef7c9eea906c3ff9a001ca7b94f375)
1 /*
2  * natd - Network Address Translation Daemon for FreeBSD.
3  *
4  * This software is provided free of charge, with no
5  * warranty of any kind, either expressed or implied.
6  * Use at your own risk.
7  *
8  * You may copy, modify and distribute this software (icmp.c) freely.
9  *
10  * Ari Suutari <suutari@iki.fi>
11  */
12 
13 #include <stdlib.h>
14 #include <stdio.h>
15 #include <unistd.h>
16 #include <string.h>
17 #include <ctype.h>
18 
19 #include <sys/types.h>
20 #include <sys/socket.h>
21 #include <sys/time.h>
22 #include <errno.h>
23 #include <signal.h>
24 
25 #include <netdb.h>
26 
27 #include <netinet/in.h>
28 #include <netinet/in_systm.h>
29 #include <netinet/ip.h>
30 #include <netinet/ip_icmp.h>
31 
32 #include <alias.h>
33 
34 #include "natd.h"
35 
36 int SendNeedFragIcmp (int sock, struct ip* failedDgram, int mtu)
37 {
38 	char			icmpBuf[IP_MAXPACKET];
39 	struct ip*		ip;
40 	struct icmp*		icmp;
41 	int			icmpLen;
42 	int			failBytes;
43 	int			failHdrLen;
44 	struct sockaddr_in	addr;
45 	int			wrote;
46 	struct in_addr		swap;
47 /*
48  * Don't send error if packet is
49  * not the first fragment.
50  */
51 	if (ntohs (failedDgram->ip_off) & ~(IP_MF | IP_DF))
52 		return 0;
53 /*
54  * Dont respond if failed datagram is ICMP.
55  */
56 	if (failedDgram->ip_p == IPPROTO_ICMP)
57 		return 0;
58 /*
59  * Start building the message.
60  */
61 	ip   = (struct ip*) icmpBuf;
62 	icmp = (struct icmp*) (icmpBuf + sizeof (struct ip));
63 /*
64  * Complete ICMP part.
65  */
66 	icmp->icmp_type  	= ICMP_UNREACH;
67 	icmp->icmp_code		= ICMP_UNREACH_NEEDFRAG;
68 	icmp->icmp_cksum	= 0;
69 	icmp->icmp_void		= 0;
70 	icmp->icmp_nextmtu	= htons (mtu);
71 /*
72  * Copy header + 64 bits of original datagram.
73  */
74 	failHdrLen = (failedDgram->ip_hl << 2);
75 	failBytes  = failedDgram->ip_len - failHdrLen;
76 	if (failBytes > 8)
77 		failBytes = 8;
78 
79 	failBytes += failHdrLen;
80 	icmpLen    = ICMP_MINLEN + failBytes;
81 
82 	memcpy (&icmp->icmp_ip, failedDgram, failBytes);
83 /*
84  * Calculate checksum.
85  */
86 	icmp->icmp_cksum = LibAliasInternetChecksum (mla, (u_short*) icmp,
87 							icmpLen);
88 /*
89  * Add IP header using old IP header as template.
90  */
91 	memcpy (ip, failedDgram, sizeof (struct ip));
92 
93 	ip->ip_v	= 4;
94 	ip->ip_hl	= 5;
95 	ip->ip_len	= htons (sizeof (struct ip) + icmpLen);
96 	ip->ip_p	= IPPROTO_ICMP;
97 	ip->ip_tos	= 0;
98 
99 	swap = ip->ip_dst;
100 	ip->ip_dst = ip->ip_src;
101 	ip->ip_src = swap;
102 
103 	LibAliasIn (mla, (char*) ip, IP_MAXPACKET);
104 
105 	addr.sin_family		= AF_INET;
106 	addr.sin_addr		= ip->ip_dst;
107 	addr.sin_port		= 0;
108 /*
109  * Put packet into processing queue.
110  */
111 	wrote = sendto (sock,
112 		        icmp,
113 	    		icmpLen,
114 	    		0,
115 	    		(struct sockaddr*) &addr,
116 	    		sizeof addr);
117 
118 	if (wrote != icmpLen)
119 		Warn ("Cannot send ICMP message.");
120 
121 	return 1;
122 }
123 
124 
125