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 * $FreeBSD: stable/9/sbin/natd/icmp.c 131567 2004-07-04 12:53:54Z phk $
13 */
14
15 #include <stdlib.h>
16 #include <stdio.h>
17 #include <unistd.h>
18 #include <string.h>
19 #include <ctype.h>
20
21 #include <sys/types.h>
22 #include <sys/socket.h>
23 #include <sys/time.h>
24 #include <errno.h>
25 #include <signal.h>
26
27 #include <netdb.h>
28
29 #include <netinet/in.h>
30 #include <netinet/in_systm.h>
31 #include <netinet/ip.h>
32 #include <netinet/ip_icmp.h>
33 #include <machine/in_cksum.h>
34
35 #include <alias.h>
36
37 #include "natd.h"
38
SendNeedFragIcmp(int sock,struct ip * failedDgram,int mtu)39 int SendNeedFragIcmp (int sock, struct ip* failedDgram, int mtu)
40 {
41 char icmpBuf[IP_MAXPACKET];
42 struct ip* ip;
43 struct icmp* icmp;
44 int icmpLen;
45 int failBytes;
46 int failHdrLen;
47 struct sockaddr_in addr;
48 int wrote;
49 struct in_addr swap;
50 /*
51 * Don't send error if packet is
52 * not the first fragment.
53 */
54 if (ntohs (failedDgram->ip_off) & ~(IP_MF | IP_DF))
55 return 0;
56 /*
57 * Dont respond if failed datagram is ICMP.
58 */
59 if (failedDgram->ip_p == IPPROTO_ICMP)
60 return 0;
61 /*
62 * Start building the message.
63 */
64 ip = (struct ip*) icmpBuf;
65 icmp = (struct icmp*) (icmpBuf + sizeof (struct ip));
66 /*
67 * Complete ICMP part.
68 */
69 icmp->icmp_type = ICMP_UNREACH;
70 icmp->icmp_code = ICMP_UNREACH_NEEDFRAG;
71 icmp->icmp_cksum = 0;
72 icmp->icmp_void = 0;
73 icmp->icmp_nextmtu = htons (mtu);
74 /*
75 * Copy header + 64 bits of original datagram.
76 */
77 failHdrLen = (failedDgram->ip_hl << 2);
78 failBytes = failedDgram->ip_len - failHdrLen;
79 if (failBytes > 8)
80 failBytes = 8;
81
82 failBytes += failHdrLen;
83 icmpLen = ICMP_MINLEN + failBytes;
84
85 memcpy (&icmp->icmp_ip, failedDgram, failBytes);
86 /*
87 * Calculate checksum.
88 */
89 icmp->icmp_cksum = LibAliasInternetChecksum (mla, (u_short*) icmp,
90 icmpLen);
91 /*
92 * Add IP header using old IP header as template.
93 */
94 memcpy (ip, failedDgram, sizeof (struct ip));
95
96 ip->ip_v = 4;
97 ip->ip_hl = 5;
98 ip->ip_len = htons (sizeof (struct ip) + icmpLen);
99 ip->ip_p = IPPROTO_ICMP;
100 ip->ip_tos = 0;
101
102 swap = ip->ip_dst;
103 ip->ip_dst = ip->ip_src;
104 ip->ip_src = swap;
105
106 LibAliasIn (mla, (char*) ip, IP_MAXPACKET);
107
108 addr.sin_family = AF_INET;
109 addr.sin_addr = ip->ip_dst;
110 addr.sin_port = 0;
111 /*
112 * Put packet into processing queue.
113 */
114 wrote = sendto (sock,
115 icmp,
116 icmpLen,
117 0,
118 (struct sockaddr*) &addr,
119 sizeof addr);
120
121 if (wrote != icmpLen)
122 Warn ("Cannot send ICMP message.");
123
124 return 1;
125 }
126
127
128