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
SendNeedFragIcmp(int sock,struct ip * failedDgram,int mtu)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