1 /*
2 ip_frag.c
3
4 Dug Song <dugsong@anzen.com>
5
6 Copyright (c) 1999 Anzen Computing. All rights reserved.
7
8 Redistribution and use in source and binary forms, with or without
9 modification, are permitted provided that the following conditions
10 are met:
11
12 1. Redistributions of source code must retain the above copyright
13 notice, this list of conditions and the following disclaimer.
14 2. Redistributions in binary form must reproduce the above copyright
15 notice, this list of conditions and the following disclaimer in the
16 documentation and/or other materials provided with the distribution.
17 3. All advertising materials mentioning features or use of this software
18 must display the following acknowledgement:
19 This product includes software developed by Anzen Computing.
20 4. Neither the name of Anzen Computing nor the names of its
21 contributors may be used to endorse or promote products derived
22 from this software without specific prior written permission.
23
24 THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
25 WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
26 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
27 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
28 DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
30 GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
31 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
32 IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
33 OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
34 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
35
36 $Id: ip_frag.c,v 1.18 1999/06/25 19:11:37 dugsong Exp $
37 */
38
39 #include "config.h"
40 #ifdef HAVE_SYS_PARAM_H
41 #include <sys/param.h>
42 #endif
43 #include <libnet.h>
44 #include "list.h"
45 #include "ip_frag.h"
46
47 #if defined(OpenBSD) && (OpenBSD < 199905)
48 /* XXX - OpenBSD 2.4 sendto() bug - see fragrouter/test/mies.c. */
49 #define MINLASTFRAG 4
50 #else
51 #define MINLASTFRAG 0
52 #endif
53
54 int ip_frag_preserve_headers = 0;
55
56 void
ip_frag_init(int preserve_headers)57 ip_frag_init(int preserve_headers)
58 {
59 ip_frag_preserve_headers = preserve_headers;
60 }
61
62 ELEM *
ip_frag_make(u_char * pkt,int pktlen,int fragsize)63 ip_frag_make(u_char *pkt, int pktlen, int fragsize)
64 {
65 ELEM *new, *list = NULL;
66 struct ip *iph = (struct ip *)pkt;
67 int ip_hl = iph->ip_hl * 4;
68 u_short ip_len = ntohs(iph->ip_len);
69 u_char *ip_blob = pkt + ip_hl;
70 u_char *ip_end = pkt + ip_len;
71 u_char *p, *data;
72 int len = fragsize;
73
74 /* Preserve transport protocol header, if specified. */
75 if (ip_frag_preserve_headers) {
76 switch (iph->ip_p) {
77 case IPPROTO_TCP:
78 len = ((struct tcphdr *)(pkt + ip_hl))->th_off * 4;
79 break;
80 case IPPROTO_UDP:
81 len = UDP_H;
82 break;
83 case IPPROTO_ICMP:
84 len = ICMP_ECHO_H; /* XXX */
85 break;
86 case IPPROTO_IGMP:
87 len = IGMP_H;
88 break;
89 default:
90 len = fragsize; /* XXX */
91 break;
92 }
93 if (len & 7) len = (len & ~7) + 8;
94 }
95 /* Make sure fragmentation is valid for this packet. */
96 if (pktlen <= ip_hl + len + MINLASTFRAG || fragsize % 8 != 0)
97 return NULL;
98
99 /* Fragment packet. */
100 for (p = ip_blob ; p < ip_end ; ) {
101
102 /* Copy in IP header and data. */
103 if (!(data = malloc(ip_hl + len))) return NULL;
104 memcpy(data, pkt, ip_hl);
105 memcpy(data + ip_hl, p, len);
106
107 /* Correct IP length, IP fragment offset. */
108 ((struct ip *)data)->ip_len = htons(ip_hl + len);
109 ((struct ip *)data)->ip_off =
110 htons(((p + len < ip_end) ? IP_MF : 0) | ((p - ip_blob) >> 3));
111
112 /* Add to our IP fragment list. */
113 new = list_elem(data, ip_hl + len);
114 free(data);
115 if (!(list = list_add(list, new)))
116 return NULL;
117
118 /* Determine next fragment size. */
119 p += len;
120 len = ip_end - p;
121 if (len > fragsize + MINLASTFRAG)
122 len = fragsize;
123 }
124 return (list->head);
125 }
126
127 ELEM *
ip_frag_add_overwrite(ELEM * list)128 ip_frag_add_overwrite(ELEM *list)
129 {
130 ELEM *f, *new;
131 u_char nulls[PACKET], *newdata;
132 int newoff, newlen;
133
134 memset(nulls, 0, sizeof(nulls));
135
136 for (f = list ; f && f->next ; f = f->next) {
137 struct ip *iph = (struct ip *)f->data;
138 int ip_hl = iph->ip_hl * 4;
139
140 /* Build new null data fragment, half the length of the current fragment
141 and overlapping its latter half. */
142 newlen = (ntohs(iph->ip_len) - ip_hl) / 2;
143 newoff = ntohs(iph->ip_off) + (newlen >> 3);
144
145 /* Copy in IP header and data. */
146 if (!(newdata = malloc(ip_hl + newlen))) return NULL;
147 memcpy(newdata, f->data, ip_hl);
148 memcpy(newdata + ip_hl, nulls, newlen);
149
150 /* Correct IP length, IP fragment offset. */
151 ((struct ip *)newdata)->ip_len = htons(ip_hl + newlen);
152 ((struct ip *)newdata)->ip_off = htons(newoff);
153
154 /* Add null fragment after current fragment. */
155 new = list_elem(newdata, IP_H + newlen);
156 free(newdata);
157
158 if (!list_add(f, new))
159 return NULL;
160
161 /* Swap them. */
162 if (!list_swap(f))
163 return NULL;
164 }
165 return list;
166 }
167