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1 office 1 /**
2 * @file ipv4_proto.h
3 * @author Ambroz Bizjak <ambrop7@gmail.com>
4 *
5 * @section LICENSE
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * 3. Neither the name of the author nor the
15 * names of its contributors may be used to endorse or promote products
16 * derived from this software without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
20 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
21 * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
22 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
23 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
24 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
25 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
27 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 *
29 * @section DESCRIPTION
30 *
31 * Definitions for the IPv4 protocol.
32 */
33  
34 #ifndef BADVPN_MISC_IPV4_PROTO_H
35 #define BADVPN_MISC_IPV4_PROTO_H
36  
37 #include <stdint.h>
38 #include <string.h>
39  
40 #include <misc/debug.h>
41 #include <misc/byteorder.h>
42 #include <misc/packed.h>
43 #include <misc/read_write_int.h>
44  
45 #define IPV4_PROTOCOL_IGMP 2
46 #define IPV4_PROTOCOL_UDP 17
47  
48 B_START_PACKED
49 struct ipv4_header {
50 uint8_t version4_ihl4;
51 uint8_t ds;
52 uint16_t total_length;
53 //
54 uint16_t identification;
55 uint16_t flags3_fragmentoffset13;
56 //
57 uint8_t ttl;
58 uint8_t protocol;
59 uint16_t checksum;
60 //
61 uint32_t source_address;
62 //
63 uint32_t destination_address;
64 } B_PACKED;
65 B_END_PACKED
66  
67 #define IPV4_GET_VERSION(_header) (((_header).version4_ihl4&0xF0)>>4)
68 #define IPV4_GET_IHL(_header) (((_header).version4_ihl4&0x0F)>>0)
69  
70 #define IPV4_MAKE_VERSION_IHL(size) (((size)/4) + (4 << 4))
71  
72 static uint16_t ipv4_checksum (const struct ipv4_header *header, const char *extra, uint16_t extra_len)
73 {
74 ASSERT(extra_len % 2 == 0)
75 ASSERT(extra_len == 0 || extra)
76  
77 uint32_t t = 0;
78  
79 for (uint16_t i = 0; i < sizeof(*header) / 2; i++) {
80 t += badvpn_read_be16((const char *)header + 2 * i);
81 }
82  
83 for (uint16_t i = 0; i < extra_len / 2; i++) {
84 t += badvpn_read_be16((const char *)extra + 2 * i);
85 }
86  
87 while (t >> 16) {
88 t = (t & 0xFFFF) + (t >> 16);
89 }
90  
91 return hton16(~t);
92 }
93  
94 static int ipv4_check (uint8_t *data, int data_len, struct ipv4_header *out_header, uint8_t **out_payload, int *out_payload_len)
95 {
96 ASSERT(data_len >= 0)
97 ASSERT(out_header)
98 ASSERT(out_payload)
99 ASSERT(out_payload_len)
100  
101 // check base header
102 if (data_len < sizeof(struct ipv4_header)) {
103 return 0;
104 }
105 memcpy(out_header, data, sizeof(*out_header));
106  
107 // check version
108 if (IPV4_GET_VERSION(*out_header) != 4) {
109 return 0;
110 }
111  
112 // check options
113 uint16_t header_len = IPV4_GET_IHL(*out_header) * 4;
114 if (header_len < sizeof(struct ipv4_header)) {
115 return 0;
116 }
117 if (header_len > data_len) {
118 return 0;
119 }
120  
121 // check total length
122 uint16_t total_length = ntoh16(out_header->total_length);
123 if (total_length < header_len) {
124 return 0;
125 }
126 if (total_length > data_len) {
127 return 0;
128 }
129  
130 // check checksum
131 uint16_t checksum_in_packet = out_header->checksum;
132 out_header->checksum = hton16(0);
133 uint16_t checksum_computed = ipv4_checksum(out_header, (char *)data + sizeof(*out_header), header_len - sizeof(*out_header));
134 out_header->checksum = checksum_in_packet;
135 if (checksum_in_packet != checksum_computed) {
136 return 0;
137 }
138  
139 *out_payload = data + header_len;
140 *out_payload_len = total_length - header_len;
141  
142 return 1;
143 }
144  
145 #endif