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1 | /* SPDX-License-Identifier: LGPL-2.1+ */ | |
2 | /*** | |
3 | Copyright © 2013 Intel Corporation. All rights reserved. | |
4 | Copyright © 2014 Tom Gundersen | |
5 | ***/ | |
6 | ||
7 | #include <errno.h> | |
8 | #include <net/ethernet.h> | |
9 | #include <net/if_arp.h> | |
10 | #include <string.h> | |
11 | ||
12 | #include "dhcp-internal.h" | |
13 | #include "dhcp-protocol.h" | |
14 | ||
15 | #define DHCP_CLIENT_MIN_OPTIONS_SIZE 312 | |
16 | ||
17 | int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid, | |
18 | uint8_t type, uint16_t arp_type, size_t optlen, | |
19 | size_t *optoffset) { | |
20 | size_t offset = 0; | |
21 | int r; | |
22 | ||
23 | assert(IN_SET(op, BOOTREQUEST, BOOTREPLY)); | |
24 | assert(IN_SET(arp_type, ARPHRD_ETHER, ARPHRD_INFINIBAND)); | |
25 | ||
26 | message->op = op; | |
27 | message->htype = arp_type; | |
28 | message->hlen = (arp_type == ARPHRD_ETHER) ? ETHER_ADDR_LEN : 0; | |
29 | message->xid = htobe32(xid); | |
30 | message->magic = htobe32(DHCP_MAGIC_COOKIE); | |
31 | ||
32 | r = dhcp_option_append(message, optlen, &offset, 0, | |
33 | SD_DHCP_OPTION_MESSAGE_TYPE, 1, &type); | |
34 | if (r < 0) | |
35 | return r; | |
36 | ||
37 | *optoffset = offset; | |
38 | ||
39 | return 0; | |
40 | } | |
41 | ||
42 | uint16_t dhcp_packet_checksum(uint8_t *buf, size_t len) { | |
43 | uint64_t *buf_64 = (uint64_t*)buf; | |
44 | uint64_t *end_64 = buf_64 + (len / sizeof(uint64_t)); | |
45 | uint64_t sum = 0; | |
46 | ||
47 | /* See RFC1071 */ | |
48 | ||
49 | while (buf_64 < end_64) { | |
50 | sum += *buf_64; | |
51 | if (sum < *buf_64) | |
52 | /* wrap around in one's complement */ | |
53 | sum++; | |
54 | ||
55 | buf_64++; | |
56 | } | |
57 | ||
58 | if (len % sizeof(uint64_t)) { | |
59 | /* If the buffer is not aligned to 64-bit, we need | |
60 | to zero-pad the last few bytes and add them in */ | |
61 | uint64_t buf_tail = 0; | |
62 | ||
63 | memcpy(&buf_tail, buf_64, len % sizeof(uint64_t)); | |
64 | ||
65 | sum += buf_tail; | |
66 | if (sum < buf_tail) | |
67 | /* wrap around */ | |
68 | sum++; | |
69 | } | |
70 | ||
71 | while (sum >> 16) | |
72 | sum = (sum & 0xffff) + (sum >> 16); | |
73 | ||
74 | return ~sum; | |
75 | } | |
76 | ||
77 | void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr, | |
78 | uint16_t source_port, be32_t destination_addr, | |
79 | uint16_t destination_port, uint16_t len) { | |
80 | packet->ip.version = IPVERSION; | |
81 | packet->ip.ihl = DHCP_IP_SIZE / 4; | |
82 | packet->ip.tot_len = htobe16(len); | |
83 | ||
84 | packet->ip.tos = IPTOS_CLASS_CS6; | |
85 | ||
86 | packet->ip.protocol = IPPROTO_UDP; | |
87 | packet->ip.saddr = source_addr; | |
88 | packet->ip.daddr = destination_addr; | |
89 | ||
90 | packet->udp.source = htobe16(source_port); | |
91 | packet->udp.dest = htobe16(destination_port); | |
92 | ||
93 | packet->udp.len = htobe16(len - DHCP_IP_SIZE); | |
94 | ||
95 | packet->ip.check = packet->udp.len; | |
96 | packet->udp.check = dhcp_packet_checksum((uint8_t*)&packet->ip.ttl, len - 8); | |
97 | ||
98 | packet->ip.ttl = IPDEFTTL; | |
99 | packet->ip.check = 0; | |
100 | packet->ip.check = dhcp_packet_checksum((uint8_t*)&packet->ip, DHCP_IP_SIZE); | |
101 | } | |
102 | ||
103 | int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum, uint16_t port) { | |
104 | size_t hdrlen; | |
105 | ||
106 | assert(packet); | |
107 | ||
108 | /* IP */ | |
109 | ||
110 | if (packet->ip.version != IPVERSION) { | |
111 | log_debug("ignoring packet: not IPv4"); | |
112 | return -EINVAL; | |
113 | } | |
114 | ||
115 | if (packet->ip.ihl < 5) { | |
116 | log_debug("ignoring packet: IPv4 IHL (%u words) invalid", | |
117 | packet->ip.ihl); | |
118 | return -EINVAL; | |
119 | } | |
120 | ||
121 | hdrlen = packet->ip.ihl * 4; | |
122 | if (hdrlen < 20) { | |
123 | log_debug("ignoring packet: IPv4 IHL (%zu bytes) " | |
124 | "smaller than minimum (20 bytes)", hdrlen); | |
125 | return -EINVAL; | |
126 | } | |
127 | ||
128 | if (len < hdrlen) { | |
129 | log_debug("ignoring packet: packet (%zu bytes) " | |
130 | "smaller than expected (%zu) by IP header", len, | |
131 | hdrlen); | |
132 | return -EINVAL; | |
133 | } | |
134 | ||
135 | /* UDP */ | |
136 | ||
137 | if (packet->ip.protocol != IPPROTO_UDP) { | |
138 | log_debug("ignoring packet: not UDP"); | |
139 | return -EINVAL; | |
140 | } | |
141 | ||
142 | if (len < hdrlen + be16toh(packet->udp.len)) { | |
143 | log_debug("ignoring packet: packet (%zu bytes) " | |
144 | "smaller than expected (%zu) by UDP header", len, | |
145 | hdrlen + be16toh(packet->udp.len)); | |
146 | return -EINVAL; | |
147 | } | |
148 | ||
149 | if (be16toh(packet->udp.dest) != port) { | |
150 | log_debug("ignoring packet: to port %u, which " | |
151 | "is not the DHCP client port (%u)", | |
152 | be16toh(packet->udp.dest), port); | |
153 | return -EINVAL; | |
154 | } | |
155 | ||
156 | /* checksums - computing these is relatively expensive, so only do it | |
157 | if all the other checks have passed | |
158 | */ | |
159 | ||
160 | if (dhcp_packet_checksum((uint8_t*)&packet->ip, hdrlen)) { | |
161 | log_debug("ignoring packet: invalid IP checksum"); | |
162 | return -EINVAL; | |
163 | } | |
164 | ||
165 | if (checksum && packet->udp.check) { | |
166 | packet->ip.check = packet->udp.len; | |
167 | packet->ip.ttl = 0; | |
168 | ||
169 | if (dhcp_packet_checksum((uint8_t*)&packet->ip.ttl, | |
170 | be16toh(packet->udp.len) + 12)) { | |
171 | log_debug("ignoring packet: invalid UDP checksum"); | |
172 | return -EINVAL; | |
173 | } | |
174 | } | |
175 | ||
176 | return 0; | |
177 | } |