1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
|
/* vi: set sw=4 ts=4: */
/* clientpacket.c
*
* Packet generation and dispatching functions for the DHCP client.
*
* Russ Dill <Russ.Dill@asu.edu> July 2001
*
* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
*/
#include <features.h>
#if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION
#include <netpacket/packet.h>
#include <net/ethernet.h>
#else
#include <asm/types.h>
#include <linux/if_packet.h>
#include <linux/if_ether.h>
#endif
#include "common.h"
#include "dhcpd.h"
#include "dhcpc.h"
#include "options.h"
/* Create a random xid */
unsigned long random_xid(void)
{
static int initialized;
if (!initialized) {
unsigned long seed;
if (open_read_close("/dev/urandom", &seed, sizeof(seed)) < 0) {
bb_info_msg("Cannot load seed "
"from /dev/urandom: %s", strerror(errno));
seed = time(0);
}
srand(seed);
initialized++;
}
return rand();
}
/* initialize a packet with the proper defaults */
static void init_packet(struct dhcpMessage *packet, char type)
{
udhcp_init_header(packet, type);
memcpy(packet->chaddr, client_config.arp, 6);
if (client_config.clientid)
add_option_string(packet->options, client_config.clientid);
if (client_config.hostname) add_option_string(packet->options, client_config.hostname);
if (client_config.fqdn) add_option_string(packet->options, client_config.fqdn);
add_option_string(packet->options, client_config.vendorclass);
}
/* Add a parameter request list for stubborn DHCP servers. Pull the data
* from the struct in options.c. Don't do bounds checking here because it
* goes towards the head of the packet. */
static void add_requests(struct dhcpMessage *packet)
{
int end = end_option(packet->options);
int i, len = 0;
packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
for (i = 0; dhcp_options[i].code; i++)
if (dhcp_options[i].flags & OPTION_REQ)
packet->options[end + OPT_DATA + len++] = dhcp_options[i].code;
packet->options[end + OPT_LEN] = len;
packet->options[end + OPT_DATA + len] = DHCP_END;
}
/* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
int send_discover(unsigned long xid, unsigned long requested)
{
struct dhcpMessage packet;
init_packet(&packet, DHCPDISCOVER);
packet.xid = xid;
if (requested)
add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
add_requests(&packet);
bb_info_msg("Sending discover...");
return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
}
/* Broadcasts a DHCP request message */
int send_selecting(unsigned long xid, unsigned long server, unsigned long requested)
{
struct dhcpMessage packet;
struct in_addr addr;
init_packet(&packet, DHCPREQUEST);
packet.xid = xid;
add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
add_simple_option(packet.options, DHCP_SERVER_ID, server);
add_requests(&packet);
addr.s_addr = requested;
bb_info_msg("Sending select for %s...", inet_ntoa(addr));
return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
}
/* Unicasts or broadcasts a DHCP renew message */
int send_renew(unsigned long xid, unsigned long server, unsigned long ciaddr)
{
struct dhcpMessage packet;
int ret = 0;
init_packet(&packet, DHCPREQUEST);
packet.xid = xid;
packet.ciaddr = ciaddr;
add_requests(&packet);
bb_info_msg("Sending renew...");
if (server)
ret = udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
else ret = udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
return ret;
}
/* Unicasts a DHCP release message */
int send_release(unsigned long server, unsigned long ciaddr)
{
struct dhcpMessage packet;
init_packet(&packet, DHCPRELEASE);
packet.xid = random_xid();
packet.ciaddr = ciaddr;
add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr);
add_simple_option(packet.options, DHCP_SERVER_ID, server);
bb_info_msg("Sending release...");
return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
}
/* return -1 on errors that are fatal for the socket, -2 for those that aren't */
int get_raw_packet(struct dhcpMessage *payload, int fd)
{
int bytes;
struct udp_dhcp_packet packet;
uint32_t source, dest;
uint16_t check;
memset(&packet, 0, sizeof(struct udp_dhcp_packet));
bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
if (bytes < 0) {
DEBUG("Cannot read on raw listening socket - ignoring");
usleep(500000); /* possible down interface, looping condition */
return -1;
}
if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
DEBUG("Message too short, ignoring");
return -2;
}
if (bytes < ntohs(packet.ip.tot_len)) {
DEBUG("Truncated packet");
return -2;
}
/* ignore any extra garbage bytes */
bytes = ntohs(packet.ip.tot_len);
/* Make sure its the right packet for us, and that it passes sanity checks */
if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
|| packet.ip.ihl != sizeof(packet.ip) >> 2
|| packet.udp.dest != htons(CLIENT_PORT)
|| bytes > (int) sizeof(struct udp_dhcp_packet)
|| ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
) {
DEBUG("Unrelated/bogus packet");
return -2;
}
/* check IP checksum */
check = packet.ip.check;
packet.ip.check = 0;
if (check != udhcp_checksum(&(packet.ip), sizeof(packet.ip))) {
DEBUG("bad IP header checksum, ignoring");
return -1;
}
/* verify the UDP checksum by replacing the header with a psuedo header */
source = packet.ip.saddr;
dest = packet.ip.daddr;
check = packet.udp.check;
packet.udp.check = 0;
memset(&packet.ip, 0, sizeof(packet.ip));
packet.ip.protocol = IPPROTO_UDP;
packet.ip.saddr = source;
packet.ip.daddr = dest;
packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
if (check && check != udhcp_checksum(&packet, bytes)) {
bb_error_msg("packet with bad UDP checksum received, ignoring");
return -2;
}
memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
if (ntohl(payload->cookie) != DHCP_MAGIC) {
bb_error_msg("received bogus message (bad magic) - ignoring");
return -2;
}
DEBUG("oooooh!!! got some!");
return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
}
|
