1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * Packet ops
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4 | *
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5 | * Rewrite by Russ Dill <Russ.Dill@asu.edu> July 2001
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6 | *
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7 | * Licensed under GPLv2, see file LICENSE in this source tree.
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8 | */
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9 | #include "common.h"
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10 | #include "dhcpd.h"
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11 | #include <netinet/in.h>
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12 | #include <netinet/if_ether.h>
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13 | #include <netpacket/packet.h>
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14 |
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15 | void FAST_FUNC udhcp_init_header(struct dhcp_packet *packet, char type)
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16 | {
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17 | memset(packet, 0, sizeof(*packet));
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18 | packet->op = BOOTREQUEST; /* if client to a server */
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19 | switch (type) {
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20 | case DHCPOFFER:
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21 | case DHCPACK:
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22 | case DHCPNAK:
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23 | packet->op = BOOTREPLY; /* if server to client */
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24 | }
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25 | packet->htype = 1; /* ethernet */
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26 | packet->hlen = 6;
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27 | packet->cookie = htonl(DHCP_MAGIC);
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28 | if (DHCP_END != 0)
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29 | packet->options[0] = DHCP_END;
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30 | udhcp_add_simple_option(packet, DHCP_MESSAGE_TYPE, type);
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31 | }
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32 |
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33 | #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 2
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34 | void FAST_FUNC udhcp_dump_packet(struct dhcp_packet *packet)
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35 | {
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36 | char buf[sizeof(packet->chaddr)*2 + 1];
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37 |
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38 | if (dhcp_verbose < 2)
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39 | return;
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40 |
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41 | bb_error_msg(
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42 | //"op %x"
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43 | //" htype %x"
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44 | " hlen %x"
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45 | //" hops %x"
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46 | " xid %x"
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47 | //" secs %x"
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48 | //" flags %x"
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49 | " ciaddr %x"
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50 | " yiaddr %x"
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51 | " siaddr %x"
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52 | " giaddr %x"
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53 | //" chaddr %s"
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54 | //" sname %s"
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55 | //" file %s"
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56 | //" cookie %x"
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57 | //" options %s"
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58 | //, packet->op
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59 | //, packet->htype
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60 | , packet->hlen
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61 | //, packet->hops
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62 | , packet->xid
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63 | //, packet->secs
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64 | //, packet->flags
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65 | , packet->ciaddr
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66 | , packet->yiaddr
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67 | , packet->siaddr_nip
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68 | , packet->gateway_nip
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69 | //, packet->chaddr[16]
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70 | //, packet->sname[64]
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71 | //, packet->file[128]
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72 | //, packet->cookie
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73 | //, packet->options[]
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74 | );
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75 | *bin2hex(buf, (void *) packet->chaddr, sizeof(packet->chaddr)) = '\0';
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76 | bb_error_msg("chaddr %s", buf);
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77 | }
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78 | #endif
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79 |
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80 | /* Read a packet from socket fd, return -1 on read error, -2 on packet error */
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81 | int FAST_FUNC udhcp_recv_kernel_packet(struct dhcp_packet *packet, int fd)
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82 | {
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83 | int bytes;
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84 |
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85 | memset(packet, 0, sizeof(*packet));
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86 | bytes = safe_read(fd, packet, sizeof(*packet));
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87 | if (bytes < 0) {
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88 | log1("packet read error, ignoring");
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89 | return bytes; /* returns -1 */
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90 | }
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91 |
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92 | if (bytes < offsetof(struct dhcp_packet, options)
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93 | || packet->cookie != htonl(DHCP_MAGIC)
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94 | ) {
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95 | bb_error_msg("packet with bad magic, ignoring");
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96 | return -2;
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97 | }
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98 | log1("received %s", "a packet");
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99 | udhcp_dump_packet(packet);
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100 |
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101 | return bytes;
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102 | }
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103 |
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104 | /* Construct a ip/udp header for a packet, send packet */
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105 | int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
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106 | uint32_t source_nip, int source_port,
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107 | uint32_t dest_nip, int dest_port, const uint8_t *dest_arp,
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108 | int ifindex)
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109 | {
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110 | struct sockaddr_ll dest_sll;
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111 | struct ip_udp_dhcp_packet packet;
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112 | unsigned padding;
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113 | int fd;
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114 | int result = -1;
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115 | const char *msg;
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116 |
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117 | fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
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118 | if (fd < 0) {
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119 | msg = "socket(%s)";
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120 | goto ret_msg;
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121 | }
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122 |
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123 | memset(&dest_sll, 0, sizeof(dest_sll));
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124 | memset(&packet, 0, offsetof(struct ip_udp_dhcp_packet, data));
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125 | packet.data = *dhcp_pkt; /* struct copy */
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126 |
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127 | dest_sll.sll_family = AF_PACKET;
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128 | dest_sll.sll_protocol = htons(ETH_P_IP);
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129 | dest_sll.sll_ifindex = ifindex;
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130 | dest_sll.sll_halen = 6;
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131 | memcpy(dest_sll.sll_addr, dest_arp, 6);
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132 |
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133 | if (bind(fd, (struct sockaddr *)&dest_sll, sizeof(dest_sll)) < 0) {
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134 | msg = "bind(%s)";
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135 | goto ret_close;
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136 | }
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137 |
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138 | /* We were sending full-sized DHCP packets (zero padded),
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139 | * but some badly configured servers were seen dropping them.
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140 | * Apparently they drop all DHCP packets >576 *ethernet* octets big,
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141 | * whereas they may only drop packets >576 *IP* octets big
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142 | * (which for typical Ethernet II means 590 octets: 6+6+2 + 576).
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143 | *
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144 | * In order to work with those buggy servers,
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145 | * we truncate packets after end option byte.
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146 | *
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147 | * However, RFC 1542 says "The IP Total Length and UDP Length
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148 | * must be large enough to contain the minimal BOOTP header of 300 octets".
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149 | * Thus, we retain enough padding to not go below 300 BOOTP bytes.
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150 | * Some devices have filters which drop DHCP packets shorter than that.
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151 | */
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152 | padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(packet.data.options);
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153 | if (padding > DHCP_SIZE - 300)
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154 | padding = DHCP_SIZE - 300;
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155 |
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156 | packet.ip.protocol = IPPROTO_UDP;
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157 | packet.ip.saddr = source_nip;
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158 | packet.ip.daddr = dest_nip;
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159 | packet.udp.source = htons(source_port);
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160 | packet.udp.dest = htons(dest_port);
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161 | /* size, excluding IP header: */
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162 | packet.udp.len = htons(UDP_DHCP_SIZE - padding);
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163 | /* for UDP checksumming, ip.len is set to UDP packet len */
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164 | packet.ip.tot_len = packet.udp.len;
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165 | packet.udp.check = inet_cksum((uint16_t *)&packet,
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166 | IP_UDP_DHCP_SIZE - padding);
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167 | /* but for sending, it is set to IP packet len */
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168 | packet.ip.tot_len = htons(IP_UDP_DHCP_SIZE - padding);
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169 | packet.ip.ihl = sizeof(packet.ip) >> 2;
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170 | packet.ip.version = IPVERSION;
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171 | packet.ip.ttl = IPDEFTTL;
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172 | packet.ip.check = inet_cksum((uint16_t *)&packet.ip, sizeof(packet.ip));
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173 |
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174 | udhcp_dump_packet(dhcp_pkt);
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175 | result = sendto(fd, &packet, IP_UDP_DHCP_SIZE - padding, /*flags:*/ 0,
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176 | (struct sockaddr *) &dest_sll, sizeof(dest_sll));
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177 | msg = "sendto";
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178 | ret_close:
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179 | close(fd);
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180 | if (result < 0) {
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181 | ret_msg:
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182 | bb_perror_msg(msg, "PACKET");
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183 | }
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184 | return result;
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185 | }
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186 |
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187 | /* Let the kernel do all the work for packet generation */
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188 | int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
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189 | uint32_t source_nip, int source_port,
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190 | uint32_t dest_nip, int dest_port)
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191 | {
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192 | struct sockaddr_in sa;
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193 | unsigned padding;
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194 | int fd;
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195 | int result = -1;
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196 | const char *msg;
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197 |
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198 | fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
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199 | if (fd < 0) {
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200 | msg = "socket(%s)";
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201 | goto ret_msg;
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202 | }
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203 | setsockopt_reuseaddr(fd);
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204 |
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205 | memset(&sa, 0, sizeof(sa));
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206 | sa.sin_family = AF_INET;
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207 | sa.sin_port = htons(source_port);
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208 | sa.sin_addr.s_addr = source_nip;
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209 | if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
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210 | msg = "bind(%s)";
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211 | goto ret_close;
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212 | }
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213 |
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214 | memset(&sa, 0, sizeof(sa));
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215 | sa.sin_family = AF_INET;
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216 | sa.sin_port = htons(dest_port);
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217 | sa.sin_addr.s_addr = dest_nip;
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218 | if (connect(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
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219 | msg = "connect";
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220 | goto ret_close;
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221 | }
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222 |
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223 | udhcp_dump_packet(dhcp_pkt);
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224 | padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(dhcp_pkt->options);
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225 | if (padding > DHCP_SIZE - 300)
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226 | padding = DHCP_SIZE - 300;
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227 | result = safe_write(fd, dhcp_pkt, DHCP_SIZE - padding);
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228 | msg = "write";
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229 | ret_close:
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230 | close(fd);
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231 | if (result < 0) {
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232 | ret_msg:
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233 | bb_perror_msg(msg, "UDP");
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234 | }
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235 | return result;
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236 | }
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