320 lines
9.6 KiB
C
320 lines
9.6 KiB
C
#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>
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#include <netinet/in.h>
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <features.h>
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#include <netpacket/packet.h>
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#include <net/ethernet.h>
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#include <errno.h>
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#include "packet.h"
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#include "dhcpmsg.h"
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#include "socket.h"
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#include "arp.h"
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#include "ifchange.h"
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#include "sys.h"
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#include "log.h"
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#include "io.h"
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#include "dhcpd.h"
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#include "options.h"
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/* Read a packet from socket fd, return -1 on read error, -2 on packet error */
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int get_packet(struct dhcpMessage *packet, int fd)
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{
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int bytes;
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memset(packet, 0, DHCP_SIZE);
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bytes = safe_read(fd, (char *)packet, DHCP_SIZE);
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if (bytes == -1) {
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log_line("Read on listen socket failed: %s", strerror(errno));
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return -1;
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}
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if (ntohl(packet->cookie) != DHCP_MAGIC) {
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log_error("Packet with bad magic number, ignoring.");
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return -2;
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}
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log_line("Received a packet");
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return bytes;
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}
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/* Compute Internet Checksum for @count bytes beginning at location @addr. */
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uint16_t checksum(void *addr, int count)
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{
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register int32_t sum = 0;
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uint16_t *source = (uint16_t *)addr;
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while (count > 1) {
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sum += *source++;
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count -= 2;
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}
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/* Add left-over byte, if any */
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if (count > 0) {
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/* Make sure that the left-over byte is added correctly both
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* with little and big endian hosts */
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uint16_t tmp = 0;
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*(uint8_t *)&tmp = *(uint8_t *)source;
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sum += tmp;
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}
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/* Fold 32-bit sum to 16 bits */
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while (sum >> 16)
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sum = (sum & 0xffff) + (sum >> 16);
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return ~sum;
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}
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/* Constuct a ip/udp header for a packet, and specify the source and dest
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* hardware address */
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int raw_packet(struct dhcpMessage *payload, uint32_t source_ip,
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int source_port, uint32_t dest_ip, int dest_port,
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unsigned char *dest_arp, int ifindex)
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{
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struct sockaddr_ll dest;
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struct ip_udp_dhcp_packet packet;
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int fd, r = -1;
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unsigned int padding;
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if ((fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0) {
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log_error("raw_packet: socket failed: %s", strerror(errno));
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goto out;
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}
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memset(&dest, 0, sizeof dest);
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memset(&packet, 0, offsetof(struct ip_udp_dhcp_packet, data));
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packet.data = *payload; /* struct copy */
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dest.sll_family = AF_PACKET;
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dest.sll_protocol = htons(ETH_P_IP);
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dest.sll_ifindex = ifindex;
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dest.sll_halen = 6;
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memcpy(dest.sll_addr, dest_arp, 6);
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if (bind(fd, (struct sockaddr *)&dest, sizeof(struct sockaddr_ll)) < 0) {
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log_error("raw_packet: bind failed: %s", strerror(errno));
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goto out_fd;
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}
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/* We were sending full-sized DHCP packets (zero padded),
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* but some badly configured servers were seen dropping them.
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* Apparently they drop all DHCP packets >576 *ethernet* octets big,
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* whereas they may only drop packets >576 *IP* octets big
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* (which for typical Ethernet II means 590 octets: 6+6+2 + 576).
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*
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* In order to work with those buggy servers,
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* we truncate packets after end option byte.
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*/
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padding = DHCP_OPTIONS_BUFSIZE - 1 - end_option(packet.data.options);
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packet.ip.protocol = IPPROTO_UDP;
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packet.ip.saddr = source_ip;
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packet.ip.daddr = dest_ip;
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packet.udp.source = htons(source_port);
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packet.udp.dest = htons(dest_port);
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/* size, excluding IP header: */
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packet.udp.len = htons(UPD_DHCP_SIZE - padding);
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/* for UDP checksumming, ip.len is set to UDP packet len */
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packet.ip.tot_len = packet.udp.len;
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packet.udp.check = checksum(&packet, IP_UPD_DHCP_SIZE - padding);
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/* but for sending, it is set to IP packet len */
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packet.ip.tot_len = htons(IP_UPD_DHCP_SIZE - padding);
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packet.ip.ihl = sizeof packet.ip >> 2;
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packet.ip.version = IPVERSION;
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packet.ip.ttl = IPDEFTTL;
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packet.ip.check = checksum(&packet.ip, sizeof packet.ip);
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r = safe_sendto(fd, (const char *)&packet, IP_UPD_DHCP_SIZE - padding,
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0, (struct sockaddr *)&dest, sizeof dest);
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if (r == -1)
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log_error("raw_packet: sendto failed: %s", strerror(errno));
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out_fd:
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close(fd);
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out:
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return r;
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}
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/* Let the kernel do all the work for packet generation */
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int kernel_packet(struct dhcpMessage *payload, uint32_t source_ip,
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int source_port, uint32_t dest_ip, int dest_port)
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{
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struct sockaddr_in client;
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int opt = 1, fd, result = -1;
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unsigned int padding;
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if ((fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
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goto out;
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if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof opt) == -1)
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goto out_fd;
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memset(&client, 0, sizeof(client));
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client.sin_family = AF_INET;
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client.sin_port = htons(source_port);
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client.sin_addr.s_addr = source_ip;
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if (bind(fd, (struct sockaddr *)&client, sizeof(struct sockaddr)) == -1)
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goto out_fd;
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memset(&client, 0, sizeof(client));
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client.sin_family = AF_INET;
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client.sin_port = htons(dest_port);
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client.sin_addr.s_addr = dest_ip;
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if (connect(fd, (struct sockaddr *)&client, sizeof(struct sockaddr)) == -1)
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goto out_fd;
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padding = DHCP_OPTIONS_BUFSIZE - 1 - end_option(payload->options);
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result = safe_write(fd, (const char *)payload, DHCP_SIZE - padding);
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if (result == -1)
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log_error("kernel_packet: write failed: %s", strerror(errno));
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out_fd:
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close(fd);
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out:
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return result;
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}
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/* Switch listen socket between raw (if-bound), kernel (ip-bound), and none */
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void change_listen_mode(struct client_state_t *cs, int new_mode)
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{
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log_line("entering %s listen mode",
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new_mode ? (new_mode == 1 ? "kernel" : "raw") : "none");
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cs->listenMode = new_mode;
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if (cs->listenFd >= 0) {
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epoll_del(cs, cs->listenFd);
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close(cs->listenFd);
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cs->listenFd = -1;
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}
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if (new_mode == LM_KERNEL) {
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cs->listenFd = listen_socket(INADDR_ANY, CLIENT_PORT,
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client_config.interface);
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epoll_add(cs, cs->listenFd);
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}
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else if (new_mode == LM_RAW) {
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cs->listenFd = raw_socket(client_config.ifindex);
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epoll_add(cs, cs->listenFd);
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}
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else /* LM_NONE */
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return;
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if (cs->listenFd < 0) {
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log_error("FATAL: couldn't listen on socket: %s.", strerror(errno));
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exit(EXIT_FAILURE);
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}
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}
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static void init_selecting_packet(struct client_state_t *cs,
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struct dhcpMessage *packet,
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unsigned char *message)
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{
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unsigned char *temp = NULL;
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/* Must be a DHCPOFFER to one of our xid's */
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if (*message == DHCPOFFER) {
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if ((temp = get_option(packet, DHCP_SERVER_ID))) {
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/* Memcpy to a temp buffer to force alignment */
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memcpy(&cs->serverAddr, temp, 4);
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cs->xid = packet->xid;
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cs->requestedIP = packet->yiaddr;
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/* enter requesting state */
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cs->dhcpState = DS_REQUESTING;
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cs->timeout = 0;
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cs->packetNum = 0;
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} else {
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log_line("No server ID in message");
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}
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}
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}
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static void dhcp_ack_or_nak_packet(struct client_state_t *cs,
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struct dhcpMessage *packet,
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unsigned char *message)
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{
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unsigned char *temp = NULL;
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if (*message == DHCPACK) {
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if (!(temp = get_option(packet, DHCP_LEASE_TIME))) {
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log_line("No lease time received, assuming 1h.");
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cs->lease = 60 * 60;
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} else {
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/* Memcpy to a temp buffer to force alignment */
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memcpy(&cs->lease, temp, 4);
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cs->lease = ntohl(cs->lease);
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/* Enforce upper and lower bounds on lease. */
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cs->lease &= 0x0fffffff;
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if (cs->lease < RETRY_DELAY)
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cs->lease = RETRY_DELAY;
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}
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arp_check(cs, packet);
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// Can transition from DS_ARP_CHECK to DS_BOUND or DS_INIT_SELECTING.
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} else if (*message == DHCPNAK) {
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/* return to init state */
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log_line("Received DHCP NAK.");
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ifchange(packet, IFCHANGE_NAK);
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if (cs->dhcpState != DS_REQUESTING)
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ifchange(NULL, IFCHANGE_DECONFIG);
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cs->dhcpState = DS_INIT_SELECTING;
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cs->timeout = 0;
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cs->requestedIP = 0;
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cs->packetNum = 0;
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change_listen_mode(cs, LM_RAW);
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// XXX: this isn't rfc compliant: should be exp backoff
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sleep(3); /* avoid excessive network traffic */
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}
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}
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void handle_packet(struct client_state_t *cs)
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{
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unsigned char *message = NULL;
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int len;
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struct dhcpMessage packet;
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if (cs->listenMode == LM_KERNEL)
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len = get_packet(&packet, cs->listenFd);
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else if (cs->listenMode == LM_RAW)
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len = get_raw_packet(&packet, cs->listenFd);
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else /* LM_NONE */
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return;
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if (len == -1 && errno != EINTR) {
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log_error("reopening socket.");
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change_listen_mode(cs, cs->listenMode); /* just close and reopen */
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}
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if (len < 0)
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return;
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if (packet.xid != cs->xid) {
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log_line("Ignoring XID %lx (our xid is %lx).",
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(uint32_t) packet.xid, cs->xid);
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return;
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}
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if ((message = get_option(&packet, DHCP_MESSAGE_TYPE)) == NULL) {
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log_line("couldnt get option from packet -- ignoring");
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return;
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}
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switch (cs->dhcpState) {
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case DS_INIT_SELECTING:
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init_selecting_packet(cs, &packet, message);
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break;
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case DS_ARP_CHECK:
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/* We ignore dhcp packets for now. This state will
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* be changed by the callback for arp ping.
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*/
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break;
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case DS_RENEW_REQUESTED:
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case DS_REQUESTING:
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case DS_RENEWING:
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case DS_REBINDING:
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dhcp_ack_or_nak_packet(cs, &packet, message);
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break;
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case DS_BOUND:
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case DS_RELEASED:
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default:
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break;
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}
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}
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