ndhc/ndhc/packet.c

#include <unistd.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <features.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <errno.h>

#include "packet.h"
#include "log.h"
#include "io.h"
#include "dhcpd.h"
#include "options.h"

void init_header(struct dhcpMessage *packet, char type)
{
    memset(packet, 0, sizeof(struct dhcpMessage));
    switch (type) {
        case DHCPDISCOVER:
        case DHCPREQUEST:
        case DHCPRELEASE:
        case DHCPINFORM:
	    packet->op = BOOTREQUEST;
	    break;
        case DHCPOFFER:
        case DHCPACK:
        case DHCPNAK:
	    packet->op = BOOTREPLY;
    }
    packet->htype = ETH_10MB;
    packet->hlen = ETH_10MB_LEN;
    packet->cookie = htonl(DHCP_MAGIC);
    packet->options[0] = DHCP_END;
    add_simple_option(packet->options, DHCP_MESSAGE_TYPE, type);
}

/* read a packet from socket fd, return -1 on read error, -2 on packet error */
int get_packet(struct dhcpMessage *packet, int fd)
{
    int bytes;
    int i;
    const char broken_vendors[][8] = {
	"MSFT 98",
	""
    };
    unsigned char *vendor;

    memset(packet, 0, sizeof(struct dhcpMessage));
    bytes = read(fd, packet, sizeof(struct dhcpMessage));
    if (bytes < 0) {
	log_line("couldn't read on listening socket, ignoring");
	return -1;
    }

    if (ntohl(packet->cookie) != DHCP_MAGIC) {
	log_error("received bogus message, ignoring.");
	return -2;
    }
    log_line("Received a packet");

    if (packet->op == BOOTREQUEST
	&& (vendor = get_option(packet, DHCP_VENDOR)))
    {
	for (i = 0; broken_vendors[i][0]; i++) {
	    if (vendor[OPT_LEN - 2] == (unsigned char)strlen(broken_vendors[i])
		&& !strncmp((char *)vendor, broken_vendors[i],
			    vendor[OPT_LEN - 2]))
	    {
		log_line("broken client (%s), forcing broadcast",
			 broken_vendors[i]);
		packet->flags |= htons(BROADCAST_FLAG);
	    }
	}
    }
    return bytes;
}

uint16_t checksum(void *addr, int count)
{
    /* Compute Internet Checksum for "count" bytes
     *         beginning at location "addr".
     */
    register int32_t sum = 0;
    uint16_t *source = (uint16_t *)addr;

    while (count > 1)  {
	sum += *source++;
	count -= 2;
    }

    /*  Add left-over byte, if any */
    if (count > 0) {
	/* Make sure that the left-over byte is added correctly both
	 * with little and big endian hosts */
	uint16_t tmp = 0;
	*(unsigned char *) (&tmp) = * (unsigned char *) source;
	sum += tmp;
    }
    /*  Fold 32-bit sum to 16 bits */
    while (sum >> 16)
	sum = (sum & 0xffff) + (sum >> 16);

    return ~sum;
}

/* Constuct a ip/udp header for a packet, and specify the source and dest
 * hardware address */
int raw_packet(struct dhcpMessage *payload, uint32_t source_ip,
	       int source_port, uint32_t dest_ip, int dest_port,
	       unsigned char *dest_arp, int ifindex)
{
    int fd, result = -1;
    struct sockaddr_ll dest;
    struct udp_dhcp_packet packet;

    if ((fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0) {
	log_error("socket call failed: %s", strerror(errno));
	goto out;
    }

    memset(&dest, 0, sizeof(dest));
    memset(&packet, 0, sizeof(packet));

    dest.sll_family = AF_PACKET;
    dest.sll_protocol = htons(ETH_P_IP);
    dest.sll_ifindex = ifindex;
    dest.sll_halen = 6;
    memcpy(dest.sll_addr, dest_arp, 6);
    if (bind(fd, (struct sockaddr *)&dest, sizeof(struct sockaddr_ll)) < 0) {
	log_error("bind call failed: %s", strerror(errno));
	goto out_fd;
    }

    packet.ip.protocol = IPPROTO_UDP;
    packet.ip.saddr = source_ip;
    packet.ip.daddr = dest_ip;
    packet.udp.source = htons(source_port);
    packet.udp.dest = htons(dest_port);
    /* cheat on the psuedo-header */
    packet.udp.len = htons(sizeof(packet.udp) + sizeof(struct dhcpMessage));
    packet.ip.tot_len = packet.udp.len;
    memcpy(&(packet.data), payload, sizeof(struct dhcpMessage));
    packet.udp.check = checksum(&packet, sizeof(struct udp_dhcp_packet));

    packet.ip.tot_len = htons(sizeof(struct udp_dhcp_packet));
    packet.ip.ihl = sizeof(packet.ip) >> 2;
    packet.ip.version = IPVERSION;
    packet.ip.ttl = IPDEFTTL;
    packet.ip.check = checksum(&(packet.ip), sizeof(packet.ip));

    int remain = sizeof(struct udp_dhcp_packet);
    int sent = 0;
    while (1) {
	result = sendto(fd, ((char *)&packet) + sent, remain - sent, 0,
			(struct sockaddr *)&dest, sizeof dest);
	if (result == -1) {
	    if (errno == EINTR)
		continue;
	    log_error("raw_packet: sendto failed: %s", strerror(errno));
	    break;
	}
	sent += result;
	if (remain == sent)
	    break;
    }
  out_fd:
    close(fd);
  out:
    return result;
}

/* Let the kernel do all the work for packet generation */
int kernel_packet(struct dhcpMessage *payload, uint32_t source_ip,
		  int source_port, uint32_t dest_ip, int dest_port)
{
    int opt = 1, fd, result = -1;
    struct sockaddr_in client;

    if ((fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
	goto out;

    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof opt) == -1)
	goto out_fd;

    memset(&client, 0, sizeof(client));
    client.sin_family = AF_INET;
    client.sin_port = htons(source_port);
    client.sin_addr.s_addr = source_ip;

    if (bind(fd, (struct sockaddr *)&client, sizeof(struct sockaddr)) == -1)
	goto out_fd;

    memset(&client, 0, sizeof(client));
    client.sin_family = AF_INET;
    client.sin_port = htons(dest_port);
    client.sin_addr.s_addr = dest_ip;

    if (connect(fd, (struct sockaddr *)&client, sizeof(struct sockaddr)) == -1)
	goto out_fd;

    result = safe_write(fd, (const char *)payload, sizeof(struct dhcpMessage));
    if (result == -1)
	log_error("kernel_packet: write failed: %s", strerror(errno));
  out_fd:
    close(fd);
  out:
    return result;
}