source: MondoRescue/trunk/mindi-busybox/networking/udhcp/packet.c@ 904

#include <unistd.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <features.h>
#if (__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 <errno.h>

#include "common.h"
#include "packet.h"
#include "dhcpd.h"
#include "options.h"


void udhcp_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 udhcp_get_packet(struct dhcpMessage *packet, int fd)
{
    static const char broken_vendors[][8] = {
        "MSFT 98",
        ""
    };
    int bytes;
    int i;
    char unsigned *vendor;

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

    if (ntohl(packet->cookie) != DHCP_MAGIC) {
        LOG(LOG_ERR, "received bogus message, ignoring");
        return -2;
    }
    DEBUG(LOG_INFO, "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] == (uint8_t) strlen(broken_vendors[i]) &&
                !strncmp((char*)vendor, broken_vendors[i], vendor[OPT_LEN - 2])) {
                DEBUG(LOG_INFO, "broken client (%s), forcing broadcast",
                    broken_vendors[i]);
                packet->flags |= htons(BROADCAST_FLAG);
            }
        }
    }

    return bytes;
}


uint16_t udhcp_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)  {
        /*  This is the inner loop */
        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;
        *(uint8_t *) (&tmp) = * (uint8_t *) source;
        sum += tmp;
    }
    /*  Fold 32-bit sum to 16 bits */
    while (sum >> 16)
        sum = (sum & 0xffff) + (sum >> 16);

    return ~sum;
}


/* Construct a ip/udp header for a packet, and specify the source and dest hardware address */
int udhcp_raw_packet(struct dhcpMessage *payload, uint32_t source_ip, int source_port,
           uint32_t dest_ip, int dest_port, uint8_t *dest_arp, int ifindex)
{
    int fd;
    int result;
    struct sockaddr_ll dest;
    struct udp_dhcp_packet packet;

    if ((fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP))) < 0) {
        DEBUG(LOG_ERR, "socket call failed: %m");
        return -1;
    }

    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) {
        DEBUG(LOG_ERR, "bind call failed: %m");
        close(fd);
        return -1;
    }

    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);
    packet.udp.len = htons(sizeof(packet.udp) + sizeof(struct dhcpMessage)); /* cheat on the psuedo-header */
    packet.ip.tot_len = packet.udp.len;
    memcpy(&(packet.data), payload, sizeof(struct dhcpMessage));
    packet.udp.check = udhcp_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 = udhcp_checksum(&(packet.ip), sizeof(packet.ip));

    result = sendto(fd, &packet, sizeof(struct udp_dhcp_packet), 0, (struct sockaddr *) &dest, sizeof(dest));
    if (result <= 0) {
        DEBUG(LOG_ERR, "write on socket failed: %m");
    }
    close(fd);
    return result;
}


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

    if ((fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
        return -1;

    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (char *) &n, sizeof(n)) == -1) {
        close(fd);
        return -1;
    }

    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) {
        close(fd);
        return -1;
    }

    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) {
        close(fd);
        return -1;
    }

    result = write(fd, payload, sizeof(struct dhcpMessage));
    close(fd);
    return result;
}