/* 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 */
uint32_t FAST_FUNC random_xid(void)
{
        static smallint initialized;

        if (!initialized) {
                srand(monotonic_us());
                initialized = 1;
        }
        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);
        if ((type != DHCPDECLINE) && (type != DHCPRELEASE))
                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_param_req_option(struct dhcpMessage *packet)
{
        uint8_t c;
        int end = end_option(packet->options);
        int i, len = 0;

        for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
                if (((dhcp_options[i].flags & OPTION_REQ)
                     && !client_config.no_default_options)
                 || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
                ) {
                        packet->options[end + OPT_DATA + len] = c;
                        len++;
                }
        }
        if (len) {
                packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
                packet->options[end + OPT_LEN] = len;
                packet->options[end + OPT_DATA + len] = DHCP_END;
        }
}

/* RFC 2131
 * 4.4.4 Use of broadcast and unicast
 *
 * The DHCP client broadcasts DHCPDISCOVER, DHCPREQUEST and DHCPINFORM
 * messages, unless the client knows the address of a DHCP server.
 * The client unicasts DHCPRELEASE messages to the server. Because
 * the client is declining the use of the IP address supplied by the server,
 * the client broadcasts DHCPDECLINE messages.
 *
 * When the DHCP client knows the address of a DHCP server, in either
 * INIT or REBOOTING state, the client may use that address
 * in the DHCPDISCOVER or DHCPREQUEST rather than the IP broadcast address.
 * The client may also use unicast to send DHCPINFORM messages
 * to a known DHCP server. If the client receives no response to DHCP
 * messages sent to the IP address of a known DHCP server, the DHCP
 * client reverts to using the IP broadcast address.
 */

static int raw_bcast_from_client_config_ifindex(struct dhcpMessage *packet)
{
        return udhcp_send_raw_packet(packet,
                /*src*/ INADDR_ANY, CLIENT_PORT,
                /*dst*/ INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR,
                client_config.ifindex);
}


#if ENABLE_FEATURE_UDHCPC_ARPING
/* Broadcast a DHCP decline message */
int FAST_FUNC send_decline(uint32_t xid, uint32_t server, uint32_t requested)
{
        struct dhcpMessage packet;

        init_packet(&packet, DHCPDECLINE);
        packet.xid = xid;
        add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
        add_simple_option(packet.options, DHCP_SERVER_ID, server);

        bb_info_msg("Sending decline...");

        return raw_bcast_from_client_config_ifindex(&packet);
}
#endif

/* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
int FAST_FUNC send_discover(uint32_t xid, uint32_t requested)
{
        struct dhcpMessage packet;

        init_packet(&packet, DHCPDISCOVER);
        packet.xid = xid;
        if (requested)
                add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);

        /* Explicitly saying that we want RFC-compliant packets helps
         * some buggy DHCP servers to NOT send bigger packets */
        add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));

        add_param_req_option(&packet);

        bb_info_msg("Sending discover...");
        return raw_bcast_from_client_config_ifindex(&packet);
}


/* Broadcasts a DHCP request message */
/* RFC 2131 3.1 paragraph 3:
 * "The client _broadcasts_ a DHCPREQUEST message..."
 */
int FAST_FUNC send_select(uint32_t xid, uint32_t server, uint32_t 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_param_req_option(&packet);

        addr.s_addr = requested;
        bb_info_msg("Sending select for %s...", inet_ntoa(addr));
        return raw_bcast_from_client_config_ifindex(&packet);
}


/* Unicasts or broadcasts a DHCP renew message */
int FAST_FUNC send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
{
        struct dhcpMessage packet;

        init_packet(&packet, DHCPREQUEST);
        packet.xid = xid;
        packet.ciaddr = ciaddr;

        add_param_req_option(&packet);
        bb_info_msg("Sending renew...");
        if (server)
                return udhcp_send_kernel_packet(&packet,
                        ciaddr, CLIENT_PORT,
                        server, SERVER_PORT);

        return raw_bcast_from_client_config_ifindex(&packet);
}


/* Unicasts a DHCP release message */
int FAST_FUNC send_release(uint32_t server, uint32_t ciaddr)
{
        struct dhcpMessage packet;

        init_packet(&packet, DHCPRELEASE);
        packet.xid = random_xid();
        packet.ciaddr = ciaddr;

        add_simple_option(packet.options, DHCP_SERVER_ID, server);

        bb_info_msg("Sending release...");
        return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
}


/* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
int FAST_FUNC udhcp_recv_raw_packet(struct dhcpMessage *payload, int fd)
{
        int bytes;
        struct udp_dhcp_packet packet;
        uint16_t check;

        memset(&packet, 0, sizeof(packet));
        bytes = safe_read(fd, &packet, sizeof(packet));
        if (bytes < 0) {
                DEBUG("Cannot read on raw listening socket - ignoring");
                /* NB: possible down interface, etc. Caller should pause. */
                return bytes; /* returns -1 */
        }

        if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
                DEBUG("Packet is too short, ignoring");
                return -2;
        }

        if (bytes < ntohs(packet.ip.tot_len)) {
                /* packet is bigger than sizeof(packet), we did partial read */
                DEBUG("Oversized packet, ignoring");
                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(packet) - can't happen */
         || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
        ) {
                DEBUG("Unrelated/bogus packet");
                return -2;
        }

        /* verify 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 -2;
        }

        /* verify UDP checksum. IP header has to be modified for this */
        memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
        /* ip.xx fields which are not memset: protocol, check, saddr, daddr */
        packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
        check = packet.udp.check;
        packet.udp.check = 0;
        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 (payload->cookie != htonl(DHCP_MAGIC)) {
                bb_error_msg("received bogus message (bad magic), ignoring");
                return -2;
        }
        DEBUG("Got valid DHCP packet");
        return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
}