busybox/networking/udhcp/serverpacket.c

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/* vi: set sw=4 ts=4: */
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/* serverpacket.c
*
* Construct and send DHCP server packets
*
* Russ Dill <Russ.Dill@asu.edu> July 2001
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include "common.h"
#include "dhcpc.h"
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#include "dhcpd.h"
#include "options.h"
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/* send a packet to gateway_nip using the kernel ip stack */
static int send_packet_to_relay(struct dhcp_packet *dhcp_pkt)
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{
log1("Forwarding packet to relay");
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return udhcp_send_kernel_packet(dhcp_pkt,
server_config.server_nip, SERVER_PORT,
dhcp_pkt->gateway_nip, SERVER_PORT);
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}
/* send a packet to a specific mac address and ip address by creating our own ip packet */
static int send_packet_to_client(struct dhcp_packet *dhcp_pkt, int force_broadcast)
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{
const uint8_t *chaddr;
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uint32_t ciaddr;
// Was:
//if (force_broadcast) { /* broadcast */ }
//else if (dhcp_pkt->ciaddr) { /* unicast to dhcp_pkt->ciaddr */ }
//else if (dhcp_pkt->flags & htons(BROADCAST_FLAG)) { /* broadcast */ }
//else { /* unicast to dhcp_pkt->yiaddr */ }
// But this is wrong: yiaddr is _our_ idea what client's IP is
// (for example, from lease file). Client may not know that,
// and may not have UDP socket listening on that IP!
// We should never unicast to dhcp_pkt->yiaddr!
// dhcp_pkt->ciaddr, OTOH, comes from client's request packet,
// and can be used.
if (force_broadcast
|| (dhcp_pkt->flags & htons(BROADCAST_FLAG))
|| !dhcp_pkt->ciaddr
) {
log1("Broadcasting packet to client");
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ciaddr = INADDR_BROADCAST;
chaddr = MAC_BCAST_ADDR;
} else {
log1("Unicasting packet to client ciaddr");
ciaddr = dhcp_pkt->ciaddr;
chaddr = dhcp_pkt->chaddr;
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}
return udhcp_send_raw_packet(dhcp_pkt,
/*src*/ server_config.server_nip, SERVER_PORT,
/*dst*/ ciaddr, CLIENT_PORT, chaddr,
server_config.ifindex);
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}
/* send a dhcp packet, if force broadcast is set, the packet will be broadcast to the client */
static int send_packet(struct dhcp_packet *dhcp_pkt, int force_broadcast)
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{
if (dhcp_pkt->gateway_nip)
return send_packet_to_relay(dhcp_pkt);
return send_packet_to_client(dhcp_pkt, force_broadcast);
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}
static void init_packet(struct dhcp_packet *packet, struct dhcp_packet *oldpacket, char type)
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{
udhcp_init_header(packet, type);
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packet->xid = oldpacket->xid;
memcpy(packet->chaddr, oldpacket->chaddr, sizeof(oldpacket->chaddr));
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packet->flags = oldpacket->flags;
packet->gateway_nip = oldpacket->gateway_nip;
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packet->ciaddr = oldpacket->ciaddr;
add_simple_option(packet->options, DHCP_SERVER_ID, server_config.server_nip);
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}
/* add in the bootp options */
static void add_bootp_options(struct dhcp_packet *packet)
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{
packet->siaddr_nip = server_config.siaddr_nip;
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if (server_config.sname)
strncpy((char*)packet->sname, server_config.sname, sizeof(packet->sname) - 1);
if (server_config.boot_file)
strncpy((char*)packet->file, server_config.boot_file, sizeof(packet->file) - 1);
}
static uint32_t select_lease_time(struct dhcp_packet *packet)
{
uint32_t lease_time_sec = server_config.max_lease_sec;
uint8_t *lease_time_opt = get_option(packet, DHCP_LEASE_TIME);
if (lease_time_opt) {
move_from_unaligned32(lease_time_sec, lease_time_opt);
lease_time_sec = ntohl(lease_time_sec);
if (lease_time_sec > server_config.max_lease_sec)
lease_time_sec = server_config.max_lease_sec;
if (lease_time_sec < server_config.min_lease_sec)
lease_time_sec = server_config.min_lease_sec;
}
return lease_time_sec;
}
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/* send a DHCP OFFER to a DHCP DISCOVER */
int FAST_FUNC send_offer(struct dhcp_packet *oldpacket)
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{
struct dhcp_packet packet;
uint32_t req_nip;
uint32_t lease_time_sec = server_config.max_lease_sec;
uint32_t static_lease_ip;
uint8_t *req_ip_opt, *p_host_name;
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struct option_set *curr;
struct in_addr addr;
init_packet(&packet, oldpacket, DHCPOFFER);
static_lease_ip = get_static_nip_by_mac(server_config.static_leases, oldpacket->chaddr);
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/* ADDME: if static, short circuit */
if (!static_lease_ip) {
struct dyn_lease *lease;
lease = find_lease_by_mac(oldpacket->chaddr);
/* The client is in our lease/offered table */
if (lease) {
signed_leasetime_t tmp = lease->expires - time(NULL);
if (tmp >= 0)
lease_time_sec = tmp;
packet.yiaddr = lease->lease_nip;
}
/* Or the client has requested an IP */
else if ((req_ip_opt = get_option(oldpacket, DHCP_REQUESTED_IP)) != NULL
/* (read IP) */
&& (move_from_unaligned32(req_nip, req_ip_opt), 1)
/* and the IP is in the lease range */
&& ntohl(req_nip) >= server_config.start_ip
&& ntohl(req_nip) <= server_config.end_ip
/* and is not already taken/offered */
&& (!(lease = find_lease_by_nip(req_nip))
/* or its taken, but expired */
|| is_expired_lease(lease))
) {
packet.yiaddr = req_nip;
}
/* Otherwise, find a free IP */
else {
packet.yiaddr = find_free_or_expired_nip(oldpacket->chaddr);
}
if (!packet.yiaddr) {
bb_error_msg("no IP addresses to give - OFFER abandoned");
return -1;
}
p_host_name = get_option(oldpacket, DHCP_HOST_NAME);
if (!add_lease(packet.chaddr, packet.yiaddr, server_config.offer_time, p_host_name)) {
bb_error_msg("lease pool is full - OFFER abandoned");
return -1;
}
lease_time_sec = select_lease_time(oldpacket);
} else {
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/* It is a static lease... use it */
packet.yiaddr = static_lease_ip;
}
add_simple_option(packet.options, DHCP_LEASE_TIME, htonl(lease_time_sec));
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curr = server_config.options;
while (curr) {
if (curr->data[OPT_CODE] != DHCP_LEASE_TIME)
add_option_string(packet.options, curr->data);
curr = curr->next;
}
add_bootp_options(&packet);
addr.s_addr = packet.yiaddr;
bb_info_msg("Sending OFFER of %s", inet_ntoa(addr));
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return send_packet(&packet, 0);
}
int FAST_FUNC send_NAK(struct dhcp_packet *oldpacket)
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{
struct dhcp_packet packet;
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init_packet(&packet, oldpacket, DHCPNAK);
log1("Sending NAK");
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return send_packet(&packet, 1);
}
int FAST_FUNC send_ACK(struct dhcp_packet *oldpacket, uint32_t yiaddr)
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{
struct dhcp_packet packet;
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struct option_set *curr;
uint32_t lease_time_sec;
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struct in_addr addr;
uint8_t *p_host_name;
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init_packet(&packet, oldpacket, DHCPACK);
packet.yiaddr = yiaddr;
lease_time_sec = select_lease_time(oldpacket);
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add_simple_option(packet.options, DHCP_LEASE_TIME, htonl(lease_time_sec));
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curr = server_config.options;
while (curr) {
if (curr->data[OPT_CODE] != DHCP_LEASE_TIME)
add_option_string(packet.options, curr->data);
curr = curr->next;
}
add_bootp_options(&packet);
addr.s_addr = packet.yiaddr;
bb_info_msg("Sending ACK to %s", inet_ntoa(addr));
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if (send_packet(&packet, 0) < 0)
return -1;
p_host_name = get_option(oldpacket, DHCP_HOST_NAME);
add_lease(packet.chaddr, packet.yiaddr, lease_time_sec, p_host_name);
if (ENABLE_FEATURE_UDHCPD_WRITE_LEASES_EARLY) {
/* rewrite the file with leases at every new acceptance */
write_leases();
}
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return 0;
}
int FAST_FUNC send_inform(struct dhcp_packet *oldpacket)
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{
struct dhcp_packet packet;
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struct option_set *curr;
init_packet(&packet, oldpacket, DHCPACK);
curr = server_config.options;
while (curr) {
if (curr->data[OPT_CODE] != DHCP_LEASE_TIME)
add_option_string(packet.options, curr->data);
curr = curr->next;
}
add_bootp_options(&packet);
return send_packet(&packet, 0);
}