busybox/networking/udhcp/leases.c
Michel Stam 9f41271f3c udhcpd: add option for tweaking arpping
Some clients have a very short timeout for sending the DHCP
DISCOVER, shorter than the arpping timeout of 2000 milliseconds
that udhcpd uses by default.

This patch allows tweaking the timeout, or disabling of arpping
altogether, at the risk of handing out addresses which are
already in use.

function                                             old     new   delta
udhcpd_main                                         1460    1501     +41
udhcpc_main                                         2814    2851     +37
packed_usage                                       29957   29974     +17
arpping                                              477     493     +16
find_free_or_expired_nip                             161     174     +13
send_offer                                           285     292      +7
nobody_responds_to_arp                                85      89      +4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 7/0 up/down: 135/0)             Total: 135 bytes

Signed-off-by: Michel Stam <m.stam@fugro.nl>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2014-10-30 11:59:04 +01:00

205 lines
5.1 KiB
C

/* vi: set sw=4 ts=4: */
/*
* Russ Dill <Russ.Dill@asu.edu> July 2001
*
* Licensed under GPLv2, see file LICENSE in this source tree.
*/
#include "common.h"
#include "dhcpd.h"
/* Find the oldest expired lease, NULL if there are no expired leases */
static struct dyn_lease *oldest_expired_lease(void)
{
struct dyn_lease *oldest_lease = NULL;
leasetime_t oldest_time = time(NULL);
unsigned i;
/* Unexpired leases have g_leases[i].expires >= current time
* and therefore can't ever match */
for (i = 0; i < server_config.max_leases; i++) {
if (g_leases[i].expires < oldest_time) {
oldest_time = g_leases[i].expires;
oldest_lease = &g_leases[i];
}
}
return oldest_lease;
}
/* Clear out all leases with matching nonzero chaddr OR yiaddr.
* If chaddr == NULL, this is a conflict lease.
*/
static void clear_leases(const uint8_t *chaddr, uint32_t yiaddr)
{
unsigned i;
for (i = 0; i < server_config.max_leases; i++) {
if ((chaddr && memcmp(g_leases[i].lease_mac, chaddr, 6) == 0)
|| (yiaddr && g_leases[i].lease_nip == yiaddr)
) {
memset(&g_leases[i], 0, sizeof(g_leases[i]));
}
}
}
/* Add a lease into the table, clearing out any old ones.
* If chaddr == NULL, this is a conflict lease.
*/
struct dyn_lease* FAST_FUNC add_lease(
const uint8_t *chaddr, uint32_t yiaddr,
leasetime_t leasetime,
const char *hostname, int hostname_len)
{
struct dyn_lease *oldest;
/* clean out any old ones */
clear_leases(chaddr, yiaddr);
oldest = oldest_expired_lease();
if (oldest) {
memset(oldest, 0, sizeof(*oldest));
if (hostname) {
char *p;
hostname_len++; /* include NUL */
if (hostname_len > sizeof(oldest->hostname))
hostname_len = sizeof(oldest->hostname);
p = safe_strncpy(oldest->hostname, hostname, hostname_len);
/* sanitization (s/non-ASCII/^/g) */
while (*p) {
if (*p < ' ' || *p > 126)
*p = '^';
p++;
}
}
if (chaddr)
memcpy(oldest->lease_mac, chaddr, 6);
oldest->lease_nip = yiaddr;
oldest->expires = time(NULL) + leasetime;
}
return oldest;
}
/* True if a lease has expired */
int FAST_FUNC is_expired_lease(struct dyn_lease *lease)
{
return (lease->expires < (leasetime_t) time(NULL));
}
/* Find the first lease that matches MAC, NULL if no match */
struct dyn_lease* FAST_FUNC find_lease_by_mac(const uint8_t *mac)
{
unsigned i;
for (i = 0; i < server_config.max_leases; i++)
if (memcmp(g_leases[i].lease_mac, mac, 6) == 0)
return &g_leases[i];
return NULL;
}
/* Find the first lease that matches IP, NULL is no match */
struct dyn_lease* FAST_FUNC find_lease_by_nip(uint32_t nip)
{
unsigned i;
for (i = 0; i < server_config.max_leases; i++)
if (g_leases[i].lease_nip == nip)
return &g_leases[i];
return NULL;
}
/* Check if the IP is taken; if it is, add it to the lease table */
static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac, unsigned arpping_ms)
{
struct in_addr temp;
int r;
r = arpping(nip, safe_mac,
server_config.server_nip,
server_config.server_mac,
server_config.interface,
arpping_ms);
if (r)
return r;
temp.s_addr = nip;
bb_info_msg("%s belongs to someone, reserving it for %u seconds",
inet_ntoa(temp), (unsigned)server_config.conflict_time);
add_lease(NULL, nip, server_config.conflict_time, NULL, 0);
return 0;
}
/* Find a new usable (we think) address */
uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac, unsigned arpping_ms)
{
uint32_t addr;
struct dyn_lease *oldest_lease = NULL;
#if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
uint32_t stop;
unsigned i, hash;
/* hash hwaddr: use the SDBM hashing algorithm. Seems to give good
* dispersal even with similarly-valued "strings".
*/
hash = 0;
for (i = 0; i < 6; i++)
hash += safe_mac[i] + (hash << 6) + (hash << 16) - hash;
/* pick a seed based on hwaddr then iterate until we find a free address. */
addr = server_config.start_ip
+ (hash % (1 + server_config.end_ip - server_config.start_ip));
stop = addr;
#else
addr = server_config.start_ip;
#define stop (server_config.end_ip + 1)
#endif
do {
uint32_t nip;
struct dyn_lease *lease;
/* ie, 192.168.55.0 */
if ((addr & 0xff) == 0)
goto next_addr;
/* ie, 192.168.55.255 */
if ((addr & 0xff) == 0xff)
goto next_addr;
nip = htonl(addr);
/* skip our own address */
if (nip == server_config.server_nip)
goto next_addr;
/* is this a static lease addr? */
if (is_nip_reserved(server_config.static_leases, nip))
goto next_addr;
lease = find_lease_by_nip(nip);
if (!lease) {
//TODO: DHCP servers do not always sit on the same subnet as clients: should *ping*, not arp-ping!
if (nobody_responds_to_arp(nip, safe_mac, arpping_ms))
return nip;
} else {
if (!oldest_lease || lease->expires < oldest_lease->expires)
oldest_lease = lease;
}
next_addr:
addr++;
#if ENABLE_FEATURE_UDHCPD_BASE_IP_ON_MAC
if (addr > server_config.end_ip)
addr = server_config.start_ip;
#endif
} while (addr != stop);
if (oldest_lease
&& is_expired_lease(oldest_lease)
&& nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac, arpping_ms)
) {
return oldest_lease->lease_nip;
}
return 0;
}