/* vi: set sw=4 ts=4: */
/*
- * arpping.c
- *
* Mostly stolen from: dhcpcd - DHCP client daemon
* by Yoichi Hariguchi <yoichi@fore.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
*/
-
#include <netinet/if_ether.h>
#include <net/if_arp.h>
#include "common.h"
#include "dhcpd.h"
-
struct arpMsg {
/* Ethernet header */
uint8_t h_dest[6]; /* 00 destination ether addr */
uint8_t tHaddr[6]; /* 20 target's hardware address */
uint8_t tInaddr[4]; /* 26 target's IP address */
uint8_t pad[18]; /* 2a pad for min. ethernet payload (60 bytes) */
-} ATTRIBUTE_PACKED;
+} PACKED;
+enum {
+ ARP_MSG_SIZE = 0x2a
+};
/* Returns 1 if no reply received */
-
-int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *interface)
+int FAST_FUNC arpping(uint32_t test_nip,
+ const uint8_t *safe_mac,
+ uint32_t from_ip,
+ uint8_t *from_mac,
+ const char *interface)
{
- int timeout_ms = 2000;
+ int timeout_ms;
struct pollfd pfd[1];
#define s (pfd[0].fd) /* socket */
int rv = 1; /* "no reply received" yet */
}
if (setsockopt_broadcast(s) == -1) {
- bb_perror_msg("cannot setsocketopt on raw socket");
+ bb_perror_msg("can't enable bcast on raw socket");
goto ret;
}
arp.operation = htons(ARPOP_REQUEST); /* ARP op code */
memcpy(arp.sHaddr, from_mac, 6); /* source hardware address */
memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
- /* tHaddr */ /* target hardware address */
- memcpy(arp.tInaddr, &test_ip, sizeof(test_ip)); /* target IP address */
+ /* tHaddr is zero-filled */ /* target hardware address */
+ memcpy(arp.tInaddr, &test_nip, sizeof(test_nip));/* target IP address */
memset(&addr, 0, sizeof(addr));
safe_strncpy(addr.sa_data, interface, sizeof(addr.sa_data));
- if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0)
+ if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0) {
+ // TODO: error message? caller didn't expect us to fail,
+ // just returning 1 "no reply received" misleads it.
goto ret;
+ }
/* wait for arp reply, and check it */
+ timeout_ms = 2000;
do {
+ typedef uint32_t aliased_uint32_t FIX_ALIASING;
int r;
- unsigned prevTime = monotonic_us();
+ unsigned prevTime = monotonic_ms();
pfd[0].events = POLLIN;
r = safe_poll(pfd, 1, timeout_ms);
- if (r < 0) {
+ if (r < 0)
break;
- } else if (r) {
- if (read(s, &arp, sizeof(arp)) < 0)
+ if (r) {
+ r = safe_read(s, &arp, sizeof(arp));
+ if (r < 0)
break;
- if (arp.operation == htons(ARPOP_REPLY)
- && memcmp(arp.tHaddr, from_mac, 6) == 0
- && *((uint32_t *) arp.sInaddr) == test_ip
+
+ //log3("sHaddr %02x:%02x:%02x:%02x:%02x:%02x",
+ // arp.sHaddr[0], arp.sHaddr[1], arp.sHaddr[2],
+ // arp.sHaddr[3], arp.sHaddr[4], arp.sHaddr[5]);
+
+ if (r >= ARP_MSG_SIZE
+ && arp.operation == htons(ARPOP_REPLY)
+ /* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */
+ /* && memcmp(arp.tHaddr, from_mac, 6) == 0 */
+ && *(aliased_uint32_t*)arp.sInaddr == test_nip
) {
- rv = 0;
+ /* if ARP source MAC matches safe_mac
+ * (which is client's MAC), then it's not a conflict
+ * (client simply already has this IP and replies to ARPs!)
+ */
+ if (!safe_mac || memcmp(safe_mac, arp.sHaddr, 6) != 0)
+ rv = 0;
+ //else log2("sHaddr == safe_mac");
break;
}
}
- timeout_ms -= (monotonic_us() - prevTime) / 1000;
- } while (timeout_ms > 0);
+ timeout_ms -= (unsigned)monotonic_ms() - prevTime + 1;
+
+ /* We used to check "timeout_ms > 0", but
+ * this is more under/overflow-resistant
+ * (people did see overflows here when system time jumps):
+ */
+ } while ((unsigned)timeout_ms <= 2000);
ret:
close(s);
- DEBUG("%srp reply received for this address", rv ? "No a" : "A");
+ log1("%srp reply received for this address", rv ? "No a" : "A");
return rv;
}