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/* 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 tarball for details.
*/
#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 h_source[6]; /* 06 source ether addr */
uint16_t h_proto; /* 0c packet type ID field */
/* ARP packet */
uint16_t htype; /* 0e hardware type (must be ARPHRD_ETHER) */
uint16_t ptype; /* 10 protocol type (must be ETH_P_IP) */
uint8_t hlen; /* 12 hardware address length (must be 6) */
uint8_t plen; /* 13 protocol address length (must be 4) */
uint16_t operation; /* 14 ARP opcode */
uint8_t sHaddr[6]; /* 16 sender's hardware address */
uint8_t sInaddr[4]; /* 1c sender's IP address */
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) */
} PACKED;
enum {
ARP_MSG_SIZE = 0x2a
};
/* Returns 1 if no reply received */
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;
struct pollfd pfd[1];
#define s (pfd[0].fd) /* socket */
int rv = 1; /* "no reply received" yet */
struct sockaddr addr; /* for interface name */
struct arpMsg arp;
s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
if (s == -1) {
bb_perror_msg(bb_msg_can_not_create_raw_socket);
return -1;
}
if (setsockopt_broadcast(s) == -1) {
bb_perror_msg("can't enable bcast on raw socket");
goto ret;
}
/* send arp request */
memset(&arp, 0, sizeof(arp));
memset(arp.h_dest, 0xff, 6); /* MAC DA */
memcpy(arp.h_source, from_mac, 6); /* MAC SA */
arp.h_proto = htons(ETH_P_ARP); /* protocol type (Ethernet) */
arp.htype = htons(ARPHRD_ETHER); /* hardware type */
arp.ptype = htons(ETH_P_IP); /* protocol type (ARP message) */
arp.hlen = 6; /* hardware address length */
arp.plen = 4; /* protocol address length */
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 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) {
// 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_ms();
pfd[0].events = POLLIN;
r = safe_poll(pfd, 1, timeout_ms);
if (r < 0)
break;
if (r) {
r = safe_read(s, &arp, sizeof(arp));
if (r < 0)
break;
//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
) {
/* 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 -= (unsigned)monotonic_ms() - prevTime;
} while (timeout_ms > 0);
ret:
close(s);
log1("%srp reply received for this address", rv ? "No a" : "A");
return rv;
}
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