/* vi: set sw=4 ts=4: */ /* * arpping.c * * Mostly stolen from: dhcpcd - DHCP client daemon * by Yoichi Hariguchi <yoichi@fore.com> */ #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) */ } ATTRIBUTE_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 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("cannot 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-fiiled */ /* target hardware address */ memcpy(arp.tInaddr, &test_ip, sizeof(test_ip)); /* 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 { int r; unsigned prevTime = monotonic_us(); pfd[0].events = POLLIN; r = safe_poll(pfd, 1, timeout_ms); if (r < 0) break; if (r) { r = read(s, &arp, sizeof(arp)); if (r < 0) break; 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 */ && *((uint32_t *) arp.sInaddr) == test_ip ) { rv = 0; break; } } timeout_ms -= (monotonic_us() - prevTime) / 1000; } while (timeout_ms > 0); ret: close(s); DEBUG("%srp reply received for this address", rv ? "No a" : "A"); return rv; }