| 1 | /* vi: set sw=4 ts=4: */
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| 2 | /*
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| 3 | * Mostly stolen from: dhcpcd - DHCP client daemon
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| 4 | * by Yoichi Hariguchi <yoichi@fore.com>
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| 5 | *
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| 6 | * Licensed under GPLv2, see file LICENSE in this source tree.
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| 7 | */
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| 8 | #include <netinet/if_ether.h>
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| 9 | #include <net/if_arp.h>
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| 10 |
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| 11 | #include "common.h"
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| 12 | #include "dhcpd.h"
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| 13 |
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| 14 | struct arpMsg {
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| 15 | /* Ethernet header */
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| 16 | uint8_t h_dest[6]; /* 00 destination ether addr */
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| 17 | uint8_t h_source[6]; /* 06 source ether addr */
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| 18 | uint16_t h_proto; /* 0c packet type ID field */
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| 19 |
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| 20 | /* ARP packet */
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| 21 | uint16_t htype; /* 0e hardware type (must be ARPHRD_ETHER) */
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| 22 | uint16_t ptype; /* 10 protocol type (must be ETH_P_IP) */
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| 23 | uint8_t hlen; /* 12 hardware address length (must be 6) */
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| 24 | uint8_t plen; /* 13 protocol address length (must be 4) */
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| 25 | uint16_t operation; /* 14 ARP opcode */
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| 26 | uint8_t sHaddr[6]; /* 16 sender's hardware address */
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| 27 | uint8_t sInaddr[4]; /* 1c sender's IP address */
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| 28 | uint8_t tHaddr[6]; /* 20 target's hardware address */
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| 29 | uint8_t tInaddr[4]; /* 26 target's IP address */
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| 30 | uint8_t pad[18]; /* 2a pad for min. ethernet payload (60 bytes) */
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| 31 | } PACKED;
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| 32 |
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| 33 | enum {
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| 34 | ARP_MSG_SIZE = 0x2a
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| 35 | };
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| 36 |
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| 37 | /* Returns 1 if no reply received */
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| 38 | int FAST_FUNC arpping(uint32_t test_nip,
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| 39 | const uint8_t *safe_mac,
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| 40 | uint32_t from_ip,
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| 41 | uint8_t *from_mac,
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| 42 | const char *interface,
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| 43 | unsigned timeo)
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| 44 | {
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| 45 | int timeout_ms;
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| 46 | struct pollfd pfd[1];
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| 47 | #define s (pfd[0].fd) /* socket */
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| 48 | int rv = 1; /* "no reply received" yet */
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| 49 | struct sockaddr addr; /* for interface name */
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| 50 | struct arpMsg arp;
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| 51 |
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| 52 | if (!timeo)
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| 53 | return 1;
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| 54 |
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| 55 | s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
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| 56 | if (s == -1) {
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| 57 | bb_perror_msg(bb_msg_can_not_create_raw_socket);
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| 58 | return -1;
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| 59 | }
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| 60 |
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| 61 | if (setsockopt_broadcast(s) == -1) {
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| 62 | bb_perror_msg("can't enable bcast on raw socket");
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| 63 | goto ret;
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| 64 | }
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| 65 |
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| 66 | /* send arp request */
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| 67 | memset(&arp, 0, sizeof(arp));
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| 68 | memset(arp.h_dest, 0xff, 6); /* MAC DA */
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| 69 | memcpy(arp.h_source, from_mac, 6); /* MAC SA */
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| 70 | arp.h_proto = htons(ETH_P_ARP); /* protocol type (Ethernet) */
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| 71 | arp.htype = htons(ARPHRD_ETHER); /* hardware type */
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| 72 | arp.ptype = htons(ETH_P_IP); /* protocol type (ARP message) */
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| 73 | arp.hlen = 6; /* hardware address length */
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| 74 | arp.plen = 4; /* protocol address length */
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| 75 | arp.operation = htons(ARPOP_REQUEST); /* ARP op code */
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| 76 | memcpy(arp.sHaddr, from_mac, 6); /* source hardware address */
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| 77 | memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
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| 78 | /* tHaddr is zero-filled */ /* target hardware address */
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| 79 | memcpy(arp.tInaddr, &test_nip, sizeof(test_nip));/* target IP address */
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| 80 |
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| 81 | memset(&addr, 0, sizeof(addr));
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| 82 | safe_strncpy(addr.sa_data, interface, sizeof(addr.sa_data));
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| 83 | if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0) {
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| 84 | // TODO: error message? caller didn't expect us to fail,
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| 85 | // just returning 1 "no reply received" misleads it.
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| 86 | goto ret;
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| 87 | }
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| 88 |
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| 89 | /* wait for arp reply, and check it */
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| 90 | timeout_ms = (int)timeo;
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| 91 | do {
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| 92 | typedef uint32_t aliased_uint32_t FIX_ALIASING;
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| 93 | int r;
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| 94 | unsigned prevTime = monotonic_ms();
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| 95 |
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| 96 | pfd[0].events = POLLIN;
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| 97 | r = safe_poll(pfd, 1, timeout_ms);
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| 98 | if (r < 0)
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| 99 | break;
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| 100 | if (r) {
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| 101 | r = safe_read(s, &arp, sizeof(arp));
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| 102 | if (r < 0)
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| 103 | break;
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| 104 |
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| 105 | //log3("sHaddr %02x:%02x:%02x:%02x:%02x:%02x",
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| 106 | // arp.sHaddr[0], arp.sHaddr[1], arp.sHaddr[2],
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| 107 | // arp.sHaddr[3], arp.sHaddr[4], arp.sHaddr[5]);
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| 108 |
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| 109 | if (r >= ARP_MSG_SIZE
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| 110 | && arp.operation == htons(ARPOP_REPLY)
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| 111 | /* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */
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| 112 | /* && memcmp(arp.tHaddr, from_mac, 6) == 0 */
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| 113 | && *(aliased_uint32_t*)arp.sInaddr == test_nip
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| 114 | ) {
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| 115 | /* if ARP source MAC matches safe_mac
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| 116 | * (which is client's MAC), then it's not a conflict
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| 117 | * (client simply already has this IP and replies to ARPs!)
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| 118 | */
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| 119 | if (!safe_mac || memcmp(safe_mac, arp.sHaddr, 6) != 0)
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| 120 | rv = 0;
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| 121 | //else log2("sHaddr == safe_mac");
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| 122 | break;
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| 123 | }
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| 124 | }
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| 125 | timeout_ms -= (unsigned)monotonic_ms() - prevTime + 1;
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| 126 |
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| 127 | /* We used to check "timeout_ms > 0", but
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| 128 | * this is more under/overflow-resistant
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| 129 | * (people did see overflows here when system time jumps):
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| 130 | */
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| 131 | } while ((unsigned)timeout_ms <= timeo);
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| 132 |
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| 133 | ret:
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| 134 | close(s);
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| 135 | log1("%srp reply received for this address", rv ? "no a" : "A");
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| 136 | return rv;
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| 137 | }
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