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 | {
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44 | int timeout_ms;
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45 | struct pollfd pfd[1];
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46 | #define s (pfd[0].fd) /* socket */
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47 | int rv = 1; /* "no reply received" yet */
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48 | struct sockaddr addr; /* for interface name */
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49 | struct arpMsg arp;
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50 |
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51 | s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
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52 | if (s == -1) {
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53 | bb_perror_msg(bb_msg_can_not_create_raw_socket);
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54 | return -1;
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55 | }
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56 |
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57 | if (setsockopt_broadcast(s) == -1) {
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58 | bb_perror_msg("can't enable bcast on raw socket");
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59 | goto ret;
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60 | }
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61 |
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62 | /* send arp request */
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63 | memset(&arp, 0, sizeof(arp));
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64 | memset(arp.h_dest, 0xff, 6); /* MAC DA */
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65 | memcpy(arp.h_source, from_mac, 6); /* MAC SA */
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66 | arp.h_proto = htons(ETH_P_ARP); /* protocol type (Ethernet) */
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67 | arp.htype = htons(ARPHRD_ETHER); /* hardware type */
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68 | arp.ptype = htons(ETH_P_IP); /* protocol type (ARP message) */
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69 | arp.hlen = 6; /* hardware address length */
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70 | arp.plen = 4; /* protocol address length */
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71 | arp.operation = htons(ARPOP_REQUEST); /* ARP op code */
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72 | memcpy(arp.sHaddr, from_mac, 6); /* source hardware address */
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73 | memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
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74 | /* tHaddr is zero-filled */ /* target hardware address */
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75 | memcpy(arp.tInaddr, &test_nip, sizeof(test_nip));/* target IP address */
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76 |
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77 | memset(&addr, 0, sizeof(addr));
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78 | safe_strncpy(addr.sa_data, interface, sizeof(addr.sa_data));
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79 | if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0) {
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80 | // TODO: error message? caller didn't expect us to fail,
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81 | // just returning 1 "no reply received" misleads it.
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82 | goto ret;
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83 | }
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84 |
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85 | /* wait for arp reply, and check it */
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86 | timeout_ms = 2000;
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87 | do {
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88 | typedef uint32_t aliased_uint32_t FIX_ALIASING;
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89 | int r;
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90 | unsigned prevTime = monotonic_ms();
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91 |
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92 | pfd[0].events = POLLIN;
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93 | r = safe_poll(pfd, 1, timeout_ms);
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94 | if (r < 0)
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95 | break;
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96 | if (r) {
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97 | r = safe_read(s, &arp, sizeof(arp));
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98 | if (r < 0)
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99 | break;
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100 |
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101 | //log3("sHaddr %02x:%02x:%02x:%02x:%02x:%02x",
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102 | // arp.sHaddr[0], arp.sHaddr[1], arp.sHaddr[2],
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103 | // arp.sHaddr[3], arp.sHaddr[4], arp.sHaddr[5]);
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104 |
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105 | if (r >= ARP_MSG_SIZE
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106 | && arp.operation == htons(ARPOP_REPLY)
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107 | /* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */
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108 | /* && memcmp(arp.tHaddr, from_mac, 6) == 0 */
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109 | && *(aliased_uint32_t*)arp.sInaddr == test_nip
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110 | ) {
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111 | /* if ARP source MAC matches safe_mac
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112 | * (which is client's MAC), then it's not a conflict
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113 | * (client simply already has this IP and replies to ARPs!)
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114 | */
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115 | if (!safe_mac || memcmp(safe_mac, arp.sHaddr, 6) != 0)
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116 | rv = 0;
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117 | //else log2("sHaddr == safe_mac");
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118 | break;
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119 | }
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120 | }
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121 | timeout_ms -= (unsigned)monotonic_ms() - prevTime;
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122 | } while (timeout_ms > 0);
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123 |
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124 | ret:
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125 | close(s);
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126 | log1("%srp reply received for this address", rv ? "No a" : "A");
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127 | return rv;
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128 | }
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