blob: 155ec01e28328befa119f619b3acdbaa75f0a3da
1 | /* vi: set sw=4 ts=4: */ |
2 | /* |
3 | * Mostly stolen from: dhcpcd - DHCP client daemon |
4 | * by Yoichi Hariguchi <yoichi@fore.com> |
5 | * |
6 | * Licensed under GPLv2, see file LICENSE in this source tree. |
7 | */ |
8 | #include <netinet/if_ether.h> |
9 | #include <net/if_arp.h> |
10 | |
11 | #include "common.h" |
12 | #include "dhcpd.h" |
13 | |
14 | struct arpMsg { |
15 | /* Ethernet header */ |
16 | uint8_t h_dest[6]; /* 00 destination ether addr */ |
17 | uint8_t h_source[6]; /* 06 source ether addr */ |
18 | uint16_t h_proto; /* 0c packet type ID field */ |
19 | |
20 | /* ARP packet */ |
21 | uint16_t htype; /* 0e hardware type (must be ARPHRD_ETHER) */ |
22 | uint16_t ptype; /* 10 protocol type (must be ETH_P_IP) */ |
23 | uint8_t hlen; /* 12 hardware address length (must be 6) */ |
24 | uint8_t plen; /* 13 protocol address length (must be 4) */ |
25 | uint16_t operation; /* 14 ARP opcode */ |
26 | uint8_t sHaddr[6]; /* 16 sender's hardware address */ |
27 | uint8_t sInaddr[4]; /* 1c sender's IP address */ |
28 | uint8_t tHaddr[6]; /* 20 target's hardware address */ |
29 | uint8_t tInaddr[4]; /* 26 target's IP address */ |
30 | uint8_t pad[18]; /* 2a pad for min. ethernet payload (60 bytes) */ |
31 | } PACKED; |
32 | |
33 | enum { |
34 | ARP_MSG_SIZE = 0x2a |
35 | }; |
36 | |
37 | /* Returns 1 if no reply received */ |
38 | int FAST_FUNC arpping(uint32_t test_nip, |
39 | const uint8_t *safe_mac, |
40 | uint32_t from_ip, |
41 | uint8_t *from_mac, |
42 | const char *interface) |
43 | { |
44 | int timeout_ms; |
45 | struct pollfd pfd[1]; |
46 | #define s (pfd[0].fd) /* socket */ |
47 | int rv = 1; /* "no reply received" yet */ |
48 | struct sockaddr addr; /* for interface name */ |
49 | struct arpMsg arp; |
50 | |
51 | s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)); |
52 | if (s == -1) { |
53 | bb_perror_msg("%s", bb_msg_can_not_create_raw_socket); |
54 | return -1; |
55 | } |
56 | |
57 | if (setsockopt_broadcast(s) == -1) { |
58 | bb_perror_msg("can't enable bcast on raw socket"); |
59 | goto ret; |
60 | } |
61 | |
62 | /* send arp request */ |
63 | memset(&arp, 0, sizeof(arp)); |
64 | memset(arp.h_dest, 0xff, 6); /* MAC DA */ |
65 | memcpy(arp.h_source, from_mac, 6); /* MAC SA */ |
66 | arp.h_proto = htons(ETH_P_ARP); /* protocol type (Ethernet) */ |
67 | arp.htype = htons(ARPHRD_ETHER); /* hardware type */ |
68 | arp.ptype = htons(ETH_P_IP); /* protocol type (ARP message) */ |
69 | arp.hlen = 6; /* hardware address length */ |
70 | arp.plen = 4; /* protocol address length */ |
71 | arp.operation = htons(ARPOP_REQUEST); /* ARP op code */ |
72 | memcpy(arp.sHaddr, from_mac, 6); /* source hardware address */ |
73 | memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */ |
74 | /* tHaddr is zero-filled */ /* target hardware address */ |
75 | memcpy(arp.tInaddr, &test_nip, sizeof(test_nip));/* target IP address */ |
76 | |
77 | memset(&addr, 0, sizeof(addr)); |
78 | safe_strncpy(addr.sa_data, interface, sizeof(addr.sa_data)); |
79 | if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0) { |
80 | // TODO: error message? caller didn't expect us to fail, |
81 | // just returning 1 "no reply received" misleads it. |
82 | goto ret; |
83 | } |
84 | |
85 | /* wait for arp reply, and check it */ |
86 | timeout_ms = 2000; |
87 | do { |
88 | typedef uint32_t aliased_uint32_t FIX_ALIASING; |
89 | int r; |
90 | unsigned prevTime = monotonic_ms(); |
91 | |
92 | pfd[0].events = POLLIN; |
93 | r = safe_poll(pfd, 1, timeout_ms); |
94 | if (r < 0) |
95 | break; |
96 | if (r) { |
97 | r = safe_read(s, &arp, sizeof(arp)); |
98 | if (r < 0) |
99 | break; |
100 | |
101 | //log3("sHaddr %02x:%02x:%02x:%02x:%02x:%02x", |
102 | // arp.sHaddr[0], arp.sHaddr[1], arp.sHaddr[2], |
103 | // arp.sHaddr[3], arp.sHaddr[4], arp.sHaddr[5]); |
104 | |
105 | if (r >= ARP_MSG_SIZE |
106 | && arp.operation == htons(ARPOP_REPLY) |
107 | /* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */ |
108 | /* && memcmp(arp.tHaddr, from_mac, 6) == 0 */ |
109 | && *(aliased_uint32_t*)arp.sInaddr == test_nip |
110 | ) { |
111 | /* if ARP source MAC matches safe_mac |
112 | * (which is client's MAC), then it's not a conflict |
113 | * (client simply already has this IP and replies to ARPs!) |
114 | */ |
115 | if (!safe_mac || memcmp(safe_mac, arp.sHaddr, 6) != 0) |
116 | rv = 0; |
117 | //else log2("sHaddr == safe_mac"); |
118 | break; |
119 | } |
120 | } |
121 | timeout_ms -= (unsigned)monotonic_ms() - prevTime + 1; |
122 | |
123 | /* We used to check "timeout_ms > 0", but |
124 | * this is more under/overflow-resistant |
125 | * (people did see overflows here when system time jumps): |
126 | */ |
127 | } while ((unsigned)timeout_ms <= 2000); |
128 | |
129 | ret: |
130 | close(s); |
131 | log1("%srp reply received for this address", rv ? "No a" : "A"); |
132 | return rv; |
133 | } |
134 |