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
13 struct arpMsg {
14 /* Ethernet header */
15 uint8_t h_dest[6]; /* 00 destination ether addr */
16 uint8_t h_source[6]; /* 06 source ether addr */
17 uint16_t h_proto; /* 0c packet type ID field */
18
19 /* ARP packet */
20 uint16_t htype; /* 0e hardware type (must be ARPHRD_ETHER) */
21 uint16_t ptype; /* 10 protocol type (must be ETH_P_IP) */
22 uint8_t hlen; /* 12 hardware address length (must be 6) */
23 uint8_t plen; /* 13 protocol address length (must be 4) */
24 uint16_t operation; /* 14 ARP opcode */
25 uint8_t sHaddr[6]; /* 16 sender's hardware address */
26 uint8_t sInaddr[4]; /* 1c sender's IP address */
27 uint8_t tHaddr[6]; /* 20 target's hardware address */
28 uint8_t tInaddr[4]; /* 26 target's IP address */
29 uint8_t pad[18]; /* 2a pad for min. ethernet payload (60 bytes) */
30 } PACKED;
31
32 enum {
33 ARP_MSG_SIZE = 0x2a
34 };
35
36 /* Returns 1 if no reply received */
arpping(uint32_t test_nip,const uint8_t * safe_mac,uint32_t from_ip,uint8_t * from_mac,const char * interface,unsigned timeo)37 int FAST_FUNC arpping(uint32_t test_nip,
38 const uint8_t *safe_mac,
39 uint32_t from_ip,
40 uint8_t *from_mac,
41 const char *interface,
42 unsigned timeo)
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 const char *msg;
51
52 if (!timeo)
53 return 1;
54
55 s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
56 if (s == -1) {
57 bb_simple_perror_msg(bb_msg_can_not_create_raw_socket);
58 return -1;
59 }
60
61 if (setsockopt_broadcast(s) == -1) {
62 bb_simple_perror_msg("can't enable bcast on ARP socket");
63 goto ret;
64 }
65
66 /* send arp request */
67 memset(&arp, 0, sizeof(arp));
68 memset(arp.h_dest, 0xff, 6); /* MAC DA */
69 memcpy(arp.h_source, from_mac, 6); /* MAC SA */
70 arp.h_proto = htons(ETH_P_ARP); /* protocol type (Ethernet) */
71 arp.htype = htons(ARPHRD_ETHER); /* hardware type */
72 arp.ptype = htons(ETH_P_IP); /* protocol type (ARP message) */
73 arp.hlen = 6; /* hardware address length */
74 arp.plen = 4; /* protocol address length */
75 arp.operation = htons(ARPOP_REQUEST); /* ARP op code */
76 memcpy(arp.sHaddr, from_mac, 6); /* source hardware address */
77 memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
78 /* tHaddr is zero-filled */ /* target hardware address */
79 memcpy(arp.tInaddr, &test_nip, sizeof(test_nip));/* target IP address */
80
81 memset(&addr, 0, sizeof(addr));
82 safe_strncpy(addr.sa_data, interface, sizeof(addr.sa_data));
83 if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0) {
84 // TODO: error message? caller didn't expect us to fail,
85 // just returning 1 "no reply received" misleads it.
86 goto ret;
87 }
88
89 /* wait for arp reply, and check it */
90 timeout_ms = (int)timeo;
91 do {
92 typedef uint32_t aliased_uint32_t FIX_ALIASING;
93 int r;
94 unsigned prevTime = monotonic_ms();
95
96 pfd[0].events = POLLIN;
97 r = safe_poll(pfd, 1, timeout_ms);
98 if (r < 0)
99 break;
100 if (r) {
101 r = safe_read(s, &arp, sizeof(arp));
102 if (r < 0)
103 break;
104
105 //log3("sHaddr %02x:%02x:%02x:%02x:%02x:%02x",
106 // arp.sHaddr[0], arp.sHaddr[1], arp.sHaddr[2],
107 // arp.sHaddr[3], arp.sHaddr[4], arp.sHaddr[5]);
108
109 if (r >= ARP_MSG_SIZE
110 && arp.operation == htons(ARPOP_REPLY)
111 /* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */
112 /* && memcmp(arp.tHaddr, from_mac, 6) == 0 */
113 && *(aliased_uint32_t*)arp.sInaddr == test_nip
114 ) {
115 /* if ARP source MAC matches safe_mac
116 * (which is client's MAC), then it's not a conflict
117 * (client simply already has this IP and replies to ARPs!)
118 */
119 if (!safe_mac || memcmp(safe_mac, arp.sHaddr, 6) != 0)
120 rv = 0;
121 //else log2("sHaddr == safe_mac");
122 break;
123 }
124 }
125 timeout_ms -= (unsigned)monotonic_ms() - prevTime + 1;
126
127 /* We used to check "timeout_ms > 0", but
128 * this is more under/overflow-resistant
129 * (people did see overflows here when system time jumps):
130 */
131 } while ((unsigned)timeout_ms <= timeo);
132
133 ret:
134 close(s);
135 msg = "no ARP reply received for this address";
136 if (rv == 0)
137 msg += 3;
138 log1s(msg);
139 return rv;
140 }
141