path: root/networking/udhcp/arpping.c (plain)
blob: 778b1d795a6168e468dc6bcec6ebc0d3600a9c72

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 */
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
51	if (!timeo)
52	return 1;
53
54	s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
55	if (s == -1) {
56	bb_perror_msg("%s", bb_msg_can_not_create_raw_socket);
57	return -1;
58	}
59
60	if (setsockopt_broadcast(s) == -1) {
61	bb_perror_msg("can't enable bcast on raw socket");
62	goto ret;
63	}
64
65	/* send arp request */
66	memset(&arp, 0, sizeof(arp));
67	memset(arp.h_dest, 0xff, 6); /* MAC DA */
68	memcpy(arp.h_source, from_mac, 6); /* MAC SA */
69	arp.h_proto = htons(ETH_P_ARP); /* protocol type (Ethernet) */
70	arp.htype = htons(ARPHRD_ETHER); /* hardware type */
71	arp.ptype = htons(ETH_P_IP); /* protocol type (ARP message) */
72	arp.hlen = 6; /* hardware address length */
73	arp.plen = 4; /* protocol address length */
74	arp.operation = htons(ARPOP_REQUEST); /* ARP op code */
75	memcpy(arp.sHaddr, from_mac, 6); /* source hardware address */
76	memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
77	/* tHaddr is zero-filled */ /* target hardware address */
78	memcpy(arp.tInaddr, &test_nip, sizeof(test_nip));/* target IP address */
79
80	memset(&addr, 0, sizeof(addr));
81	safe_strncpy(addr.sa_data, interface, sizeof(addr.sa_data));
82	if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0) {
83	// TODO: error message? caller didn't expect us to fail,
84	// just returning 1 "no reply received" misleads it.
85	goto ret;
86	}
87
88	/* wait for arp reply, and check it */
89	timeout_ms = (int)timeo;
90	do {
91	typedef uint32_t aliased_uint32_t FIX_ALIASING;
92	int r;
93	unsigned prevTime = monotonic_ms();
94
95	pfd[0].events = POLLIN;
96	r = safe_poll(pfd, 1, timeout_ms);
97	if (r < 0)
98	break;
99	if (r) {
100	r = safe_read(s, &arp, sizeof(arp));
101	if (r < 0)
102	break;
103
104	//log3("sHaddr %02x:%02x:%02x:%02x:%02x:%02x",
105	// arp.sHaddr[0], arp.sHaddr[1], arp.sHaddr[2],
106	// arp.sHaddr[3], arp.sHaddr[4], arp.sHaddr[5]);
107
108	if (r >= ARP_MSG_SIZE
109	&& arp.operation == htons(ARPOP_REPLY)
110	/* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */
111	/* && memcmp(arp.tHaddr, from_mac, 6) == 0 */
112	&& *(aliased_uint32_t*)arp.sInaddr == test_nip
113	) {
114	/* if ARP source MAC matches safe_mac
115	* (which is client's MAC), then it's not a conflict
116	* (client simply already has this IP and replies to ARPs!)
117	*/
118	if (!safe_mac || memcmp(safe_mac, arp.sHaddr, 6) != 0)
119	rv = 0;
120	//else log2("sHaddr == safe_mac");
121	break;
122	}
123	}
124	timeout_ms -= (unsigned)monotonic_ms() - prevTime + 1;
125
126	/* We used to check "timeout_ms > 0", but
127	* this is more under/overflow-resistant
128	* (people did see overflows here when system time jumps):
129	*/
130	} while ((unsigned)timeout_ms <= timeo);
131
132	ret:
133	close(s);
134	log1("%srp reply received for this address", rv ? "no a" : "A");
135	return rv;
136	}
137