LXR busybox/networking/udhcp/arpping.c

   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
  13struct 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
  32enum {
  33        ARP_MSG_SIZE = 0x2a
  34};
  35
  36/* Returns 1 if no reply received */
  37int 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(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