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        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