net/dns.c

   1 /*
   2  * DNS support driver
   3  *
   4  * Copyright (c) 2008 Pieter Voorthuijsen <pieter.voorthuijsen@prodrive.nl>
   5  * Copyright (c) 2009 Robin Getz <rgetz@blackfin.uclinux.org>
   6  *
   7  * This is a simple DNS implementation for U-Boot. It will use the first IP
   8  * in the DNS response as net_server_ip. This can then be used for any other
   9  * network related activities.
  10  *
  11  * The packet handling is partly based on TADNS, original copyrights
  12  * follow below.
  13  *
  14  */
  15
  16 /*
  17  * Copyright (c) 2004-2005 Sergey Lyubka <valenok@gmail.com>
  18  *
  19  * "THE BEER-WARE LICENSE" (Revision 42):
  20  * Sergey Lyubka wrote this file.  As long as you retain this notice you
  21  * can do whatever you want with this stuff. If we meet some day, and you think
  22  * this stuff is worth it, you can buy me a beer in return.
  23  */
  24
  25 #include <common.h>
  26 #include <command.h>
  27 #include <env.h>
  28 #include <log.h>
  29 #include <net.h>
  30 #include <asm/unaligned.h>
  31
  32 #include "dns.h"
  33
  34 char *net_dns_resolve;  /* The host to resolve  */
  35 char *net_dns_env_var;  /* The envvar to store the answer in */
  36
  37 static int dns_our_port;
  38
  39 /*
  40  * make port a little random (1024-17407)
  41  * This keeps the math somewhat trivial to compute, and seems to work with
  42  * all supported protocols/clients/servers
  43  */
  44 static unsigned int random_port(void)
  45 {
  46         return 1024 + (get_timer(0) % 0x4000);
  47 }
  48
  49 static void dns_send(void)
  50 {
  51         struct header *header;
  52         int n, name_len;
  53         uchar *p, *pkt;
  54         const char *s;
  55         const char *name;
  56         enum dns_query_type qtype = DNS_A_RECORD;
  57
  58         name = net_dns_resolve;
  59         pkt = (uchar *)(net_tx_packet + net_eth_hdr_size() + IP_UDP_HDR_SIZE);
  60         p = pkt;
  61
  62         /* Prepare DNS packet header */
  63         header           = (struct header *)pkt;
  64         header->tid      = 1;
  65         header->flags    = htons(0x100);        /* standard query */
  66         header->nqueries = htons(1);            /* Just one query */
  67         header->nanswers = 0;
  68         header->nauth    = 0;
  69         header->nother   = 0;
  70
  71         /* Encode DNS name */
  72         name_len = strlen(name);
  73         p = (uchar *)&header->data;     /* For encoding host name into packet */
  74
  75         do {
  76                 s = strchr(name, '.');
  77                 if (!s)
  78                         s = name + name_len;
  79
  80                 n = s - name;                   /* Chunk length */
  81                 *p++ = n;                       /* Copy length  */
  82                 memcpy(p, name, n);             /* Copy chunk   */
  83                 p += n;
  84
  85                 if (*s == '.')
  86                         n++;
  87
  88                 name += n;
  89                 name_len -= n;
  90         } while (*s != '\0');
  91
  92         *p++ = 0;                       /* Mark end of host name */
  93         *p++ = 0;                       /* Some servers require double null */
  94         *p++ = (unsigned char) qtype;   /* Query Type */
  95
  96         *p++ = 0;
  97         *p++ = 1;                               /* Class: inet, 0x0001 */
  98
  99         n = p - pkt;                            /* Total packet length */
 100         debug("Packet size %d\n", n);
 101
 102         dns_our_port = random_port();
 103
 104         net_send_udp_packet(net_server_ethaddr, net_dns_server,
 105                             DNS_SERVICE_PORT, dns_our_port, n);
 106         debug("DNS packet sent\n");
 107 }
 108
 109 static void dns_timeout_handler(void)
 110 {
 111         puts("Timeout\n");
 112         net_set_state(NETLOOP_FAIL);
 113 }
 114
 115 static void dns_handler(uchar *pkt, unsigned dest, struct in_addr sip,
 116                         unsigned src, unsigned len)
 117 {
 118         struct header *header;
 119         const unsigned char *p, *e, *s;
 120         u16 type, i;
 121         int found, stop, dlen;
 122         char ip_str[22];
 123         struct in_addr ip_addr;
 124
 125
 126         debug("%s\n", __func__);
 127         if (dest != dns_our_port)
 128                 return;
 129
 130         for (i = 0; i < len; i += 4)
 131                 debug("0x%p - 0x%.2x  0x%.2x  0x%.2x  0x%.2x\n",
 132                       pkt+i, pkt[i], pkt[i+1], pkt[i+2], pkt[i+3]);
 133
 134         /* We sent one query. We want to have a single answer: */
 135         header = (struct header *)pkt;
 136         if (ntohs(header->nqueries) != 1)
 137                 return;
 138
 139         /* Received 0 answers */
 140         if (header->nanswers == 0) {
 141                 puts("DNS: host not found\n");
 142                 net_set_state(NETLOOP_SUCCESS);
 143                 return;
 144         }
 145
 146         /* Skip host name */
 147         s = &header->data[0];
 148         e = pkt + len;
 149         for (p = s; p < e && *p != '\0'; p++)
 150                 continue;
 151
 152         /* We sent query class 1, query type 1 */
 153         if (&p[5] > e || get_unaligned_be16(p+1) != DNS_A_RECORD) {
 154                 puts("DNS: response was not an A record\n");
 155                 net_set_state(NETLOOP_SUCCESS);
 156                 return;
 157         }
 158
 159         /* Go to the first answer section */
 160         p += 5;
 161
 162         /* Loop through the answers, we want A type answer */
 163         for (found = stop = 0; !stop && &p[12] < e; ) {
 164                 /* Skip possible name in CNAME answer */
 165                 if (*p != 0xc0) {
 166                         while (*p && &p[12] < e)
 167                                 p++;
 168                         p--;
 169                 }
 170                 debug("Name (Offset in header): %d\n", p[1]);
 171
 172                 type = get_unaligned_be16(p+2);
 173                 debug("type = %d\n", type);
 174                 if (type == DNS_CNAME_RECORD) {
 175                         /* CNAME answer. shift to the next section */
 176                         debug("Found canonical name\n");
 177                         dlen = get_unaligned_be16(p+10);
 178                         debug("dlen = %d\n", dlen);
 179                         p += 12 + dlen;
 180                 } else if (type == DNS_A_RECORD) {
 181                         debug("Found A-record\n");
 182                         found = 1;
 183                         stop = 1;
 184                 } else {
 185                         debug("Unknown type\n");
 186                         stop = 1;
 187                 }
 188         }
 189
 190         if (found && &p[12] < e) {
 191                 dlen = get_unaligned_be16(p+10);
 192                 p += 12;
 193                 memcpy(&ip_addr, p, 4);
 194
 195                 if (p + dlen <= e) {
 196                         ip_to_string(ip_addr, ip_str);
 197                         printf("%s\n", ip_str);
 198                         if (net_dns_env_var)
 199                                 env_set(net_dns_env_var, ip_str);
 200                 } else {
 201                         puts("server responded with invalid IP number\n");
 202                 }
 203         }
 204
 205         net_set_state(NETLOOP_SUCCESS);
 206 }
 207
 208 void dns_start(void)
 209 {
 210         debug("%s\n", __func__);
 211
 212         net_set_timeout_handler(DNS_TIMEOUT, dns_timeout_handler);
 213         net_set_udp_handler(dns_handler);
 214
 215         /* Clear a previous MAC address, the server IP might have changed. */
 216         memset(net_server_ethaddr, 0, sizeof(net_server_ethaddr));
 217
 218         dns_send();
 219 }