slirp/tftp.c

   1 /*
   2  * tftp.c - a simple, read-only tftp server for qemu
   3  *
   4  * Copyright (c) 2004 Magnus Damm <damm@opensource.se>
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include <slirp.h>
  26
  27 struct tftp_session {
  28     int in_use;
  29     unsigned char filename[TFTP_FILENAME_MAX];
  30
  31     struct in_addr client_ip;
  32     u_int16_t client_port;
  33
  34     int timestamp;
  35 };
  36
  37 struct tftp_session tftp_sessions[TFTP_SESSIONS_MAX];
  38
  39 const char *tftp_prefix;
  40
  41 static void tftp_session_update(struct tftp_session *spt)
  42 {
  43     spt->timestamp = curtime;
  44     spt->in_use = 1;
  45 }
  46
  47 static void tftp_session_terminate(struct tftp_session *spt)
  48 {
  49   spt->in_use = 0;
  50 }
  51
  52 static int tftp_session_allocate(struct tftp_t *tp)
  53 {
  54   struct tftp_session *spt;
  55   int k;
  56
  57   for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
  58     spt = &tftp_sessions[k];
  59
  60     if (!spt->in_use)
  61         goto found;
  62
  63     /* sessions time out after 5 inactive seconds */
  64     if ((int)(curtime - spt->timestamp) > 5000)
  65         goto found;
  66   }
  67
  68   return -1;
  69
  70  found:
  71   memset(spt, 0, sizeof(*spt));
  72   memcpy(&spt->client_ip, &tp->ip.ip_src, sizeof(spt->client_ip));
  73   spt->client_port = tp->udp.uh_sport;
  74
  75   tftp_session_update(spt);
  76
  77   return k;
  78 }
  79
  80 static int tftp_session_find(struct tftp_t *tp)
  81 {
  82   struct tftp_session *spt;
  83   int k;
  84
  85   for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
  86     spt = &tftp_sessions[k];
  87
  88     if (spt->in_use) {
  89       if (!memcmp(&spt->client_ip, &tp->ip.ip_src, sizeof(spt->client_ip))) {
  90         if (spt->client_port == tp->udp.uh_sport) {
  91           return k;
  92         }
  93       }
  94     }
  95   }
  96
  97   return -1;
  98 }
  99
 100 static int tftp_read_data(struct tftp_session *spt, u_int16_t block_nr,
 101                           u_int8_t *buf, int len)
 102 {
 103   int fd;
 104   int bytes_read = 0;
 105
 106   fd = open(spt->filename, O_RDONLY | O_BINARY);
 107
 108   if (fd < 0) {
 109     return -1;
 110   }
 111
 112   if (len) {
 113     lseek(fd, block_nr * 512, SEEK_SET);
 114
 115     bytes_read = read(fd, buf, len);
 116   }
 117
 118   close(fd);
 119
 120   return bytes_read;
 121 }
 122
 123 static int tftp_send_oack(struct tftp_session *spt,
 124                           const char *key, uint32_t value,
 125                           struct tftp_t *recv_tp)
 126 {
 127     struct sockaddr_in saddr, daddr;
 128     struct mbuf *m;
 129     struct tftp_t *tp;
 130     int n = 0;
 131
 132     m = m_get();
 133
 134     if (!m)
 135         return -1;
 136
 137     memset(m->m_data, 0, m->m_size);
 138
 139     m->m_data += if_maxlinkhdr;
 140     tp = (void *)m->m_data;
 141     m->m_data += sizeof(struct udpiphdr);
 142
 143     tp->tp_op = htons(TFTP_OACK);
 144     n += sprintf(tp->x.tp_buf + n, "%s", key) + 1;
 145     n += sprintf(tp->x.tp_buf + n, "%u", value) + 1;
 146
 147     saddr.sin_addr = recv_tp->ip.ip_dst;
 148     saddr.sin_port = recv_tp->udp.uh_dport;
 149
 150     daddr.sin_addr = spt->client_ip;
 151     daddr.sin_port = spt->client_port;
 152
 153     m->m_len = sizeof(struct tftp_t) - 514 + n -
 154         sizeof(struct ip) - sizeof(struct udphdr);
 155     udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
 156
 157     return 0;
 158 }
 159
 160
 161
 162 static int tftp_send_error(struct tftp_session *spt,
 163                            u_int16_t errorcode, const char *msg,
 164                            struct tftp_t *recv_tp)
 165 {
 166   struct sockaddr_in saddr, daddr;
 167   struct mbuf *m;
 168   struct tftp_t *tp;
 169   int nobytes;
 170
 171   m = m_get();
 172
 173   if (!m) {
 174     return -1;
 175   }
 176
 177   memset(m->m_data, 0, m->m_size);
 178
 179   m->m_data += if_maxlinkhdr;
 180   tp = (void *)m->m_data;
 181   m->m_data += sizeof(struct udpiphdr);
 182
 183   tp->tp_op = htons(TFTP_ERROR);
 184   tp->x.tp_error.tp_error_code = htons(errorcode);
 185   strcpy(tp->x.tp_error.tp_msg, msg);
 186
 187   saddr.sin_addr = recv_tp->ip.ip_dst;
 188   saddr.sin_port = recv_tp->udp.uh_dport;
 189
 190   daddr.sin_addr = spt->client_ip;
 191   daddr.sin_port = spt->client_port;
 192
 193   nobytes = 2;
 194
 195   m->m_len = sizeof(struct tftp_t) - 514 + 3 + strlen(msg) -
 196         sizeof(struct ip) - sizeof(struct udphdr);
 197
 198   udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
 199
 200   tftp_session_terminate(spt);
 201
 202   return 0;
 203 }
 204
 205 static int tftp_send_data(struct tftp_session *spt,
 206                           u_int16_t block_nr,
 207                           struct tftp_t *recv_tp)
 208 {
 209   struct sockaddr_in saddr, daddr;
 210   struct mbuf *m;
 211   struct tftp_t *tp;
 212   int nobytes;
 213
 214   if (block_nr < 1) {
 215     return -1;
 216   }
 217
 218   m = m_get();
 219
 220   if (!m) {
 221     return -1;
 222   }
 223
 224   memset(m->m_data, 0, m->m_size);
 225
 226   m->m_data += if_maxlinkhdr;
 227   tp = (void *)m->m_data;
 228   m->m_data += sizeof(struct udpiphdr);
 229
 230   tp->tp_op = htons(TFTP_DATA);
 231   tp->x.tp_data.tp_block_nr = htons(block_nr);
 232
 233   saddr.sin_addr = recv_tp->ip.ip_dst;
 234   saddr.sin_port = recv_tp->udp.uh_dport;
 235
 236   daddr.sin_addr = spt->client_ip;
 237   daddr.sin_port = spt->client_port;
 238
 239   nobytes = tftp_read_data(spt, block_nr - 1, tp->x.tp_data.tp_buf, 512);
 240
 241   if (nobytes < 0) {
 242     m_free(m);
 243
 244     /* send "file not found" error back */
 245
 246     tftp_send_error(spt, 1, "File not found", tp);
 247
 248     return -1;
 249   }
 250
 251   m->m_len = sizeof(struct tftp_t) - (512 - nobytes) -
 252         sizeof(struct ip) - sizeof(struct udphdr);
 253
 254   udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
 255
 256   if (nobytes == 512) {
 257     tftp_session_update(spt);
 258   }
 259   else {
 260     tftp_session_terminate(spt);
 261   }
 262
 263   return 0;
 264 }
 265
 266 static void tftp_handle_rrq(struct tftp_t *tp, int pktlen)
 267 {
 268   struct tftp_session *spt;
 269   int s, k, n;
 270   u_int8_t *src, *dst;
 271
 272   s = tftp_session_allocate(tp);
 273
 274   if (s < 0) {
 275     return;
 276   }
 277
 278   spt = &tftp_sessions[s];
 279
 280   src = tp->x.tp_buf;
 281   dst = spt->filename;
 282   n = pktlen - ((uint8_t *)&tp->x.tp_buf[0] - (uint8_t *)tp);
 283
 284   /* get name */
 285
 286   for (k = 0; k < n; k++) {
 287     if (k < TFTP_FILENAME_MAX) {
 288       dst[k] = src[k];
 289     }
 290     else {
 291       return;
 292     }
 293
 294     if (src[k] == '\0') {
 295       break;
 296     }
 297   }
 298
 299   if (k >= n) {
 300     return;
 301   }
 302
 303   k++;
 304
 305   /* check mode */
 306   if ((n - k) < 6) {
 307     return;
 308   }
 309
 310   if (memcmp(&src[k], "octet\0", 6) != 0) {
 311       tftp_send_error(spt, 4, "Unsupported transfer mode", tp);
 312       return;
 313   }
 314
 315   k += 6; /* skipping octet */
 316
 317   /* do sanity checks on the filename */
 318
 319   if ((spt->filename[0] != '/')
 320       || (spt->filename[strlen(spt->filename) - 1] == '/')
 321       ||  strstr(spt->filename, "/../")) {
 322       tftp_send_error(spt, 2, "Access violation", tp);
 323       return;
 324   }
 325
 326   /* only allow exported prefixes */
 327
 328   if (!tftp_prefix
 329       || (strncmp(spt->filename, tftp_prefix, strlen(tftp_prefix)) != 0)) {
 330       tftp_send_error(spt, 2, "Access violation", tp);
 331       return;
 332   }
 333
 334   /* check if the file exists */
 335
 336   if (tftp_read_data(spt, 0, spt->filename, 0) < 0) {
 337       tftp_send_error(spt, 1, "File not found", tp);
 338       return;
 339   }
 340
 341   if (src[n - 1] != 0) {
 342       tftp_send_error(spt, 2, "Access violation", tp);
 343       return;
 344   }
 345
 346   while (k < n) {
 347       const char *key, *value;
 348
 349       key = src + k;
 350       k += strlen(key) + 1;
 351
 352       if (k >= n) {
 353           tftp_send_error(spt, 2, "Access violation", tp);
 354           return;
 355       }
 356
 357       value = src + k;
 358       k += strlen(value) + 1;
 359
 360       if (strcmp(key, "tsize") == 0) {
 361           int tsize = atoi(value);
 362           struct stat stat_p;
 363
 364           if (tsize == 0 && tftp_prefix) {
 365               char buffer[1024];
 366               int len;
 367
 368               len = snprintf(buffer, sizeof(buffer), "%s/%s",
 369                              tftp_prefix, spt->filename);
 370
 371               if (stat(buffer, &stat_p) == 0)
 372                   tsize = stat_p.st_size;
 373               else {
 374                   tftp_send_error(spt, 1, "File not found", tp);
 375                   return;
 376               }
 377           }
 378
 379           tftp_send_oack(spt, "tsize", tsize, tp);
 380       }
 381   }
 382
 383   tftp_send_data(spt, 1, tp);
 384 }
 385
 386 static void tftp_handle_ack(struct tftp_t *tp, int pktlen)
 387 {
 388   int s;
 389
 390   s = tftp_session_find(tp);
 391
 392   if (s < 0) {
 393     return;
 394   }
 395
 396   if (tftp_send_data(&tftp_sessions[s],
 397                      ntohs(tp->x.tp_data.tp_block_nr) + 1,
 398                      tp) < 0) {
 399     return;
 400   }
 401 }
 402
 403 void tftp_input(struct mbuf *m)
 404 {
 405   struct tftp_t *tp = (struct tftp_t *)m->m_data;
 406
 407   switch(ntohs(tp->tp_op)) {
 408   case TFTP_RRQ:
 409     tftp_handle_rrq(tp, m->m_len);
 410     break;
 411
 412   case TFTP_ACK:
 413     tftp_handle_ack(tp, m->m_len);
 414     break;
 415   }
 416 }