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   char buffer[1024];
 106   int n;
 107
 108   n = snprintf(buffer, sizeof(buffer), "%s/%s",
 109                tftp_prefix, spt->filename);
 110   if (n >= sizeof(buffer))
 111     return -1;
 112
 113   fd = open(buffer, O_RDONLY | O_BINARY);
 114
 115   if (fd < 0) {
 116     return -1;
 117   }
 118
 119   if (len) {
 120     lseek(fd, block_nr * 512, SEEK_SET);
 121
 122     bytes_read = read(fd, buf, len);
 123   }
 124
 125   close(fd);
 126
 127   return bytes_read;
 128 }
 129
 130 static int tftp_send_oack(struct tftp_session *spt,
 131                           const char *key, uint32_t value,
 132                           struct tftp_t *recv_tp)
 133 {
 134     struct sockaddr_in saddr, daddr;
 135     struct mbuf *m;
 136     struct tftp_t *tp;
 137     int n = 0;
 138
 139     m = m_get();
 140
 141     if (!m)
 142         return -1;
 143
 144     memset(m->m_data, 0, m->m_size);
 145
 146     m->m_data += if_maxlinkhdr;
 147     tp = (void *)m->m_data;
 148     m->m_data += sizeof(struct udpiphdr);
 149
 150     tp->tp_op = htons(TFTP_OACK);
 151     n += sprintf(tp->x.tp_buf + n, "%s", key) + 1;
 152     n += sprintf(tp->x.tp_buf + n, "%u", value) + 1;
 153
 154     saddr.sin_addr = recv_tp->ip.ip_dst;
 155     saddr.sin_port = recv_tp->udp.uh_dport;
 156
 157     daddr.sin_addr = spt->client_ip;
 158     daddr.sin_port = spt->client_port;
 159
 160     m->m_len = sizeof(struct tftp_t) - 514 + n -
 161         sizeof(struct ip) - sizeof(struct udphdr);
 162     udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
 163
 164     return 0;
 165 }
 166
 167
 168
 169 static int tftp_send_error(struct tftp_session *spt,
 170                            u_int16_t errorcode, const char *msg,
 171                            struct tftp_t *recv_tp)
 172 {
 173   struct sockaddr_in saddr, daddr;
 174   struct mbuf *m;
 175   struct tftp_t *tp;
 176   int nobytes;
 177
 178   m = m_get();
 179
 180   if (!m) {
 181     return -1;
 182   }
 183
 184   memset(m->m_data, 0, m->m_size);
 185
 186   m->m_data += if_maxlinkhdr;
 187   tp = (void *)m->m_data;
 188   m->m_data += sizeof(struct udpiphdr);
 189
 190   tp->tp_op = htons(TFTP_ERROR);
 191   tp->x.tp_error.tp_error_code = htons(errorcode);
 192   strcpy(tp->x.tp_error.tp_msg, msg);
 193
 194   saddr.sin_addr = recv_tp->ip.ip_dst;
 195   saddr.sin_port = recv_tp->udp.uh_dport;
 196
 197   daddr.sin_addr = spt->client_ip;
 198   daddr.sin_port = spt->client_port;
 199
 200   nobytes = 2;
 201
 202   m->m_len = sizeof(struct tftp_t) - 514 + 3 + strlen(msg) -
 203         sizeof(struct ip) - sizeof(struct udphdr);
 204
 205   udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
 206
 207   tftp_session_terminate(spt);
 208
 209   return 0;
 210 }
 211
 212 static int tftp_send_data(struct tftp_session *spt,
 213                           u_int16_t block_nr,
 214                           struct tftp_t *recv_tp)
 215 {
 216   struct sockaddr_in saddr, daddr;
 217   struct mbuf *m;
 218   struct tftp_t *tp;
 219   int nobytes;
 220
 221   if (block_nr < 1) {
 222     return -1;
 223   }
 224
 225   m = m_get();
 226
 227   if (!m) {
 228     return -1;
 229   }
 230
 231   memset(m->m_data, 0, m->m_size);
 232
 233   m->m_data += if_maxlinkhdr;
 234   tp = (void *)m->m_data;
 235   m->m_data += sizeof(struct udpiphdr);
 236
 237   tp->tp_op = htons(TFTP_DATA);
 238   tp->x.tp_data.tp_block_nr = htons(block_nr);
 239
 240   saddr.sin_addr = recv_tp->ip.ip_dst;
 241   saddr.sin_port = recv_tp->udp.uh_dport;
 242
 243   daddr.sin_addr = spt->client_ip;
 244   daddr.sin_port = spt->client_port;
 245
 246   nobytes = tftp_read_data(spt, block_nr - 1, tp->x.tp_data.tp_buf, 512);
 247
 248   if (nobytes < 0) {
 249     m_free(m);
 250
 251     /* send "file not found" error back */
 252
 253     tftp_send_error(spt, 1, "File not found", tp);
 254
 255     return -1;
 256   }
 257
 258   m->m_len = sizeof(struct tftp_t) - (512 - nobytes) -
 259         sizeof(struct ip) - sizeof(struct udphdr);
 260
 261   udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
 262
 263   if (nobytes == 512) {
 264     tftp_session_update(spt);
 265   }
 266   else {
 267     tftp_session_terminate(spt);
 268   }
 269
 270   return 0;
 271 }
 272
 273 static void tftp_handle_rrq(struct tftp_t *tp, int pktlen)
 274 {
 275   struct tftp_session *spt;
 276   int s, k, n;
 277   u_int8_t *src, *dst;
 278
 279   s = tftp_session_allocate(tp);
 280
 281   if (s < 0) {
 282     return;
 283   }
 284
 285   spt = &tftp_sessions[s];
 286
 287   src = tp->x.tp_buf;
 288   dst = spt->filename;
 289   n = pktlen - ((uint8_t *)&tp->x.tp_buf[0] - (uint8_t *)tp);
 290
 291   /* get name */
 292
 293   for (k = 0; k < n; k++) {
 294     if (k < TFTP_FILENAME_MAX) {
 295       dst[k] = src[k];
 296     }
 297     else {
 298       return;
 299     }
 300
 301     if (src[k] == '\0') {
 302       break;
 303     }
 304   }
 305
 306   if (k >= n) {
 307     return;
 308   }
 309
 310   k++;
 311
 312   /* check mode */
 313   if ((n - k) < 6) {
 314     return;
 315   }
 316
 317   if (memcmp(&src[k], "octet\0", 6) != 0) {
 318       tftp_send_error(spt, 4, "Unsupported transfer mode", tp);
 319       return;
 320   }
 321
 322   k += 6; /* skipping octet */
 323
 324   /* do sanity checks on the filename */
 325
 326   if ((spt->filename[0] != '/')
 327       || (spt->filename[strlen(spt->filename) - 1] == '/')
 328       ||  strstr(spt->filename, "/../")) {
 329       tftp_send_error(spt, 2, "Access violation", tp);
 330       return;
 331   }
 332
 333   /* only allow exported prefixes */
 334
 335   if (!tftp_prefix) {
 336       tftp_send_error(spt, 2, "Access violation", tp);
 337       return;
 338   }
 339
 340   /* check if the file exists */
 341
 342   if (tftp_read_data(spt, 0, spt->filename, 0) < 0) {
 343       tftp_send_error(spt, 1, "File not found", tp);
 344       return;
 345   }
 346
 347   if (src[n - 1] != 0) {
 348       tftp_send_error(spt, 2, "Access violation", tp);
 349       return;
 350   }
 351
 352   while (k < n) {
 353       const char *key, *value;
 354
 355       key = src + k;
 356       k += strlen(key) + 1;
 357
 358       if (k >= n) {
 359           tftp_send_error(spt, 2, "Access violation", tp);
 360           return;
 361       }
 362
 363       value = src + k;
 364       k += strlen(value) + 1;
 365
 366       if (strcmp(key, "tsize") == 0) {
 367           int tsize = atoi(value);
 368           struct stat stat_p;
 369
 370           if (tsize == 0 && tftp_prefix) {
 371               char buffer[1024];
 372               int len;
 373
 374               len = snprintf(buffer, sizeof(buffer), "%s/%s",
 375                              tftp_prefix, spt->filename);
 376
 377               if (stat(buffer, &stat_p) == 0)
 378                   tsize = stat_p.st_size;
 379               else {
 380                   tftp_send_error(spt, 1, "File not found", tp);
 381                   return;
 382               }
 383           }
 384
 385           tftp_send_oack(spt, "tsize", tsize, tp);
 386       }
 387   }
 388
 389   tftp_send_data(spt, 1, tp);
 390 }
 391
 392 static void tftp_handle_ack(struct tftp_t *tp, int pktlen)
 393 {
 394   int s;
 395
 396   s = tftp_session_find(tp);
 397
 398   if (s < 0) {
 399     return;
 400   }
 401
 402   if (tftp_send_data(&tftp_sessions[s],
 403                      ntohs(tp->x.tp_data.tp_block_nr) + 1,
 404                      tp) < 0) {
 405     return;
 406   }
 407 }
 408
 409 void tftp_input(struct mbuf *m)
 410 {
 411   struct tftp_t *tp = (struct tftp_t *)m->m_data;
 412
 413   switch(ntohs(tp->tp_op)) {
 414   case TFTP_RRQ:
 415     tftp_handle_rrq(tp, m->m_len);
 416     break;
 417
 418   case TFTP_ACK:
 419     tftp_handle_ack(tp, m->m_len);
 420     break;
 421   }
 422 }