slirp/src/tftp.c

   1 /* SPDX-License-Identifier: MIT */
   2 /*
   3  * tftp.c - a simple, read-only tftp server for qemu
   4  *
   5  * Copyright (c) 2004 Magnus Damm <damm@opensource.se>
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a copy
   8  * of this software and associated documentation files (the "Software"), to deal
   9  * in the Software without restriction, including without limitation the rights
  10  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  11  * copies of the Software, and to permit persons to whom the Software is
  12  * furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included in
  15  * all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  18  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  20  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  21  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  22  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  23  * THE SOFTWARE.
  24  */
  25
  26 #include "slirp.h"
  27
  28 #include <sys/types.h>
  29 #include <sys/stat.h>
  30 #include <fcntl.h>
  31
  32 static inline int tftp_session_in_use(struct tftp_session *spt)
  33 {
  34     return (spt->slirp != NULL);
  35 }
  36
  37 static inline void tftp_session_update(struct tftp_session *spt)
  38 {
  39     spt->timestamp = curtime;
  40 }
  41
  42 static void tftp_session_terminate(struct tftp_session *spt)
  43 {
  44     if (spt->fd >= 0) {
  45         close(spt->fd);
  46         spt->fd = -1;
  47     }
  48     g_free(spt->filename);
  49     spt->slirp = NULL;
  50 }
  51
  52 static int tftp_session_allocate(Slirp *slirp, struct sockaddr_storage *srcsas,
  53                                  struct tftp_t *tp)
  54 {
  55   struct tftp_session *spt;
  56   int k;
  57
  58   for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
  59     spt = &slirp->tftp_sessions[k];
  60
  61     if (!tftp_session_in_use(spt))
  62         goto found;
  63
  64     /* sessions time out after 5 inactive seconds */
  65     if ((int)(curtime - spt->timestamp) > 5000) {
  66         tftp_session_terminate(spt);
  67         goto found;
  68     }
  69   }
  70
  71   return -1;
  72
  73  found:
  74   memset(spt, 0, sizeof(*spt));
  75   memcpy(&spt->client_addr, srcsas, sockaddr_size(srcsas));
  76   spt->fd = -1;
  77   spt->block_size = 512;
  78   spt->client_port = tp->udp.uh_sport;
  79   spt->slirp = slirp;
  80
  81   tftp_session_update(spt);
  82
  83   return k;
  84 }
  85
  86 static int tftp_session_find(Slirp *slirp, struct sockaddr_storage *srcsas,
  87                              struct tftp_t *tp)
  88 {
  89   struct tftp_session *spt;
  90   int k;
  91
  92   for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
  93     spt = &slirp->tftp_sessions[k];
  94
  95     if (tftp_session_in_use(spt)) {
  96       if (sockaddr_equal(&spt->client_addr, srcsas)) {
  97         if (spt->client_port == tp->udp.uh_sport) {
  98           return k;
  99         }
 100       }
 101     }
 102   }
 103
 104   return -1;
 105 }
 106
 107 static int tftp_read_data(struct tftp_session *spt, uint32_t block_nr,
 108                           uint8_t *buf, int len)
 109 {
 110     int bytes_read = 0;
 111
 112     if (spt->fd < 0) {
 113         spt->fd = open(spt->filename, O_RDONLY | O_BINARY);
 114     }
 115
 116     if (spt->fd < 0) {
 117         return -1;
 118     }
 119
 120     if (len) {
 121         lseek(spt->fd, block_nr * spt->block_size, SEEK_SET);
 122
 123         bytes_read = read(spt->fd, buf, len);
 124     }
 125
 126     return bytes_read;
 127 }
 128
 129 static struct tftp_t *tftp_prep_mbuf_data(struct tftp_session *spt,
 130                                           struct mbuf *m)
 131 {
 132     struct tftp_t *tp;
 133
 134     memset(m->m_data, 0, m->m_size);
 135
 136     m->m_data += IF_MAXLINKHDR;
 137     if (spt->client_addr.ss_family == AF_INET6) {
 138         m->m_data += sizeof(struct ip6);
 139     } else {
 140         m->m_data += sizeof(struct ip);
 141     }
 142     tp = (void *)m->m_data;
 143     m->m_data += sizeof(struct udphdr);
 144
 145     return tp;
 146 }
 147
 148 static void tftp_udp_output(struct tftp_session *spt, struct mbuf *m,
 149                             struct tftp_t *recv_tp)
 150 {
 151     if (spt->client_addr.ss_family == AF_INET6) {
 152         struct sockaddr_in6 sa6, da6;
 153
 154         sa6.sin6_addr = spt->slirp->vhost_addr6;
 155         sa6.sin6_port = recv_tp->udp.uh_dport;
 156         da6.sin6_addr = ((struct sockaddr_in6 *)&spt->client_addr)->sin6_addr;
 157         da6.sin6_port = spt->client_port;
 158
 159         udp6_output(NULL, m, &sa6, &da6);
 160     } else {
 161         struct sockaddr_in sa4, da4;
 162
 163         sa4.sin_addr = spt->slirp->vhost_addr;
 164         sa4.sin_port = recv_tp->udp.uh_dport;
 165         da4.sin_addr = ((struct sockaddr_in *)&spt->client_addr)->sin_addr;
 166         da4.sin_port = spt->client_port;
 167
 168         udp_output(NULL, m, &sa4, &da4, IPTOS_LOWDELAY);
 169     }
 170 }
 171
 172 static int tftp_send_oack(struct tftp_session *spt,
 173                           const char *keys[], uint32_t values[], int nb,
 174                           struct tftp_t *recv_tp)
 175 {
 176     struct mbuf *m;
 177     struct tftp_t *tp;
 178     int i, n = 0;
 179
 180     m = m_get(spt->slirp);
 181
 182     if (!m)
 183         return -1;
 184
 185     tp = tftp_prep_mbuf_data(spt, m);
 186
 187     tp->tp_op = htons(TFTP_OACK);
 188     for (i = 0; i < nb; i++) {
 189         n += snprintf(tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%s",
 190                       keys[i]) + 1;
 191         n += snprintf(tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%u",
 192                       values[i]) + 1;
 193     }
 194
 195     m->m_len = sizeof(struct tftp_t) - (TFTP_BLOCKSIZE_MAX + 2) + n
 196                - sizeof(struct udphdr);
 197     tftp_udp_output(spt, m, recv_tp);
 198
 199     return 0;
 200 }
 201
 202 static void tftp_send_error(struct tftp_session *spt,
 203                             uint16_t errorcode, const char *msg,
 204                             struct tftp_t *recv_tp)
 205 {
 206   struct mbuf *m;
 207   struct tftp_t *tp;
 208
 209   DEBUG_TFTP("tftp error msg: %s", msg);
 210
 211   m = m_get(spt->slirp);
 212
 213   if (!m) {
 214     goto out;
 215   }
 216
 217   tp = tftp_prep_mbuf_data(spt, m);
 218
 219   tp->tp_op = htons(TFTP_ERROR);
 220   tp->x.tp_error.tp_error_code = htons(errorcode);
 221   slirp_pstrcpy((char *)tp->x.tp_error.tp_msg, sizeof(tp->x.tp_error.tp_msg), msg);
 222
 223   m->m_len = sizeof(struct tftp_t) - (TFTP_BLOCKSIZE_MAX + 2) + 3 + strlen(msg)
 224              - sizeof(struct udphdr);
 225   tftp_udp_output(spt, m, recv_tp);
 226
 227 out:
 228   tftp_session_terminate(spt);
 229 }
 230
 231 static void tftp_send_next_block(struct tftp_session *spt,
 232                                  struct tftp_t *recv_tp)
 233 {
 234   struct mbuf *m;
 235   struct tftp_t *tp;
 236   int nobytes;
 237
 238   m = m_get(spt->slirp);
 239
 240   if (!m) {
 241     return;
 242   }
 243
 244   tp = tftp_prep_mbuf_data(spt, m);
 245
 246   tp->tp_op = htons(TFTP_DATA);
 247   tp->x.tp_data.tp_block_nr = htons((spt->block_nr + 1) & 0xffff);
 248
 249   nobytes = tftp_read_data(spt, spt->block_nr, tp->x.tp_data.tp_buf,
 250                            spt->block_size);
 251
 252   if (nobytes < 0) {
 253     m_free(m);
 254
 255     /* send "file not found" error back */
 256
 257     tftp_send_error(spt, 1, "File not found", tp);
 258
 259     return;
 260   }
 261
 262   m->m_len = sizeof(struct tftp_t) - (TFTP_BLOCKSIZE_MAX - nobytes)
 263              - sizeof(struct udphdr);
 264   tftp_udp_output(spt, m, recv_tp);
 265
 266   if (nobytes == spt->block_size) {
 267     tftp_session_update(spt);
 268   }
 269   else {
 270     tftp_session_terminate(spt);
 271   }
 272
 273   spt->block_nr++;
 274 }
 275
 276 static void tftp_handle_rrq(Slirp *slirp, struct sockaddr_storage *srcsas,
 277                             struct tftp_t *tp, int pktlen)
 278 {
 279   struct tftp_session *spt;
 280   int s, k;
 281   size_t prefix_len;
 282   char *req_fname;
 283   const char *option_name[2];
 284   uint32_t option_value[2];
 285   int nb_options = 0;
 286
 287   /* check if a session already exists and if so terminate it */
 288   s = tftp_session_find(slirp, srcsas, tp);
 289   if (s >= 0) {
 290     tftp_session_terminate(&slirp->tftp_sessions[s]);
 291   }
 292
 293   s = tftp_session_allocate(slirp, srcsas, tp);
 294
 295   if (s < 0) {
 296     return;
 297   }
 298
 299   spt = &slirp->tftp_sessions[s];
 300
 301   /* unspecified prefix means service disabled */
 302   if (!slirp->tftp_prefix) {
 303       tftp_send_error(spt, 2, "Access violation", tp);
 304       return;
 305   }
 306
 307   /* skip header fields */
 308   k = 0;
 309   pktlen -= offsetof(struct tftp_t, x.tp_buf);
 310
 311   /* prepend tftp_prefix */
 312   prefix_len = strlen(slirp->tftp_prefix);
 313   spt->filename = g_malloc(prefix_len + TFTP_FILENAME_MAX + 2);
 314   memcpy(spt->filename, slirp->tftp_prefix, prefix_len);
 315   spt->filename[prefix_len] = '/';
 316
 317   /* get name */
 318   req_fname = spt->filename + prefix_len + 1;
 319
 320   while (1) {
 321     if (k >= TFTP_FILENAME_MAX || k >= pktlen) {
 322       tftp_send_error(spt, 2, "Access violation", tp);
 323       return;
 324     }
 325     req_fname[k] = tp->x.tp_buf[k];
 326     if (req_fname[k++] == '\0') {
 327       break;
 328     }
 329   }
 330
 331   DEBUG_TFTP("tftp rrq file: %s", req_fname);
 332
 333   /* check mode */
 334   if ((pktlen - k) < 6) {
 335     tftp_send_error(spt, 2, "Access violation", tp);
 336     return;
 337   }
 338
 339   if (strcasecmp(&tp->x.tp_buf[k], "octet") != 0) {
 340       tftp_send_error(spt, 4, "Unsupported transfer mode", tp);
 341       return;
 342   }
 343
 344   k += 6; /* skipping octet */
 345
 346   /* do sanity checks on the filename */
 347   if (!strncmp(req_fname, "../", 3) ||
 348       req_fname[strlen(req_fname) - 1] == '/' ||
 349       strstr(req_fname, "/../")) {
 350       tftp_send_error(spt, 2, "Access violation", tp);
 351       return;
 352   }
 353
 354   /* check if the file exists */
 355   if (tftp_read_data(spt, 0, NULL, 0) < 0) {
 356       tftp_send_error(spt, 1, "File not found", tp);
 357       return;
 358   }
 359
 360   if (tp->x.tp_buf[pktlen - 1] != 0) {
 361       tftp_send_error(spt, 2, "Access violation", tp);
 362       return;
 363   }
 364
 365   while (k < pktlen && nb_options < G_N_ELEMENTS(option_name)) {
 366       const char *key, *value;
 367
 368       key = &tp->x.tp_buf[k];
 369       k += strlen(key) + 1;
 370
 371       if (k >= pktlen) {
 372           tftp_send_error(spt, 2, "Access violation", tp);
 373           return;
 374       }
 375
 376       value = &tp->x.tp_buf[k];
 377       k += strlen(value) + 1;
 378
 379       if (strcasecmp(key, "tsize") == 0) {
 380           int tsize = atoi(value);
 381           struct stat stat_p;
 382
 383           if (tsize == 0) {
 384               if (stat(spt->filename, &stat_p) == 0)
 385                   tsize = stat_p.st_size;
 386               else {
 387                   tftp_send_error(spt, 1, "File not found", tp);
 388                   return;
 389               }
 390           }
 391
 392           option_name[nb_options] = "tsize";
 393           option_value[nb_options] = tsize;
 394           nb_options++;
 395       } else if (strcasecmp(key, "blksize") == 0) {
 396           int blksize = atoi(value);
 397
 398           /* Accept blksize up to our maximum size */
 399           if (blksize > 0) {
 400               spt->block_size = MIN(blksize, TFTP_BLOCKSIZE_MAX);
 401               option_name[nb_options] = "blksize";
 402               option_value[nb_options] = spt->block_size;
 403               nb_options++;
 404           }
 405       }
 406   }
 407
 408   if (nb_options > 0) {
 409       assert(nb_options <= G_N_ELEMENTS(option_name));
 410       tftp_send_oack(spt, option_name, option_value, nb_options, tp);
 411       return;
 412   }
 413
 414   spt->block_nr = 0;
 415   tftp_send_next_block(spt, tp);
 416 }
 417
 418 static void tftp_handle_ack(Slirp *slirp, struct sockaddr_storage *srcsas,
 419                             struct tftp_t *tp, int pktlen)
 420 {
 421   int s;
 422
 423   s = tftp_session_find(slirp, srcsas, tp);
 424
 425   if (s < 0) {
 426     return;
 427   }
 428
 429   tftp_send_next_block(&slirp->tftp_sessions[s], tp);
 430 }
 431
 432 static void tftp_handle_error(Slirp *slirp, struct sockaddr_storage *srcsas,
 433                               struct tftp_t *tp, int pktlen)
 434 {
 435   int s;
 436
 437   s = tftp_session_find(slirp, srcsas, tp);
 438
 439   if (s < 0) {
 440     return;
 441   }
 442
 443   tftp_session_terminate(&slirp->tftp_sessions[s]);
 444 }
 445
 446 void tftp_input(struct sockaddr_storage *srcsas, struct mbuf *m)
 447 {
 448   struct tftp_t *tp = (struct tftp_t *)m->m_data;
 449
 450   switch(ntohs(tp->tp_op)) {
 451   case TFTP_RRQ:
 452     tftp_handle_rrq(m->slirp, srcsas, tp, m->m_len);
 453     break;
 454
 455   case TFTP_ACK:
 456     tftp_handle_ack(m->slirp, srcsas, tp, m->m_len);
 457     break;
 458
 459   case TFTP_ERROR:
 460     tftp_handle_error(m->slirp, srcsas, tp, m->m_len);
 461     break;
 462   }
 463 }