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_error(struct tftp_session *spt,
 124                            u_int16_t errorcode, const char *msg,
 125                            struct tftp_t *recv_tp)
 126 {
 127   struct sockaddr_in saddr, daddr;
 128   struct mbuf *m;
 129   struct tftp_t *tp;
 130   int nobytes;
 131
 132   m = m_get();
 133
 134   if (!m) {
 135     return -1;
 136   }
 137
 138   memset(m->m_data, 0, m->m_size);
 139
 140   m->m_data += if_maxlinkhdr;
 141   tp = (void *)m->m_data;
 142   m->m_data += sizeof(struct udpiphdr);
 143
 144   tp->tp_op = htons(TFTP_ERROR);
 145   tp->x.tp_error.tp_error_code = htons(errorcode);
 146   strcpy(tp->x.tp_error.tp_msg, msg);
 147
 148   saddr.sin_addr = recv_tp->ip.ip_dst;
 149   saddr.sin_port = recv_tp->udp.uh_dport;
 150
 151   daddr.sin_addr = spt->client_ip;
 152   daddr.sin_port = spt->client_port;
 153
 154   nobytes = 2;
 155
 156   m->m_len = sizeof(struct tftp_t) - 514 + 3 + strlen(msg) -
 157         sizeof(struct ip) - sizeof(struct udphdr);
 158
 159   udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
 160
 161   tftp_session_terminate(spt);
 162
 163   return 0;
 164 }
 165
 166 static int tftp_send_data(struct tftp_session *spt,
 167                           u_int16_t block_nr,
 168                           struct tftp_t *recv_tp)
 169 {
 170   struct sockaddr_in saddr, daddr;
 171   struct mbuf *m;
 172   struct tftp_t *tp;
 173   int nobytes;
 174
 175   if (block_nr < 1) {
 176     return -1;
 177   }
 178
 179   m = m_get();
 180
 181   if (!m) {
 182     return -1;
 183   }
 184
 185   memset(m->m_data, 0, m->m_size);
 186
 187   m->m_data += if_maxlinkhdr;
 188   tp = (void *)m->m_data;
 189   m->m_data += sizeof(struct udpiphdr);
 190
 191   tp->tp_op = htons(TFTP_DATA);
 192   tp->x.tp_data.tp_block_nr = htons(block_nr);
 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 = tftp_read_data(spt, block_nr - 1, tp->x.tp_data.tp_buf, 512);
 201
 202   if (nobytes < 0) {
 203     m_free(m);
 204
 205     /* send "file not found" error back */
 206
 207     tftp_send_error(spt, 1, "File not found", tp);
 208
 209     return -1;
 210   }
 211
 212   m->m_len = sizeof(struct tftp_t) - (512 - nobytes) -
 213         sizeof(struct ip) - sizeof(struct udphdr);
 214
 215   udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
 216
 217   if (nobytes == 512) {
 218     tftp_session_update(spt);
 219   }
 220   else {
 221     tftp_session_terminate(spt);
 222   }
 223
 224   return 0;
 225 }
 226
 227 static void tftp_handle_rrq(struct tftp_t *tp, int pktlen)
 228 {
 229   struct tftp_session *spt;
 230   int s, k, n;
 231   u_int8_t *src, *dst;
 232
 233   s = tftp_session_allocate(tp);
 234
 235   if (s < 0) {
 236     return;
 237   }
 238
 239   spt = &tftp_sessions[s];
 240
 241   src = tp->x.tp_buf;
 242   dst = spt->filename;
 243   n = pktlen - ((uint8_t *)&tp->x.tp_buf[0] - (uint8_t *)tp);
 244
 245   /* get name */
 246
 247   for (k = 0; k < n; k++) {
 248     if (k < TFTP_FILENAME_MAX) {
 249       dst[k] = src[k];
 250     }
 251     else {
 252       return;
 253     }
 254
 255     if (src[k] == '\0') {
 256       break;
 257     }
 258   }
 259
 260   if (k >= n) {
 261     return;
 262   }
 263
 264   k++;
 265
 266   /* check mode */
 267   if ((n - k) < 6) {
 268     return;
 269   }
 270
 271   if (memcmp(&src[k], "octet\0", 6) != 0) {
 272       tftp_send_error(spt, 4, "Unsupported transfer mode", tp);
 273       return;
 274   }
 275
 276   /* do sanity checks on the filename */
 277
 278   if ((spt->filename[0] != '/')
 279       || (spt->filename[strlen(spt->filename) - 1] == '/')
 280       ||  strstr(spt->filename, "/../")) {
 281       tftp_send_error(spt, 2, "Access violation", tp);
 282       return;
 283   }
 284
 285   /* only allow exported prefixes */
 286
 287   if (!tftp_prefix
 288       || (strncmp(spt->filename, tftp_prefix, strlen(tftp_prefix)) != 0)) {
 289       tftp_send_error(spt, 2, "Access violation", tp);
 290       return;
 291   }
 292
 293   /* check if the file exists */
 294
 295   if (tftp_read_data(spt, 0, spt->filename, 0) < 0) {
 296       tftp_send_error(spt, 1, "File not found", tp);
 297       return;
 298   }
 299
 300   tftp_send_data(spt, 1, tp);
 301 }
 302
 303 static void tftp_handle_ack(struct tftp_t *tp, int pktlen)
 304 {
 305   int s;
 306
 307   s = tftp_session_find(tp);
 308
 309   if (s < 0) {
 310     return;
 311   }
 312
 313   if (tftp_send_data(&tftp_sessions[s],
 314                      ntohs(tp->x.tp_data.tp_block_nr) + 1,
 315                      tp) < 0) {
 316     return;
 317   }
 318 }
 319
 320 void tftp_input(struct mbuf *m)
 321 {
 322   struct tftp_t *tp = (struct tftp_t *)m->m_data;
 323
 324   switch(ntohs(tp->tp_op)) {
 325   case TFTP_RRQ:
 326     tftp_handle_rrq(tp, m->m_len);
 327     break;
 328
 329   case TFTP_ACK:
 330     tftp_handle_ack(tp, m->m_len);
 331     break;
 332   }
 333 }