tftp.c revision 8b23a6c7e1aee255004dd19098d4c2462b61b849 
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#include <fcntl.h>
27#include <sys/stat.h>
28
29struct tftp_session {
30    int in_use;
31    unsigned char filename[TFTP_FILENAME_MAX];
32
33    uint32_t client_ip;
34    uint16_t client_port;
35
36    int timestamp;
37};
38
39struct tftp_session tftp_sessions[TFTP_SESSIONS_MAX];
40
41const char *tftp_prefix;
42
43static void tftp_session_update(struct tftp_session *spt)
44{
45    spt->timestamp = curtime;
46    spt->in_use = 1;
47}
48
49static void tftp_session_terminate(struct tftp_session *spt)
50{
51  spt->in_use = 0;
52}
53
54static int tftp_session_allocate(struct tftp_t *tp)
55{
56  struct tftp_session *spt;
57  int k;
58
59  for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
60    spt = &tftp_sessions[k];
61
62    if (!spt->in_use)
63        goto found;
64
65    /* sessions time out after 5 inactive seconds */
66    if ((int)(curtime - spt->timestamp) > 5000)
67        goto found;
68  }
69
70  return -1;
71
72 found:
73  memset(spt, 0, sizeof(*spt));
74  spt->client_ip   = ip_geth(tp->ip.ip_src);
75  spt->client_port = port_geth(tp->udp.uh_sport);
76
77  tftp_session_update(spt);
78
79  return k;
80}
81
82static int tftp_session_find(struct tftp_t *tp)
83{
84  struct tftp_session *spt;
85  int k;
86
87  for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
88    spt = &tftp_sessions[k];
89
90    if (spt->in_use) {
91      if (spt->client_ip == ip_geth(tp->ip.ip_src)) {
92	if (spt->client_port == port_geth(tp->udp.uh_sport)) {
93	  return k;
94	}
95      }
96    }
97  }
98
99  return -1;
100}
101
102static int tftp_read_data(struct tftp_session *spt, u_int16_t block_nr,
103			  u_int8_t *buf, int len)
104{
105  int fd;
106  int bytes_read = 0;
107  char buffer[1024];
108  int n;
109
110  n = snprintf(buffer, sizeof(buffer), "%s/%s",
111               tftp_prefix, spt->filename);
112  if (n >= sizeof(buffer))
113      return -1;
114
115  fd = open(buffer, O_RDONLY | O_BINARY);
116
117  if (fd < 0) {
118    return -1;
119  }
120
121  if (len) {
122    lseek(fd, block_nr * 512, SEEK_SET);
123
124    bytes_read = read(fd, buf, len);
125  }
126
127  close(fd);
128
129  return bytes_read;
130}
131
132static int tftp_send_oack(struct tftp_session *spt,
133                          const char *key, uint32_t value,
134                          struct tftp_t *recv_tp)
135{
136    SockAddress  saddr, daddr;
137    MBuf m;
138    struct tftp_t *tp;
139    int n = 0;
140
141    m = mbuf_alloc();
142
143    if (!m)
144        return -1;
145
146    memset(m->m_data, 0, m->m_size);
147
148    m->m_data += if_maxlinkhdr;
149    tp = (void *)m->m_data;
150    m->m_data += sizeof(struct udpiphdr);
151
152    tp->tp_op = htons(TFTP_OACK);
153    n += sprintf((char*)tp->x.tp_buf + n, "%s", key) + 1;
154    n += sprintf((char*)tp->x.tp_buf + n, "%u", value) + 1;
155
156    sock_address_init_inet( &saddr,
157                            ip_geth(recv_tp->ip.ip_dst),
158                            port_geth(recv_tp->udp.uh_dport) );
159
160    sock_address_init_inet( &daddr,
161                            spt->client_ip,
162                            spt->client_port );
163
164    m->m_len = sizeof(struct tftp_t) - 514 + n -
165            sizeof(struct ip) - sizeof(struct udphdr);
166    udp_output2_(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
167
168    return 0;
169}
170
171
172
173static int tftp_send_error(struct tftp_session *spt,
174			   u_int16_t errorcode, const char *msg,
175			   struct tftp_t *recv_tp)
176{
177  SockAddress saddr, daddr;
178  MBuf m;
179  struct tftp_t *tp;
180  int nobytes;
181
182  m = mbuf_alloc();
183
184  if (!m) {
185    return -1;
186  }
187
188  memset(m->m_data, 0, m->m_size);
189
190  m->m_data += if_maxlinkhdr;
191  tp = (void *)m->m_data;
192  m->m_data += sizeof(struct udpiphdr);
193
194  tp->tp_op = htons(TFTP_ERROR);
195  tp->x.tp_error.tp_error_code = htons(errorcode);
196  strcpy((char*)tp->x.tp_error.tp_msg, msg);
197
198  sock_address_init_inet( &saddr,
199                          ip_geth(recv_tp->ip.ip_dst),
200                          port_geth(recv_tp->udp.uh_dport) );
201
202  sock_address_init_inet( &daddr,
203                          spt->client_ip,
204                          spt->client_port );
205
206  nobytes = 2;
207
208  m->m_len = sizeof(struct tftp_t) - 514 + 3 + strlen(msg) -
209        sizeof(struct ip) - sizeof(struct udphdr);
210
211  udp_output2_(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
212
213  tftp_session_terminate(spt);
214
215  return 0;
216}
217
218static int tftp_send_data(struct tftp_session *spt,
219			  u_int16_t block_nr,
220			  struct tftp_t *recv_tp)
221{
222  SockAddress saddr, daddr;
223  MBuf m;
224  struct tftp_t *tp;
225  int nobytes;
226
227  if (block_nr < 1) {
228    return -1;
229  }
230
231  m = mbuf_alloc();
232
233  if (!m) {
234    return -1;
235  }
236
237  memset(m->m_data, 0, m->m_size);
238
239  m->m_data += if_maxlinkhdr;
240  tp = (void *)m->m_data;
241  m->m_data += sizeof(struct udpiphdr);
242
243  tp->tp_op = htons(TFTP_DATA);
244  tp->x.tp_data.tp_block_nr = htons(block_nr);
245
246  sock_address_init_inet( &saddr,
247                          ip_geth(recv_tp->ip.ip_dst),
248                          port_geth(recv_tp->udp.uh_dport) );
249
250  sock_address_init_inet( &daddr,
251                          spt->client_ip,
252                          spt->client_port );
253
254  nobytes = tftp_read_data(spt, block_nr - 1, tp->x.tp_data.tp_buf, 512);
255
256  if (nobytes < 0) {
257    mbuf_free(m);
258
259    /* send "file not found" error back */
260
261    tftp_send_error(spt, 1, "File not found", tp);
262
263    return -1;
264  }
265
266  m->m_len = sizeof(struct tftp_t) - (512 - nobytes) -
267        sizeof(struct ip) - sizeof(struct udphdr);
268
269  udp_output2_(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
270
271  if (nobytes == 512) {
272    tftp_session_update(spt);
273  }
274  else {
275    tftp_session_terminate(spt);
276  }
277
278  return 0;
279}
280
281static void tftp_handle_rrq(struct tftp_t *tp, int pktlen)
282{
283  struct tftp_session *spt;
284  int s, k, n;
285  u_int8_t *src, *dst;
286
287  s = tftp_session_allocate(tp);
288
289  if (s < 0) {
290    return;
291  }
292
293  spt = &tftp_sessions[s];
294
295  src = tp->x.tp_buf;
296  dst = spt->filename;
297  n = pktlen - ((uint8_t *)&tp->x.tp_buf[0] - (uint8_t *)tp);
298
299  /* get name */
300
301  for (k = 0; k < n; k++) {
302    if (k < TFTP_FILENAME_MAX) {
303      dst[k] = src[k];
304    }
305    else {
306      return;
307    }
308
309    if (src[k] == '\0') {
310      break;
311    }
312  }
313
314  if (k >= n) {
315    return;
316  }
317
318  k++;
319
320  /* check mode */
321  if ((n - k) < 6) {
322    return;
323  }
324
325  if (memcmp(&src[k], "octet\0", 6) != 0) {
326      tftp_send_error(spt, 4, "Unsupported transfer mode", tp);
327      return;
328  }
329
330  k += 6;  /* skipping octet */
331
332  /* do sanity checks on the filename */
333
334  if ((spt->filename[0] != '/')
335      || (spt->filename[strlen((const char*)spt->filename) - 1] == '/')
336      ||  strstr((const char*)spt->filename, "/../")) {
337      tftp_send_error(spt, 2, "Access violation", tp);
338      return;
339  }
340
341  /* only allow exported prefixes */
342
343  if (!tftp_prefix) {
344      tftp_send_error(spt, 2, "Access violation", tp);
345      return;
346  }
347
348  /* check if the file exists */
349
350  if (tftp_read_data(spt, 0, spt->filename, 0) < 0) {
351      tftp_send_error(spt, 1, "File not found", tp);
352      return;
353  }
354
355  if (src[n - 1] != 0) {
356      tftp_send_error(spt, 2, "Access violation", tp);
357      return;
358  }
359
360  while (k < n) {
361      const char *key, *value;
362
363      key = (const char*)src + k;
364      k += strlen(key) + 1;
365
366      if (k >= n) {
367          tftp_send_error(spt, 2, "Access violation", tp);
368          return;
369      }
370
371      value = (const char*)src + k;
372      k += strlen(value) + 1;
373
374      if (strcmp(key, "tsize") == 0) {
375          int tsize = atoi(value);
376          struct stat stat_p;
377
378          if (tsize == 0 && tftp_prefix) {
379              char buffer[1024];
380              int len;
381
382              len = snprintf(buffer, sizeof(buffer), "%s/%s",
383                             tftp_prefix, spt->filename);
384
385              if (stat(buffer, &stat_p) == 0)
386                  tsize = stat_p.st_size;
387              else {
388                  tftp_send_error(spt, 1, "File not found", tp);
389                  return;
390              }
391          }
392
393          tftp_send_oack(spt, "tsize", tsize, tp);
394      }
395  }
396
397  tftp_send_data(spt, 1, tp);
398}
399
400static void tftp_handle_ack(struct tftp_t *tp, int pktlen)
401{
402  int s;
403
404  s = tftp_session_find(tp);
405
406  if (s < 0) {
407    return;
408  }
409
410  if (tftp_send_data(&tftp_sessions[s],
411		     ntohs(tp->x.tp_data.tp_block_nr) + 1,
412		     tp) < 0) {
413    return;
414  }
415}
416
417void tftp_input(MBuf m)
418{
419  struct tftp_t *tp = (struct tftp_t *)m->m_data;
420
421  switch(ntohs(tp->tp_op)) {
422  case TFTP_RRQ:
423    tftp_handle_rrq(tp, m->m_len);
424    break;
425
426  case TFTP_ACK:
427    tftp_handle_ack(tp, m->m_len);
428    break;
429  }
430}
431