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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 "qemu-common.h" // for pstrcpy
27 
28 struct tftp_session {
29     int in_use;
30     unsigned char filename[TFTP_FILENAME_MAX];
31 
32     uint32_t client_ip;
33     uint16_t client_port;
34 
35     int timestamp;
36 };
37 
38 static struct tftp_session tftp_sessions[TFTP_SESSIONS_MAX];
39 
40 const char *tftp_prefix;
41 
tftp_session_update(struct tftp_session * spt)42 static void tftp_session_update(struct tftp_session *spt)
43 {
44     spt->timestamp = curtime;
45     spt->in_use = 1;
46 }
47 
tftp_session_terminate(struct tftp_session * spt)48 static void tftp_session_terminate(struct tftp_session *spt)
49 {
50   spt->in_use = 0;
51 }
52 
tftp_session_allocate(struct tftp_t * tp)53 static int tftp_session_allocate(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 = &tftp_sessions[k];
60 
61     if (!spt->in_use)
62         goto found;
63 
64     /* sessions time out after 5 inactive seconds */
65     if ((int)(curtime - spt->timestamp) > 5000)
66         goto found;
67   }
68 
69   return -1;
70 
71  found:
72   memset(spt, 0, sizeof(*spt));
73   spt->client_ip   = ip_geth(tp->ip.ip_src);
74   spt->client_port = port_geth(tp->udp.uh_sport);
75 
76   tftp_session_update(spt);
77 
78   return k;
79 }
80 
tftp_session_find(struct tftp_t * tp)81 static int tftp_session_find(struct tftp_t *tp)
82 {
83   struct tftp_session *spt;
84   int k;
85 
86   for (k = 0; k < TFTP_SESSIONS_MAX; k++) {
87     spt = &tftp_sessions[k];
88 
89     if (spt->in_use) {
90       if (spt->client_ip == ip_geth(tp->ip.ip_src)) {
91 		if (spt->client_port == port_geth(tp->udp.uh_sport)) {
92 		  return k;
93 		}
94       }
95     }
96   }
97 
98   return -1;
99 }
100 
tftp_read_data(struct tftp_session * spt,u_int16_t block_nr,u_int8_t * buf,int len)101 static int tftp_read_data(struct tftp_session *spt, u_int16_t block_nr,
102 			  u_int8_t *buf, int len)
103 {
104   int fd;
105   int bytes_read = 0;
106   char buffer[1024];
107   int n;
108 
109   n = snprintf(buffer, sizeof(buffer), "%s/%s",
110 	       tftp_prefix, spt->filename);
111   if (n >= sizeof(buffer))
112     return -1;
113 
114   fd = open(buffer, O_RDONLY | O_BINARY);
115 
116   if (fd < 0) {
117     return -1;
118   }
119 
120   if (len) {
121     lseek(fd, block_nr * 512, SEEK_SET);
122 
123     bytes_read = read(fd, buf, len);
124   }
125 
126   close(fd);
127 
128   return bytes_read;
129 }
130 
tftp_send_oack(struct tftp_session * spt,const char * key,uint32_t value,struct tftp_t * recv_tp)131 static int tftp_send_oack(struct tftp_session *spt,
132                           const char *key, uint32_t value,
133                           struct tftp_t *recv_tp)
134 {
135     SockAddress  saddr, daddr;
136     struct mbuf *m;
137     struct tftp_t *tp;
138     int n = 0;
139 
140     m = m_get();
141 
142     if (!m)
143 	return -1;
144 
145     memset(m->m_data, 0, m->m_size);
146 
147     m->m_data += IF_MAXLINKHDR;
148     tp = (void *)m->m_data;
149     m->m_data += sizeof(struct udpiphdr);
150 
151     tp->tp_op = htons(TFTP_OACK);
152     n += snprintf((char *)tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%s",
153                   key) + 1;
154     n += snprintf((char *)tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%u",
155                   value) + 1;
156 
157     sock_address_init_inet( &saddr,
158                             ip_geth(recv_tp->ip.ip_dst),
159                             port_geth(recv_tp->udp.uh_dport) );
160 
161     sock_address_init_inet( &daddr,
162                             spt->client_ip,
163                             spt->client_port );
164 
165     m->m_len = sizeof(struct tftp_t) - 514 + n -
166         sizeof(struct ip) - sizeof(struct udphdr);
167     udp_output2_(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
168 
169     return 0;
170 }
171 
172 
173 
tftp_send_error(struct tftp_session * spt,u_int16_t errorcode,const char * msg,struct tftp_t * recv_tp)174 static int tftp_send_error(struct tftp_session *spt,
175 			   u_int16_t errorcode, const char *msg,
176 			   struct tftp_t *recv_tp)
177 {
178   SockAddress saddr, daddr;
179   struct mbuf *m;
180   struct tftp_t *tp;
181   int nobytes;
182 
183   m = m_get();
184 
185   if (!m) {
186     return -1;
187   }
188 
189   memset(m->m_data, 0, m->m_size);
190 
191   m->m_data += IF_MAXLINKHDR;
192   tp = (void *)m->m_data;
193   m->m_data += sizeof(struct udpiphdr);
194 
195   tp->tp_op = htons(TFTP_ERROR);
196   tp->x.tp_error.tp_error_code = htons(errorcode);
197   pstrcpy((char *)tp->x.tp_error.tp_msg, sizeof(tp->x.tp_error.tp_msg), msg);
198 
199   sock_address_init_inet( &saddr,
200                           ip_geth(recv_tp->ip.ip_dst),
201                           port_geth(recv_tp->udp.uh_dport) );
202 
203   sock_address_init_inet( &daddr,
204                           spt->client_ip,
205                           spt->client_port );
206 
207   nobytes = 2;
208 
209   m->m_len = sizeof(struct tftp_t) - 514 + 3 + strlen(msg) -
210         sizeof(struct ip) - sizeof(struct udphdr);
211 
212   udp_output2_(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
213 
214   tftp_session_terminate(spt);
215 
216   return 0;
217 }
218 
tftp_send_data(struct tftp_session * spt,u_int16_t block_nr,struct tftp_t * recv_tp)219 static int tftp_send_data(struct tftp_session *spt,
220 			  u_int16_t block_nr,
221 			  struct tftp_t *recv_tp)
222 {
223   SockAddress saddr, daddr;
224   struct mbuf *m;
225   struct tftp_t *tp;
226   int nobytes;
227 
228   if (block_nr < 1) {
229     return -1;
230   }
231 
232   m = m_get();
233 
234   if (!m) {
235     return -1;
236   }
237 
238   memset(m->m_data, 0, m->m_size);
239 
240   m->m_data += IF_MAXLINKHDR;
241   tp = (void *)m->m_data;
242   m->m_data += sizeof(struct udpiphdr);
243 
244   tp->tp_op = htons(TFTP_DATA);
245   tp->x.tp_data.tp_block_nr = htons(block_nr);
246 
247   sock_address_init_inet( &saddr,
248                           ip_geth(recv_tp->ip.ip_dst),
249                           port_geth(recv_tp->udp.uh_dport) );
250 
251   sock_address_init_inet( &daddr,
252                           spt->client_ip,
253                           spt->client_port );
254 
255   nobytes = tftp_read_data(spt, block_nr - 1, tp->x.tp_data.tp_buf, 512);
256 
257   if (nobytes < 0) {
258     m_free(m);
259 
260     /* send "file not found" error back */
261 
262     tftp_send_error(spt, 1, "File not found", tp);
263 
264     return -1;
265   }
266 
267   m->m_len = sizeof(struct tftp_t) - (512 - nobytes) -
268         sizeof(struct ip) - sizeof(struct udphdr);
269 
270   udp_output2_(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
271 
272   if (nobytes == 512) {
273     tftp_session_update(spt);
274   }
275   else {
276     tftp_session_terminate(spt);
277   }
278 
279   return 0;
280 }
281 
tftp_handle_rrq(struct tftp_t * tp,int pktlen)282 static void tftp_handle_rrq(struct tftp_t *tp, int pktlen)
283 {
284   struct tftp_session *spt;
285   int s, k, n;
286   u_int8_t *src, *dst;
287 
288   s = tftp_session_allocate(tp);
289 
290   if (s < 0) {
291     return;
292   }
293 
294   spt = &tftp_sessions[s];
295 
296   src = tp->x.tp_buf;
297   dst = spt->filename;
298   n = pktlen - ((uint8_t *)&tp->x.tp_buf[0] - (uint8_t *)tp);
299 
300   /* get name */
301 
302   for (k = 0; k < n; k++) {
303     if (k < TFTP_FILENAME_MAX) {
304       dst[k] = src[k];
305     }
306     else {
307       return;
308     }
309 
310     if (src[k] == '\0') {
311       break;
312     }
313   }
314 
315   if (k >= n) {
316     return;
317   }
318 
319   k++;
320 
321   /* check mode */
322   if ((n - k) < 6) {
323     return;
324   }
325 
326   if (memcmp(&src[k], "octet\0", 6) != 0) {
327       tftp_send_error(spt, 4, "Unsupported transfer mode", tp);
328       return;
329   }
330 
331   k += 6; /* skipping octet */
332 
333   /* do sanity checks on the filename */
334 
335   if ((spt->filename[0] != '/')
336       || (spt->filename[strlen((char *)spt->filename) - 1] == '/')
337       ||  strstr((char *)spt->filename, "/../")) {
338       tftp_send_error(spt, 2, "Access violation", tp);
339       return;
340   }
341 
342   /* only allow exported prefixes */
343 
344   if (!tftp_prefix) {
345       tftp_send_error(spt, 2, "Access violation", tp);
346       return;
347   }
348 
349   /* check if the file exists */
350 
351   if (tftp_read_data(spt, 0, spt->filename, 0) < 0) {
352       tftp_send_error(spt, 1, "File not found", tp);
353       return;
354   }
355 
356   if (src[n - 1] != 0) {
357       tftp_send_error(spt, 2, "Access violation", tp);
358       return;
359   }
360 
361   while (k < n) {
362       const char *key, *value;
363 
364       key = (char *)src + k;
365       k += strlen(key) + 1;
366 
367       if (k >= n) {
368 	  tftp_send_error(spt, 2, "Access violation", tp);
369 	  return;
370       }
371 
372       value = (char *)src + k;
373       k += strlen(value) + 1;
374 
375       if (strcmp(key, "tsize") == 0) {
376 	  int tsize = atoi(value);
377 	  struct stat stat_p;
378 
379 	  if (tsize == 0 && tftp_prefix) {
380 	      char buffer[1024];
381 	      int len;
382 
383 	      len = snprintf(buffer, sizeof(buffer), "%s/%s",
384 			     tftp_prefix, spt->filename);
385 
386 	      if (stat(buffer, &stat_p) == 0)
387 		  tsize = stat_p.st_size;
388 	      else {
389 		  tftp_send_error(spt, 1, "File not found", tp);
390 		  return;
391 	      }
392 	  }
393 
394 	  tftp_send_oack(spt, "tsize", tsize, tp);
395       }
396   }
397 
398   tftp_send_data(spt, 1, tp);
399 }
400 
tftp_handle_ack(struct tftp_t * tp,int pktlen)401 static void tftp_handle_ack(struct tftp_t *tp, int pktlen)
402 {
403   int s;
404 
405   s = tftp_session_find(tp);
406 
407   if (s < 0) {
408     return;
409   }
410 
411   if (tftp_send_data(&tftp_sessions[s],
412 		     ntohs(tp->x.tp_data.tp_block_nr) + 1,
413 		     tp) < 0) {
414     return;
415   }
416 }
417 
tftp_input(struct mbuf * m)418 void tftp_input(struct mbuf *m)
419 {
420   struct tftp_t *tp = (struct tftp_t *)m->m_data;
421 
422   switch(ntohs(tp->tp_op)) {
423   case TFTP_RRQ:
424     tftp_handle_rrq(tp, m->m_len);
425     break;
426 
427   case TFTP_ACK:
428     tftp_handle_ack(tp, m->m_len);
429     break;
430   }
431 }
432