tftpd.c revision 20052 
1/*
2 * Copyright (c) 1983, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *	This product includes software developed by the University of
16 *	California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 *
33 *	$Id: tftpd.c,v 1.4 1996/09/22 21:56:07 wosch Exp $
34 */
35
36#ifndef lint
37static char copyright[] =
38"@(#) Copyright (c) 1983, 1993\n\
39	The Regents of the University of California.  All rights reserved.\n";
40#endif /* not lint */
41
42#ifndef lint
43static char sccsid[] = "@(#)tftpd.c	8.1 (Berkeley) 6/4/93";
44#endif /* not lint */
45
46/*
47 * Trivial file transfer protocol server.
48 *
49 * This version includes many modifications by Jim Guyton
50 * <guyton@rand-unix>.
51 */
52
53#include <sys/param.h>
54#include <sys/ioctl.h>
55#include <sys/stat.h>
56#include <sys/socket.h>
57#include <sys/types.h>
58
59#include <netinet/in.h>
60#include <arpa/tftp.h>
61#include <arpa/inet.h>
62
63#include <ctype.h>
64#include <errno.h>
65#include <fcntl.h>
66#include <netdb.h>
67#include <setjmp.h>
68#include <signal.h>
69#include <stdio.h>
70#include <stdlib.h>
71#include <string.h>
72#include <syslog.h>
73#include <unistd.h>
74#include <pwd.h>
75
76#include "tftpsubs.h"
77
78#define	TIMEOUT		5
79
80int	peer;
81int	rexmtval = TIMEOUT;
82int	maxtimeout = 5*TIMEOUT;
83
84#define	PKTSIZE	SEGSIZE+4
85char	buf[PKTSIZE];
86char	ackbuf[PKTSIZE];
87struct	sockaddr_in from;
88int	fromlen;
89
90void	tftp __P((struct tftphdr *, int));
91
92/*
93 * Null-terminated directory prefix list for absolute pathname requests and
94 * search list for relative pathname requests.
95 *
96 * MAXDIRS should be at least as large as the number of arguments that
97 * inetd allows (currently 20).
98 */
99#define MAXDIRS	20
100static struct dirlist {
101	char	*name;
102	int	len;
103} dirs[MAXDIRS+1];
104static int	suppress_naks;
105static int	logging;
106
107static char *errtomsg __P((int));
108static void  nak __P((int));
109static char *verifyhost __P((struct sockaddr_in *));
110
111int
112main(argc, argv)
113	int argc;
114	char *argv[];
115{
116	register struct tftphdr *tp;
117	register int n;
118	int ch, on;
119	struct sockaddr_in sin;
120	char *chroot_dir = NULL;
121	struct passwd *nobody;
122
123	openlog("tftpd", LOG_PID, LOG_FTP);
124	while ((ch = getopt(argc, argv, "lns:")) != EOF) {
125		switch (ch) {
126		case 'l':
127			logging = 1;
128			break;
129		case 'n':
130			suppress_naks = 1;
131			break;
132		case 's':
133			chroot_dir = optarg;
134			break;
135		default:
136			syslog(LOG_WARNING, "ignoring unknown option -%c", ch);
137		}
138	}
139	if (optind < argc) {
140		struct dirlist *dirp;
141
142		/* Get list of directory prefixes. Skip relative pathnames. */
143		for (dirp = dirs; optind < argc && dirp < &dirs[MAXDIRS];
144		     optind++) {
145			if (argv[optind][0] == '/') {
146				dirp->name = argv[optind];
147				dirp->len  = strlen(dirp->name);
148				dirp++;
149			}
150		}
151	}
152	else if (chroot_dir) {
153		dirs->name = "/";
154		dirs->len = 1;
155	}
156
157	on = 1;
158	if (ioctl(0, FIONBIO, &on) < 0) {
159		syslog(LOG_ERR, "ioctl(FIONBIO): %m\n");
160		exit(1);
161	}
162	fromlen = sizeof (from);
163	n = recvfrom(0, buf, sizeof (buf), 0,
164	    (struct sockaddr *)&from, &fromlen);
165	if (n < 0) {
166		syslog(LOG_ERR, "recvfrom: %m\n");
167		exit(1);
168	}
169	/*
170	 * Now that we have read the message out of the UDP
171	 * socket, we fork and exit.  Thus, inetd will go back
172	 * to listening to the tftp port, and the next request
173	 * to come in will start up a new instance of tftpd.
174	 *
175	 * We do this so that inetd can run tftpd in "wait" mode.
176	 * The problem with tftpd running in "nowait" mode is that
177	 * inetd may get one or more successful "selects" on the
178	 * tftp port before we do our receive, so more than one
179	 * instance of tftpd may be started up.  Worse, if tftpd
180	 * break before doing the above "recvfrom", inetd would
181	 * spawn endless instances, clogging the system.
182	 */
183	{
184		int pid;
185		int i, j;
186
187		for (i = 1; i < 20; i++) {
188		    pid = fork();
189		    if (pid < 0) {
190				sleep(i);
191				/*
192				 * flush out to most recently sent request.
193				 *
194				 * This may drop some request, but those
195				 * will be resent by the clients when
196				 * they timeout.  The positive effect of
197				 * this flush is to (try to) prevent more
198				 * than one tftpd being started up to service
199				 * a single request from a single client.
200				 */
201				j = sizeof from;
202				i = recvfrom(0, buf, sizeof (buf), 0,
203				    (struct sockaddr *)&from, &j);
204				if (i > 0) {
205					n = i;
206					fromlen = j;
207				}
208		    } else {
209				break;
210		    }
211		}
212		if (pid < 0) {
213			syslog(LOG_ERR, "fork: %m\n");
214			exit(1);
215		} else if (pid != 0) {
216			exit(0);
217		}
218	}
219
220	/*
221	 * Since we exit here, we should do that only after the above
222	 * recvfrom to keep inetd from constantly forking should there
223	 * be a problem.  See the above comment about system clogging.
224	 */
225	if (chroot_dir) {
226		/* Must get this before chroot because /etc might go away */
227		if ((nobody = getpwnam("nobody")) == NULL) {
228			syslog(LOG_ERR, "nobody: no such user");
229			exit(1);
230		}
231		if (chroot(chroot_dir)) {
232			syslog(LOG_ERR, "chroot: %s: %m", chroot_dir);
233			exit(1);
234		}
235		chdir( "/" );
236		setuid(nobody->pw_uid);
237	}
238
239	from.sin_family = AF_INET;
240	alarm(0);
241	close(0);
242	close(1);
243	peer = socket(AF_INET, SOCK_DGRAM, 0);
244	if (peer < 0) {
245		syslog(LOG_ERR, "socket: %m\n");
246		exit(1);
247	}
248	memset(&sin, 0, sizeof(sin));
249	sin.sin_family = AF_INET;
250	if (bind(peer, (struct sockaddr *)&sin, sizeof (sin)) < 0) {
251		syslog(LOG_ERR, "bind: %m\n");
252		exit(1);
253	}
254	if (connect(peer, (struct sockaddr *)&from, sizeof(from)) < 0) {
255		syslog(LOG_ERR, "connect: %m\n");
256		exit(1);
257	}
258	tp = (struct tftphdr *)buf;
259	tp->th_opcode = ntohs(tp->th_opcode);
260	if (tp->th_opcode == RRQ || tp->th_opcode == WRQ)
261		tftp(tp, n);
262	exit(1);
263}
264
265struct formats;
266int	validate_access __P((char **, int));
267void	sendfile __P((struct formats *));
268void	recvfile __P((struct formats *));
269
270struct formats {
271	char	*f_mode;
272	int	(*f_validate) __P((char **, int));
273	void	(*f_send) __P((struct formats *));
274	void	(*f_recv) __P((struct formats *));
275	int	f_convert;
276} formats[] = {
277	{ "netascii",	validate_access,	sendfile,	recvfile, 1 },
278	{ "octet",	validate_access,	sendfile,	recvfile, 0 },
279#ifdef notdef
280	{ "mail",	validate_user,		sendmail,	recvmail, 1 },
281#endif
282	{ 0 }
283};
284
285/*
286 * Handle initial connection protocol.
287 */
288void
289tftp(tp, size)
290	struct tftphdr *tp;
291	int size;
292{
293	register char *cp;
294	int first = 1, ecode;
295	register struct formats *pf;
296	char *filename, *mode;
297
298	filename = cp = tp->th_stuff;
299again:
300	while (cp < buf + size) {
301		if (*cp == '\0')
302			break;
303		cp++;
304	}
305	if (*cp != '\0') {
306		nak(EBADOP);
307		exit(1);
308	}
309	if (first) {
310		mode = ++cp;
311		first = 0;
312		goto again;
313	}
314	for (cp = mode; *cp; cp++)
315		if (isupper(*cp))
316			*cp = tolower(*cp);
317	for (pf = formats; pf->f_mode; pf++)
318		if (strcmp(pf->f_mode, mode) == 0)
319			break;
320	if (pf->f_mode == 0) {
321		nak(EBADOP);
322		exit(1);
323	}
324	ecode = (*pf->f_validate)(&filename, tp->th_opcode);
325	if (logging) {
326		syslog(LOG_INFO, "%s: %s request for %s: %s",
327			verifyhost(&from),
328			tp->th_opcode == WRQ ? "write" : "read",
329			filename, errtomsg(ecode));
330	}
331	if (ecode) {
332		/*
333		 * Avoid storms of naks to a RRQ broadcast for a relative
334		 * bootfile pathname from a diskless Sun.
335		 */
336		if (suppress_naks && *filename != '/' && ecode == ENOTFOUND)
337			exit(0);
338		nak(ecode);
339		exit(1);
340	}
341	if (tp->th_opcode == WRQ)
342		(*pf->f_recv)(pf);
343	else
344		(*pf->f_send)(pf);
345	exit(0);
346}
347
348
349FILE *file;
350
351/*
352 * Validate file access.  Since we
353 * have no uid or gid, for now require
354 * file to exist and be publicly
355 * readable/writable.
356 * If we were invoked with arguments
357 * from inetd then the file must also be
358 * in one of the given directory prefixes.
359 * Note also, full path name must be
360 * given as we have no login directory.
361 */
362int
363validate_access(filep, mode)
364	char **filep;
365	int mode;
366{
367	struct stat stbuf;
368	int	fd;
369	struct dirlist *dirp;
370	static char pathname[MAXPATHLEN];
371	char *filename = *filep;
372
373	/*
374	 * Prevent tricksters from getting around the directory restrictions
375	 */
376	if (strstr(filename, "/../"))
377		return (EACCESS);
378
379	if (*filename == '/') {
380		/*
381		 * Allow the request if it's in one of the approved locations.
382		 * Special case: check the null prefix ("/") by looking
383		 * for length = 1 and relying on the arg. processing that
384		 * it's a /.
385		 */
386		for (dirp = dirs; dirp->name != NULL; dirp++) {
387			if (dirp->len == 1 ||
388			    (!strncmp(filename, dirp->name, dirp->len) &&
389			     filename[dirp->len] == '/'))
390				    break;
391		}
392		/* If directory list is empty, allow access to any file */
393		if (dirp->name == NULL && dirp != dirs)
394			return (EACCESS);
395		if (stat(filename, &stbuf) < 0)
396			return (errno == ENOENT ? ENOTFOUND : EACCESS);
397		if ((stbuf.st_mode & S_IFMT) != S_IFREG)
398			return (ENOTFOUND);
399		if (mode == RRQ) {
400			if ((stbuf.st_mode & S_IROTH) == 0)
401				return (EACCESS);
402		} else {
403			if ((stbuf.st_mode & S_IWOTH) == 0)
404				return (EACCESS);
405		}
406	} else {
407		int err;
408
409		/*
410		 * Relative file name: search the approved locations for it.
411		 * Don't allow write requests that avoid directory
412		 * restrictions.
413		 */
414
415		if (!strncmp(filename, "../", 3))
416			return (EACCESS);
417
418		/*
419		 * If the file exists in one of the directories and isn't
420		 * readable, continue looking. However, change the error code
421		 * to give an indication that the file exists.
422		 */
423		err = ENOTFOUND;
424		for (dirp = dirs; dirp->name != NULL; dirp++) {
425			sprintf(pathname, "%s/%s", dirp->name, filename);
426			if (stat(pathname, &stbuf) == 0 &&
427			    (stbuf.st_mode & S_IFMT) == S_IFREG) {
428				if ((stbuf.st_mode & S_IROTH) != 0) {
429					break;
430				}
431				err = EACCESS;
432			}
433		}
434		if (dirp->name == NULL)
435			return (err);
436		*filep = filename = pathname;
437	}
438	fd = open(filename, mode == RRQ ? O_RDONLY : O_WRONLY|O_TRUNC);
439	if (fd < 0)
440		return (errno + 100);
441	file = fdopen(fd, (mode == RRQ)? "r":"w");
442	if (file == NULL) {
443		return errno+100;
444	}
445	return (0);
446}
447
448int	timeout;
449jmp_buf	timeoutbuf;
450
451void
452timer()
453{
454
455	timeout += rexmtval;
456	if (timeout >= maxtimeout)
457		exit(1);
458	longjmp(timeoutbuf, 1);
459}
460
461/*
462 * Send the requested file.
463 */
464void
465sendfile(pf)
466	struct formats *pf;
467{
468	struct tftphdr *dp, *r_init();
469	register struct tftphdr *ap;    /* ack packet */
470	register int size, n;
471	volatile int block;
472
473	signal(SIGALRM, timer);
474	dp = r_init();
475	ap = (struct tftphdr *)ackbuf;
476	block = 1;
477	do {
478		size = readit(file, &dp, pf->f_convert);
479		if (size < 0) {
480			nak(errno + 100);
481			goto abort;
482		}
483		dp->th_opcode = htons((u_short)DATA);
484		dp->th_block = htons((u_short)block);
485		timeout = 0;
486		(void)setjmp(timeoutbuf);
487
488send_data:
489		if (send(peer, dp, size + 4, 0) != size + 4) {
490			syslog(LOG_ERR, "tftpd: write: %m\n");
491			goto abort;
492		}
493		read_ahead(file, pf->f_convert);
494		for ( ; ; ) {
495			alarm(rexmtval);        /* read the ack */
496			n = recv(peer, ackbuf, sizeof (ackbuf), 0);
497			alarm(0);
498			if (n < 0) {
499				syslog(LOG_ERR, "tftpd: read: %m\n");
500				goto abort;
501			}
502			ap->th_opcode = ntohs((u_short)ap->th_opcode);
503			ap->th_block = ntohs((u_short)ap->th_block);
504
505			if (ap->th_opcode == ERROR)
506				goto abort;
507
508			if (ap->th_opcode == ACK) {
509				if (ap->th_block == block)
510					break;
511				/* Re-synchronize with the other side */
512				(void) synchnet(peer);
513				if (ap->th_block == (block -1))
514					goto send_data;
515			}
516
517		}
518		block++;
519	} while (size == SEGSIZE);
520abort:
521	(void) fclose(file);
522}
523
524void
525justquit()
526{
527	exit(0);
528}
529
530
531/*
532 * Receive a file.
533 */
534void
535recvfile(pf)
536	struct formats *pf;
537{
538	struct tftphdr *dp, *w_init();
539	register struct tftphdr *ap;    /* ack buffer */
540	register int n, size;
541	volatile int block;
542
543	signal(SIGALRM, timer);
544	dp = w_init();
545	ap = (struct tftphdr *)ackbuf;
546	block = 0;
547	do {
548		timeout = 0;
549		ap->th_opcode = htons((u_short)ACK);
550		ap->th_block = htons((u_short)block);
551		block++;
552		(void) setjmp(timeoutbuf);
553send_ack:
554		if (send(peer, ackbuf, 4, 0) != 4) {
555			syslog(LOG_ERR, "tftpd: write: %m\n");
556			goto abort;
557		}
558		write_behind(file, pf->f_convert);
559		for ( ; ; ) {
560			alarm(rexmtval);
561			n = recv(peer, dp, PKTSIZE, 0);
562			alarm(0);
563			if (n < 0) {            /* really? */
564				syslog(LOG_ERR, "tftpd: read: %m\n");
565				goto abort;
566			}
567			dp->th_opcode = ntohs((u_short)dp->th_opcode);
568			dp->th_block = ntohs((u_short)dp->th_block);
569			if (dp->th_opcode == ERROR)
570				goto abort;
571			if (dp->th_opcode == DATA) {
572				if (dp->th_block == block) {
573					break;   /* normal */
574				}
575				/* Re-synchronize with the other side */
576				(void) synchnet(peer);
577				if (dp->th_block == (block-1))
578					goto send_ack;          /* rexmit */
579			}
580		}
581		/*  size = write(file, dp->th_data, n - 4); */
582		size = writeit(file, &dp, n - 4, pf->f_convert);
583		if (size != (n-4)) {                    /* ahem */
584			if (size < 0) nak(errno + 100);
585			else nak(ENOSPACE);
586			goto abort;
587		}
588	} while (size == SEGSIZE);
589	write_behind(file, pf->f_convert);
590	(void) fclose(file);            /* close data file */
591
592	ap->th_opcode = htons((u_short)ACK);    /* send the "final" ack */
593	ap->th_block = htons((u_short)(block));
594	(void) send(peer, ackbuf, 4, 0);
595
596	signal(SIGALRM, justquit);      /* just quit on timeout */
597	alarm(rexmtval);
598	n = recv(peer, buf, sizeof (buf), 0); /* normally times out and quits */
599	alarm(0);
600	if (n >= 4 &&                   /* if read some data */
601	    dp->th_opcode == DATA &&    /* and got a data block */
602	    block == dp->th_block) {	/* then my last ack was lost */
603		(void) send(peer, ackbuf, 4, 0);     /* resend final ack */
604	}
605abort:
606	return;
607}
608
609struct errmsg {
610	int	e_code;
611	char	*e_msg;
612} errmsgs[] = {
613	{ EUNDEF,	"Undefined error code" },
614	{ ENOTFOUND,	"File not found" },
615	{ EACCESS,	"Access violation" },
616	{ ENOSPACE,	"Disk full or allocation exceeded" },
617	{ EBADOP,	"Illegal TFTP operation" },
618	{ EBADID,	"Unknown transfer ID" },
619	{ EEXISTS,	"File already exists" },
620	{ ENOUSER,	"No such user" },
621	{ -1,		0 }
622};
623
624static char *
625errtomsg(error)
626	int error;
627{
628	static char buf[20];
629	register struct errmsg *pe;
630	if (error == 0)
631		return "success";
632	for (pe = errmsgs; pe->e_code >= 0; pe++)
633		if (pe->e_code == error)
634			return pe->e_msg;
635	sprintf(buf, "error %d", error);
636	return buf;
637}
638
639/*
640 * Send a nak packet (error message).
641 * Error code passed in is one of the
642 * standard TFTP codes, or a UNIX errno
643 * offset by 100.
644 */
645static void
646nak(error)
647	int error;
648{
649	register struct tftphdr *tp;
650	int length;
651	register struct errmsg *pe;
652
653	tp = (struct tftphdr *)buf;
654	tp->th_opcode = htons((u_short)ERROR);
655	tp->th_code = htons((u_short)error);
656	for (pe = errmsgs; pe->e_code >= 0; pe++)
657		if (pe->e_code == error)
658			break;
659	if (pe->e_code < 0) {
660		pe->e_msg = strerror(error - 100);
661		tp->th_code = EUNDEF;   /* set 'undef' errorcode */
662	}
663	strcpy(tp->th_msg, pe->e_msg);
664	length = strlen(pe->e_msg);
665	tp->th_msg[length] = '\0';
666	length += 5;
667	if (send(peer, buf, length, 0) != length)
668		syslog(LOG_ERR, "nak: %m\n");
669}
670
671static char *
672verifyhost(fromp)
673	struct sockaddr_in *fromp;
674{
675	struct hostent *hp;
676
677	hp = gethostbyaddr((char *)&fromp->sin_addr, sizeof (fromp->sin_addr),
678			    fromp->sin_family);
679	if (hp)
680		return hp->h_name;
681	else
682		return inet_ntoa(fromp->sin_addr);
683}
684