tftpd.c revision 84047 
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
34#ifndef lint
35static const char copyright[] =
36"@(#) Copyright (c) 1983, 1993\n\
37	The Regents of the University of California.  All rights reserved.\n";
38#endif /* not lint */
39
40#ifndef lint
41#if 0
42static char sccsid[] = "@(#)tftpd.c	8.1 (Berkeley) 6/4/93";
43#endif
44static const char rcsid[] =
45  "$FreeBSD: head/libexec/tftpd/tftpd.c 84047 2001-09-27 20:50:14Z obrien $";
46#endif /* not lint */
47
48/*
49 * Trivial file transfer protocol server.
50 *
51 * This version includes many modifications by Jim Guyton
52 * <guyton@rand-unix>.
53 */
54
55#include <sys/param.h>
56#include <sys/ioctl.h>
57#include <sys/stat.h>
58#include <sys/socket.h>
59#include <sys/types.h>
60
61#include <netinet/in.h>
62#include <arpa/tftp.h>
63#include <arpa/inet.h>
64
65#include <ctype.h>
66#include <errno.h>
67#include <fcntl.h>
68#include <libutil.h>
69#include <netdb.h>
70#include <pwd.h>
71#include <setjmp.h>
72#include <signal.h>
73#include <stdio.h>
74#include <stdlib.h>
75#include <string.h>
76#include <syslog.h>
77#include <unistd.h>
78
79#include "tftpsubs.h"
80
81#define	TIMEOUT		5
82#define	MAX_TIMEOUTS	5
83
84int	peer;
85int	rexmtval = TIMEOUT;
86int	max_rexmtval = 2*TIMEOUT;
87
88#define	PKTSIZE	SEGSIZE+4
89char	buf[PKTSIZE];
90char	ackbuf[PKTSIZE];
91struct	sockaddr_in from;
92int	fromlen;
93
94void	tftp __P((struct tftphdr *, int));
95
96/*
97 * Null-terminated directory prefix list for absolute pathname requests and
98 * search list for relative pathname requests.
99 *
100 * MAXDIRS should be at least as large as the number of arguments that
101 * inetd allows (currently 20).
102 */
103#define MAXDIRS	20
104static struct dirlist {
105	char	*name;
106	int	len;
107} dirs[MAXDIRS+1];
108static int	suppress_naks;
109static int	logging;
110static int	ipchroot;
111
112static char *errtomsg __P((int));
113static void  nak __P((int));
114static void  oack __P(());
115
116int
117main(argc, argv)
118	int argc;
119	char *argv[];
120{
121	register struct tftphdr *tp;
122	register int n;
123	int ch, on;
124	struct sockaddr_in sin;
125	char *chroot_dir = NULL;
126	struct passwd *nobody;
127	char *chuser = "nobody";
128
129	openlog("tftpd", LOG_PID | LOG_NDELAY, LOG_FTP);
130	while ((ch = getopt(argc, argv, "cClns:u:")) != -1) {
131		switch (ch) {
132		case 'c':
133			ipchroot = 1;
134			break;
135		case 'C':
136			ipchroot = 2;
137			break;
138		case 'l':
139			logging = 1;
140			break;
141		case 'n':
142			suppress_naks = 1;
143			break;
144		case 's':
145			chroot_dir = optarg;
146			break;
147		case 'u':
148			chuser = optarg;
149			break;
150		default:
151			syslog(LOG_WARNING, "ignoring unknown option -%c", ch);
152		}
153	}
154	if (optind < argc) {
155		struct dirlist *dirp;
156
157		/* Get list of directory prefixes. Skip relative pathnames. */
158		for (dirp = dirs; optind < argc && dirp < &dirs[MAXDIRS];
159		     optind++) {
160			if (argv[optind][0] == '/') {
161				dirp->name = argv[optind];
162				dirp->len  = strlen(dirp->name);
163				dirp++;
164			}
165		}
166	}
167	else if (chroot_dir) {
168		dirs->name = "/";
169		dirs->len = 1;
170	}
171	if (ipchroot && chroot_dir == NULL) {
172		syslog(LOG_ERR, "-c requires -s");
173		exit(1);
174	}
175
176	on = 1;
177	if (ioctl(0, FIONBIO, &on) < 0) {
178		syslog(LOG_ERR, "ioctl(FIONBIO): %m");
179		exit(1);
180	}
181	fromlen = sizeof (from);
182	n = recvfrom(0, buf, sizeof (buf), 0,
183	    (struct sockaddr *)&from, &fromlen);
184	if (n < 0) {
185		syslog(LOG_ERR, "recvfrom: %m");
186		exit(1);
187	}
188	/*
189	 * Now that we have read the message out of the UDP
190	 * socket, we fork and exit.  Thus, inetd will go back
191	 * to listening to the tftp port, and the next request
192	 * to come in will start up a new instance of tftpd.
193	 *
194	 * We do this so that inetd can run tftpd in "wait" mode.
195	 * The problem with tftpd running in "nowait" mode is that
196	 * inetd may get one or more successful "selects" on the
197	 * tftp port before we do our receive, so more than one
198	 * instance of tftpd may be started up.  Worse, if tftpd
199	 * break before doing the above "recvfrom", inetd would
200	 * spawn endless instances, clogging the system.
201	 */
202	{
203		int pid;
204		int i, j;
205
206		for (i = 1; i < 20; i++) {
207		    pid = fork();
208		    if (pid < 0) {
209				sleep(i);
210				/*
211				 * flush out to most recently sent request.
212				 *
213				 * This may drop some request, but those
214				 * will be resent by the clients when
215				 * they timeout.  The positive effect of
216				 * this flush is to (try to) prevent more
217				 * than one tftpd being started up to service
218				 * a single request from a single client.
219				 */
220				j = sizeof from;
221				i = recvfrom(0, buf, sizeof (buf), 0,
222				    (struct sockaddr *)&from, &j);
223				if (i > 0) {
224					n = i;
225					fromlen = j;
226				}
227		    } else {
228				break;
229		    }
230		}
231		if (pid < 0) {
232			syslog(LOG_ERR, "fork: %m");
233			exit(1);
234		} else if (pid != 0) {
235			exit(0);
236		}
237	}
238
239	/*
240	 * Since we exit here, we should do that only after the above
241	 * recvfrom to keep inetd from constantly forking should there
242	 * be a problem.  See the above comment about system clogging.
243	 */
244	if (chroot_dir) {
245		if (ipchroot) {
246			char *tempchroot;
247			struct stat sb;
248			int statret;
249
250			tempchroot = inet_ntoa(from.sin_addr);
251			asprintf(&tempchroot, "%s/%s", chroot_dir, tempchroot);
252			statret = stat(tempchroot, &sb);
253			if ((sb.st_mode & S_IFDIR) &&
254			    (statret == 0 || (statret == -1 && ipchroot == 1)))
255				chroot_dir = tempchroot;
256		}
257		/* Must get this before chroot because /etc might go away */
258		if ((nobody = getpwnam(chuser)) == NULL) {
259			syslog(LOG_ERR, "%s: no such user", chuser);
260			exit(1);
261		}
262		if (chroot(chroot_dir)) {
263			syslog(LOG_ERR, "chroot: %s: %m", chroot_dir);
264			exit(1);
265		}
266		chdir( "/" );
267		setuid(nobody->pw_uid);
268	}
269
270	from.sin_family = AF_INET;
271	alarm(0);
272	close(0);
273	close(1);
274	peer = socket(AF_INET, SOCK_DGRAM, 0);
275	if (peer < 0) {
276		syslog(LOG_ERR, "socket: %m");
277		exit(1);
278	}
279	memset(&sin, 0, sizeof(sin));
280	sin.sin_family = AF_INET;
281	if (bind(peer, (struct sockaddr *)&sin, sizeof (sin)) < 0) {
282		syslog(LOG_ERR, "bind: %m");
283		exit(1);
284	}
285	if (connect(peer, (struct sockaddr *)&from, sizeof(from)) < 0) {
286		syslog(LOG_ERR, "connect: %m");
287		exit(1);
288	}
289	tp = (struct tftphdr *)buf;
290	tp->th_opcode = ntohs(tp->th_opcode);
291	if (tp->th_opcode == RRQ || tp->th_opcode == WRQ)
292		tftp(tp, n);
293	exit(1);
294}
295
296struct formats;
297int	validate_access __P((char **, int));
298void	xmitfile __P((struct formats *));
299void	recvfile __P((struct formats *));
300
301struct formats {
302	char	*f_mode;
303	int	(*f_validate) __P((char **, int));
304	void	(*f_send) __P((struct formats *));
305	void	(*f_recv) __P((struct formats *));
306	int	f_convert;
307} formats[] = {
308	{ "netascii",	validate_access,	xmitfile,	recvfile, 1 },
309	{ "octet",	validate_access,	xmitfile,	recvfile, 0 },
310#ifdef notdef
311	{ "mail",	validate_user,		sendmail,	recvmail, 1 },
312#endif
313	{ 0 }
314};
315
316struct options {
317	char	*o_type;
318	char	*o_request;
319	int	o_reply;	/* turn into union if need be */
320} options[] = {
321	{ "tsize" },		/* OPT_TSIZE */
322	{ "timeout" },		/* OPT_TIMEOUT */
323	{ NULL }
324};
325
326enum opt_enum {
327	OPT_TSIZE = 0,
328	OPT_TIMEOUT,
329};
330
331/*
332 * Handle initial connection protocol.
333 */
334void
335tftp(tp, size)
336	struct tftphdr *tp;
337	int size;
338{
339	register char *cp;
340	int i, first = 1, has_options = 0, ecode;
341	register struct formats *pf;
342	char *filename, *mode, *option, *ccp;
343
344	filename = cp = tp->th_stuff;
345again:
346	while (cp < buf + size) {
347		if (*cp == '\0')
348			break;
349		cp++;
350	}
351	if (*cp != '\0') {
352		nak(EBADOP);
353		exit(1);
354	}
355	if (first) {
356		mode = ++cp;
357		first = 0;
358		goto again;
359	}
360	for (cp = mode; *cp; cp++)
361		if (isupper(*cp))
362			*cp = tolower(*cp);
363	for (pf = formats; pf->f_mode; pf++)
364		if (strcmp(pf->f_mode, mode) == 0)
365			break;
366	if (pf->f_mode == 0) {
367		nak(EBADOP);
368		exit(1);
369	}
370	while (++cp < buf + size) {
371		for (i = 2, ccp = cp; i > 0; ccp++) {
372			if (ccp >= buf + size) {
373				nak(EBADOP);
374				exit(1);
375			} else if (*ccp == '\0')
376				i--;
377		}
378		for (option = cp; *cp; cp++)
379			if (isupper(*cp))
380				*cp = tolower(*cp);
381		for (i = 0; options[i].o_type != NULL; i++)
382			if (strcmp(option, options[i].o_type) == 0) {
383				options[i].o_request = ++cp;
384				has_options = 1;
385			}
386		cp = ccp-1;
387	}
388
389	if (options[OPT_TIMEOUT].o_request) {
390		int to = atoi(options[OPT_TIMEOUT].o_request);
391		if (to < 1 || to > 255) {
392			nak(EBADOP);
393			exit(1);
394		}
395		else if (to <= max_rexmtval)
396			options[OPT_TIMEOUT].o_reply = rexmtval = to;
397		else
398			options[OPT_TIMEOUT].o_request = NULL;
399	}
400
401	ecode = (*pf->f_validate)(&filename, tp->th_opcode);
402	if (has_options)
403		oack();
404	if (logging) {
405		char host[MAXHOSTNAMELEN];
406
407		realhostname(host, sizeof(host) - 1, &from.sin_addr);
408		host[sizeof(host) - 1] = '\0';
409		syslog(LOG_INFO, "%s: %s request for %s: %s", host,
410			tp->th_opcode == WRQ ? "write" : "read",
411			filename, errtomsg(ecode));
412	}
413	if (ecode) {
414		/*
415		 * Avoid storms of naks to a RRQ broadcast for a relative
416		 * bootfile pathname from a diskless Sun.
417		 */
418		if (suppress_naks && *filename != '/' && ecode == ENOTFOUND)
419			exit(0);
420		nak(ecode);
421		exit(1);
422	}
423	if (tp->th_opcode == WRQ)
424		(*pf->f_recv)(pf);
425	else
426		(*pf->f_send)(pf);
427	exit(0);
428}
429
430
431FILE *file;
432
433/*
434 * Validate file access.  Since we
435 * have no uid or gid, for now require
436 * file to exist and be publicly
437 * readable/writable.
438 * If we were invoked with arguments
439 * from inetd then the file must also be
440 * in one of the given directory prefixes.
441 * Note also, full path name must be
442 * given as we have no login directory.
443 */
444int
445validate_access(filep, mode)
446	char **filep;
447	int mode;
448{
449	struct stat stbuf;
450	int	fd;
451	struct dirlist *dirp;
452	static char pathname[MAXPATHLEN];
453	char *filename = *filep;
454
455	/*
456	 * Prevent tricksters from getting around the directory restrictions
457	 */
458	if (strstr(filename, "/../"))
459		return (EACCESS);
460
461	if (*filename == '/') {
462		/*
463		 * Allow the request if it's in one of the approved locations.
464		 * Special case: check the null prefix ("/") by looking
465		 * for length = 1 and relying on the arg. processing that
466		 * it's a /.
467		 */
468		for (dirp = dirs; dirp->name != NULL; dirp++) {
469			if (dirp->len == 1 ||
470			    (!strncmp(filename, dirp->name, dirp->len) &&
471			     filename[dirp->len] == '/'))
472				    break;
473		}
474		/* If directory list is empty, allow access to any file */
475		if (dirp->name == NULL && dirp != dirs)
476			return (EACCESS);
477		if (stat(filename, &stbuf) < 0)
478			return (errno == ENOENT ? ENOTFOUND : EACCESS);
479		if ((stbuf.st_mode & S_IFMT) != S_IFREG)
480			return (ENOTFOUND);
481		if (mode == RRQ) {
482			if ((stbuf.st_mode & S_IROTH) == 0)
483				return (EACCESS);
484		} else {
485			if ((stbuf.st_mode & S_IWOTH) == 0)
486				return (EACCESS);
487		}
488	} else {
489		int err;
490
491		/*
492		 * Relative file name: search the approved locations for it.
493		 * Don't allow write requests that avoid directory
494		 * restrictions.
495		 */
496
497		if (!strncmp(filename, "../", 3))
498			return (EACCESS);
499
500		/*
501		 * If the file exists in one of the directories and isn't
502		 * readable, continue looking. However, change the error code
503		 * to give an indication that the file exists.
504		 */
505		err = ENOTFOUND;
506		for (dirp = dirs; dirp->name != NULL; dirp++) {
507			snprintf(pathname, sizeof(pathname), "%s/%s",
508				dirp->name, filename);
509			if (stat(pathname, &stbuf) == 0 &&
510			    (stbuf.st_mode & S_IFMT) == S_IFREG) {
511				if ((stbuf.st_mode & S_IROTH) != 0) {
512					break;
513				}
514				err = EACCESS;
515			}
516		}
517		if (dirp->name == NULL)
518			return (err);
519		*filep = filename = pathname;
520	}
521	if (options[OPT_TSIZE].o_request) {
522		if (mode == RRQ)
523			options[OPT_TSIZE].o_reply = stbuf.st_size;
524		else
525			/* XXX Allows writes of all sizes. */
526			options[OPT_TSIZE].o_reply =
527				atoi(options[OPT_TSIZE].o_request);
528	}
529	fd = open(filename, mode == RRQ ? O_RDONLY : O_WRONLY|O_TRUNC);
530	if (fd < 0)
531		return (errno + 100);
532	file = fdopen(fd, (mode == RRQ)? "r":"w");
533	if (file == NULL) {
534		return errno+100;
535	}
536	return (0);
537}
538
539int	timeouts;
540jmp_buf	timeoutbuf;
541
542void
543timer()
544{
545	if (++timeouts > MAX_TIMEOUTS)
546		exit(1);
547	longjmp(timeoutbuf, 1);
548}
549
550/*
551 * Send the requested file.
552 */
553void
554xmitfile(pf)
555	struct formats *pf;
556{
557	struct tftphdr *dp, *r_init();
558	register struct tftphdr *ap;    /* ack packet */
559	register int size, n;
560	volatile unsigned short block;
561
562	signal(SIGALRM, timer);
563	dp = r_init();
564	ap = (struct tftphdr *)ackbuf;
565	block = 1;
566	do {
567		size = readit(file, &dp, pf->f_convert);
568		if (size < 0) {
569			nak(errno + 100);
570			goto abort;
571		}
572		dp->th_opcode = htons((u_short)DATA);
573		dp->th_block = htons((u_short)block);
574		timeouts = 0;
575		(void)setjmp(timeoutbuf);
576
577send_data:
578		if (send(peer, dp, size + 4, 0) != size + 4) {
579			syslog(LOG_ERR, "write: %m");
580			goto abort;
581		}
582		read_ahead(file, pf->f_convert);
583		for ( ; ; ) {
584			alarm(rexmtval);        /* read the ack */
585			n = recv(peer, ackbuf, sizeof (ackbuf), 0);
586			alarm(0);
587			if (n < 0) {
588				syslog(LOG_ERR, "read: %m");
589				goto abort;
590			}
591			ap->th_opcode = ntohs((u_short)ap->th_opcode);
592			ap->th_block = ntohs((u_short)ap->th_block);
593
594			if (ap->th_opcode == ERROR)
595				goto abort;
596
597			if (ap->th_opcode == ACK) {
598				if (ap->th_block == block)
599					break;
600				/* Re-synchronize with the other side */
601				(void) synchnet(peer);
602				if (ap->th_block == (block -1))
603					goto send_data;
604			}
605
606		}
607		block++;
608	} while (size == SEGSIZE);
609abort:
610	(void) fclose(file);
611}
612
613void
614justquit()
615{
616	exit(0);
617}
618
619
620/*
621 * Receive a file.
622 */
623void
624recvfile(pf)
625	struct formats *pf;
626{
627	struct tftphdr *dp, *w_init();
628	register struct tftphdr *ap;    /* ack buffer */
629	register int n, size;
630	volatile unsigned short block;
631
632	signal(SIGALRM, timer);
633	dp = w_init();
634	ap = (struct tftphdr *)ackbuf;
635	block = 0;
636	do {
637		timeouts = 0;
638		ap->th_opcode = htons((u_short)ACK);
639		ap->th_block = htons((u_short)block);
640		block++;
641		(void) setjmp(timeoutbuf);
642send_ack:
643		if (send(peer, ackbuf, 4, 0) != 4) {
644			syslog(LOG_ERR, "write: %m");
645			goto abort;
646		}
647		write_behind(file, pf->f_convert);
648		for ( ; ; ) {
649			alarm(rexmtval);
650			n = recv(peer, dp, PKTSIZE, 0);
651			alarm(0);
652			if (n < 0) {            /* really? */
653				syslog(LOG_ERR, "read: %m");
654				goto abort;
655			}
656			dp->th_opcode = ntohs((u_short)dp->th_opcode);
657			dp->th_block = ntohs((u_short)dp->th_block);
658			if (dp->th_opcode == ERROR)
659				goto abort;
660			if (dp->th_opcode == DATA) {
661				if (dp->th_block == block) {
662					break;   /* normal */
663				}
664				/* Re-synchronize with the other side */
665				(void) synchnet(peer);
666				if (dp->th_block == (block-1))
667					goto send_ack;          /* rexmit */
668			}
669		}
670		/*  size = write(file, dp->th_data, n - 4); */
671		size = writeit(file, &dp, n - 4, pf->f_convert);
672		if (size != (n-4)) {                    /* ahem */
673			if (size < 0) nak(errno + 100);
674			else nak(ENOSPACE);
675			goto abort;
676		}
677	} while (size == SEGSIZE);
678	write_behind(file, pf->f_convert);
679	(void) fclose(file);            /* close data file */
680
681	ap->th_opcode = htons((u_short)ACK);    /* send the "final" ack */
682	ap->th_block = htons((u_short)(block));
683	(void) send(peer, ackbuf, 4, 0);
684
685	signal(SIGALRM, justquit);      /* just quit on timeout */
686	alarm(rexmtval);
687	n = recv(peer, buf, sizeof (buf), 0); /* normally times out and quits */
688	alarm(0);
689	if (n >= 4 &&                   /* if read some data */
690	    dp->th_opcode == DATA &&    /* and got a data block */
691	    block == dp->th_block) {	/* then my last ack was lost */
692		(void) send(peer, ackbuf, 4, 0);     /* resend final ack */
693	}
694abort:
695	return;
696}
697
698struct errmsg {
699	int	e_code;
700	char	*e_msg;
701} errmsgs[] = {
702	{ EUNDEF,	"Undefined error code" },
703	{ ENOTFOUND,	"File not found" },
704	{ EACCESS,	"Access violation" },
705	{ ENOSPACE,	"Disk full or allocation exceeded" },
706	{ EBADOP,	"Illegal TFTP operation" },
707	{ EBADID,	"Unknown transfer ID" },
708	{ EEXISTS,	"File already exists" },
709	{ ENOUSER,	"No such user" },
710	{ EOPTNEG,	"Option negotiation" },
711	{ -1,		0 }
712};
713
714static char *
715errtomsg(error)
716	int error;
717{
718	static char buf[20];
719	register struct errmsg *pe;
720	if (error == 0)
721		return "success";
722	for (pe = errmsgs; pe->e_code >= 0; pe++)
723		if (pe->e_code == error)
724			return pe->e_msg;
725	snprintf(buf, sizeof(buf), "error %d", error);
726	return buf;
727}
728
729/*
730 * Send a nak packet (error message).
731 * Error code passed in is one of the
732 * standard TFTP codes, or a UNIX errno
733 * offset by 100.
734 */
735static void
736nak(error)
737	int error;
738{
739	register struct tftphdr *tp;
740	int length;
741	register struct errmsg *pe;
742
743	tp = (struct tftphdr *)buf;
744	tp->th_opcode = htons((u_short)ERROR);
745	tp->th_code = htons((u_short)error);
746	for (pe = errmsgs; pe->e_code >= 0; pe++)
747		if (pe->e_code == error)
748			break;
749	if (pe->e_code < 0) {
750		pe->e_msg = strerror(error - 100);
751		tp->th_code = EUNDEF;   /* set 'undef' errorcode */
752	}
753	strcpy(tp->th_msg, pe->e_msg);
754	length = strlen(pe->e_msg);
755	tp->th_msg[length] = '\0';
756	length += 5;
757	if (send(peer, buf, length, 0) != length)
758		syslog(LOG_ERR, "nak: %m");
759}
760
761/*
762 * Send an oack packet (option acknowledgement).
763 */
764static void
765oack()
766{
767	struct tftphdr *tp, *ap;
768	int size, i, n;
769	char *bp;
770
771	tp = (struct tftphdr *)buf;
772	bp = buf + 2;
773	size = sizeof(buf) - 2;
774	tp->th_opcode = htons((u_short)OACK);
775	for (i = 0; options[i].o_type != NULL; i++) {
776		if (options[i].o_request) {
777			n = snprintf(bp, size, "%s%c%d", options[i].o_type,
778				     0, options[i].o_reply);
779			bp += n+1;
780			size -= n+1;
781			if (size < 0) {
782				syslog(LOG_ERR, "oack: buffer overflow");
783				exit(1);
784			}
785		}
786	}
787	size = bp - buf;
788	ap = (struct tftphdr *)ackbuf;
789	signal(SIGALRM, timer);
790	timeouts = 0;
791
792	(void)setjmp(timeoutbuf);
793	if (send(peer, buf, size, 0) != size) {
794		syslog(LOG_INFO, "oack: %m");
795		exit(1);
796	}
797
798	for (;;) {
799		alarm(rexmtval);
800		n = recv(peer, ackbuf, sizeof (ackbuf), 0);
801		alarm(0);
802		if (n < 0) {
803			syslog(LOG_ERR, "recv: %m");
804			exit(1);
805		}
806		ap->th_opcode = ntohs((u_short)ap->th_opcode);
807		ap->th_block = ntohs((u_short)ap->th_block);
808		if (ap->th_opcode == ERROR)
809			exit(1);
810		if (ap->th_opcode == ACK && ap->th_block == 0)
811			break;
812	}
813}
814