tftpd.c revision 90333 
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 90333 2002-02-07 04:49:34Z imp $";
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(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(int);
113static void  nak(int);
114static void  oack();
115
116int
117main(int argc, char *argv[])
118{
119	struct tftphdr *tp;
120	int n;
121	int ch, on;
122	struct sockaddr_in sin;
123	char *chroot_dir = NULL;
124	struct passwd *nobody;
125	char *chuser = "nobody";
126
127	openlog("tftpd", LOG_PID | LOG_NDELAY, LOG_FTP);
128	while ((ch = getopt(argc, argv, "cClns:u:")) != -1) {
129		switch (ch) {
130		case 'c':
131			ipchroot = 1;
132			break;
133		case 'C':
134			ipchroot = 2;
135			break;
136		case 'l':
137			logging = 1;
138			break;
139		case 'n':
140			suppress_naks = 1;
141			break;
142		case 's':
143			chroot_dir = optarg;
144			break;
145		case 'u':
146			chuser = optarg;
147			break;
148		default:
149			syslog(LOG_WARNING, "ignoring unknown option -%c", ch);
150		}
151	}
152	if (optind < argc) {
153		struct dirlist *dirp;
154
155		/* Get list of directory prefixes. Skip relative pathnames. */
156		for (dirp = dirs; optind < argc && dirp < &dirs[MAXDIRS];
157		     optind++) {
158			if (argv[optind][0] == '/') {
159				dirp->name = argv[optind];
160				dirp->len  = strlen(dirp->name);
161				dirp++;
162			}
163		}
164	}
165	else if (chroot_dir) {
166		dirs->name = "/";
167		dirs->len = 1;
168	}
169	if (ipchroot && chroot_dir == NULL) {
170		syslog(LOG_ERR, "-c requires -s");
171		exit(1);
172	}
173
174	on = 1;
175	if (ioctl(0, FIONBIO, &on) < 0) {
176		syslog(LOG_ERR, "ioctl(FIONBIO): %m");
177		exit(1);
178	}
179	fromlen = sizeof (from);
180	n = recvfrom(0, buf, sizeof (buf), 0,
181	    (struct sockaddr *)&from, &fromlen);
182	if (n < 0) {
183		syslog(LOG_ERR, "recvfrom: %m");
184		exit(1);
185	}
186	/*
187	 * Now that we have read the message out of the UDP
188	 * socket, we fork and exit.  Thus, inetd will go back
189	 * to listening to the tftp port, and the next request
190	 * to come in will start up a new instance of tftpd.
191	 *
192	 * We do this so that inetd can run tftpd in "wait" mode.
193	 * The problem with tftpd running in "nowait" mode is that
194	 * inetd may get one or more successful "selects" on the
195	 * tftp port before we do our receive, so more than one
196	 * instance of tftpd may be started up.  Worse, if tftpd
197	 * break before doing the above "recvfrom", inetd would
198	 * spawn endless instances, clogging the system.
199	 */
200	{
201		int pid;
202		int i, j;
203
204		for (i = 1; i < 20; i++) {
205		    pid = fork();
206		    if (pid < 0) {
207				sleep(i);
208				/*
209				 * flush out to most recently sent request.
210				 *
211				 * This may drop some request, but those
212				 * will be resent by the clients when
213				 * they timeout.  The positive effect of
214				 * this flush is to (try to) prevent more
215				 * than one tftpd being started up to service
216				 * a single request from a single client.
217				 */
218				j = sizeof from;
219				i = recvfrom(0, buf, sizeof (buf), 0,
220				    (struct sockaddr *)&from, &j);
221				if (i > 0) {
222					n = i;
223					fromlen = j;
224				}
225		    } else {
226				break;
227		    }
228		}
229		if (pid < 0) {
230			syslog(LOG_ERR, "fork: %m");
231			exit(1);
232		} else if (pid != 0) {
233			exit(0);
234		}
235	}
236
237	/*
238	 * Since we exit here, we should do that only after the above
239	 * recvfrom to keep inetd from constantly forking should there
240	 * be a problem.  See the above comment about system clogging.
241	 */
242	if (chroot_dir) {
243		if (ipchroot) {
244			char *tempchroot;
245			struct stat sb;
246			int statret;
247
248			tempchroot = inet_ntoa(from.sin_addr);
249			asprintf(&tempchroot, "%s/%s", chroot_dir, tempchroot);
250			statret = stat(tempchroot, &sb);
251			if ((sb.st_mode & S_IFDIR) &&
252			    (statret == 0 || (statret == -1 && ipchroot == 1)))
253				chroot_dir = tempchroot;
254		}
255		/* Must get this before chroot because /etc might go away */
256		if ((nobody = getpwnam(chuser)) == NULL) {
257			syslog(LOG_ERR, "%s: no such user", chuser);
258			exit(1);
259		}
260		if (chroot(chroot_dir)) {
261			syslog(LOG_ERR, "chroot: %s: %m", chroot_dir);
262			exit(1);
263		}
264		chdir( "/" );
265		setuid(nobody->pw_uid);
266		setgroups(1, &nobody->pw_gid);
267	}
268
269	from.sin_family = AF_INET;
270	alarm(0);
271	close(0);
272	close(1);
273	peer = socket(AF_INET, SOCK_DGRAM, 0);
274	if (peer < 0) {
275		syslog(LOG_ERR, "socket: %m");
276		exit(1);
277	}
278	memset(&sin, 0, sizeof(sin));
279	sin.sin_family = AF_INET;
280	if (bind(peer, (struct sockaddr *)&sin, sizeof (sin)) < 0) {
281		syslog(LOG_ERR, "bind: %m");
282		exit(1);
283	}
284	if (connect(peer, (struct sockaddr *)&from, sizeof(from)) < 0) {
285		syslog(LOG_ERR, "connect: %m");
286		exit(1);
287	}
288	tp = (struct tftphdr *)buf;
289	tp->th_opcode = ntohs(tp->th_opcode);
290	if (tp->th_opcode == RRQ || tp->th_opcode == WRQ)
291		tftp(tp, n);
292	exit(1);
293}
294
295struct formats;
296int	validate_access(char **, int);
297void	xmitfile(struct formats *);
298void	recvfile(struct formats *);
299
300struct formats {
301	char	*f_mode;
302	int	(*f_validate)(char **, int);
303	void	(*f_send)(struct formats *);
304	void	(*f_recv)(struct formats *);
305	int	f_convert;
306} formats[] = {
307	{ "netascii",	validate_access,	xmitfile,	recvfile, 1 },
308	{ "octet",	validate_access,	xmitfile,	recvfile, 0 },
309#ifdef notdef
310	{ "mail",	validate_user,		sendmail,	recvmail, 1 },
311#endif
312	{ 0 }
313};
314
315struct options {
316	char	*o_type;
317	char	*o_request;
318	int	o_reply;	/* turn into union if need be */
319} options[] = {
320	{ "tsize" },		/* OPT_TSIZE */
321	{ "timeout" },		/* OPT_TIMEOUT */
322	{ NULL }
323};
324
325enum opt_enum {
326	OPT_TSIZE = 0,
327	OPT_TIMEOUT,
328};
329
330/*
331 * Handle initial connection protocol.
332 */
333void
334tftp(struct tftphdr *tp, int size)
335{
336	char *cp;
337	int i, first = 1, has_options = 0, ecode;
338	struct formats *pf;
339	char *filename, *mode, *option, *ccp;
340
341	filename = cp = tp->th_stuff;
342again:
343	while (cp < buf + size) {
344		if (*cp == '\0')
345			break;
346		cp++;
347	}
348	if (*cp != '\0') {
349		nak(EBADOP);
350		exit(1);
351	}
352	if (first) {
353		mode = ++cp;
354		first = 0;
355		goto again;
356	}
357	for (cp = mode; *cp; cp++)
358		if (isupper(*cp))
359			*cp = tolower(*cp);
360	for (pf = formats; pf->f_mode; pf++)
361		if (strcmp(pf->f_mode, mode) == 0)
362			break;
363	if (pf->f_mode == 0) {
364		nak(EBADOP);
365		exit(1);
366	}
367	while (++cp < buf + size) {
368		for (i = 2, ccp = cp; i > 0; ccp++) {
369			if (ccp >= buf + size) {
370				/*
371				 * Don't reject the request, just stop trying
372				 * to parse the option and get on with it.
373				 * Some Apple OpenFirmware versions have
374				 * trailing garbage on the end of otherwise
375				 * valid requests.
376				 */
377				goto option_fail;
378			} else if (*ccp == '\0')
379				i--;
380		}
381		for (option = cp; *cp; cp++)
382			if (isupper(*cp))
383				*cp = tolower(*cp);
384		for (i = 0; options[i].o_type != NULL; i++)
385			if (strcmp(option, options[i].o_type) == 0) {
386				options[i].o_request = ++cp;
387				has_options = 1;
388			}
389		cp = ccp-1;
390	}
391
392option_fail:
393	if (options[OPT_TIMEOUT].o_request) {
394		int to = atoi(options[OPT_TIMEOUT].o_request);
395		if (to < 1 || to > 255) {
396			nak(EBADOP);
397			exit(1);
398		}
399		else if (to <= max_rexmtval)
400			options[OPT_TIMEOUT].o_reply = rexmtval = to;
401		else
402			options[OPT_TIMEOUT].o_request = NULL;
403	}
404
405	ecode = (*pf->f_validate)(&filename, tp->th_opcode);
406	if (has_options)
407		oack();
408	if (logging) {
409		char host[MAXHOSTNAMELEN];
410
411		realhostname(host, sizeof(host) - 1, &from.sin_addr);
412		host[sizeof(host) - 1] = '\0';
413		syslog(LOG_INFO, "%s: %s request for %s: %s", host,
414			tp->th_opcode == WRQ ? "write" : "read",
415			filename, errtomsg(ecode));
416	}
417	if (ecode) {
418		/*
419		 * Avoid storms of naks to a RRQ broadcast for a relative
420		 * bootfile pathname from a diskless Sun.
421		 */
422		if (suppress_naks && *filename != '/' && ecode == ENOTFOUND)
423			exit(0);
424		nak(ecode);
425		exit(1);
426	}
427	if (tp->th_opcode == WRQ)
428		(*pf->f_recv)(pf);
429	else
430		(*pf->f_send)(pf);
431	exit(0);
432}
433
434
435FILE *file;
436
437/*
438 * Validate file access.  Since we
439 * have no uid or gid, for now require
440 * file to exist and be publicly
441 * readable/writable.
442 * If we were invoked with arguments
443 * from inetd then the file must also be
444 * in one of the given directory prefixes.
445 * Note also, full path name must be
446 * given as we have no login directory.
447 */
448int
449validate_access(char **filep, int mode)
450{
451	struct stat stbuf;
452	int	fd;
453	struct dirlist *dirp;
454	static char pathname[MAXPATHLEN];
455	char *filename = *filep;
456
457	/*
458	 * Prevent tricksters from getting around the directory restrictions
459	 */
460	if (strstr(filename, "/../"))
461		return (EACCESS);
462
463	if (*filename == '/') {
464		/*
465		 * Allow the request if it's in one of the approved locations.
466		 * Special case: check the null prefix ("/") by looking
467		 * for length = 1 and relying on the arg. processing that
468		 * it's a /.
469		 */
470		for (dirp = dirs; dirp->name != NULL; dirp++) {
471			if (dirp->len == 1 ||
472			    (!strncmp(filename, dirp->name, dirp->len) &&
473			     filename[dirp->len] == '/'))
474				    break;
475		}
476		/* If directory list is empty, allow access to any file */
477		if (dirp->name == NULL && dirp != dirs)
478			return (EACCESS);
479		if (stat(filename, &stbuf) < 0)
480			return (errno == ENOENT ? ENOTFOUND : EACCESS);
481		if ((stbuf.st_mode & S_IFMT) != S_IFREG)
482			return (ENOTFOUND);
483		if (mode == RRQ) {
484			if ((stbuf.st_mode & S_IROTH) == 0)
485				return (EACCESS);
486		} else {
487			if ((stbuf.st_mode & S_IWOTH) == 0)
488				return (EACCESS);
489		}
490	} else {
491		int err;
492
493		/*
494		 * Relative file name: search the approved locations for it.
495		 * Don't allow write requests that avoid directory
496		 * restrictions.
497		 */
498
499		if (!strncmp(filename, "../", 3))
500			return (EACCESS);
501
502		/*
503		 * If the file exists in one of the directories and isn't
504		 * readable, continue looking. However, change the error code
505		 * to give an indication that the file exists.
506		 */
507		err = ENOTFOUND;
508		for (dirp = dirs; dirp->name != NULL; dirp++) {
509			snprintf(pathname, sizeof(pathname), "%s/%s",
510				dirp->name, filename);
511			if (stat(pathname, &stbuf) == 0 &&
512			    (stbuf.st_mode & S_IFMT) == S_IFREG) {
513				if ((stbuf.st_mode & S_IROTH) != 0) {
514					break;
515				}
516				err = EACCESS;
517			}
518		}
519		if (dirp->name == NULL)
520			return (err);
521		*filep = filename = pathname;
522	}
523	if (options[OPT_TSIZE].o_request) {
524		if (mode == RRQ)
525			options[OPT_TSIZE].o_reply = stbuf.st_size;
526		else
527			/* XXX Allows writes of all sizes. */
528			options[OPT_TSIZE].o_reply =
529				atoi(options[OPT_TSIZE].o_request);
530	}
531	fd = open(filename, mode == RRQ ? O_RDONLY : O_WRONLY|O_TRUNC);
532	if (fd < 0)
533		return (errno + 100);
534	file = fdopen(fd, (mode == RRQ)? "r":"w");
535	if (file == NULL) {
536		return errno+100;
537	}
538	return (0);
539}
540
541int	timeouts;
542jmp_buf	timeoutbuf;
543
544void
545timer(int sig __unused)
546{
547	if (++timeouts > MAX_TIMEOUTS)
548		exit(1);
549	longjmp(timeoutbuf, 1);
550}
551
552/*
553 * Send the requested file.
554 */
555void
556xmitfile(struct formats *pf)
557{
558	struct tftphdr *dp, *r_init();
559	struct tftphdr *ap;    /* ack packet */
560	int size, n;
561	volatile unsigned short block;
562
563	signal(SIGALRM, timer);
564	dp = r_init();
565	ap = (struct tftphdr *)ackbuf;
566	block = 1;
567	do {
568		size = readit(file, &dp, pf->f_convert);
569		if (size < 0) {
570			nak(errno + 100);
571			goto abort;
572		}
573		dp->th_opcode = htons((u_short)DATA);
574		dp->th_block = htons((u_short)block);
575		timeouts = 0;
576		(void)setjmp(timeoutbuf);
577
578send_data:
579		if (send(peer, dp, size + 4, 0) != size + 4) {
580			syslog(LOG_ERR, "write: %m");
581			goto abort;
582		}
583		read_ahead(file, pf->f_convert);
584		for ( ; ; ) {
585			alarm(rexmtval);        /* read the ack */
586			n = recv(peer, ackbuf, sizeof (ackbuf), 0);
587			alarm(0);
588			if (n < 0) {
589				syslog(LOG_ERR, "read: %m");
590				goto abort;
591			}
592			ap->th_opcode = ntohs((u_short)ap->th_opcode);
593			ap->th_block = ntohs((u_short)ap->th_block);
594
595			if (ap->th_opcode == ERROR)
596				goto abort;
597
598			if (ap->th_opcode == ACK) {
599				if (ap->th_block == block)
600					break;
601				/* Re-synchronize with the other side */
602				(void) synchnet(peer);
603				if (ap->th_block == (block -1))
604					goto send_data;
605			}
606
607		}
608		block++;
609	} while (size == SEGSIZE);
610abort:
611	(void) fclose(file);
612}
613
614void
615justquit(int sig __unused)
616{
617	exit(0);
618}
619
620
621/*
622 * Receive a file.
623 */
624void
625recvfile(struct formats *pf)
626{
627	struct tftphdr *dp, *w_init();
628	struct tftphdr *ap;    /* ack buffer */
629	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(int error)
716{
717	static char buf[20];
718	struct errmsg *pe;
719	if (error == 0)
720		return "success";
721	for (pe = errmsgs; pe->e_code >= 0; pe++)
722		if (pe->e_code == error)
723			return pe->e_msg;
724	snprintf(buf, sizeof(buf), "error %d", error);
725	return buf;
726}
727
728/*
729 * Send a nak packet (error message).
730 * Error code passed in is one of the
731 * standard TFTP codes, or a UNIX errno
732 * offset by 100.
733 */
734static void
735nak(int error)
736{
737	struct tftphdr *tp;
738	int length;
739	struct errmsg *pe;
740
741	tp = (struct tftphdr *)buf;
742	tp->th_opcode = htons((u_short)ERROR);
743	tp->th_code = htons((u_short)error);
744	for (pe = errmsgs; pe->e_code >= 0; pe++)
745		if (pe->e_code == error)
746			break;
747	if (pe->e_code < 0) {
748		pe->e_msg = strerror(error - 100);
749		tp->th_code = EUNDEF;   /* set 'undef' errorcode */
750	}
751	strcpy(tp->th_msg, pe->e_msg);
752	length = strlen(pe->e_msg);
753	tp->th_msg[length] = '\0';
754	length += 5;
755	if (send(peer, buf, length, 0) != length)
756		syslog(LOG_ERR, "nak: %m");
757}
758
759/*
760 * Send an oack packet (option acknowledgement).
761 */
762static void
763oack(void)
764{
765	struct tftphdr *tp, *ap;
766	int size, i, n;
767	char *bp;
768
769	tp = (struct tftphdr *)buf;
770	bp = buf + 2;
771	size = sizeof(buf) - 2;
772	tp->th_opcode = htons((u_short)OACK);
773	for (i = 0; options[i].o_type != NULL; i++) {
774		if (options[i].o_request) {
775			n = snprintf(bp, size, "%s%c%d", options[i].o_type,
776				     0, options[i].o_reply);
777			bp += n+1;
778			size -= n+1;
779			if (size < 0) {
780				syslog(LOG_ERR, "oack: buffer overflow");
781				exit(1);
782			}
783		}
784	}
785	size = bp - buf;
786	ap = (struct tftphdr *)ackbuf;
787	signal(SIGALRM, timer);
788	timeouts = 0;
789
790	(void)setjmp(timeoutbuf);
791	if (send(peer, buf, size, 0) != size) {
792		syslog(LOG_INFO, "oack: %m");
793		exit(1);
794	}
795
796	for (;;) {
797		alarm(rexmtval);
798		n = recv(peer, ackbuf, sizeof (ackbuf), 0);
799		alarm(0);
800		if (n < 0) {
801			syslog(LOG_ERR, "recv: %m");
802			exit(1);
803		}
804		ap->th_opcode = ntohs((u_short)ap->th_opcode);
805		ap->th_block = ntohs((u_short)ap->th_block);
806		if (ap->th_opcode == ERROR)
807			exit(1);
808		if (ap->th_opcode == ACK && ap->th_block == 0)
809			break;
810	}
811}
812