tftpd.c revision 86765 
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 86765 2001-11-22 05:08:35Z benno $";
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		setgroups(1, &nobody->pw_gid);
269	}
270
271	from.sin_family = AF_INET;
272	alarm(0);
273	close(0);
274	close(1);
275	peer = socket(AF_INET, SOCK_DGRAM, 0);
276	if (peer < 0) {
277		syslog(LOG_ERR, "socket: %m");
278		exit(1);
279	}
280	memset(&sin, 0, sizeof(sin));
281	sin.sin_family = AF_INET;
282	if (bind(peer, (struct sockaddr *)&sin, sizeof (sin)) < 0) {
283		syslog(LOG_ERR, "bind: %m");
284		exit(1);
285	}
286	if (connect(peer, (struct sockaddr *)&from, sizeof(from)) < 0) {
287		syslog(LOG_ERR, "connect: %m");
288		exit(1);
289	}
290	tp = (struct tftphdr *)buf;
291	tp->th_opcode = ntohs(tp->th_opcode);
292	if (tp->th_opcode == RRQ || tp->th_opcode == WRQ)
293		tftp(tp, n);
294	exit(1);
295}
296
297struct formats;
298int	validate_access __P((char **, int));
299void	xmitfile __P((struct formats *));
300void	recvfile __P((struct formats *));
301
302struct formats {
303	char	*f_mode;
304	int	(*f_validate) __P((char **, int));
305	void	(*f_send) __P((struct formats *));
306	void	(*f_recv) __P((struct formats *));
307	int	f_convert;
308} formats[] = {
309	{ "netascii",	validate_access,	xmitfile,	recvfile, 1 },
310	{ "octet",	validate_access,	xmitfile,	recvfile, 0 },
311#ifdef notdef
312	{ "mail",	validate_user,		sendmail,	recvmail, 1 },
313#endif
314	{ 0 }
315};
316
317struct options {
318	char	*o_type;
319	char	*o_request;
320	int	o_reply;	/* turn into union if need be */
321} options[] = {
322	{ "tsize" },		/* OPT_TSIZE */
323	{ "timeout" },		/* OPT_TIMEOUT */
324	{ NULL }
325};
326
327enum opt_enum {
328	OPT_TSIZE = 0,
329	OPT_TIMEOUT,
330};
331
332/*
333 * Handle initial connection protocol.
334 */
335void
336tftp(tp, size)
337	struct tftphdr *tp;
338	int size;
339{
340	register char *cp;
341	int i, first = 1, has_options = 0, ecode;
342	register struct formats *pf;
343	char *filename, *mode, *option, *ccp;
344
345	filename = cp = tp->th_stuff;
346again:
347	while (cp < buf + size) {
348		if (*cp == '\0')
349			break;
350		cp++;
351	}
352	if (*cp != '\0') {
353		nak(EBADOP);
354		exit(1);
355	}
356	if (first) {
357		mode = ++cp;
358		first = 0;
359		goto again;
360	}
361	for (cp = mode; *cp; cp++)
362		if (isupper(*cp))
363			*cp = tolower(*cp);
364	for (pf = formats; pf->f_mode; pf++)
365		if (strcmp(pf->f_mode, mode) == 0)
366			break;
367	if (pf->f_mode == 0) {
368		nak(EBADOP);
369		exit(1);
370	}
371	while (++cp < buf + size) {
372		for (i = 2, ccp = cp; i > 0; ccp++) {
373			if (ccp >= buf + size) {
374				/*
375				 * Don't reject the request, just stop trying
376				 * to parse the option and get on with it.
377				 * Some Apple OpenFirmware versions have
378				 * trailing garbage on the end of otherwise
379				 * valid requests.
380				 */
381				goto option_fail;
382			} else if (*ccp == '\0')
383				i--;
384		}
385		for (option = cp; *cp; cp++)
386			if (isupper(*cp))
387				*cp = tolower(*cp);
388		for (i = 0; options[i].o_type != NULL; i++)
389			if (strcmp(option, options[i].o_type) == 0) {
390				options[i].o_request = ++cp;
391				has_options = 1;
392			}
393		cp = ccp-1;
394	}
395
396option_fail:
397	if (options[OPT_TIMEOUT].o_request) {
398		int to = atoi(options[OPT_TIMEOUT].o_request);
399		if (to < 1 || to > 255) {
400			nak(EBADOP);
401			exit(1);
402		}
403		else if (to <= max_rexmtval)
404			options[OPT_TIMEOUT].o_reply = rexmtval = to;
405		else
406			options[OPT_TIMEOUT].o_request = NULL;
407	}
408
409	ecode = (*pf->f_validate)(&filename, tp->th_opcode);
410	if (has_options)
411		oack();
412	if (logging) {
413		char host[MAXHOSTNAMELEN];
414
415		realhostname(host, sizeof(host) - 1, &from.sin_addr);
416		host[sizeof(host) - 1] = '\0';
417		syslog(LOG_INFO, "%s: %s request for %s: %s", host,
418			tp->th_opcode == WRQ ? "write" : "read",
419			filename, errtomsg(ecode));
420	}
421	if (ecode) {
422		/*
423		 * Avoid storms of naks to a RRQ broadcast for a relative
424		 * bootfile pathname from a diskless Sun.
425		 */
426		if (suppress_naks && *filename != '/' && ecode == ENOTFOUND)
427			exit(0);
428		nak(ecode);
429		exit(1);
430	}
431	if (tp->th_opcode == WRQ)
432		(*pf->f_recv)(pf);
433	else
434		(*pf->f_send)(pf);
435	exit(0);
436}
437
438
439FILE *file;
440
441/*
442 * Validate file access.  Since we
443 * have no uid or gid, for now require
444 * file to exist and be publicly
445 * readable/writable.
446 * If we were invoked with arguments
447 * from inetd then the file must also be
448 * in one of the given directory prefixes.
449 * Note also, full path name must be
450 * given as we have no login directory.
451 */
452int
453validate_access(filep, mode)
454	char **filep;
455	int mode;
456{
457	struct stat stbuf;
458	int	fd;
459	struct dirlist *dirp;
460	static char pathname[MAXPATHLEN];
461	char *filename = *filep;
462
463	/*
464	 * Prevent tricksters from getting around the directory restrictions
465	 */
466	if (strstr(filename, "/../"))
467		return (EACCESS);
468
469	if (*filename == '/') {
470		/*
471		 * Allow the request if it's in one of the approved locations.
472		 * Special case: check the null prefix ("/") by looking
473		 * for length = 1 and relying on the arg. processing that
474		 * it's a /.
475		 */
476		for (dirp = dirs; dirp->name != NULL; dirp++) {
477			if (dirp->len == 1 ||
478			    (!strncmp(filename, dirp->name, dirp->len) &&
479			     filename[dirp->len] == '/'))
480				    break;
481		}
482		/* If directory list is empty, allow access to any file */
483		if (dirp->name == NULL && dirp != dirs)
484			return (EACCESS);
485		if (stat(filename, &stbuf) < 0)
486			return (errno == ENOENT ? ENOTFOUND : EACCESS);
487		if ((stbuf.st_mode & S_IFMT) != S_IFREG)
488			return (ENOTFOUND);
489		if (mode == RRQ) {
490			if ((stbuf.st_mode & S_IROTH) == 0)
491				return (EACCESS);
492		} else {
493			if ((stbuf.st_mode & S_IWOTH) == 0)
494				return (EACCESS);
495		}
496	} else {
497		int err;
498
499		/*
500		 * Relative file name: search the approved locations for it.
501		 * Don't allow write requests that avoid directory
502		 * restrictions.
503		 */
504
505		if (!strncmp(filename, "../", 3))
506			return (EACCESS);
507
508		/*
509		 * If the file exists in one of the directories and isn't
510		 * readable, continue looking. However, change the error code
511		 * to give an indication that the file exists.
512		 */
513		err = ENOTFOUND;
514		for (dirp = dirs; dirp->name != NULL; dirp++) {
515			snprintf(pathname, sizeof(pathname), "%s/%s",
516				dirp->name, filename);
517			if (stat(pathname, &stbuf) == 0 &&
518			    (stbuf.st_mode & S_IFMT) == S_IFREG) {
519				if ((stbuf.st_mode & S_IROTH) != 0) {
520					break;
521				}
522				err = EACCESS;
523			}
524		}
525		if (dirp->name == NULL)
526			return (err);
527		*filep = filename = pathname;
528	}
529	if (options[OPT_TSIZE].o_request) {
530		if (mode == RRQ)
531			options[OPT_TSIZE].o_reply = stbuf.st_size;
532		else
533			/* XXX Allows writes of all sizes. */
534			options[OPT_TSIZE].o_reply =
535				atoi(options[OPT_TSIZE].o_request);
536	}
537	fd = open(filename, mode == RRQ ? O_RDONLY : O_WRONLY|O_TRUNC);
538	if (fd < 0)
539		return (errno + 100);
540	file = fdopen(fd, (mode == RRQ)? "r":"w");
541	if (file == NULL) {
542		return errno+100;
543	}
544	return (0);
545}
546
547int	timeouts;
548jmp_buf	timeoutbuf;
549
550void
551timer()
552{
553	if (++timeouts > MAX_TIMEOUTS)
554		exit(1);
555	longjmp(timeoutbuf, 1);
556}
557
558/*
559 * Send the requested file.
560 */
561void
562xmitfile(pf)
563	struct formats *pf;
564{
565	struct tftphdr *dp, *r_init();
566	register struct tftphdr *ap;    /* ack packet */
567	register int size, n;
568	volatile unsigned short block;
569
570	signal(SIGALRM, timer);
571	dp = r_init();
572	ap = (struct tftphdr *)ackbuf;
573	block = 1;
574	do {
575		size = readit(file, &dp, pf->f_convert);
576		if (size < 0) {
577			nak(errno + 100);
578			goto abort;
579		}
580		dp->th_opcode = htons((u_short)DATA);
581		dp->th_block = htons((u_short)block);
582		timeouts = 0;
583		(void)setjmp(timeoutbuf);
584
585send_data:
586		if (send(peer, dp, size + 4, 0) != size + 4) {
587			syslog(LOG_ERR, "write: %m");
588			goto abort;
589		}
590		read_ahead(file, pf->f_convert);
591		for ( ; ; ) {
592			alarm(rexmtval);        /* read the ack */
593			n = recv(peer, ackbuf, sizeof (ackbuf), 0);
594			alarm(0);
595			if (n < 0) {
596				syslog(LOG_ERR, "read: %m");
597				goto abort;
598			}
599			ap->th_opcode = ntohs((u_short)ap->th_opcode);
600			ap->th_block = ntohs((u_short)ap->th_block);
601
602			if (ap->th_opcode == ERROR)
603				goto abort;
604
605			if (ap->th_opcode == ACK) {
606				if (ap->th_block == block)
607					break;
608				/* Re-synchronize with the other side */
609				(void) synchnet(peer);
610				if (ap->th_block == (block -1))
611					goto send_data;
612			}
613
614		}
615		block++;
616	} while (size == SEGSIZE);
617abort:
618	(void) fclose(file);
619}
620
621void
622justquit()
623{
624	exit(0);
625}
626
627
628/*
629 * Receive a file.
630 */
631void
632recvfile(pf)
633	struct formats *pf;
634{
635	struct tftphdr *dp, *w_init();
636	register struct tftphdr *ap;    /* ack buffer */
637	register int n, size;
638	volatile unsigned short block;
639
640	signal(SIGALRM, timer);
641	dp = w_init();
642	ap = (struct tftphdr *)ackbuf;
643	block = 0;
644	do {
645		timeouts = 0;
646		ap->th_opcode = htons((u_short)ACK);
647		ap->th_block = htons((u_short)block);
648		block++;
649		(void) setjmp(timeoutbuf);
650send_ack:
651		if (send(peer, ackbuf, 4, 0) != 4) {
652			syslog(LOG_ERR, "write: %m");
653			goto abort;
654		}
655		write_behind(file, pf->f_convert);
656		for ( ; ; ) {
657			alarm(rexmtval);
658			n = recv(peer, dp, PKTSIZE, 0);
659			alarm(0);
660			if (n < 0) {            /* really? */
661				syslog(LOG_ERR, "read: %m");
662				goto abort;
663			}
664			dp->th_opcode = ntohs((u_short)dp->th_opcode);
665			dp->th_block = ntohs((u_short)dp->th_block);
666			if (dp->th_opcode == ERROR)
667				goto abort;
668			if (dp->th_opcode == DATA) {
669				if (dp->th_block == block) {
670					break;   /* normal */
671				}
672				/* Re-synchronize with the other side */
673				(void) synchnet(peer);
674				if (dp->th_block == (block-1))
675					goto send_ack;          /* rexmit */
676			}
677		}
678		/*  size = write(file, dp->th_data, n - 4); */
679		size = writeit(file, &dp, n - 4, pf->f_convert);
680		if (size != (n-4)) {                    /* ahem */
681			if (size < 0) nak(errno + 100);
682			else nak(ENOSPACE);
683			goto abort;
684		}
685	} while (size == SEGSIZE);
686	write_behind(file, pf->f_convert);
687	(void) fclose(file);            /* close data file */
688
689	ap->th_opcode = htons((u_short)ACK);    /* send the "final" ack */
690	ap->th_block = htons((u_short)(block));
691	(void) send(peer, ackbuf, 4, 0);
692
693	signal(SIGALRM, justquit);      /* just quit on timeout */
694	alarm(rexmtval);
695	n = recv(peer, buf, sizeof (buf), 0); /* normally times out and quits */
696	alarm(0);
697	if (n >= 4 &&                   /* if read some data */
698	    dp->th_opcode == DATA &&    /* and got a data block */
699	    block == dp->th_block) {	/* then my last ack was lost */
700		(void) send(peer, ackbuf, 4, 0);     /* resend final ack */
701	}
702abort:
703	return;
704}
705
706struct errmsg {
707	int	e_code;
708	char	*e_msg;
709} errmsgs[] = {
710	{ EUNDEF,	"Undefined error code" },
711	{ ENOTFOUND,	"File not found" },
712	{ EACCESS,	"Access violation" },
713	{ ENOSPACE,	"Disk full or allocation exceeded" },
714	{ EBADOP,	"Illegal TFTP operation" },
715	{ EBADID,	"Unknown transfer ID" },
716	{ EEXISTS,	"File already exists" },
717	{ ENOUSER,	"No such user" },
718	{ EOPTNEG,	"Option negotiation" },
719	{ -1,		0 }
720};
721
722static char *
723errtomsg(error)
724	int error;
725{
726	static char buf[20];
727	register struct errmsg *pe;
728	if (error == 0)
729		return "success";
730	for (pe = errmsgs; pe->e_code >= 0; pe++)
731		if (pe->e_code == error)
732			return pe->e_msg;
733	snprintf(buf, sizeof(buf), "error %d", error);
734	return buf;
735}
736
737/*
738 * Send a nak packet (error message).
739 * Error code passed in is one of the
740 * standard TFTP codes, or a UNIX errno
741 * offset by 100.
742 */
743static void
744nak(error)
745	int error;
746{
747	register struct tftphdr *tp;
748	int length;
749	register struct errmsg *pe;
750
751	tp = (struct tftphdr *)buf;
752	tp->th_opcode = htons((u_short)ERROR);
753	tp->th_code = htons((u_short)error);
754	for (pe = errmsgs; pe->e_code >= 0; pe++)
755		if (pe->e_code == error)
756			break;
757	if (pe->e_code < 0) {
758		pe->e_msg = strerror(error - 100);
759		tp->th_code = EUNDEF;   /* set 'undef' errorcode */
760	}
761	strcpy(tp->th_msg, pe->e_msg);
762	length = strlen(pe->e_msg);
763	tp->th_msg[length] = '\0';
764	length += 5;
765	if (send(peer, buf, length, 0) != length)
766		syslog(LOG_ERR, "nak: %m");
767}
768
769/*
770 * Send an oack packet (option acknowledgement).
771 */
772static void
773oack()
774{
775	struct tftphdr *tp, *ap;
776	int size, i, n;
777	char *bp;
778
779	tp = (struct tftphdr *)buf;
780	bp = buf + 2;
781	size = sizeof(buf) - 2;
782	tp->th_opcode = htons((u_short)OACK);
783	for (i = 0; options[i].o_type != NULL; i++) {
784		if (options[i].o_request) {
785			n = snprintf(bp, size, "%s%c%d", options[i].o_type,
786				     0, options[i].o_reply);
787			bp += n+1;
788			size -= n+1;
789			if (size < 0) {
790				syslog(LOG_ERR, "oack: buffer overflow");
791				exit(1);
792			}
793		}
794	}
795	size = bp - buf;
796	ap = (struct tftphdr *)ackbuf;
797	signal(SIGALRM, timer);
798	timeouts = 0;
799
800	(void)setjmp(timeoutbuf);
801	if (send(peer, buf, size, 0) != size) {
802		syslog(LOG_INFO, "oack: %m");
803		exit(1);
804	}
805
806	for (;;) {
807		alarm(rexmtval);
808		n = recv(peer, ackbuf, sizeof (ackbuf), 0);
809		alarm(0);
810		if (n < 0) {
811			syslog(LOG_ERR, "recv: %m");
812			exit(1);
813		}
814		ap->th_opcode = ntohs((u_short)ap->th_opcode);
815		ap->th_block = ntohs((u_short)ap->th_block);
816		if (ap->th_opcode == ERROR)
817			exit(1);
818		if (ap->th_opcode == ACK && ap->th_block == 0)
819			break;
820	}
821}
822