BSD 4.4 Lite Libexec Sources

3 files changed, 765 insertions, 0 deletions

diff --git a/libexec/tftpd/Makefile b/libexec/tftpd/Makefile
new file mode 100644
index 0000000..f94acc0
--- /dev/null
+++ b/libexec/tftpd/Makefile
@@ -0,0 +1,9 @@
+#	@(#)Makefile	8.1 (Berkeley) 6/4/93
+
+PROG=	tftpd
+SRCS=	tftpd.c tftpsubs.c
+MAN8=	tftpd.0
+CFLAGS+=-I${.CURDIR}/../../usr.bin/tftp
+.PATH:	${.CURDIR}/../../usr.bin/tftp
+
+.include <bsd.prog.mk>
diff --git a/libexec/tftpd/tftpd.8 b/libexec/tftpd/tftpd.8
new file mode 100644
index 0000000..430c1c4
--- /dev/null
+++ b/libexec/tftpd/tftpd.8
@@ -0,0 +1,106 @@
+.\" Copyright (c) 1983, 1991, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"	@(#)tftpd.8	8.1 (Berkeley) 6/4/93
+.\"
+.Dd June 4, 1993
+.Dt TFTPD 8
+.Os BSD 4.2
+.Sh NAME
+.Nm tftpd
+.Nd
+Internet Trivial File Transfer Protocol server
+.Sh SYNOPSIS
+.Nm tftpd
+.Op Fl l
+.Op Fl n
+.Op Ar directory ...
+.Sh DESCRIPTION
+.Nm Tftpd
+is a server which supports the
+Internet Trivial File Transfer
+Protocol (\c
+.Tn RFC 783).
+The
+.Tn TFTP
+server operates
+at the port indicated in the
+.Ql tftp
+service description;
+see
+.Xr services 5 .
+The server is normally started by
+.Xr inetd 8 .
+.Pp
+The use of
+.Xr tftp 1
+does not require an account or password on the remote system.
+Due to the lack of authentication information, 
+.Nm tftpd
+will allow only publicly readable files to be
+accessed.
+Files containing the string ``/\|\fB.\|.\fP\|/'' are not allowed.
+Files may be written only if they already exist and are publicly writable.
+Note that this extends the concept of
+.Dq public
+to include
+all users on all hosts that can be reached through the network;
+this may not be appropriate on all systems, and its implications
+should be considered before enabling tftp service.
+The server should have the user ID with the lowest possible privilege.
+.Pp
+Access to files may be restricted by invoking
+.Nm tftpd
+with a list of directories by including up to 20 pathnames
+as server program arguments in
+.Pa /etc/inetd.conf .
+In this case access is restricted to files whose
+names are prefixed by the one of the given directories.
+The given directories are also treated as a search path for 
+relative filename requests.
+.Pp
+The options are:
+.Bl -tag -width Ds
+.It Fl l
+Logs all requests using
+.Xr syslog 3 .
+.It Fl n
+Suppresses negative acknowledgement of requests for nonexistent
+relative filenames.
+.El
+.Sh SEE ALSO
+.Xr tftp 1 ,
+.Xr inetd 8
+.Sh HISTORY
+The
+.Nm
+command appeared in
+.Bx 4.2 .
diff --git a/libexec/tftpd/tftpd.c b/libexec/tftpd/tftpd.c
new file mode 100644
index 0000000..2c74e3d
--- /dev/null
+++ b/libexec/tftpd/tftpd.c
@@ -0,0 +1,650 @@
+/*
+ * Copyright (c) 1983, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *	This product includes software developed by the University of
+ *	California, Berkeley and its contributors.
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef lint
+static char copyright[] =
+"@(#) Copyright (c) 1983, 1993\n\
+	The Regents of the University of California.  All rights reserved.\n";
+#endif /* not lint */
+
+#ifndef lint
+static char sccsid[] = "@(#)tftpd.c	8.1 (Berkeley) 6/4/93";
+#endif /* not lint */
+
+/*
+ * Trivial file transfer protocol server.
+ *
+ * This version includes many modifications by Jim Guyton
+ * <guyton@rand-unix>.
+ */
+
+#include <sys/param.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+
+#include <netinet/in.h>
+#include <arpa/tftp.h>
+#include <arpa/inet.h>
+
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <netdb.h>
+#include <setjmp.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syslog.h>
+#include <unistd.h>
+
+#include "tftpsubs.h"
+
+#define	TIMEOUT		5
+
+int	peer;
+int	rexmtval = TIMEOUT;
+int	maxtimeout = 5*TIMEOUT;
+
+#define	PKTSIZE	SEGSIZE+4
+char	buf[PKTSIZE];
+char	ackbuf[PKTSIZE];
+struct	sockaddr_in from;
+int	fromlen;
+
+void	tftp __P((struct tftphdr *, int));
+
+/*
+ * Null-terminated directory prefix list for absolute pathname requests and
+ * search list for relative pathname requests.
+ *
+ * MAXDIRS should be at least as large as the number of arguments that
+ * inetd allows (currently 20).
+ */
+#define MAXDIRS	20
+static struct dirlist {
+	char	*name;
+	int	len;
+} dirs[MAXDIRS+1];
+static int	suppress_naks;
+static int	logging;
+
+static char *errtomsg __P((int));
+static void  nak __P((int));
+static char *verifyhost __P((struct sockaddr_in *));
+
+int
+main(argc, argv)
+	int argc;
+	char *argv[];
+{
+	register struct tftphdr *tp;
+	register int n;
+	int ch, on;
+	struct sockaddr_in sin;
+
+	openlog("tftpd", LOG_PID, LOG_FTP);
+	while ((ch = getopt(argc, argv, "ln")) != EOF) {
+		switch (ch) {
+		case 'l':
+			logging = 1;
+			break;
+		case 'n':
+			suppress_naks = 1;
+			break;
+		default:
+			syslog(LOG_WARNING, "ignoring unknown option -%c", ch);
+		}
+	}
+	if (optind < argc) {
+		struct dirlist *dirp;
+
+		/* Get list of directory prefixes. Skip relative pathnames. */
+		for (dirp = dirs; optind < argc && dirp < &dirs[MAXDIRS];
+		     optind++) {
+			if (argv[optind][0] == '/') {
+				dirp->name = argv[optind];
+				dirp->len  = strlen(dirp->name);
+				dirp++;
+			}
+		}
+	}
+
+	on = 1;
+	if (ioctl(0, FIONBIO, &on) < 0) {
+		syslog(LOG_ERR, "ioctl(FIONBIO): %m\n");
+		exit(1);
+	}
+	fromlen = sizeof (from);
+	n = recvfrom(0, buf, sizeof (buf), 0,
+	    (struct sockaddr *)&from, &fromlen);
+	if (n < 0) {
+		syslog(LOG_ERR, "recvfrom: %m\n");
+		exit(1);
+	}
+	/*
+	 * Now that we have read the message out of the UDP
+	 * socket, we fork and exit.  Thus, inetd will go back
+	 * to listening to the tftp port, and the next request
+	 * to come in will start up a new instance of tftpd.
+	 *
+	 * We do this so that inetd can run tftpd in "wait" mode.
+	 * The problem with tftpd running in "nowait" mode is that
+	 * inetd may get one or more successful "selects" on the
+	 * tftp port before we do our receive, so more than one
+	 * instance of tftpd may be started up.  Worse, if tftpd
+	 * break before doing the above "recvfrom", inetd would
+	 * spawn endless instances, clogging the system.
+	 */
+	{
+		int pid;
+		int i, j;
+
+		for (i = 1; i < 20; i++) {
+		    pid = fork();
+		    if (pid < 0) {
+				sleep(i);
+				/*
+				 * flush out to most recently sent request.
+				 *
+				 * This may drop some request, but those
+				 * will be resent by the clients when
+				 * they timeout.  The positive effect of
+				 * this flush is to (try to) prevent more
+				 * than one tftpd being started up to service
+				 * a single request from a single client.
+				 */
+				j = sizeof from;
+				i = recvfrom(0, buf, sizeof (buf), 0,
+				    (struct sockaddr *)&from, &j);
+				if (i > 0) {
+					n = i;
+					fromlen = j;
+				}
+		    } else {
+				break;
+		    }
+		}
+		if (pid < 0) {
+			syslog(LOG_ERR, "fork: %m\n");
+			exit(1);
+		} else if (pid != 0) {
+			exit(0);
+		}
+	}
+	from.sin_family = AF_INET;
+	alarm(0);
+	close(0);
+	close(1);
+	peer = socket(AF_INET, SOCK_DGRAM, 0);
+	if (peer < 0) {
+		syslog(LOG_ERR, "socket: %m\n");
+		exit(1);
+	}
+	memset(&sin, 0, sizeof(sin));
+	sin.sin_family = AF_INET;
+	if (bind(peer, (struct sockaddr *)&sin, sizeof (sin)) < 0) {
+		syslog(LOG_ERR, "bind: %m\n");
+		exit(1);
+	}
+	if (connect(peer, (struct sockaddr *)&from, sizeof(from)) < 0) {
+		syslog(LOG_ERR, "connect: %m\n");
+		exit(1);
+	}
+	tp = (struct tftphdr *)buf;
+	tp->th_opcode = ntohs(tp->th_opcode);
+	if (tp->th_opcode == RRQ || tp->th_opcode == WRQ)
+		tftp(tp, n);
+	exit(1);
+}
+
+struct formats;
+int	validate_access __P((char **, int));
+void	sendfile __P((struct formats *));
+void	recvfile __P((struct formats *));
+
+struct formats {
+	char	*f_mode;
+	int	(*f_validate) __P((char **, int));
+	void	(*f_send) __P((struct formats *));
+	void	(*f_recv) __P((struct formats *));
+	int	f_convert;
+} formats[] = {
+	{ "netascii",	validate_access,	sendfile,	recvfile, 1 },
+	{ "octet",	validate_access,	sendfile,	recvfile, 0 },
+#ifdef notdef
+	{ "mail",	validate_user,		sendmail,	recvmail, 1 },
+#endif
+	{ 0 }
+};
+
+/*
+ * Handle initial connection protocol.
+ */
+void
+tftp(tp, size)
+	struct tftphdr *tp;
+	int size;
+{
+	register char *cp;
+	int first = 1, ecode;
+	register struct formats *pf;
+	char *filename, *mode;
+
+	filename = cp = tp->th_stuff;
+again:
+	while (cp < buf + size) {
+		if (*cp == '\0')
+			break;
+		cp++;
+	}
+	if (*cp != '\0') {
+		nak(EBADOP);
+		exit(1);
+	}
+	if (first) {
+		mode = ++cp;
+		first = 0;
+		goto again;
+	}
+	for (cp = mode; *cp; cp++)
+		if (isupper(*cp))
+			*cp = tolower(*cp);
+	for (pf = formats; pf->f_mode; pf++)
+		if (strcmp(pf->f_mode, mode) == 0)
+			break;
+	if (pf->f_mode == 0) {
+		nak(EBADOP);
+		exit(1);
+	}
+	ecode = (*pf->f_validate)(&filename, tp->th_opcode);
+	if (logging) {
+		syslog(LOG_INFO, "%s: %s request for %s: %s",
+			verifyhost(&from),
+			tp->th_opcode == WRQ ? "write" : "read",
+			filename, errtomsg(ecode));
+	}
+	if (ecode) {
+		/*
+		 * Avoid storms of naks to a RRQ broadcast for a relative
+		 * bootfile pathname from a diskless Sun.
+		 */
+		if (suppress_naks && *filename != '/' && ecode == ENOTFOUND)
+			exit(0);
+		nak(ecode);
+		exit(1);
+	}
+	if (tp->th_opcode == WRQ)
+		(*pf->f_recv)(pf);
+	else
+		(*pf->f_send)(pf);
+	exit(0);
+}
+
+
+FILE *file;
+
+/*
+ * Validate file access.  Since we
+ * have no uid or gid, for now require
+ * file to exist and be publicly
+ * readable/writable.
+ * If we were invoked with arguments
+ * from inetd then the file must also be
+ * in one of the given directory prefixes.
+ * Note also, full path name must be
+ * given as we have no login directory.
+ */
+int
+validate_access(filep, mode)
+	char **filep;
+	int mode;
+{
+	struct stat stbuf;
+	int	fd;
+	struct dirlist *dirp;
+	static char pathname[MAXPATHLEN];
+	char *filename = *filep;
+
+	/*
+	 * Prevent tricksters from getting around the directory restrictions
+	 */
+	if (strstr(filename, "/../"))
+		return (EACCESS);
+
+	if (*filename == '/') {
+		/*
+		 * Allow the request if it's in one of the approved locations.
+		 * Special case: check the null prefix ("/") by looking
+		 * for length = 1 and relying on the arg. processing that
+		 * it's a /.
+		 */
+		for (dirp = dirs; dirp->name != NULL; dirp++) {
+			if (dirp->len == 1 ||
+			    (!strncmp(filename, dirp->name, dirp->len) &&
+			     filename[dirp->len] == '/'))
+				    break;
+		}
+		/* If directory list is empty, allow access to any file */
+		if (dirp->name == NULL && dirp != dirs)
+			return (EACCESS);
+		if (stat(filename, &stbuf) < 0)
+			return (errno == ENOENT ? ENOTFOUND : EACCESS);
+		if ((stbuf.st_mode & S_IFMT) != S_IFREG)
+			return (ENOTFOUND);
+		if (mode == RRQ) {
+			if ((stbuf.st_mode & S_IROTH) == 0)
+				return (EACCESS);
+		} else {
+			if ((stbuf.st_mode & S_IWOTH) == 0)
+				return (EACCESS);
+		}
+	} else {
+		int err;
+
+		/*
+		 * Relative file name: search the approved locations for it.
+		 * Don't allow write requests or ones that avoid directory
+		 * restrictions.
+		 */
+
+		if (mode != RRQ || !strncmp(filename, "../", 3))
+			return (EACCESS);
+
+		/*
+		 * If the file exists in one of the directories and isn't
+		 * readable, continue looking. However, change the error code
+		 * to give an indication that the file exists.
+		 */
+		err = ENOTFOUND;
+		for (dirp = dirs; dirp->name != NULL; dirp++) {
+			sprintf(pathname, "%s/%s", dirp->name, filename);
+			if (stat(pathname, &stbuf) == 0 &&
+			    (stbuf.st_mode & S_IFMT) == S_IFREG) {
+				if ((stbuf.st_mode & S_IROTH) != 0) {
+					break;
+				}
+				err = EACCESS;
+			}
+		}
+		if (dirp->name == NULL)
+			return (err);
+		*filep = filename = pathname;
+	}
+	fd = open(filename, mode == RRQ ? 0 : 1);
+	if (fd < 0)
+		return (errno + 100);
+	file = fdopen(fd, (mode == RRQ)? "r":"w");
+	if (file == NULL) {
+		return errno+100;
+	}
+	return (0);
+}
+
+int	timeout;
+jmp_buf	timeoutbuf;
+
+void
+timer()
+{
+
+	timeout += rexmtval;
+	if (timeout >= maxtimeout)
+		exit(1);
+	longjmp(timeoutbuf, 1);
+}
+
+/*
+ * Send the requested file.
+ */
+void
+sendfile(pf)
+	struct formats *pf;
+{
+	struct tftphdr *dp, *r_init();
+	register struct tftphdr *ap;    /* ack packet */
+	register int size, n;
+	volatile int block;
+
+	signal(SIGALRM, timer);
+	dp = r_init();
+	ap = (struct tftphdr *)ackbuf;
+	block = 1;
+	do {
+		size = readit(file, &dp, pf->f_convert);
+		if (size < 0) {
+			nak(errno + 100);
+			goto abort;
+		}
+		dp->th_opcode = htons((u_short)DATA);
+		dp->th_block = htons((u_short)block);
+		timeout = 0;
+		(void)setjmp(timeoutbuf);
+
+send_data:
+		if (send(peer, dp, size + 4, 0) != size + 4) {
+			syslog(LOG_ERR, "tftpd: write: %m\n");
+			goto abort;
+		}
+		read_ahead(file, pf->f_convert);
+		for ( ; ; ) {
+			alarm(rexmtval);        /* read the ack */
+			n = recv(peer, ackbuf, sizeof (ackbuf), 0);
+			alarm(0);
+			if (n < 0) {
+				syslog(LOG_ERR, "tftpd: read: %m\n");
+				goto abort;
+			}
+			ap->th_opcode = ntohs((u_short)ap->th_opcode);
+			ap->th_block = ntohs((u_short)ap->th_block);
+
+			if (ap->th_opcode == ERROR)
+				goto abort;
+
+			if (ap->th_opcode == ACK) {
+				if (ap->th_block == block)
+					break;
+				/* Re-synchronize with the other side */
+				(void) synchnet(peer);
+				if (ap->th_block == (block -1))
+					goto send_data;
+			}
+
+		}
+		block++;
+	} while (size == SEGSIZE);
+abort:
+	(void) fclose(file);
+}
+
+void
+justquit()
+{
+	exit(0);
+}
+
+
+/*
+ * Receive a file.
+ */
+void
+recvfile(pf)
+	struct formats *pf;
+{
+	struct tftphdr *dp, *w_init();
+	register struct tftphdr *ap;    /* ack buffer */
+	register int n, size;
+	volatile int block;
+
+	signal(SIGALRM, timer);
+	dp = w_init();
+	ap = (struct tftphdr *)ackbuf;
+	block = 0;
+	do {
+		timeout = 0;
+		ap->th_opcode = htons((u_short)ACK);
+		ap->th_block = htons((u_short)block);
+		block++;
+		(void) setjmp(timeoutbuf);
+send_ack:
+		if (send(peer, ackbuf, 4, 0) != 4) {
+			syslog(LOG_ERR, "tftpd: write: %m\n");
+			goto abort;
+		}
+		write_behind(file, pf->f_convert);
+		for ( ; ; ) {
+			alarm(rexmtval);
+			n = recv(peer, dp, PKTSIZE, 0);
+			alarm(0);
+			if (n < 0) {            /* really? */
+				syslog(LOG_ERR, "tftpd: read: %m\n");
+				goto abort;
+			}
+			dp->th_opcode = ntohs((u_short)dp->th_opcode);
+			dp->th_block = ntohs((u_short)dp->th_block);
+			if (dp->th_opcode == ERROR)
+				goto abort;
+			if (dp->th_opcode == DATA) {
+				if (dp->th_block == block) {
+					break;   /* normal */
+				}
+				/* Re-synchronize with the other side */
+				(void) synchnet(peer);
+				if (dp->th_block == (block-1))
+					goto send_ack;          /* rexmit */
+			}
+		}
+		/*  size = write(file, dp->th_data, n - 4); */
+		size = writeit(file, &dp, n - 4, pf->f_convert);
+		if (size != (n-4)) {                    /* ahem */
+			if (size < 0) nak(errno + 100);
+			else nak(ENOSPACE);
+			goto abort;
+		}
+	} while (size == SEGSIZE);
+	write_behind(file, pf->f_convert);
+	(void) fclose(file);            /* close data file */
+
+	ap->th_opcode = htons((u_short)ACK);    /* send the "final" ack */
+	ap->th_block = htons((u_short)(block));
+	(void) send(peer, ackbuf, 4, 0);
+
+	signal(SIGALRM, justquit);      /* just quit on timeout */
+	alarm(rexmtval);
+	n = recv(peer, buf, sizeof (buf), 0); /* normally times out and quits */
+	alarm(0);
+	if (n >= 4 &&                   /* if read some data */
+	    dp->th_opcode == DATA &&    /* and got a data block */
+	    block == dp->th_block) {	/* then my last ack was lost */
+		(void) send(peer, ackbuf, 4, 0);     /* resend final ack */
+	}
+abort:
+	return;
+}
+
+struct errmsg {
+	int	e_code;
+	char	*e_msg;
+} errmsgs[] = {
+	{ EUNDEF,	"Undefined error code" },
+	{ ENOTFOUND,	"File not found" },
+	{ EACCESS,	"Access violation" },
+	{ ENOSPACE,	"Disk full or allocation exceeded" },
+	{ EBADOP,	"Illegal TFTP operation" },
+	{ EBADID,	"Unknown transfer ID" },
+	{ EEXISTS,	"File already exists" },
+	{ ENOUSER,	"No such user" },
+	{ -1,		0 }
+};
+
+static char *
+errtomsg(error)
+	int error;
+{
+	static char buf[20];
+	register struct errmsg *pe;
+	if (error == 0)
+		return "success";
+	for (pe = errmsgs; pe->e_code >= 0; pe++)
+		if (pe->e_code == error)
+			return pe->e_msg;
+	sprintf(buf, "error %d", error);
+	return buf;
+}
+
+/*
+ * Send a nak packet (error message).
+ * Error code passed in is one of the
+ * standard TFTP codes, or a UNIX errno
+ * offset by 100.
+ */
+static void
+nak(error)
+	int error;
+{
+	register struct tftphdr *tp;
+	int length;
+	register struct errmsg *pe;
+
+	tp = (struct tftphdr *)buf;
+	tp->th_opcode = htons((u_short)ERROR);
+	tp->th_code = htons((u_short)error);
+	for (pe = errmsgs; pe->e_code >= 0; pe++)
+		if (pe->e_code == error)
+			break;
+	if (pe->e_code < 0) {
+		pe->e_msg = strerror(error - 100);
+		tp->th_code = EUNDEF;   /* set 'undef' errorcode */
+	}
+	strcpy(tp->th_msg, pe->e_msg);
+	length = strlen(pe->e_msg);
+	tp->th_msg[length] = '\0';
+	length += 5;
+	if (send(peer, buf, length, 0) != length)
+		syslog(LOG_ERR, "nak: %m\n");
+}
+
+static char *
+verifyhost(fromp)
+	struct sockaddr_in *fromp;
+{
+	struct hostent *hp;
+
+	hp = gethostbyaddr((char *)&fromp->sin_addr, sizeof (fromp->sin_addr),
+			    fromp->sin_family);
+	if (hp)
+		return hp->h_name;
+	else
+		return inet_ntoa(fromp->sin_addr);
+}