Patrick Welche <prlw1@cam.ac.uk>

[netbsd-mini2440.git] / libexec / tftpd / tftpd.c

/*      $NetBSD: tftpd.c,v 1.32 2009/03/16 01:56:21 lukem Exp $ */

/*
 * 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. 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.
 */

#include <sys/cdefs.h>
#ifndef lint
__COPYRIGHT("@(#) Copyright (c) 1983, 1993\
 The Regents of the University of California.  All rights reserved.");
#if 0
static char sccsid[] = "@(#)tftpd.c     8.1 (Berkeley) 6/4/93";
#else
__RCSID("$NetBSD: tftpd.c,v 1.32 2009/03/16 01:56:21 lukem Exp $");
#endif
#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 <grp.h>
#include <netdb.h>
#include <pwd.h>
#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <time.h>
#include <unistd.h>

#include "tftpsubs.h"

#define DEFAULTUSER     "nobody"

#define TIMEOUT         5

static int      peer;
static int      rexmtval = TIMEOUT;
static int      maxtimeout = 5*TIMEOUT;

static char     buf[MAXPKTSIZE];
static char     ackbuf[PKTSIZE];
static char     oackbuf[PKTSIZE];
static struct   sockaddr_storage from;
static socklen_t        fromlen;
static int      debug;

static int      tftp_opt_tsize = 0;
static int      tftp_blksize = SEGSIZE;
static int      tftp_tsize = 0;

/*
 * 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 int      secure;
static char     pathsep = '\0';
static char     *securedir;

struct formats;

static const char *errtomsg(int);
static void     nak(int);
static void     tftp(struct tftphdr *, int);
static void     usage(void) __attribute__((__noreturn__));
static char     *verifyhost(struct sockaddr *);
static void     justquit(int);
static void     recvfile(struct formats *, int, int);
static void     sendfile(struct formats *, int, int);
static void     timer(int);
static const char *opcode(int);
static int      validate_access(char **, int);

static struct formats {
        const char      *f_mode;
        int             (*f_validate)(char **, int);
        void            (*f_send)(struct formats *, int, int);
        void            (*f_recv)(struct formats *, int, int);
        int             f_convert;
} formats[] = {
        { "netascii",   validate_access,        sendfile,       recvfile, 1 },
        { "octet",      validate_access,        sendfile,       recvfile, 0 },
        { .f_mode = NULL }
};

static void
usage(void)
{

        syslog(LOG_ERR,
    "Usage: %s [-dln] [-u user] [-g group] [-s directory] [-p pathsep] [directory ...]",
                    getprogname());
        exit(1);
}

int
main(int argc, char *argv[])
{
        struct sockaddr_storage me;
        struct passwd   *pwent;
        struct group    *grent;
        struct tftphdr  *tp;
        const char      *tgtuser, *tgtgroup;
        char *ep;
        int     n, ch, on, fd;
        int     soopt;
        socklen_t len;
        uid_t   curuid, tgtuid;
        gid_t   curgid, tgtgid;
        long    nid;

        n = 0;
        fd = 0;
        tzset();
        openlog("tftpd", LOG_PID | LOG_NDELAY, LOG_DAEMON);
        tgtuser = DEFAULTUSER;
        tgtgroup = NULL;
        curuid = getuid();
        curgid = getgid();

        while ((ch = getopt(argc, argv, "dg:lnp:s:u:w:")) != -1)
                switch (ch) {
                case 'd':
                        debug++;
                        break;

                case 'g':
                        tgtgroup = optarg;
                        break;

                case 'l':
                        logging = 1;
                        break;

                case 'n':
                        suppress_naks = 1;
                        break;

                case 'p':
                        if (optarg[0] == '\0' || optarg[1] != '\0')
                                usage();
                        pathsep = optarg[0];
                        break;

                case 's':
                        secure = 1;
                        securedir = optarg;
                        break;

                case 'u':
                        tgtuser = optarg;
                        break;

                default:
                        usage();
                        break;
                }

        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++;
                        }
                }
        }

        if (*tgtuser == '\0' || (tgtgroup != NULL && *tgtgroup == '\0'))
                usage();

        nid = (strtol(tgtuser, &ep, 10));
        if (*ep == '\0') {
                if (nid > UID_MAX) {
                        syslog(LOG_ERR, "uid %ld is too large", nid);
                        exit(1);
                }
                pwent = getpwuid((uid_t)nid);
        } else
                pwent = getpwnam(tgtuser);
        if (pwent == NULL) {
                syslog(LOG_ERR, "unknown user `%s'", tgtuser);
                exit(1);
        }
        tgtuid = pwent->pw_uid;
        tgtgid = pwent->pw_gid;

        if (tgtgroup != NULL) {
                nid = (strtol(tgtgroup, &ep, 10));
                if (*ep == '\0') {
                        if (nid > GID_MAX) {
                                syslog(LOG_ERR, "gid %ld is too large", nid);
                                exit(1);
                        }
                        grent = getgrgid((gid_t)nid);
                } else
                        grent = getgrnam(tgtgroup);
                if (grent != NULL)
                        tgtgid = grent->gr_gid;
                else {
                        syslog(LOG_ERR, "unknown group `%s'", tgtgroup);
                        exit(1);
                }
        }

        if (secure) {
                if (chdir(securedir) < 0) {
                        syslog(LOG_ERR, "chdir %s: %m", securedir);
                        exit(1);
                }
                if (chroot(".")) {
                        syslog(LOG_ERR, "chroot: %m");
                        exit(1);
                }
        }

        if (logging)
                syslog(LOG_DEBUG, "running as user `%s' (%d), group `%s' (%d)",
                    tgtuser, tgtuid, tgtgroup ? tgtgroup : "(unspecified)",
                    tgtgid);
        if (curgid != tgtgid) {
                if (setgid(tgtgid)) {
                        syslog(LOG_ERR, "setgid to %d: %m", (int)tgtgid);
                        exit(1);
                }
                if (setgroups(0, NULL)) {
                        syslog(LOG_ERR, "setgroups: %m");
                        exit(1);
                }
        }

        if (curuid != tgtuid) {
                if (setuid(tgtuid)) {
                        syslog(LOG_ERR, "setuid to %d: %m", (int)tgtuid);
                        exit(1);
                }
        }

        on = 1;
        if (ioctl(fd, FIONBIO, &on) < 0) {
                syslog(LOG_ERR, "ioctl(FIONBIO): %m");
                exit(1);
        }
        fromlen = sizeof (from);
        n = recvfrom(fd, buf, sizeof (buf), 0,
            (struct sockaddr *)&from, &fromlen);
        if (n < 0) {
                syslog(LOG_ERR, "recvfrom: %m");
                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;
                socklen_t 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(fd, 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");
                        exit(1);
                } else if (pid != 0) {
                        exit(0);
                }
        }

        /*
         * remember what address this was sent to, so we can respond on the
         * same interface
         */
        len = sizeof(me);
        if (getsockname(fd, (struct sockaddr *)&me, &len) == 0) {
                switch (me.ss_family) {
                case AF_INET:
                        ((struct sockaddr_in *)&me)->sin_port = 0;
                        break;
                case AF_INET6:
                        ((struct sockaddr_in6 *)&me)->sin6_port = 0;
                        break;
                default:
                        /* unsupported */
                        break;
                }
        } else {
                memset(&me, 0, sizeof(me));
                me.ss_family = from.ss_family;
                me.ss_len = from.ss_len;
        }

        alarm(0);
        close(fd);
        close(1);
        peer = socket(from.ss_family, SOCK_DGRAM, 0);
        if (peer < 0) {
                syslog(LOG_ERR, "socket: %m");
                exit(1);
        }
        if (bind(peer, (struct sockaddr *)&me, me.ss_len) < 0) {
                syslog(LOG_ERR, "bind: %m");
                exit(1);
        }
        if (connect(peer, (struct sockaddr *)&from, from.ss_len) < 0) {
                syslog(LOG_ERR, "connect: %m");
                exit(1);
        }
        soopt = 65536;  /* larger than we'll ever need */
        if (setsockopt(peer, SOL_SOCKET, SO_SNDBUF, (void *) &soopt, sizeof(soopt)) < 0) {
                syslog(LOG_ERR, "set SNDBUF: %m");
                exit(1);
        }
        if (setsockopt(peer, SOL_SOCKET, SO_RCVBUF, (void *) &soopt, sizeof(soopt)) < 0) {
                syslog(LOG_ERR, "set RCVBUF: %m");
                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);
}

static int
blk_handler(struct tftphdr *tp, char *opt, char *val, char *ack,
            int *ackl, int *ec)
{
        unsigned long bsize;
        char *endp;
        int l;

        /*
         * On these failures, we could just ignore the blocksize option.
         * Perhaps that should be a command-line option.
         */
        errno = 0;
        bsize = strtoul(val, &endp, 10);
        if ((bsize == ULONG_MAX && errno == ERANGE) || *endp) {
                syslog(LOG_NOTICE, "%s: %s request for %s: "
                        "illegal value %s for blksize option",
                        verifyhost((struct sockaddr *)&from),
                        tp->th_opcode == WRQ ? "write" : "read",
                        tp->th_stuff, val);
                return 0;
        }
        if (bsize < 8 || bsize > 65464) {
                syslog(LOG_NOTICE, "%s: %s request for %s: "
                        "out of range value %s for blksize option",
                        verifyhost((struct sockaddr *)&from),
                        tp->th_opcode == WRQ ? "write" : "read",
                        tp->th_stuff, val);
                return 0;
        }

        tftp_blksize = bsize;
        strcpy(ack + *ackl, "blksize");
        *ackl += 8;
        l = sprintf(ack + *ackl, "%lu", bsize);
        *ackl += l + 1;

        return 0;
}

static int
timeout_handler(struct tftphdr *tp, char *opt, char *val, char *ack,
                int *ackl, int *ec)
{
        unsigned long tout;
        char *endp;
        int l;

        errno = 0;
        tout = strtoul(val, &endp, 10);
        if ((tout == ULONG_MAX && errno == ERANGE) || *endp) {
                syslog(LOG_NOTICE, "%s: %s request for %s: "
                        "illegal value %s for timeout option",
                        verifyhost((struct sockaddr *)&from),
                        tp->th_opcode == WRQ ? "write" : "read",
                        tp->th_stuff, val);
                return 0;
        }
        if (tout < 1 || tout > 255) {
                syslog(LOG_NOTICE, "%s: %s request for %s: "
                        "out of range value %s for timeout option",
                        verifyhost((struct sockaddr *)&from),
                        tp->th_opcode == WRQ ? "write" : "read",
                        tp->th_stuff, val);
                return 0;
        }

        rexmtval = tout;
        strcpy(ack + *ackl, "timeout");
        *ackl += 8;
        l = sprintf(ack + *ackl, "%lu", tout);
        *ackl += l + 1;

        /*
         * Arbitrarily pick a maximum timeout on a request to 3
         * retransmissions if the interval timeout is more than
         * one minute.  Longest possible timeout is therefore
         * 3 * 255 - 1, or 764 seconds.
         */
        if (rexmtval > 60) {
                maxtimeout = rexmtval * 3;
        } else {
                maxtimeout = rexmtval * 5;
        }

        return 0;
}

static int
tsize_handler(struct tftphdr *tp, char *opt, char *val, char *ack,
              int *ackl, int *ec)
{
        unsigned long fsize;
        char *endp;

        /*
         * Maximum file even with extended tftp is 65535 blocks of
         * length 65464, or 4290183240 octets (4784056 less than 2^32).
         * unsigned long is at least 32 bits on all NetBSD archs.
         */

        errno = 0;
        fsize = strtoul(val, &endp, 10);
        if ((fsize == ULONG_MAX && errno == ERANGE) || *endp) {
                syslog(LOG_NOTICE, "%s: %s request for %s: "
                        "illegal value %s for tsize option",
                        verifyhost((struct sockaddr *)&from),
                        tp->th_opcode == WRQ ? "write" : "read",
                        tp->th_stuff, val);
                return 0;
        }
        if (fsize > (unsigned long) 65535 * 65464) {
                syslog(LOG_NOTICE, "%s: %s request for %s: "
                        "out of range value %s for tsize option",
                        verifyhost((struct sockaddr *)&from),
                        tp->th_opcode == WRQ ? "write" : "read",
                        tp->th_stuff, val);
                return 0;
        }

        tftp_opt_tsize = 1;
        tftp_tsize = fsize;
        /*
         * We will report this later -- either replying with the fsize (WRQ)
         * or replying with the actual filesize (RRQ).
         */

        return 0;
}

static const struct tftp_options {
        const char *o_name;
        int (*o_handler)(struct tftphdr *, char *, char *, char *,
                         int *, int *);
} options[] = {
        { "blksize", blk_handler },
        { "timeout", timeout_handler },
        { "tsize", tsize_handler },
        { .o_name = NULL }
};

/*
 * Get options for an extended tftp session.  Stuff the ones we
 * recognize in oackbuf.
 */
static int
get_options(struct tftphdr *tp, char *cp, int size, char *ackb,
    int *alen, int *err)
{
        const struct tftp_options *op;
        char *option, *value, *endp;
        int r, rv=0, ec=0;

        endp = cp + size;
        while (cp < endp) {
                option = cp;
                while (*cp && cp < endp) {
                        *cp = tolower((unsigned char)*cp);
                        cp++;
                }
                if (*cp) {
                        /* if we have garbage at the end, just ignore it */
                        break;
                }
                cp++;   /* skip over NUL */
                value = cp;
                while (*cp && cp < endp) {
                        cp++;
                }
                if (*cp) {
                        /* if we have garbage at the end, just ignore it */
                        break;
                }
                cp++;
                for (op = options; op->o_name; op++) {
                        if (strcmp(op->o_name, option) == 0)
                                break;
                }
                if (op->o_name) {
                        r = op->o_handler(tp, option, value, ackb, alen, &ec);
                        if (r < 0) {
                                rv = -1;
                                break;
                        }
                        rv++;
                } /* else ignore unknown options */
        }
        
        if (rv < 0)
                *err = ec;

        return rv;
}

/*
 * Handle initial connection protocol.
 */
static void
tftp(struct tftphdr *tp, int size)
{
        struct formats *pf;
        char    *cp;
        char    *filename, *mode;
        int      first, ecode, alen, etftp = 0, r;

        ecode = 0;      /* XXX gcc */
        first = 1;
        mode = NULL;

        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++)
                *cp = tolower((unsigned char)*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);
        }
        /*
         * cp currently points to the NUL byte following the mode.
         *
         * If we have some valid options, then let's assume that we're
         * now dealing with an extended tftp session.  Note that if we
         * don't get any options, then we *must* assume that we do not
         * have an extended tftp session.  If we get options, we fill
         * in the ack buf to acknowledge them.  If we skip that, then
         * the client *must* assume that we are not using an extended
         * session.
         */
        size -= (++cp - (char *) tp);
        if (size > 0 && *cp) {
                alen = 2; /* Skip over opcode */
                r = get_options(tp, cp, size, oackbuf, &alen, &ecode);
                if (r > 0) {
                        etftp = 1;
                } else if (r < 0) {
                        nak(ecode);
                        exit(1);
                }
        }
        /*
         * Globally replace the path separator given in the -p option
         * with / to cope with clients expecting a non-unix path separator.
         */
        if (pathsep != '\0') {
                for (cp = filename; *cp != '\0'; ++cp) {
                        if (*cp == pathsep)
                                *cp = '/';
                }
        }
        ecode = (*pf->f_validate)(&filename, tp->th_opcode);
        if (logging) {
                syslog(LOG_INFO, "%s: %s request for %s: %s",
                        verifyhost((struct sockaddr *)&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 (etftp) {
                struct tftphdr *oack_h;

                if (tftp_opt_tsize) {
                        int l;

                        strcpy(oackbuf + alen, "tsize");
                        alen += 6;
                        l = sprintf(oackbuf + alen, "%u", tftp_tsize);
                        alen += l + 1;
                }
                oack_h = (struct tftphdr *) oackbuf;
                oack_h->th_opcode = htons(OACK);
        }

        if (tp->th_opcode == WRQ)
                (*pf->f_recv)(pf, etftp, alen);
        else
                (*pf->f_send)(pf, etftp, alen);
        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.
 */
int
validate_access(char **filep, int mode)
{
        struct stat      stbuf;
        struct dirlist  *dirp;
        static char      pathname[MAXPATHLEN];
        char            *filename;
        int              fd;

        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 (!S_ISREG(stbuf.st_mode))
                        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 {
                /*
                 * Relative file name: search the approved locations for it.
                 */

                if (!strncmp(filename, "../", 3))
                        return (EACCESS);

                /*
                 * Find the first file that exists in any of the directories,
                 * check access on it.
                 */
                if (dirs[0].name != NULL) {
                        for (dirp = dirs; dirp->name != NULL; dirp++) {
                                snprintf(pathname, sizeof pathname, "%s/%s",
                                    dirp->name, filename);
                                if (stat(pathname, &stbuf) == 0 &&
                                    (stbuf.st_mode & S_IFMT) == S_IFREG) {
                                        break;
                                }
                        }
                        if (dirp->name == NULL)
                                return (ENOTFOUND);
                        if (mode == RRQ && !(stbuf.st_mode & S_IROTH))
                                return (EACCESS);
                        if (mode == WRQ && !(stbuf.st_mode & S_IWOTH))
                                return (EACCESS);
                        *filep = filename = pathname;
                } else {
                        /*
                         * If there's no directory list, take our cue from the
                         * absolute file request check above (*filename == '/'),
                         * and allow access to anything.
                         */
                        if (stat(filename, &stbuf) < 0)
                                return (errno == ENOENT ? ENOTFOUND : EACCESS);
                        if (!S_ISREG(stbuf.st_mode))
                                return (ENOTFOUND);
                        if (mode == RRQ) {
                                if ((stbuf.st_mode & S_IROTH) == 0)
                                        return (EACCESS);
                        } else {
                                if ((stbuf.st_mode & S_IWOTH) == 0)
                                        return (EACCESS);
                        }
                        *filep = filename;
                }
        }

        if (tftp_opt_tsize && mode == RRQ)
                tftp_tsize = (unsigned long) stbuf.st_size;

        fd = open(filename, mode == RRQ ? O_RDONLY : O_WRONLY | O_TRUNC);
        if (fd < 0)
                return (errno + 100);
        file = fdopen(fd, (mode == RRQ)? "r":"w");
        if (file == NULL) {
                close(fd);
                return (errno + 100);
        }
        return (0);
}

static int      timeout;
static jmp_buf  timeoutbuf;

static void
timer(int dummy)
{

        timeout += rexmtval;
        if (timeout >= maxtimeout)
                exit(1);
        longjmp(timeoutbuf, 1);
}

static const char *
opcode(int code)
{
        static char obuf[64];

        switch (code) {
        case RRQ:
                return "RRQ";
        case WRQ:
                return "WRQ";
        case DATA:
                return "DATA";
        case ACK:
                return "ACK";
        case ERROR:
                return "ERROR";
        case OACK:
                return "OACK";
        default:
                (void)snprintf(obuf, sizeof(obuf), "*code 0x%x*", code);
                return obuf;
        }
}

/*
 * Send the requested file.
 */
static void
sendfile(struct formats *pf, volatile int etftp, int acklength)
{
        volatile unsigned int block;
        struct tftphdr  *dp;
        struct tftphdr  *ap;    /* ack packet */
        volatile int     size;
        int n;

        signal(SIGALRM, timer);
        ap = (struct tftphdr *)ackbuf;
        if (etftp) {
                dp = (struct tftphdr *)oackbuf;
                size = acklength - 4;
                block = 0;
        } else {
                dp = r_init();
                size = 0;
                block = 1;
        }

        do {
                if (block > 0) {
                        size = readit(file, &dp, tftp_blksize, 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 (!etftp && debug)
                        syslog(LOG_DEBUG, "Send DATA %u", block);
                if ((n = send(peer, dp, size + 4, 0)) != size + 4) {
                        syslog(LOG_ERR, "tftpd: write: %m");
                        goto abort;
                }
                if (block)
                        read_ahead(file, tftp_blksize, pf->f_convert);
                for ( ; ; ) {
                        alarm(rexmtval);        /* read the ack */
                        n = recv(peer, ackbuf, tftp_blksize, 0);
                        alarm(0);
                        if (n < 0) {
                                syslog(LOG_ERR, "tftpd: read: %m");
                                goto abort;
                        }
                        ap->th_opcode = ntohs((u_short)ap->th_opcode);
                        ap->th_block = ntohs((u_short)ap->th_block);
                        switch (ap->th_opcode) {
                        case ERROR:
                                goto abort;

                        case ACK:
                                if (etftp && ap->th_block == 0) {
                                        etftp = 0;
                                        acklength = 0;
                                        dp = r_init();
                                        goto done;
                                }
                                if (ap->th_block == (u_short)block)
                                        goto done;
                                if (debug)
                                        syslog(LOG_DEBUG, "Resync ACK %u != %u",
                                            (unsigned int)ap->th_block, block);
                                /* Re-synchronize with the other side */
                                (void) synchnet(peer, tftp_blksize);
                                if (ap->th_block == (u_short)(block - 1))
                                        goto send_data;
                        default:
                                syslog(LOG_INFO, "Received %s in sendfile\n",
                                    opcode(dp->th_opcode));
                        }

                }
done:
                if (debug)
                        syslog(LOG_DEBUG, "Received ACK for block %u", block);
                if (block == UINT16_MAX && size == tftp_blksize)
                        syslog(LOG_WARNING,
                            "Block number wrapped (hint: increase block size)");
                block++;
        } while (size == tftp_blksize || block == 1);
abort:
        (void) fclose(file);
}

static void
justquit(int dummy)
{

        exit(0);
}

/*
 * Receive a file.
 */
static void
recvfile(struct formats *pf, volatile int etftp, volatile int acklength)
{
        volatile unsigned int block;
        struct tftphdr  *dp;
        struct tftphdr  *ap;    /* ack buffer */
        volatile int size;
        int n;

        signal(SIGALRM, timer);
        dp = w_init();
        ap = (struct tftphdr *)oackbuf;
        block = 0;
        do {
                timeout = 0;
                if (etftp == 0) {
                        ap = (struct tftphdr *)ackbuf;
                        ap->th_opcode = htons((u_short)ACK);
                        ap->th_block = htons((u_short)block);
                        acklength = 4;
                }
                if (debug)
                        syslog(LOG_DEBUG, "Sending ACK for block %u\n", block);
                if (block == UINT16_MAX)
                        syslog(LOG_WARNING,
                            "Block number wrapped (hint: increase block size)");
                block++;
                (void) setjmp(timeoutbuf);
send_ack:
                ap = (struct tftphdr *) (etftp ? oackbuf : ackbuf);
                if (send(peer, ap, acklength, 0) != acklength) {
                        syslog(LOG_ERR, "tftpd: write: %m");
                        goto abort;
                }
                write_behind(file, pf->f_convert);
                for ( ; ; ) {
                        alarm(rexmtval);
                        n = recv(peer, dp, tftp_blksize + 4, 0);
                        alarm(0);
                        if (n < 0) {            /* really? */
                                syslog(LOG_ERR, "tftpd: read: %m");
                                goto abort;
                        }
                        etftp = 0;
                        dp->th_opcode = ntohs((u_short)dp->th_opcode);
                        dp->th_block = ntohs((u_short)dp->th_block);
                        if (debug)
                                syslog(LOG_DEBUG, "Received %s for block %u",
                                    opcode(dp->th_opcode),
                                    (unsigned int)dp->th_block);

                        switch (dp->th_opcode) {
                        case ERROR:
                                goto abort;
                        case DATA:
                                if (dp->th_block == block)
                                        goto done;   /* normal */
                                if (debug)
                                        syslog(LOG_DEBUG, "Resync %u != %u",
                                            (unsigned int)dp->th_block, block);
                                /* Re-synchronize with the other side */
                                (void) synchnet(peer, tftp_blksize);
                                if (dp->th_block == (block-1))
                                        goto send_ack;          /* rexmit */
                                break;
                        default:
                                syslog(LOG_INFO, "Received %s in recvfile\n",
                                    opcode(dp->th_opcode));
                                break;
                        }
                }
done:
                if (debug)
                        syslog(LOG_DEBUG, "Got block %u", block);
                /*  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 == tftp_blksize);
        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));
        if (debug)
                syslog(LOG_DEBUG, "Send final ACK %u", 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;
}

const struct errmsg {
        int              e_code;
        const 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" },
        { EOPTNEG,      "Option negotiation failed" },
        { -1,           0 }
};

static const char *
errtomsg(int error)
{
        static char ebuf[20];
        const 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);
        snprintf(ebuf, sizeof(ebuf), "error %d", error);
        return (ebuf);
}

/*
 * 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(int error)
{
        const struct errmsg *pe;
        struct tftphdr *tp;
        int     length;
        size_t  msglen;

        tp = (struct tftphdr *)buf;
        tp->th_opcode = htons((u_short)ERROR);
        msglen = sizeof(buf) - (&tp->th_msg[0] - buf);
        for (pe = errmsgs; pe->e_code >= 0; pe++)
                if (pe->e_code == error)
                        break;
        if (pe->e_code < 0) {
                tp->th_code = EUNDEF;   /* set 'undef' errorcode */
                strlcpy(tp->th_msg, strerror(error - 100), msglen);
        } else {
                tp->th_code = htons((u_short)error);
                strlcpy(tp->th_msg, pe->e_msg, msglen);
        }
        if (debug)
                syslog(LOG_DEBUG, "Send NACK %s", tp->th_msg);
        length = strlen(tp->th_msg);
        msglen = &tp->th_msg[length + 1] - buf;
        if (send(peer, buf, msglen, 0) != msglen)
                syslog(LOG_ERR, "nak: %m");
}

static char *
verifyhost(struct sockaddr *fromp)
{
        static char hbuf[MAXHOSTNAMELEN];

        if (getnameinfo(fromp, fromp->sa_len, hbuf, sizeof(hbuf), NULL, 0, 0))
                strlcpy(hbuf, "?", sizeof(hbuf));
        return (hbuf);
}