libexec/tftpd/tftpd.c

   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  * @(#) Copyright (c) 1983, 1993 The Regents of the University of California.  All rights reserved.
  34  * @(#)tftpd.c  8.1 (Berkeley) 6/4/93
  35  * $FreeBSD: src/libexec/tftpd/tftpd.c,v 1.15.2.5 2003/04/06 19:42:56 dwmalone Exp $
  36  */
  37
  38 /*
  39  * Trivial file transfer protocol server.
  40  *
  41  * This version includes many modifications by Jim Guyton
  42  * <guyton@rand-unix>.
  43  */
  44
  45 #include <sys/param.h>
  46 #include <sys/ioctl.h>
  47 #include <sys/stat.h>
  48 #include <sys/socket.h>
  49 #include <sys/types.h>
  50
  51 #include <netinet/in.h>
  52 #include <arpa/tftp.h>
  53 #include <arpa/inet.h>
  54
  55 #include <ctype.h>
  56 #include <errno.h>
  57 #include <fcntl.h>
  58 #include <libutil.h>
  59 #include <netdb.h>
  60 #include <pwd.h>
  61 #include <setjmp.h>
  62 #include <signal.h>
  63 #include <stdio.h>
  64 #include <stdlib.h>
  65 #include <string.h>
  66 #include <syslog.h>
  67 #include <unistd.h>
  68
  69 #include "tftpsubs.h"
  70
  71 #define TIMEOUT         5
  72 #define MAX_TIMEOUTS    5
  73
  74 int     peer;
  75 int     rexmtval = TIMEOUT;
  76 int     max_rexmtval = 2*TIMEOUT;
  77
  78 #define PKTSIZE SEGSIZE+4
  79 char    buf[PKTSIZE];
  80 char    ackbuf[PKTSIZE];
  81 struct  sockaddr_storage from;
  82 int     fromlen;
  83
  84 void    tftp(struct tftphdr *, int);
  85 static void unmappedaddr(struct sockaddr_in6 *);
  86
  87 /*
  88  * Null-terminated directory prefix list for absolute pathname requests and
  89  * search list for relative pathname requests.
  90  *
  91  * MAXDIRS should be at least as large as the number of arguments that
  92  * inetd allows (currently 20).
  93  */
  94 #define MAXDIRS 20
  95 static struct dirlist {
  96         const char      *name;
  97         int     len;
  98 } dirs[MAXDIRS+1];
  99 static int      suppress_naks;
 100 static int      logging;
 101 static int      ipchroot;
 102
 103 static const char *errtomsg(int);
 104 static void  nak(int);
 105 static void  oack(void);
 106
 107 static void  timer(int);
 108 static void  justquit(int);
 109
 110 int
 111 main(int argc, char *argv[])
 112 {
 113         struct tftphdr *tp;
 114         int n;
 115         int ch, on;
 116         struct sockaddr_storage me;
 117         int len;
 118         char *chroot_dir = NULL;
 119         struct passwd *nobody;
 120         const char *chuser = "nobody";
 121
 122         openlog("tftpd", LOG_PID | LOG_NDELAY, LOG_FTP);
 123         while ((ch = getopt(argc, argv, "cClns:u:")) != -1) {
 124                 switch (ch) {
 125                 case 'c':
 126                         ipchroot = 1;
 127                         break;
 128                 case 'C':
 129                         ipchroot = 2;
 130                         break;
 131                 case 'l':
 132                         logging = 1;
 133                         break;
 134                 case 'n':
 135                         suppress_naks = 1;
 136                         break;
 137                 case 's':
 138                         chroot_dir = optarg;
 139                         break;
 140                 case 'u':
 141                         chuser = optarg;
 142                         break;
 143                 default:
 144                         syslog(LOG_WARNING, "ignoring unknown option -%c", ch);
 145                 }
 146         }
 147         if (optind < argc) {
 148                 struct dirlist *dirp;
 149
 150                 /* Get list of directory prefixes. Skip relative pathnames. */
 151                 for (dirp = dirs; optind < argc && dirp < &dirs[MAXDIRS];
 152                      optind++) {
 153                         if (argv[optind][0] == '/') {
 154                                 dirp->name = argv[optind];
 155                                 dirp->len  = strlen(dirp->name);
 156                                 dirp++;
 157                         }
 158                 }
 159         }
 160         else if (chroot_dir) {
 161                 dirs->name = "/";
 162                 dirs->len = 1;
 163         }
 164         if (ipchroot && chroot_dir == NULL) {
 165                 syslog(LOG_ERR, "-c requires -s");
 166                 exit(1);
 167         }
 168
 169         on = 1;
 170         if (ioctl(0, FIONBIO, &on) < 0) {
 171                 syslog(LOG_ERR, "ioctl(FIONBIO): %m");
 172                 exit(1);
 173         }
 174         fromlen = sizeof (from);
 175         n = recvfrom(0, buf, sizeof (buf), 0,
 176             (struct sockaddr *)&from, &fromlen);
 177         if (n < 0) {
 178                 syslog(LOG_ERR, "recvfrom: %m");
 179                 exit(1);
 180         }
 181         /*
 182          * Now that we have read the message out of the UDP
 183          * socket, we fork and exit.  Thus, inetd will go back
 184          * to listening to the tftp port, and the next request
 185          * to come in will start up a new instance of tftpd.
 186          *
 187          * We do this so that inetd can run tftpd in "wait" mode.
 188          * The problem with tftpd running in "nowait" mode is that
 189          * inetd may get one or more successful "selects" on the
 190          * tftp port before we do our receive, so more than one
 191          * instance of tftpd may be started up.  Worse, if tftpd
 192          * break before doing the above "recvfrom", inetd would
 193          * spawn endless instances, clogging the system.
 194          */
 195         {
 196                 int pid;
 197                 int i, j;
 198
 199                 for (i = 1; i < 20; i++) {
 200                     pid = fork();
 201                     if (pid < 0) {
 202                                 sleep(i);
 203                                 /*
 204                                  * flush out to most recently sent request.
 205                                  *
 206                                  * This may drop some request, but those
 207                                  * will be resent by the clients when
 208                                  * they timeout.  The positive effect of
 209                                  * this flush is to (try to) prevent more
 210                                  * than one tftpd being started up to service
 211                                  * a single request from a single client.
 212                                  */
 213                                 j = sizeof from;
 214                                 i = recvfrom(0, buf, sizeof (buf), 0,
 215                                     (struct sockaddr *)&from, &j);
 216                                 if (i > 0) {
 217                                         n = i;
 218                                         fromlen = j;
 219                                 }
 220                     } else {
 221                                 break;
 222                     }
 223                 }
 224                 if (pid < 0) {
 225                         syslog(LOG_ERR, "fork: %m");
 226                         exit(1);
 227                 } else if (pid != 0) {
 228                         exit(0);
 229                 }
 230         }
 231
 232         /*
 233          * Since we exit here, we should do that only after the above
 234          * recvfrom to keep inetd from constantly forking should there
 235          * be a problem.  See the above comment about system clogging.
 236          */
 237         if (chroot_dir) {
 238                 if (ipchroot) {
 239                         char *tempchroot;
 240                         struct stat sb;
 241                         int statret;
 242                         struct sockaddr_storage ss;
 243                         char hbuf[NI_MAXHOST];
 244
 245                         memcpy(&ss, &from, from.ss_len);
 246                         unmappedaddr((struct sockaddr_in6 *)&ss);
 247                         getnameinfo((struct sockaddr *)&ss, ss.ss_len,
 248                                     hbuf, sizeof(hbuf), NULL, 0,
 249                                     NI_NUMERICHOST | NI_WITHSCOPEID);
 250                         asprintf(&tempchroot, "%s/%s", chroot_dir, hbuf);
 251                         statret = stat(tempchroot, &sb);
 252                         if ((sb.st_mode & S_IFDIR) &&
 253                             (statret == 0 || (statret == -1 && ipchroot == 1)))
 254                                 chroot_dir = tempchroot;
 255                 }
 256                 /* Must get this before chroot because /etc might go away */
 257                 if ((nobody = getpwnam(chuser)) == NULL) {
 258                         syslog(LOG_ERR, "%s: no such user", chuser);
 259                         exit(1);
 260                 }
 261                 if (chroot(chroot_dir)) {
 262                         syslog(LOG_ERR, "chroot: %s: %m", chroot_dir);
 263                         exit(1);
 264                 }
 265                 chdir( "/" );
 266                 setuid(nobody->pw_uid);
 267                 setgroups(1, &nobody->pw_gid);
 268         }
 269
 270         len = sizeof(me);
 271         if (getsockname(0, (struct sockaddr *)&me, &len) == 0) {
 272                 switch (me.ss_family) {
 273                 case AF_INET:
 274                         ((struct sockaddr_in *)&me)->sin_port = 0;
 275                         break;
 276                 case AF_INET6:
 277                         ((struct sockaddr_in6 *)&me)->sin6_port = 0;
 278                         break;
 279                 default:
 280                         /* unsupported */
 281                         break;
 282                 }
 283         } else {
 284                 memset(&me, 0, sizeof(me));
 285                 me.ss_family = from.ss_family;
 286                 me.ss_len = from.ss_len;
 287         }
 288         alarm(0);
 289         close(0);
 290         close(1);
 291         peer = socket(from.ss_family, SOCK_DGRAM, 0);
 292         if (peer < 0) {
 293                 syslog(LOG_ERR, "socket: %m");
 294                 exit(1);
 295         }
 296         if (bind(peer, (struct sockaddr *)&me, me.ss_len) < 0) {
 297                 syslog(LOG_ERR, "bind: %m");
 298                 exit(1);
 299         }
 300         if (connect(peer, (struct sockaddr *)&from, from.ss_len) < 0) {
 301                 syslog(LOG_ERR, "connect: %m");
 302                 exit(1);
 303         }
 304         tp = (struct tftphdr *)buf;
 305         tp->th_opcode = ntohs(tp->th_opcode);
 306         if (tp->th_opcode == RRQ || tp->th_opcode == WRQ)
 307                 tftp(tp, n);
 308         exit(1);
 309 }
 310
 311 struct formats;
 312 int     validate_access(char **, int);
 313 void    xmitfile(struct formats *);
 314 void    recvfile(struct formats *);
 315
 316 struct formats {
 317         const char      *f_mode;
 318         int     (*f_validate)(char **, int);
 319         void    (*f_send)(struct formats *);
 320         void    (*f_recv)(struct formats *);
 321         int     f_convert;
 322 } formats[] = {
 323         { "netascii",   validate_access,        xmitfile,       recvfile, 1 },
 324         { "octet",      validate_access,        xmitfile,       recvfile, 0 },
 325 #ifdef notdef
 326         { "mail",       validate_user,          sendmail,       recvmail, 1 },
 327 #endif
 328         { 0,            NULL,                   NULL,           NULL,     0 }
 329 };
 330
 331 struct options {
 332         const char      *o_type;
 333         char    *o_request;
 334         int     o_reply;        /* turn into union if need be */
 335 } options[] = {
 336         { "tsize",      NULL, 0 },              /* OPT_TSIZE */
 337         { "timeout",    NULL, 0 },              /* OPT_TIMEOUT */
 338         { NULL,         NULL, 0 }
 339 };
 340
 341 enum opt_enum {
 342         OPT_TSIZE = 0,
 343         OPT_TIMEOUT,
 344 };
 345
 346 /*
 347  * Handle initial connection protocol.
 348  */
 349 void
 350 tftp(struct tftphdr *tp, int size)
 351 {
 352         char *cp;
 353         size_t i;
 354         int first = 1, has_options = 0, ecode;
 355         struct formats *pf;
 356         char *filename, *mode = NULL, *option, *ccp;
 357         char fnbuf[MAXPATHLEN];
 358
 359         cp = tp->th_stuff;
 360 again:
 361         while (cp < buf + size) {
 362                 if (*cp == '\0')
 363                         break;
 364                 cp++;
 365         }
 366         if (*cp != '\0') {
 367                 nak(EBADOP);
 368                 exit(1);
 369         }
 370         i = cp - tp->th_stuff;
 371         if (i >= sizeof(fnbuf)) {
 372                 nak(EBADOP);
 373                 exit(1);
 374         }
 375         memcpy(fnbuf, tp->th_stuff, i);
 376         fnbuf[i] = '\0';
 377         filename = fnbuf;
 378         if (first) {
 379                 mode = ++cp;
 380                 first = 0;
 381                 goto again;
 382         }
 383         for (cp = mode; *cp; cp++)
 384                 if (isupper(*cp))
 385                         *cp = tolower(*cp);
 386         for (pf = formats; pf->f_mode; pf++)
 387                 if (strcmp(pf->f_mode, mode) == 0)
 388                         break;
 389         if (pf->f_mode == NULL) {
 390                 nak(EBADOP);
 391                 exit(1);
 392         }
 393         while (++cp < buf + size) {
 394                 for (i = 2, ccp = cp; i > 0; ccp++) {
 395                         if (ccp >= buf + size) {
 396                                 /*
 397                                  * Don't reject the request, just stop trying
 398                                  * to parse the option and get on with it.
 399                                  * Some Apple OpenFirmware versions have
 400                                  * trailing garbage on the end of otherwise
 401                                  * valid requests.
 402                                  */
 403                                 goto option_fail;
 404                         } else if (*ccp == '\0')
 405                                 i--;
 406                 }
 407                 for (option = cp; *cp; cp++)
 408                         if (isupper(*cp))
 409                                 *cp = tolower(*cp);
 410                 for (i = 0; options[i].o_type != NULL; i++)
 411                         if (strcmp(option, options[i].o_type) == 0) {
 412                                 options[i].o_request = ++cp;
 413                                 has_options = 1;
 414                         }
 415                 cp = ccp-1;
 416         }
 417
 418 option_fail:
 419         if (options[OPT_TIMEOUT].o_request) {
 420                 int to = atoi(options[OPT_TIMEOUT].o_request);
 421                 if (to < 1 || to > 255) {
 422                         nak(EBADOP);
 423                         exit(1);
 424                 }
 425                 else if (to <= max_rexmtval)
 426                         options[OPT_TIMEOUT].o_reply = rexmtval = to;
 427                 else
 428                         options[OPT_TIMEOUT].o_request = NULL;
 429         }
 430
 431         ecode = (*pf->f_validate)(&filename, tp->th_opcode);
 432         if (has_options)
 433                 oack();
 434         if (logging) {
 435                 char hbuf[NI_MAXHOST];
 436
 437                 getnameinfo((struct sockaddr *)&from, from.ss_len,
 438                             hbuf, sizeof(hbuf), NULL, 0,
 439                             NI_WITHSCOPEID);
 440                 syslog(LOG_INFO, "%s: %s request for %s: %s", hbuf,
 441                         tp->th_opcode == WRQ ? "write" : "read",
 442                         filename, errtomsg(ecode));
 443         }
 444         if (ecode) {
 445                 /*
 446                  * Avoid storms of naks to a RRQ broadcast for a relative
 447                  * bootfile pathname from a diskless Sun.
 448                  */
 449                 if (suppress_naks && *filename != '/' && ecode == ENOTFOUND)
 450                         exit(0);
 451                 nak(ecode);
 452                 exit(1);
 453         }
 454         if (tp->th_opcode == WRQ)
 455                 (*pf->f_recv)(pf);
 456         else
 457                 (*pf->f_send)(pf);
 458         exit(0);
 459 }
 460
 461
 462 FILE *file;
 463
 464 /*
 465  * Validate file access.  Since we
 466  * have no uid or gid, for now require
 467  * file to exist and be publicly
 468  * readable/writable.
 469  * If we were invoked with arguments
 470  * from inetd then the file must also be
 471  * in one of the given directory prefixes.
 472  * Note also, full path name must be
 473  * given as we have no login directory.
 474  */
 475 int
 476 validate_access(char **filep, int mode)
 477 {
 478         struct stat stbuf;
 479         int     fd;
 480         struct dirlist *dirp;
 481         static char pathname[MAXPATHLEN];
 482         char *filename = *filep;
 483
 484         /*
 485          * Prevent tricksters from getting around the directory restrictions
 486          */
 487         if (strstr(filename, "/../"))
 488                 return (EACCESS);
 489
 490         if (*filename == '/') {
 491                 /*
 492                  * Allow the request if it's in one of the approved locations.
 493                  * Special case: check the null prefix ("/") by looking
 494                  * for length = 1 and relying on the arg. processing that
 495                  * it's a /.
 496                  */
 497                 for (dirp = dirs; dirp->name != NULL; dirp++) {
 498                         if (dirp->len == 1 ||
 499                             (!strncmp(filename, dirp->name, dirp->len) &&
 500                              filename[dirp->len] == '/'))
 501                                     break;
 502                 }
 503                 /* If directory list is empty, allow access to any file */
 504                 if (dirp->name == NULL && dirp != dirs)
 505                         return (EACCESS);
 506                 if (stat(filename, &stbuf) < 0)
 507                         return (errno == ENOENT ? ENOTFOUND : EACCESS);
 508                 if ((stbuf.st_mode & S_IFMT) != S_IFREG)
 509                         return (ENOTFOUND);
 510                 if (mode == RRQ) {
 511                         if ((stbuf.st_mode & S_IROTH) == 0)
 512                                 return (EACCESS);
 513                 } else {
 514                         if ((stbuf.st_mode & S_IWOTH) == 0)
 515                                 return (EACCESS);
 516                 }
 517         } else {
 518                 int err;
 519
 520                 /*
 521                  * Relative file name: search the approved locations for it.
 522                  * Don't allow write requests that avoid directory
 523                  * restrictions.
 524                  */
 525
 526                 if (!strncmp(filename, "../", 3))
 527                         return (EACCESS);
 528
 529                 /*
 530                  * If the file exists in one of the directories and isn't
 531                  * readable, continue looking. However, change the error code
 532                  * to give an indication that the file exists.
 533                  */
 534                 err = ENOTFOUND;
 535                 for (dirp = dirs; dirp->name != NULL; dirp++) {
 536                         snprintf(pathname, sizeof(pathname), "%s/%s",
 537                                 dirp->name, filename);
 538                         if (stat(pathname, &stbuf) == 0 &&
 539                             (stbuf.st_mode & S_IFMT) == S_IFREG) {
 540                                 if ((stbuf.st_mode & S_IROTH) != 0) {
 541                                         break;
 542                                 }
 543                                 err = EACCESS;
 544                         }
 545                 }
 546                 if (dirp->name == NULL)
 547                         return (err);
 548                 *filep = filename = pathname;
 549         }
 550         if (options[OPT_TSIZE].o_request) {
 551                 if (mode == RRQ)
 552                         options[OPT_TSIZE].o_reply = stbuf.st_size;
 553                 else
 554                         /* XXX Allows writes of all sizes. */
 555                         options[OPT_TSIZE].o_reply =
 556                                 atoi(options[OPT_TSIZE].o_request);
 557         }
 558         fd = open(filename, mode == RRQ ? O_RDONLY : O_WRONLY|O_TRUNC);
 559         if (fd < 0)
 560                 return (errno + 100);
 561         file = fdopen(fd, (mode == RRQ)? "r":"w");
 562         if (file == NULL) {
 563                 return errno+100;
 564         }
 565         return (0);
 566 }
 567
 568 int     timeouts;
 569 jmp_buf timeoutbuf;
 570
 571 void
 572 timer(int sig __unused)
 573 {
 574         if (++timeouts > MAX_TIMEOUTS)
 575                 exit(1);
 576         longjmp(timeoutbuf, 1);
 577 }
 578
 579 /*
 580  * Send the requested file.
 581  */
 582 void
 583 xmitfile(struct formats *pf)
 584 {
 585         struct tftphdr *dp;
 586         struct tftphdr *ap;    /* ack packet */
 587         int size, n;
 588         volatile unsigned short block;
 589
 590         signal(SIGALRM, timer);
 591         dp = r_init();
 592         ap = (struct tftphdr *)ackbuf;
 593         block = 1;
 594         do {
 595                 size = readit(file, &dp, pf->f_convert);
 596                 if (size < 0) {
 597                         nak(errno + 100);
 598                         goto abort;
 599                 }
 600                 dp->th_opcode = htons((u_short)DATA);
 601                 dp->th_block = htons((u_short)block);
 602                 timeouts = 0;
 603                 (void)setjmp(timeoutbuf);
 604
 605 send_data:
 606                 {
 607                         int i, t = 1;
 608                         for (i = 0; ; i++){
 609                                 if (send(peer, dp, size + 4, 0) != size + 4) {
 610                                         sleep(t);
 611                                         t = (t < 32) ? t<< 1 : t;
 612                                         if (i >= 12) {
 613                                                 syslog(LOG_ERR, "write: %m");
 614                                                 goto abort;
 615                                         }
 616                                 }
 617                                 break;
 618                         }
 619                 }
 620                 read_ahead(file, pf->f_convert);
 621                 for ( ; ; ) {
 622                         alarm(rexmtval);        /* read the ack */
 623                         n = recv(peer, ackbuf, sizeof (ackbuf), 0);
 624                         alarm(0);
 625                         if (n < 0) {
 626                                 syslog(LOG_ERR, "read: %m");
 627                                 goto abort;
 628                         }
 629                         ap->th_opcode = ntohs((u_short)ap->th_opcode);
 630                         ap->th_block = ntohs((u_short)ap->th_block);
 631
 632                         if (ap->th_opcode == ERROR)
 633                                 goto abort;
 634
 635                         if (ap->th_opcode == ACK) {
 636                                 if (ap->th_block == block)
 637                                         break;
 638                                 /* Re-synchronize with the other side */
 639                                 (void) synchnet(peer);
 640                                 if (ap->th_block == (block -1))
 641                                         goto send_data;
 642                         }
 643
 644                 }
 645                 block++;
 646         } while (size == SEGSIZE);
 647 abort:
 648         (void) fclose(file);
 649 }
 650
 651 void
 652 justquit(int sig __unused)
 653 {
 654         exit(0);
 655 }
 656
 657
 658 /*
 659  * Receive a file.
 660  */
 661 void
 662 recvfile(struct formats *pf)
 663 {
 664         struct tftphdr *dp;
 665         struct tftphdr *ap;    /* ack buffer */
 666         int n, size;
 667         volatile unsigned short block;
 668
 669         signal(SIGALRM, timer);
 670         dp = w_init();
 671         ap = (struct tftphdr *)ackbuf;
 672         block = 0;
 673         do {
 674                 timeouts = 0;
 675                 ap->th_opcode = htons((u_short)ACK);
 676                 ap->th_block = htons((u_short)block);
 677                 block++;
 678                 (void) setjmp(timeoutbuf);
 679 send_ack:
 680                 if (send(peer, ackbuf, 4, 0) != 4) {
 681                         syslog(LOG_ERR, "write: %m");
 682                         goto abort;
 683                 }
 684                 write_behind(file, pf->f_convert);
 685                 for ( ; ; ) {
 686                         alarm(rexmtval);
 687                         n = recv(peer, dp, PKTSIZE, 0);
 688                         alarm(0);
 689                         if (n < 0) {            /* really? */
 690                                 syslog(LOG_ERR, "read: %m");
 691                                 goto abort;
 692                         }
 693                         dp->th_opcode = ntohs((u_short)dp->th_opcode);
 694                         dp->th_block = ntohs((u_short)dp->th_block);
 695                         if (dp->th_opcode == ERROR)
 696                                 goto abort;
 697                         if (dp->th_opcode == DATA) {
 698                                 if (dp->th_block == block) {
 699                                         break;   /* normal */
 700                                 }
 701                                 /* Re-synchronize with the other side */
 702                                 (void) synchnet(peer);
 703                                 if (dp->th_block == (block-1))
 704                                         goto send_ack;          /* rexmit */
 705                         }
 706                 }
 707                 /*  size = write(file, dp->th_data, n - 4); */
 708                 size = writeit(file, &dp, n - 4, pf->f_convert);
 709                 if (size != (n-4)) {                    /* ahem */
 710                         if (size < 0) nak(errno + 100);
 711                         else nak(ENOSPACE);
 712                         goto abort;
 713                 }
 714         } while (size == SEGSIZE);
 715         write_behind(file, pf->f_convert);
 716         (void) fclose(file);            /* close data file */
 717
 718         ap->th_opcode = htons((u_short)ACK);    /* send the "final" ack */
 719         ap->th_block = htons((u_short)(block));
 720         (void) send(peer, ackbuf, 4, 0);
 721
 722         signal(SIGALRM, justquit);      /* just quit on timeout */
 723         alarm(rexmtval);
 724         n = recv(peer, buf, sizeof (buf), 0); /* normally times out and quits */
 725         alarm(0);
 726         if (n >= 4 &&                   /* if read some data */
 727             dp->th_opcode == DATA &&    /* and got a data block */
 728             block == dp->th_block) {    /* then my last ack was lost */
 729                 (void) send(peer, ackbuf, 4, 0);     /* resend final ack */
 730         }
 731 abort:
 732         return;
 733 }
 734
 735 struct errmsg {
 736         int     e_code;
 737         const char      *e_msg;
 738 } errmsgs[] = {
 739         { EUNDEF,       "Undefined error code" },
 740         { ENOTFOUND,    "File not found" },
 741         { EACCESS,      "Access violation" },
 742         { ENOSPACE,     "Disk full or allocation exceeded" },
 743         { EBADOP,       "Illegal TFTP operation" },
 744         { EBADID,       "Unknown transfer ID" },
 745         { EEXISTS,      "File already exists" },
 746         { ENOUSER,      "No such user" },
 747         { EOPTNEG,      "Option negotiation" },
 748         { -1,           0 }
 749 };
 750
 751 static const char *
 752 errtomsg(int error)
 753 {
 754         static char ebuf[20];
 755         struct errmsg *pe;
 756         if (error == 0)
 757                 return "success";
 758         for (pe = errmsgs; pe->e_code >= 0; pe++)
 759                 if (pe->e_code == error)
 760                         return pe->e_msg;
 761         snprintf(ebuf, sizeof(buf), "error %d", error);
 762         return ebuf;
 763 }
 764
 765 /*
 766  * Send a nak packet (error message).
 767  * Error code passed in is one of the
 768  * standard TFTP codes, or a UNIX errno
 769  * offset by 100.
 770  */
 771 static void
 772 nak(int error)
 773 {
 774         struct tftphdr *tp;
 775         int length;
 776         struct errmsg *pe;
 777
 778         tp = (struct tftphdr *)buf;
 779         tp->th_opcode = htons((u_short)ERROR);
 780         tp->th_code = htons((u_short)error);
 781         for (pe = errmsgs; pe->e_code >= 0; pe++)
 782                 if (pe->e_code == error)
 783                         break;
 784         if (pe->e_code < 0) {
 785                 pe->e_msg = strerror(error - 100);
 786                 tp->th_code = EUNDEF;   /* set 'undef' errorcode */
 787         }
 788         strcpy(tp->th_msg, pe->e_msg);
 789         length = strlen(pe->e_msg);
 790         tp->th_msg[length] = '\0';
 791         length += 5;
 792         if (send(peer, buf, length, 0) != length)
 793                 syslog(LOG_ERR, "nak: %m");
 794 }
 795
 796 /* translate IPv4 mapped IPv6 address to IPv4 address */
 797 static void
 798 unmappedaddr(struct sockaddr_in6 *sin6)
 799 {
 800         struct sockaddr_in *sin4;
 801         u_int32_t addr;
 802         int port;
 803
 804         if (sin6->sin6_family != AF_INET6 ||
 805             !IN6_IS_ADDR_V4MAPPED(&sin6->sin6_addr))
 806                 return;
 807         sin4 = (struct sockaddr_in *)sin6;
 808         addr = *(u_int32_t *)&sin6->sin6_addr.s6_addr[12];
 809         port = sin6->sin6_port;
 810         memset(sin4, 0, sizeof(struct sockaddr_in));
 811         sin4->sin_addr.s_addr = addr;
 812         sin4->sin_port = port;
 813         sin4->sin_family = AF_INET;
 814         sin4->sin_len = sizeof(struct sockaddr_in);
 815 }
 816
 817 /*
 818  * Send an oack packet (option acknowledgement).
 819  */
 820 static void
 821 oack(void)
 822 {
 823         struct tftphdr *tp, *ap;
 824         int size, i, n;
 825         char *bp;
 826
 827         tp = (struct tftphdr *)buf;
 828         bp = buf + 2;
 829         size = sizeof(buf) - 2;
 830         tp->th_opcode = htons((u_short)OACK);
 831         for (i = 0; options[i].o_type != NULL; i++) {
 832                 if (options[i].o_request) {
 833                         n = snprintf(bp, size, "%s%c%d", options[i].o_type,
 834                                      0, options[i].o_reply);
 835                         bp += n+1;
 836                         size -= n+1;
 837                         if (size < 0) {
 838                                 syslog(LOG_ERR, "oack: buffer overflow");
 839                                 exit(1);
 840                         }
 841                 }
 842         }
 843         size = bp - buf;
 844         ap = (struct tftphdr *)ackbuf;
 845         signal(SIGALRM, timer);
 846         timeouts = 0;
 847
 848         (void)setjmp(timeoutbuf);
 849         if (send(peer, buf, size, 0) != size) {
 850                 syslog(LOG_INFO, "oack: %m");
 851                 exit(1);
 852         }
 853
 854         for (;;) {
 855                 alarm(rexmtval);
 856                 n = recv(peer, ackbuf, sizeof (ackbuf), 0);
 857                 alarm(0);
 858                 if (n < 0) {
 859                         syslog(LOG_ERR, "recv: %m");
 860                         exit(1);
 861                 }
 862                 ap->th_opcode = ntohs((u_short)ap->th_opcode);
 863                 ap->th_block = ntohs((u_short)ap->th_block);
 864                 if (ap->th_opcode == ERROR)
 865                         exit(1);
 866                 if (ap->th_opcode == ACK && ap->th_block == 0)
 867                         break;
 868         }
 869 }