summaryrefslogtreecommitdiff
path: root/src/shred.c
blob: ddd869fedc0808f6b0872e0e75c9a63beb728112 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
/* TODO:
   - use consistent non-capitalization in error messages
   - add standard GNU copyleft comment

  - Add -r/-R/--recursive
  - Add -i/--interactive
  - Reserve -d
  - Add -L
  - Deal with the amazing variety of gettimeofday() implementation bugs.
    (Some systems use a one-arg form; still others insist that the timezone
    either be NULL or be non-NULL.  Whee.)
  - Add an unlink-all option to emulate rm.
 */

/*
 * shred.c - by Colin Plumb.
 *
 * Do a securer overwrite of given files or devices, to make it harder
 * for even very expensive hardware probing to recover the data.
 *
 * Although this process is also known as "wiping", I prefer the longer
 * name both because I think it is more evocative of what is happening and
 * because a longer name conveys a more appropriate sense of deliberateness.
 *
 * For the theory behind this, see "Secure Deletion of Data from Magnetic
 * and Solid-State Memory", on line at
 * http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html
 *
 * Just for the record, reversing one or two passes of disk overwrite
 * is not terribly difficult with hardware help.  Hook up a good-quality
 * digitizing oscilloscope to the output of the head preamplifier and copy
 * the high-res digitized data to a computer for some off-line analysis.
 * Read the "current" data and average all the pulses together to get an
 * "average" pulse on the disk.  Subtract this average pulse from all of
 * the actual pulses and you can clearly see the "echo" of the previous
 * data on the disk.
 *
 * Real hard drives have to balance the cost of the media, the head,
 * and the read circuitry.  They use better-quality media than absolutely
 * necessary to limit the cost of the read circuitry.  By throwing that
 * assumption out, and the assumption that you want the data processed
 * as fast as the hard drive can spin, you can do better.
 *
 * If asked to wipe a file, this also unlinks it, renaming it to in a
 * clever way to try to leave no trace of the original filename.
 *
 * Copyright 1997, 1998, 1999 Colin Plumb <colin@nyx.net>.  This program
 * may be freely distributed under the terms of the GNU GPL, the BSD license,
 * or Larry Wall's "Artistic License"   Even if you use the BSD license,
 * which does not require it, I'd really like to get improvements back.
 *
 * The ISAAC code still bears some resemblance to the code written
 * by Bob Jenkins, but he permits pretty unlimited use.
 *
 * This was inspired by a desire to improve on some code titled:
 * Wipe V1.0-- Overwrite and delete files.  S. 2/3/96
 * but I've rewritten everything here so completely that no trace of
 * the original remains.
 *
 * Thanks to:
 * Bob Jenkins, for his good RNG work and patience with the FSF copyright
 * paperwork.
 * Jim Meyering, for his work merging this into the GNU fileutils while
 * still letting me feel a sense of ownership and pride.  Getting me to
 * tolerate the GNU brace style was quite a feat of diplomacy.
 * Paul Eggert, for lots of useful discussion and code.  I disagree with
 * an awful lot of his suggestions, but they're disagreements worth having.
 *
 * Things to think about:
 * - Security: Is there any risk to the race
 *   between overwriting and unlinking a file?  Will it do anything
 *   drastically bad if told to attack a named pipe or socket?
 */

/* The official name of this program (e.g., no `g' prefix).  */
#define PROGRAM_NAME "shred"

#define AUTHORS "Colin Plumb"

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <getopt.h>
#include <stdio.h>
#include <assert.h>
#include <setjmp.h>
#include <signal.h>
#include <sys/types.h>

#if HAVE_CONFIG_H
/* Default fileutils build */
# include "system.h"
# include "xstrtol.h"
# include "closeout.h"
# include "error.h"
# include "human.h"
# include "quotearg.h"		/* For quotearg_colon */
# include "quote.h"		/* For quotearg_colon */
# include "xalloc.h"
# include "gtod.h"
char *xstrdup PARAMS ((char const *));

#else /* !HAVE_CONFIG_H */
/*
 * Standalone build - this file compiles by itself without autoconf and
 * the like.  No i18n, and I still have to write a stub for getopt_long,
 * but it's a lot less intertwingled than the usual GNU utilities.
 */

# include <ctype.h>	/* For isprint */
# include <string.h>	/* For memcpy, strerror */
# include <limits.h>	/* For ULONG_MAX etc. */
# include <stdlib.h>	/* For strtoul, EXIT_FAILURE */
# include <errno.h>
# include <fcntl.h>	/* For O_RDONLY etc. */
# include <unistd.h>	/* For getpid, etc. */
# include <sys/time.h>	/* For struct timeval */
# include <sys/stat.h>	/* For struct stat */

# define PACKAGE "standalone"
# define VERSION "2.0" /* Kind of arbitrary... */

# if __GNUC__ < 2 || __GNUC__ == 2 && __GNUC_MINOR__ < 5 || __STRICT_ANSI__
#  define attribute(x)
# else
#  define attribute __attribute__
#  if __GNUC__ == 2 && __GNUC_MINOR__ < 7
   /* The __-protected forms were introduced in GCC 2.6.4 */
#   define __format__ format
#   define __printf__ printf
#  endif
# endif

/* Reasonable default assumptions for time-getting */
# ifndef HAVE_GETTIMEOFDAY
#  define HAVE_GETTIMEOFDAY 1 /* Most systems have it these days */
# endif

# ifdef CLOCK_REALTIME
#  ifndef HAVE_CLOCK_GETTIME
#   define HAVE_CLOCK_GETTIME 1
#  endif
# endif

# ifndef STDOUT_FILENO
#  define STDOUT_FILENO 1
# endif

# define RETSIGTYPE int

# ifndef S_IWUSR
#  ifdef S_IWRITE
#   define S_IWUSR S_IWRITE
#  else
#   define S_IWUSR 0200
#  endif
# endif

/* POSIX doesn't require st_blksize, and 65536 is a reasonable
   upper bound for existing filesystem practice.  */
# define ST_BLKSIZE(Stat) 65536

# define uintmax_t unsigned long

/* Variant human-readable function that ignores last two args */
# define human_readable(v, b, f, t) (sprintf (b, "%lu", (unsigned long) v), b)
# define LONGEST_HUMAN_READABLE (sizeof (uintmax_t) * CHAR_BIT / 3)

/* Variant convert-to-uintmax_t function that accepts metric suffixes */
enum strtol_error
  {
    LONGINT_OK, LONGINT_INVALID, LONGINT_INVALID_SUFFIX_CHAR, LONGINT_OVERFLOW
  };
static uintmax_t
xstrtoumax (char const *ptr, char const **end, int base, uintmax_t *res,
	    char const *valid_suffixes)
{
  char *end_ptr;
  char const *p;
  static char const metric_suffixes[] = "kMGTPEZY";
  int decimal_flag;
  uintmax_t n;
  char c;

  errno = 0;
  *res = n = strtoul (ptr, &end_ptr, base);
  if (end)
    *end = end_ptr;
  if (errno)
    return LONGINT_OVERFLOW;
  if (ptr == end_ptr)
    return LONGINT_INVALID;
  c = *end_ptr;
  if (!c)
    return LONGINT_OK;
  /* Now deal with metric-style suffixes */
  if (valid_suffixes && !strchr (valid_suffixes, c))
    return LONGINT_INVALID_SUFFIX_CHAR;

  decimal_flag = 0;
  switch (c)
    {
    case 'b':
      if (n > ULONG_MAX/512)
	return LONGINT_OVERFLOW;
      n *= 512;
      break;

    case 'B':
      if (n > ULONG_MAX/102412)
	return LONGINT_OVERFLOW;
      n *= 1024;
      break;

    case 'c':
      break;

    case 'K':
      c = 'k';
      goto def;

    case 'm':
      c = 'M';
      /*FALLTHROUGH*/
def:default:
      p = strchr (metric_suffixes, c);
      if (!p)
	return LONGINT_INVALID_SUFFIX_CHAR;
      /*
       * If valid_suffixes contains '0', then xD (decimal) and xB (binary)
       * are allowed as "supersuffixes".  Binary is the default.
       */
      if (strchr (valid_suffixes, '0'))
        {
	  if (end_ptr[1] == 'B')
	    end_ptr++;
	  else if (end_ptr[1] == 'D')
	    {
	      decimal_flag = 1;
	      end_ptr++;
	    }
	}
      /* Now do the scaling */
      p++;
      if (decimal_flag)
	do {
	  if (n > ULONG_MAX/1000)
	    return LONGINT_OVERFLOW;
	  n *= 1000;
	} while (--p > metric_suffixes);
      else
	do {
	  if (n > ULONG_MAX/1024)
	    return LONGINT_OVERFLOW;
	  n *= 1024;
	} while (--p > metric_suffixes);
    }

  /* Final wrapup */
  if (end)
    *end = end_ptr+1;	/* Extra suffix is allowed if it's expected */
  else if (end_ptr[1])
    return LONGINT_INVALID_SUFFIX_CHAR;
  *res = n;
  return LONGINT_OK;
}

/* Dummy i18n stubs */
# define _(x) x
# define N_(x) x
# define setlocale(x,y) (void) 0
# define bindtextdomain(x,y) (void) 0
# define textdomain(x) (void) 0

/*
 * Print a message with `fprintf (stderr, FORMAT, ...)';
 *    if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM).
 *       If STATUS is nonzero, terminate the program with `exit (STATUS)'.
 */
static void error (int status, int errnum, const char *format, ...)
	attribute ((__format__ (__printf__, 3, 4)));

extern char const *program_name;
static void
error (int status, int errnum, const char *format, ...)
{
  va_list ap;

  if (program_name)
    {
      fputs (program_name, stderr);
      fputs (": ", stderr);
    }
  va_start (ap, format);
  vfprintf (stderr, format, ap);
  va_end (ap);
  if (errnum)
    {
      fputs (": ", stderr);
      fputs (strerror (errnum), stderr);
    }
  putc ('\n', stderr);

  if (status)
    exit (status);
}

/*
 * GNU programs actually check for failure closing standard output.
 * This seems unnecessary, until your shell script starts hitting
 * ENOSPC and doing bizarre things with zero-length files.
 */
static void
close_stdout (void)
{
  if (ferror (stdout))
    error (EXIT_FAILURE, 0, _("write error"));
  if (fclose (stdout) != 0)
    error (EXIT_FAILURE, errno, _("write error"));
}

/*
 * Quote the argument (including colon characters) into the buffer.
 * Return the buffer size used (including trailing null byte.)
 * If this is larger than the bufsize, it is an estimate of the space
 * needed.
 */
static size_t
quotearg_colon_buf (char const *arg, char *buf, size_t bufsize)
{
  /* Some systems don't have \a or \e, so this is ASCII-dependent */
  static char const escaped[] = "\7\b\33\f\n\r\t\v";
  static char const escapes[] = "abefnrtv";
  int c;
  size_t pos = 0;
  char const *p;

  while ((c = (unsigned char) *arg++) != 0)
    {
      if (isprint (c))
        {
	  if (strchr ("\\:", c))	/* Anything else we should quote? */
	    if (pos++ < bufsize) *buf++ = '\\';
	}
      else
	{
	  if (pos++ < bufsize) *buf++ = '\\';
	  p = strchr (escaped, c); /* c is never 0, so this is okay */
	  if (p)
	    {
	      c = escapes[p-escaped];
	    }
	  else
	    {
	      if ('0' <= *arg && *arg <= '9')
		c += 256; /* Force 3-digit form if followed by a digit */
	      if (c > 077)
		if (pos++ < bufsize) *buf++ = "0123"[c>>6 & 3];
	      if (c > 07)
		if (pos++ < bufsize) *buf++ = "01234567"[c>>3 & 7];
	      c = "01234567"[c & 7];
	    }
	}
	if (pos++ < bufsize) *buf++ = c;
    }
    if (pos++ < bufsize) *buf++ = 0;
    return pos;
}

/* Quote metacharacters in a filename */
char const *
quotearg_colon (char const *arg)
{
  static char *buf = 0;
  size_t bufsize = 0;
  size_t newsize;

  while ((newsize = quotearg_colon_buf (arg, buf, bufsize)) > bufsize)
    {
      buf = realloc (buf, newsize);
      if (!buf)
	error (EXIT_FAILURE, 0, _("memory exhausted"));
      bufsize = newsize;
    }
  return buf;
}

void *
xmalloc (size_t n)
{
  void *p = malloc (n);
  if (!p)
    error (EXIT_FAILURE, 0, _("memory exhausted"));
  return p;
}

char *
xstrdup (char const *string)
{
  return strcpy (xmalloc (strlen (string) + 1), string);
}

#endif /* ! HAVE_CONFIG_H */

#ifndef O_NOCTTY
# define O_NOCTTY 0  /* This is a very optional frill */
#endif

/* Some systems don't support some file types.  */
#ifndef S_ISFIFO
# define S_ISFIFO(mode) 0
#endif
#ifndef S_ISLNK
# define S_ISLNK(mode) 0
#endif
#ifndef S_ISSOCK
# define S_ISSOCK(mode) 0
#endif

#define DEFAULT_PASSES 25	/* Default */

/* How often to update wiping display */
#define VERBOSE_UPDATE	150*1024

/* If positive, the units to use when printing sizes;
   if negative, the human-readable base.  */
#define OUTPUT_BLOCK_SIZE (-1024)

struct Options
{
  int force;		/* -f flag: chmod files if necessary */
  size_t n_iterations;	/* -n flag: Number of iterations */
  off_t size;		/* -s flag: size of file */
  int remove_file;	/* -u flag: remove file after shredding */
  int verbose;		/* -v flag: Print progress */
  int exact;		/* -x flag: Do not round up file size */
  int zero_fill;	/* -z flag: Add a final zero pass */
};

static struct option const long_opts[] =
{
  {"exact", no_argument, NULL, 'x'},
  {"force", no_argument, NULL, 'f'},
  {"iterations", required_argument, NULL, 'n'},
  {"size", required_argument, NULL, 's'},
  {"remove", no_argument, NULL, 'u'},
  {"verbose", no_argument, NULL, 'v'},
  {"zero", required_argument, NULL, 'z'},
  {GETOPT_HELP_OPTION_DECL},
  {GETOPT_VERSION_OPTION_DECL},
  {NULL, 0, NULL, 0}
};

/* Global variable for error printing purposes */
char const *program_name; /* Initialized before any possible use */

void
usage (int status)
{
  if (status != 0)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
	     program_name);
  else
    {
      printf (_("Usage: %s [OPTIONS] FILE [...]\n"), program_name);
      printf (_("\
Overwrite the specified FILE(s) repeatedly, in order to make it harder\n\
for even very expensive hardware probing to recover the data.\n\
\n\
  -f, --force    change permissions to allow writing if necessary\n\
  -n, --iterations=N  Overwrite N times instead of the default (%d)\n\
  -s, --size=N   shred this many bytes (suffixes like k, M, G accepted)\n\
  -u, --remove   truncate and remove file after overwriting\n\
  -v, --verbose  show progress\n\
  -x, --exact    do not round file sizes up to the next full block\n\
  -z, --zero     add a final overwrite with zeros to hide shredding\n\
  -              shred standard output\n\
      --help     display this help and exit\n\
      --version  print version information and exit\n\
\n\
Delete FILE(s) if --remove (-u) is specified.  The default is not to remove\n\
the files because it is common to operate on device files like /dev/hda,\n\
and those files usually should not be removed.  When operating on regular\n\
files, most people use the --remove option.\n\
\n\
CAUTION: Note that shred relies on a very important assumption:\n\
that the filesystem overwrites data in place.  This is the traditional\n\
way to do things, but many modern filesystem designs do not satisfy this\n\
assumption.  The following are examples of filesystems on which shred is\n\
not effective:\n\
\n\
* log-structured or journaled filesystems, such as those supplied with\n\
  AIX and Solaris (and JFS, ReiserFS, XFS, etc.)\n\
\n\
* filesystems that write redundant data and carry on even if some writes\n\
  fail, such as RAID-based filesystems\n\
\n\
* filesystems that make snapshots, such as Network Appliance's NFS server\n\
\n\
* filesystems that cache in temporary locations, such as NFS\n\
  version 3 clients\n\
\n\
* compressed filesystems\n\
\n\
In addition, file system backups and remote mirrors may contain copies\n\
of the file that cannot be removed, and that will allow a shredded file\n\
to be recovered later.\n\
"), DEFAULT_PASSES);
      puts (_("\nReport bugs to <bug-fileutils@gnu.org>."));
    }
  exit (status);
}

#if ! HAVE_FDATASYNC
# define fdatasync(fd) -1
#endif

/*
 * --------------------------------------------------------------------
 *     Bob Jenkins' cryptographic random number generator, ISAAC.
 *     Hacked by Colin Plumb.
 *
 * We need a source of random numbers for some of the overwrite data.
 * Cryptographically secure is desirable, but it's not life-or-death
 * so I can be a little bit experimental in the choice of RNGs here.
 *
 * This generator is based somewhat on RC4, but has analysis
 * (http://ourworld.compuserve.com/homepages/bob_jenkins/randomnu.htm)
 * pointing to it actually being better.  I like it because it's nice
 * and fast, and because the author did good work analyzing it.
 * --------------------------------------------------------------------
 */

#if defined __STDC__ && __STDC__
# define UINT_MAX_32_BITS 4294967295U
#else
# define UINT_MAX_32_BITS 0xFFFFFFFF
#endif

#if ULONG_MAX == UINT_MAX_32_BITS
typedef unsigned long word32;
#else
# if UINT_MAX == UINT_MAX_32_BITS
typedef unsigned word32;
# else
#  if USHRT_MAX == UINT_MAX_32_BITS
typedef unsigned short word32;
#  else
#   if UCHAR_MAX == UINT_MAX_32_BITS
typedef unsigned char word32;
#   else
     "No 32-bit type available!"
#   endif
#  endif
# endif
#endif

/* Size of the state tables to use.  (You may change ISAAC_LOG) */
#define ISAAC_LOG 8
#define ISAAC_WORDS (1 << ISAAC_LOG)
#define ISAAC_BYTES (ISAAC_WORDS * sizeof (word32))

/* RNG state variables */
struct isaac_state
  {
    word32 mm[ISAAC_WORDS];	/* Main state array */
    word32 iv[8];		/* Seeding initial vector */
    word32 a, b, c;		/* Extra index variables */
  };

/* This index operation is more efficient on many processors */
#define ind(mm, x) \
  (* (word32 *) ((char *) (mm) + ((x) & (ISAAC_WORDS - 1) * sizeof (word32))))

/*
 * The central step.  This uses two temporaries, x and y.  mm is the
 * whole state array, while m is a pointer to the current word.  off is
 * the offset from m to the word ISAAC_WORDS/2 words away in the mm array,
 * i.e. +/- ISAAC_WORDS/2.
 */
#define isaac_step(mix, a, b, mm, m, off, r) \
( \
  a = ((a) ^ (mix)) + (m)[off], \
  x = *(m), \
  *(m) = y = ind (mm, x) + (a) + (b), \
  *(r) = b = ind (mm, (y) >> ISAAC_LOG) + x \
)

/*
 * Refill the entire R array, and update S.
 */
static void
isaac_refill (struct isaac_state *s, word32 r[/* ISAAC_WORDS */])
{
  register word32 a, b;		/* Caches of a and b */
  register word32 x, y;		/* Temps needed by isaac_step macro */
  register word32 *m = s->mm;	/* Pointer into state array */

  a = s->a;
  b = s->b + (++s->c);

  do
    {
      isaac_step (a << 13, a, b, s->mm, m, ISAAC_WORDS / 2, r);
      isaac_step (a >> 6, a, b, s->mm, m + 1, ISAAC_WORDS / 2, r + 1);
      isaac_step (a << 2, a, b, s->mm, m + 2, ISAAC_WORDS / 2, r + 2);
      isaac_step (a >> 16, a, b, s->mm, m + 3, ISAAC_WORDS / 2, r + 3);
      r += 4;
    }
  while ((m += 4) < s->mm + ISAAC_WORDS / 2);
  do
    {
      isaac_step (a << 13, a, b, s->mm, m, -ISAAC_WORDS / 2, r);
      isaac_step (a >> 6, a, b, s->mm, m + 1, -ISAAC_WORDS / 2, r + 1);
      isaac_step (a << 2, a, b, s->mm, m + 2, -ISAAC_WORDS / 2, r + 2);
      isaac_step (a >> 16, a, b, s->mm, m + 3, -ISAAC_WORDS / 2, r + 3);
      r += 4;
    }
  while ((m += 4) < s->mm + ISAAC_WORDS);
  s->a = a;
  s->b = b;
}

/*
 * The basic seed-scrambling step for initialization, based on Bob
 * Jenkins' 256-bit hash.
 */
#define mix(a,b,c,d,e,f,g,h) \
   (       a ^= b << 11, d += a, \
   b += c, b ^= c >>  2, e += b, \
   c += d, c ^= d <<  8, f += c, \
   d += e, d ^= e >> 16, g += d, \
   e += f, e ^= f << 10, h += e, \
   f += g, f ^= g >>  4, a += f, \
   g += h, g ^= h <<  8, b += g, \
   h += a, h ^= a >>  9, c += h, \
   a += b                        )

/* The basic ISAAC initialization pass.  */
static void
isaac_mix (struct isaac_state *s, word32 const seed[/* ISAAC_WORDS */])
{
  int i;
  word32 a = s->iv[0];
  word32 b = s->iv[1];
  word32 c = s->iv[2];
  word32 d = s->iv[3];
  word32 e = s->iv[4];
  word32 f = s->iv[5];
  word32 g = s->iv[6];
  word32 h = s->iv[7];

  for (i = 0; i < ISAAC_WORDS; i += 8)
    {
      a += seed[i];
      b += seed[i + 1];
      c += seed[i + 2];
      d += seed[i + 3];
      e += seed[i + 4];
      f += seed[i + 5];
      g += seed[i + 6];
      h += seed[i + 7];

      mix (a, b, c, d, e, f, g, h);

      s->mm[i] = a;
      s->mm[i + 1] = b;
      s->mm[i + 2] = c;
      s->mm[i + 3] = d;
      s->mm[i + 4] = e;
      s->mm[i + 5] = f;
      s->mm[i + 6] = g;
      s->mm[i + 7] = h;
    }

  s->iv[0] = a;
  s->iv[1] = b;
  s->iv[2] = c;
  s->iv[3] = d;
  s->iv[4] = e;
  s->iv[5] = f;
  s->iv[6] = g;
  s->iv[7] = h;
}

#if 0 /* Provided for reference only; not used in this code */
/*
 * Initialize the ISAAC RNG with the given seed material.
 * Its size MUST be a multiple of ISAAC_BYTES, and may be
 * stored in the s->mm array.
 *
 * This is a generalization of the original ISAAC initialization code
 * to support larger seed sizes.  For seed sizes of 0 and ISAAC_BYTES,
 * it is identical.
 */
static void
isaac_init (struct isaac_state *s, word32 const *seed, size_t seedsize)
{
  static word32 const iv[8] =
  {
    0x1367df5a, 0x95d90059, 0xc3163e4b, 0x0f421ad8,
    0xd92a4a78, 0xa51a3c49, 0xc4efea1b, 0x30609119};
  int i;

# if 0
  /* The initialization of iv is a precomputed form of: */
  for (i = 0; i < 7; i++)
    iv[i] = 0x9e3779b9;		/* the golden ratio */
  for (i = 0; i < 4; ++i)	/* scramble it */
    mix (iv[0], iv[1], iv[2], iv[3], iv[4], iv[5], iv[6], iv[7]);
# endif
  s->a = s->b = s->c = 0;

  for (i = 0; i < 8; i++)
    s->iv[i] = iv[i];

  if (seedsize)
    {
      /* First pass (as in reference ISAAC code) */
      isaac_mix (s, seed);
      /* Second and subsequent passes (extension to ISAAC) */
      while (seedsize -= ISAAC_BYTES)
	{
	  seed += ISAAC_WORDS;
	  for (i = 0; i < ISAAC_WORDS; i++)
	    s->mm[i] += seed[i];
	  isaac_mix (s, s->mm);
	}
    }
  else
    {
      /* The no seed case (as in reference ISAAC code) */
      for (i = 0; i < ISAAC_WORDS; i++)
	s->mm[i] = 0;
    }

  /* Final pass */
  isaac_mix (s, s->mm);
}
#endif

/* Start seeding an ISAAC structire */
static void
isaac_seed_start (struct isaac_state *s)
{
  static word32 const iv[8] =
    {
      0x1367df5a, 0x95d90059, 0xc3163e4b, 0x0f421ad8,
      0xd92a4a78, 0xa51a3c49, 0xc4efea1b, 0x30609119
    };
  int i;

#if 0
  /* The initialization of iv is a precomputed form of: */
  for (i = 0; i < 7; i++)
    iv[i] = 0x9e3779b9;		/* the golden ratio */
  for (i = 0; i < 4; ++i)	/* scramble it */
    mix (iv[0], iv[1], iv[2], iv[3], iv[4], iv[5], iv[6], iv[7]);
#endif
  for (i = 0; i < 8; i++)
    s->iv[i] = iv[i];
  /* We could initialize s->mm to zero, but why bother? */

  /* s->c gets used for a data pointer during the seeding phase */
  s->a = s->b = s->c = 0;
}

/* Add a buffer of seed material */
static void
isaac_seed_data (struct isaac_state *s, void const *buf, size_t size)
{
  unsigned char *p;
  size_t avail;
  size_t i;

  avail = sizeof s->mm - (size_t) s->c;	/* s->c is used as a write pointer */

  /* Do any full buffers that are necessary */
  while (size > avail)
    {
      p = (unsigned char *) s->mm + s->c;
      for (i = 0; i < avail; i++)
	p[i] ^= ((unsigned char const *) buf)[i];
      buf = (char const *) buf + avail;
      size -= avail;
      isaac_mix (s, s->mm);
      s->c = 0;
      avail = sizeof s->mm;
    }

  /* And the final partial block */
  p = (unsigned char *) s->mm + s->c;
  for (i = 0; i < size; i++)
    p[i] ^= ((unsigned char const *) buf)[i];
  s->c = (word32) size;
}


/* End of seeding phase; get everything ready to produce output. */
static void
isaac_seed_finish (struct isaac_state *s)
{
  isaac_mix (s, s->mm);
  isaac_mix (s, s->mm);
  /* Now reinitialize c to start things off right */
  s->c = 0;
}
#define ISAAC_SEED(s,x) isaac_seed_data (s, &(x), sizeof (x))


#if __GNUC__ >= 2 && (__i386__ || __alpha__)
/*
 * Many processors have very-high-resolution timer registers,
 * The timer registers can be made inaccessible, so we have to deal with the
 * possibility of SIGILL while we're working.
 */
static jmp_buf env;
static RETSIGTYPE
sigill_handler (int signum)
{
  (void) signum;
  longjmp (env, 1);  /* Trivial, just return an indication that it happened */
}

static void
isaac_seed_machdep (struct isaac_state *s)
{
  RETSIGTYPE (*oldhandler) (int);

  /* This is how one does try/except in C */
  oldhandler = signal (SIGILL, sigill_handler);
  if (setjmp (env))  /* ANSI: Must be entire controlling expression */
    {
      (void) signal (SIGILL, oldhandler);
    }
  else
    {
# if __i386__
      word32 t[2];
      __asm__ __volatile__ ("rdtsc" : "=a" (t[0]), "=d" (t[1]));
# endif
# if __alpha__
      unsigned long t;
      __asm__ __volatile__ ("rpcc %0" : "=r" (t));
# endif
# if _ARCH_PPC
      /* Code not used because this instruction is available only on first-
	 generation PPCs and evokes a SIGBUS on some Linux 2.4 kernels.  */
      word32 t;
      __asm__ __volatile__ ("mfspr %0,22" : "=r" (t));
# endif
# if __mips
      /* Code not used because this is not accessible from userland */
      word32 t;
      __asm__ __volatile__ ("mfc0\t%0,$9" : "=r" (t));
# endif
# if __sparc__
      /* This doesn't compile on all platforms yet.  How to fix? */
      unsigned long t;
      __asm__ __volatile__ ("rd	%%tick, %0" : "=r" (t));
# endif
     (void) signal (SIGILL, oldhandler);
     isaac_seed_data (s, &t, sizeof t);
  }
}

#else /* !(__i386__ || __alpha__) */

/* Do-nothing stub */
# define isaac_seed_machdep(s) (void) 0

#endif /* !(__i386__ || __alpha__) */


/*
 * Get seed material.  16 bytes (128 bits) is plenty, but if we have
 * /dev/urandom, we get 32 bytes = 256 bits for complete overkill.
 */
static void
isaac_seed (struct isaac_state *s)
{
  isaac_seed_start (s);

  { pid_t t = getpid ();   ISAAC_SEED (s, t); }
  { pid_t t = getppid ();  ISAAC_SEED (s, t); }
  { uid_t t = getuid ();   ISAAC_SEED (s, t); }
  { gid_t t = getgid ();   ISAAC_SEED (s, t); }

  {
#if HAVE_GETHRTIME
    hrtime_t t = gethrtime ();
    ISAAC_SEED (s, t);
#else
# if HAVE_CLOCK_GETTIME		/* POSIX ns-resolution */
    struct timespec t;
    clock_gettime (CLOCK_REALTIME, &t);
# else
#  if HAVE_GETTIMEOFDAY
    struct timeval t;
    gettimeofday (&t, (struct timezone *) 0);
#  else
    time_t t;
    t = time ((time_t *) 0);
#  endif
# endif
#endif
    ISAAC_SEED (s, t);
  }

  isaac_seed_machdep (s);

  {
    char buf[32];
    int fd = open ("/dev/urandom", O_RDONLY | O_NOCTTY);
    if (fd >= 0)
      {
	read (fd, buf, 32);
	close (fd);
	isaac_seed_data (s, buf, 32);
      }
    else
      {
	fd = open ("/dev/random", O_RDONLY | O_NONBLOCK | O_NOCTTY);
	if (fd >= 0)
	  {
	    /* /dev/random is more precious, so use less */
	    read (fd, buf, 16);
	    close (fd);
	    isaac_seed_data (s, buf, 16);
	  }
      }
  }

  isaac_seed_finish (s);
}

/* Single-word RNG built on top of ISAAC */
struct irand_state
{
  word32 r[ISAAC_WORDS];
  unsigned numleft;
  struct isaac_state *s;
};

static void
irand_init (struct irand_state *r, struct isaac_state *s)
{
  r->numleft = 0;
  r->s = s;
}

/*
 * We take from the end of the block deliberately, so if we need
 * only a small number of values, we choose the final ones which are
 * marginally better mixed than the initial ones.
 */
static word32
irand32 (struct irand_state *r)
{
  if (!r->numleft)
    {
      isaac_refill (r->s, r->r);
      r->numleft = ISAAC_WORDS;
    }
  return r->r[--r->numleft];
}

/*
 * Return a uniformly distributed random number between 0 and n,
 * inclusive.  Thus, the result is modulo n+1.
 *
 * Theory of operation: as x steps through every possible 32-bit number,
 * x % n takes each value at least 2^32 / n times (rounded down), but
 * the values less than 2^32 % n are taken one additional time.  Thus,
 * x % n is not perfectly uniform.  To fix this, the values of x less
 * than 2^32 % n are disallowed, and if the RNG produces one, we ask
 * for a new value.
 */
static word32
irand_mod (struct irand_state *r, word32 n)
{
  word32 x;
  word32 lim;

  if (!++n)
    return irand32 (r);

  lim = -n % n;			/* == (2**32-n) % n == 2**32 % n */
  do
    {
      x = irand32 (r);
    }
  while (x < lim);
  return x % n;
}

/*
 * Fill a buffer with a fixed pattern.
 *
 * The buffer must be at least 3 bytes long, even if
 * size is less.  Larger sizes are filled exactly.
 */
static void
fillpattern (int type, unsigned char *r, size_t size)
{
  size_t i;
  unsigned bits = type & 0xfff;

  bits |= bits << 12;
  ((unsigned char *) r)[0] = (bits >> 4) & 255;
  ((unsigned char *) r)[1] = (bits >> 8) & 255;
  ((unsigned char *) r)[2] = bits & 255;
  for (i = 3; i < size / 2; i *= 2)
    memcpy ((char *) r + i, (char *) r, i);
  if (i < size)
    memcpy ((char *) r + i, (char *) r, size - i);

  /* Invert the first bit of every 512-byte sector. */
  if (type & 0x1000)
    for (i = 0; i < size; i += 512)
      r[i] ^= 0x80;
}

/*
 * Fill a buffer, R (of size SIZE_MAX), with random data.
 * SIZE is rounded UP to a multiple of ISAAC_BYTES.
 */
static void
fillrand (struct isaac_state *s, word32 *r, size_t size_max, size_t size)
{
  size = (size + ISAAC_BYTES - 1) / ISAAC_BYTES;
  assert (size <= size_max);

  while (size--)
    {
      isaac_refill (s, r);
      r += ISAAC_WORDS;
    }
}

/*
 * Generate a 6-character (+ nul) pass name string
 * FIXME: allow translation of "random".
 */
#define PASS_NAME_SIZE 7
static void
passname (unsigned char const *data, char name[PASS_NAME_SIZE])
{
  if (data)
    sprintf (name, "%02x%02x%02x", data[0], data[1], data[2]);
  else
    memcpy (name, "random", PASS_NAME_SIZE);
}

/*
 * Do pass number k of n, writing "size" bytes of the given pattern "type"
 * to the file descriptor fd.   Qname, k and n are passed in only for verbose
 * progress message purposes.  If n == 0, no progress messages are printed.
 *
 * If *sizep == -1, the size is unknown, and it will be filled in as soon
 * as writing fails.
 */
static int
dopass (int fd, char const *qname, off_t *sizep, int type,
	struct isaac_state *s, unsigned long k, unsigned long n)
{
  off_t size = *sizep;
  off_t offset;			/* Current file posiiton */
  off_t thresh;			/* Offset to print next status update */
  size_t lim;			/* Amount of data to try writing */
  size_t soff;			/* Offset into buffer for next write */
  ssize_t ssize;		/* Return value from write */
#if ISAAC_WORDS > 1024
  word32 r[ISAAC_WORDS * 3];	/* Multiple of 4K and of pattern size */
#else
  word32 r[1024 * 3];		/* Multiple of 4K and of pattern size */
#endif
  char pass_string[PASS_NAME_SIZE];	/* Name of current pass */

  if (lseek (fd, (off_t) 0, SEEK_SET) == -1)
    {
      error (0, errno, _("%s: cannot rewind"), qname);
      return -1;
    }

  /* Constant fill patterns need only be set up once. */
  if (type >= 0)
    {
      lim = sizeof r;
      if ((off_t) lim > size && size != -1)
	{
	  lim = (size_t) size;
	}
      fillpattern (type, (unsigned char *) r, lim);
      passname ((unsigned char *) r, pass_string);
    }
  else
    {
      passname (0, pass_string);
    }

  /* Set position if first status update */
  thresh = 0;
  if (n)
    {
      error (0, 0, _("%s: pass %lu/%lu (%s)..."), qname, k, n, pass_string);
      thresh = VERBOSE_UPDATE;
      if (thresh > size && size != -1)
	thresh = size;
    }

  offset = 0;
  for (;;)
    {
      /* How much to write this time? */
      lim = sizeof r;
      if ((off_t) lim > size - offset && size != -1)
	{
	  if (size < offset)
	    break;
	  lim = (size_t) (size - offset);
	  if (!lim)
	    break;
	}
      if (type < 0)
	fillrand (s, r, sizeof r, lim);
      /* Loop to retry partial writes. */
      for (soff = 0; soff < lim; soff += ssize)
	{
	  ssize = write (fd, (char *) r + soff, lim - soff);
	  if (ssize <= 0)
	    {
	      if ((ssize == 0 || errno == ENOSPC)
		  && size == -1)
		{
		  /* Ah, we have found the end of the file */
		  *sizep = thresh = size = offset + soff;
		  break;
		}
	      else
		{
		  int errnum = errno;
		  char buf[LONGEST_HUMAN_READABLE + 1];
		  error (0, errnum, _("%s: error writing at offset %s"),
			 qname,
			 human_readable ((uintmax_t) (offset + soff),
					 buf, 1, 1));
		  /*
		   * I sometimes use shred on bad media, before throwing it
		   * out.  Thus, I don't want it to give up on bad blocks.
		   * This code assumes 512-byte blocks and tries to skip
		   * over them.  It works because lim is always a multiple
		   * of 512, except at the end.
		   */
		  if (errnum == EIO && soff % 512 == 0 && lim >= soff + 512
		      && size != -1)
		    {
		      if (lseek (fd, (off_t) (offset + soff + 512), SEEK_SET)
			  != -1)
			{
			  soff += 512;
			  continue;
			}
		      error (0, errno, "%s: lseek", qname);
		    }
		  return -1;
		}
	    }
	}

      /* Okay, we have written "lim" bytes. */

      if (offset + lim < offset)
	{
	  error (0, 0, _("%s: file too large"), qname);
	  return -1;
	}

      offset += lim;

      /* Time to print progress? */
      if (offset >= thresh && n)
	{
	  char offset_buf[LONGEST_HUMAN_READABLE + 1];
	  char size_buf[LONGEST_HUMAN_READABLE + 1];
	  char const *human_offset
	    = human_readable ((uintmax_t) offset, offset_buf, 1,
			      OUTPUT_BLOCK_SIZE);
	  if (size != -1)
	    error (0, 0, _("%s: pass %lu/%lu (%s)...%s/%s"), qname, k, n,
		   pass_string, human_offset,
		   human_readable ((uintmax_t) size, size_buf, 1,
				   OUTPUT_BLOCK_SIZE));
	  else
	    error (0, 0, _("%s: pass %lu/%lu (%s)...%s"), qname, k, n,
		   pass_string, human_offset);

	  thresh += VERBOSE_UPDATE;
	  if (thresh > size && size != -1)
	    thresh = size;
	  /*
	   * Force periodic syncs to keep displayed progress accurate
	   * FIXME: Should these be present even if -v is not enabled,
	   * to keep the buffer cache from filling with dirty pages?
	   * It's a common problem with programs that do lots of writes,
	   * like mkfs.
	   */
	  if (fdatasync (fd) < 0 && fsync (fd) < 0)
	    {
	      error (0, errno, "%s: fsync", qname);
	      return -1;
	    }
	}
    }

  /* Force what we just wrote to hit the media. */
  if (fdatasync (fd) < 0 && fsync (fd) < 0)
    {
      error (0, errno, "%s: fsync", qname);
      return -1;
    }
  return 0;
}

/*
 * The passes start and end with a random pass, and the passes in between
 * are done in random order.  The idea is to deprive someone trying to
 * reverse the process of knowledge of the overwrite patterns, so they
 * have the additional step of figuring out what was done to the disk
 * before they can try to reverse or cancel it.
 *
 * First, all possible 1-bit patterns.  There are two of them.
 * Then, all possible 2-bit patterns.  There are four, but the two
 * which are also 1-bit patterns can be omitted.
 * Then, all possible 3-bit patterns.  Likewise, 8-2 = 6.
 * Then, all possible 4-bit patterns.  16-4 = 12.
 *
 * The basic passes are:
 * 1-bit: 0x000, 0xFFF
 * 2-bit: 0x555, 0xAAA
 * 3-bit: 0x249, 0x492, 0x924, 0x6DB, 0xB6D, 0xDB6 (+ 1-bit)
 *        100100100100         110110110110
 *           9   2   4            D   B   6
 * 4-bit: 0x111, 0x222, 0x333, 0x444, 0x666, 0x777,
 *        0x888, 0x999, 0xBBB, 0xCCC, 0xDDD, 0xEEE (+ 1-bit, 2-bit)
 * Adding three random passes at the beginning, middle and end
 * produces the default 25-pass structure.
 *
 * The next extension would be to 5-bit and 6-bit patterns.
 * There are 30 uncovered 5-bit patterns and 64-8-2 = 46 uncovered
 * 6-bit patterns, so they would increase the time required
 * significantly.  4-bit patterns are enough for most purposes.
 *
 * The main gotcha is that this would require a trickier encoding,
 * since lcm(2,3,4) = 12 bits is easy to fit into an int, but
 * lcm(2,3,4,5) = 60 bits is not.
 *
 * One extension that is included is to complement the first bit in each
 * 512-byte block, to alter the phase of the encoded data in the more
 * complex encodings.  This doesn't apply to MFM, so the 1-bit patterns
 * are considered part of the 3-bit ones and the 2-bit patterns are
 * considered part of the 4-bit patterns.
 *
 *
 * How does the generalization to variable numbers of passes work?
 *
 * Here's how...
 * Have an ordered list of groups of passes.  Each group is a set.
 * Take as many groups as will fit, plus a random subset of the
 * last partial group, and place them into the passes list.
 * Then shuffle the passes list into random order and use that.
 *
 * One extra detail: if we can't include a large enough fraction of the
 * last group to be interesting, then just substitute random passes.
 *
 * If you want more passes than the entire list of groups can
 * provide, just start repeating from the beginning of the list.
 */
static int const
  patterns[] =
{
  -2,				/* 2 random passes */
  2, 0x000, 0xFFF,		/* 1-bit */
  2, 0x555, 0xAAA,		/* 2-bit */
  -1,				/* 1 random pass */
  6, 0x249, 0x492, 0x6DB, 0x924, 0xB6D, 0xDB6,	/* 3-bit */
  12, 0x111, 0x222, 0x333, 0x444, 0x666, 0x777,
  0x888, 0x999, 0xBBB, 0xCCC, 0xDDD, 0xEEE,	/* 4-bit */
  -1,				/* 1 random pass */
	/* The following patterns have the frst bit per block flipped */
  8, 0x1000, 0x1249, 0x1492, 0x16DB, 0x1924, 0x1B6D, 0x1DB6, 0x1FFF,
  14, 0x1111, 0x1222, 0x1333, 0x1444, 0x1555, 0x1666, 0x1777,
  0x1888, 0x1999, 0x1AAA, 0x1BBB, 0x1CCC, 0x1DDD, 0x1EEE,
  -1,				/* 1 random pass */
  0				/* End */
};

/*
 * Generate a random wiping pass pattern with num passes.
 * This is a two-stage process.  First, the passes to include
 * are chosen, and then they are shuffled into the desired
 * order.
 */
static void
genpattern (int *dest, size_t num, struct isaac_state *s)
{
  struct irand_state r;
  size_t randpasses;
  int const *p;
  int *d;
  size_t n;
  size_t accum, top, swap;
  int k;

  if (!num)
    return;

  irand_init (&r, s);

  /* Stage 1: choose the passes to use */
  p = patterns;
  randpasses = 0;
  d = dest;			/* Destination for generated pass list */
  n = num;			/* Passes remaining to fill */

  for (;;)
    {
      k = *p++;			/* Block descriptor word */
      if (!k)
	{			/* Loop back to the beginning */
	  p = patterns;
	}
      else if (k < 0)
	{			/* -k random passes */
	  k = -k;
	  if ((size_t) k >= n)
	    {
	      randpasses += n;
	      n = 0;
	      break;
	    }
	  randpasses += k;
	  n -= k;
	}
      else if ((size_t) k <= n)
	{			/* Full block of patterns */
	  memcpy (d, p, k * sizeof (int));
	  p += k;
	  d += k;
	  n -= k;
	}
      else if (n < 2 || 3 * n < (size_t) k)
	{			/* Finish with random */
	  randpasses += n;
	  break;
	}
      else
	{			/* Pad out with k of the n available */
	  do
	    {
	      if (n == (size_t) k-- || irand_mod (&r, k) < n)
		{
		  *d++ = *p;
		  n--;
		}
	      p++;
	    }
	  while (n);
	  break;
	}
    }
  top = num - randpasses;	/* Top of initialized data */
  /* assert (d == dest+top); */

  /*
   * We now have fixed patterns in the dest buffer up to
   * "top", and we need to scramble them, with "randpasses"
   * random passes evenly spaced among them.
   *
   * We want one at the beginning, one at the end, and
   * evenly spaced in between.  To do this, we basically
   * use Bresenham's line draw (a.k.a DDA) algorithm
   * to draw a line with slope (randpasses-1)/(num-1).
   * (We use a positive accumulator and count down to
   * do this.)
   *
   * So for each desired output value, we do the following:
   * - If it should be a random pass, copy the pass type
   *   to top++, out of the way of the other passes, and
   *   set the current pass to -1 (random).
   * - If it should be a normal pattern pass, choose an
   *   entry at random between here and top-1 (inclusive)
   *   and swap the current entry with that one.
   */
  randpasses--;			/* To speed up later math */
  accum = randpasses;		/* Bresenham DDA accumulator */
  for (n = 0; n < num; n++)
    {
      if (accum <= randpasses)
	{
	  accum += num - 1;
	  dest[top++] = dest[n];
	  dest[n] = -1;
	}
      else
	{
	  swap = n + irand_mod (&r, top - n - 1);
	  k = dest[n];
	  dest[n] = dest[swap];
	  dest[swap] = k;
	}
      accum -= randpasses;
    }
  /* assert (top == num); */

  memset (&r, 0, sizeof r);	/* Wipe this on general principles */
}

/*
 * The core routine to actually do the work.  This overwrites the first
 * size bytes of the given fd.  Returns -1 on error, 0 on success.
 */
static int
do_wipefd (int fd, char const *qname, struct isaac_state *s,
	   struct Options const *flags)
{
  size_t i;
  struct stat st;
  off_t size;			/* Size to write, size to read */
  unsigned long n;		/* Number of passes for printing purposes */
  int *passarray;

  n = 0;		/* dopass takes n -- 0 to mean "don't print progress" */
  if (flags->verbose)
    n = flags->n_iterations + ((flags->zero_fill) != 0);

  if (fstat (fd, &st))
    {
      error (0, errno, "%s: fstat", qname);
      return -1;
    }

  /* If we know that we can't possibly shred the file, give up now.
     Otherwise, we may go into a infinite loop writing data before we
     find that we can't rewind the device.  */
  if ((S_ISCHR (st.st_mode) && isatty (fd))
      || S_ISFIFO (st.st_mode)
      || S_ISSOCK (st.st_mode))
    {
      error (0, 0, _("%s: invalid file type"), qname);
      return -1;
    }

  /* Allocate pass array */
  passarray = xmalloc (flags->n_iterations * sizeof (int));

  size = flags->size;
  if (size == -1)
    {
      /* Accept a length of zero only if it's a regular file.
	 For any other type of file, try to get the size another way.  */
      if (S_ISREG (st.st_mode))
	{
	  size = st.st_size;
	  if (size < 0)
	    {
	      error (0, 0, _("%s: file has negative size"), qname);
	      return -1;
	    }
	}
      else
	{
	  size = lseek (fd, (off_t) 0, SEEK_END);
	  if (size <= 0)
	    {
	      /* We are unable to determine the length, up front.
		 Let dopass do that as part of its first iteration.  */
	      size = -1;
	    }
	}

      if (0 <= size && !(flags->exact))
	{
	  size += ST_BLKSIZE (st) - 1 - (size - 1) % ST_BLKSIZE (st);

	  /* If in rounding up, we've just overflowed, use the maximum.  */
	  if (size < 0)
	    size = TYPE_MAXIMUM (off_t);
	}
    }

  /* Schedule the passes in random order. */
  genpattern (passarray, flags->n_iterations, s);

  /* Do the work */
  for (i = 0; i < flags->n_iterations; i++)
    {
      if (dopass (fd, qname, &size, passarray[i], s, i + 1, n) < 0)
	{
	  memset (passarray, 0, flags->n_iterations * sizeof (int));
	  free (passarray);
	  return -1;
	}
    }

  memset (passarray, 0, flags->n_iterations * sizeof (int));
  free (passarray);

  if (flags->zero_fill)
    if (dopass (fd, qname, &size, 0, s, flags->n_iterations + 1, n) < 0)
      return -1;

  /* Okay, now deallocate the data.  The effect of ftruncate on
     non-regular files is unspecified, so don't worry about any
     errors reported for them.  */
  if (flags->remove_file && ftruncate (fd, (off_t) 0) != 0
      && S_ISREG (st.st_mode))
    {
      error (0, errno, _("%s: error truncating"), qname);
      return -1;
    }

  return 0;
}

/* A wrapper with a little more checking for fds on the command line */
static int
wipefd (int fd, char const *qname, struct isaac_state *s,
	struct Options const *flags)
{
  int fd_flags = fcntl (fd, F_GETFL);

  if (fd_flags < 0)
    {
      error (0, errno, "%s: fcntl", qname);
      return -1;
    }
  if (fd_flags & O_APPEND)
    {
      error (0, 0, _("%s: cannot shred append-only file descriptor"), qname);
      return -1;
    }
  return do_wipefd (fd, qname, s, flags);
}

/* --- Name-wiping code --- */

/* Characters allowed in a file name - a safe universal set. */
static char const nameset[] =
"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_+=%@#.";

/*
 * This increments the name, considering it as a big-endian base-N number
 * with the digits taken from nameset.  Characters not in the nameset
 * are considered to come before nameset[0].
 *
 * It's not obvious, but this will explode if name[0..len-1] contains
 * any 0 bytes.
 *
 * This returns the carry (1 on overflow).
 */
static int
incname (char *name, unsigned len)
{
  char const *p;

  if (!len)
    return 1;

  p = strchr (nameset, name[--len]);
  /* If the character is not found, replace it with a 0 digit */
  if (!p)
    {
      name[len] = nameset[0];
      return 0;
    }
  /* If this character has a successor, use it */
  if (p[1])
    {
      name[len] = p[1];
      return 0;
    }
  /* Otherwise, set this digit to 0 and increment the prefix */
  name[len] = nameset[0];
  return incname (name, len);
}

/*
 * Repeatedly rename a file with shorter and shorter names,
 * to obliterate all traces of the file name on any system that
 * adds a trailing delimiter to on-disk file names and reuses
 * the same directory slot.  Finally, unlink it.
 * The passed-in filename is modified in place to the new filename.
 * (Which is unlinked if this function succeeds, but is still present if
 * it fails for some reason.)
 *
 * The main loop is written carefully to not get stuck if all possible
 * names of a given length are occupied.  It counts down the length from
 * the original to 0.  While the length is non-zero, it tries to find an
 * unused file name of the given length.  It continues until either the
 * name is available and the rename succeeds, or it runs out of names
 * to try (incname wraps and returns 1).  Finally, it unlinks the file.
 *
 * The unlink is Unix-specific, as ANSI-standard remove has more
 * portability problems with C libraries making it "safe".  rename
 * is ANSI-standard.
 *
 * To force the directory data out, we try to open the directory and
 * invoke fdatasync on it.  This is rather non-standard, so we don't
 * insist that it works, just fall back to a global sync in that case.
 * This is fairly significantly Unix-specific.  Of course, on any
 * filesystem with synchronous metadata updates, this is unnecessary.
 */
static int
wipename (char *oldname, char const *qoldname, struct Options const *flags)
{
  char *newname, *base;	  /* Base points to filename part of newname */
  unsigned len;
  int err;
  int dir_fd;			/* Try to open directory to sync *it* */

  newname = xstrdup (oldname);
  if (flags->verbose)
    error (0, 0, _("%s: removing"), qoldname);

  /* Find the file name portion */
  base = strrchr (newname, '/');
  /* Temporary hackery to get a directory fd */
  if (base)
    {
      *base = '\0';
      dir_fd = open (newname, O_RDONLY | O_NOCTTY);
      *base = '/';
    }
  else
    {
      dir_fd = open (".", O_RDONLY | O_NOCTTY);
    }
  base = base ? base + 1 : newname;
  len = strlen (base);

  while (len)
    {
      memset (base, nameset[0], len);
      base[len] = 0;
      do
	{
	  struct stat st;
	  if (lstat (newname, &st) < 0)
	    {
	      if (rename (oldname, newname) == 0)
		{
		  if (dir_fd < 0
		      || (fdatasync (dir_fd) < 0 && fsync (dir_fd) < 0))
		    sync ();	/* Force directory out */
		  if (flags->verbose)
		    {
		      /*
		       * People seem to understand this better than talking
		       * about renaming oldname.  newname doesn't need
		       * quoting because we picked it.
		       */
		      error (0, 0, _("%s: renamed to %s"), qoldname,
			     quote (newname));
		    }
		  memcpy (oldname + (base - newname), base, len + 1);
		  break;
		}
	      else
		{
		  /* The rename failed: give up on this length.  */
		  break;
		}
	    }
	  else
	    {
	      /* newname exists, so increment BASE so we use another */
	    }
	}
      while (!incname (base, len));
      len--;
    }
  free (newname);
  err = unlink (oldname);
  if (dir_fd < 0 || (fdatasync (dir_fd) < 0 && fsync (dir_fd) < 0))
    sync ();
  close (dir_fd);
  if (!err && flags->verbose)
    error (0, 0, _("%s: removed"), qoldname);
  return err;
}

/*
 * Finally, the function that actually takes a filename and grinds
 * it into hamburger.
 *
 * FIXME
 * Detail to note: since we do not restore errno to EACCES after
 * a failed chmod, we end up printing the error code from the chmod.
 * This is actually the error that stopped us from proceeding, so
 * it's arguably the right one, and in practice it'll be either EACCES
 * again or EPERM, which both give similar error messages.
 * Does anyone disagree?
 */
static int
wipefile (char *name, char const *qname,
	  struct isaac_state *s, struct Options const *flags)
{
  int err, fd;

  fd = open (name, O_WRONLY | O_NOCTTY);
  if (fd < 0)
    {
      if (errno == EACCES && flags->force)
	{
	  if (chmod (name, S_IWUSR) >= 0) /* 0200, user-write-only */
	    fd = open (name, O_WRONLY | O_NOCTTY);
	}
      else if ((errno == ENOENT || errno == ENOTDIR)
	       && strncmp (name, "/dev/fd/", 8) == 0)
	{
	  /* We accept /dev/fd/# even if the OS doesn't support it */
	  int errnum = errno;
	  unsigned long num;
	  char *p;
	  errno = 0;
	  num = strtoul (name + 8, &p, 10);
	  /* If it's completely decimal with no leading zeros... */
	  if (errno == 0 && !*p && num <= INT_MAX &&
	      (('1' <= name[8] && name[8] <= '9')
	       || (name[8] == '0' && !name[9])))
	    {
	      return wipefd ((int) num, qname, s, flags);
	    }
	  errno = errnum;
	}
    }
  if (fd < 0)
    {
      error (0, errno, "%s", qname);
      return -1;
    }

  err = do_wipefd (fd, qname, s, flags);
  if (close (fd) != 0)
    {
      error (0, 0, "%s: close", qname);
      err = -1;
    }
  if (err == 0 && flags->remove_file)
    {
      err = wipename (name, qname, flags);
      if (err < 0)
	error (0, 0, _("%s: cannot remove"), qname);
    }
  return err;
}

int
main (int argc, char **argv)
{
  struct isaac_state s;
  int err = 0;
  struct Options flags;
  char **file;
  int n_files;
  int c;
  int i;

  program_name = argv[0];
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  atexit (close_stdout);

  GETTIMEOFDAY_INIT ();

  isaac_seed (&s);

  memset (&flags, 0, sizeof flags);

  flags.n_iterations = DEFAULT_PASSES;
  flags.size = -1;

  while ((c = getopt_long (argc, argv, "fn:s:uvxz", long_opts, NULL)) != -1)
    {
      switch (c)
	{
	case 0:
	  break;

	case 'f':
	  flags.force = 1;
	  break;

	case 'n':
	  {
	    uintmax_t tmp;
	    if (xstrtoumax (optarg, NULL, 10, &tmp, NULL) != LONGINT_OK
		|| (word32) tmp != tmp
		|| ((size_t) (tmp * sizeof (int)) / sizeof (int) != tmp))
	      {
		error (1, 0, _("%s: invalid number of passes"),
		       quotearg_colon (optarg));
	      }
	    flags.n_iterations = (size_t) tmp;
	  }
	  break;

	case 'u':
	  flags.remove_file = 1;
	  break;

	case 's':
	  {
	    uintmax_t tmp;
	    if (xstrtoumax (optarg, NULL, 0, &tmp, "cbBkMGTPEZY0")
		!= LONGINT_OK)
	      {
		error (1, 0, _("%s: invalid file size"),
		       quotearg_colon (optarg));
	      }
	    flags.size = tmp;
	  }
	  break;

	case 'v':
	  flags.verbose = 1;
	  break;

	case 'x':
	  flags.exact = 1;
	  break;

	case 'z':
	  flags.zero_fill = 1;
	  break;

	case_GETOPT_HELP_CHAR;

	case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);

	default:
	  usage (1);
	}
    }

  file = argv + optind;
  n_files = argc - optind;

  if (n_files == 0)
    {
      error (0, 0, _("missing file argument"));
      usage (1);
    }

  for (i = 0; i < n_files; i++)
    {
      char const *qname = quotearg_colon (file[i]);
      if (strcmp (file[i], "-") == 0)
	{
	  if (wipefd (STDOUT_FILENO, qname, &s, &flags) < 0)
	    err = 1;
	}
      else
	{
	  /* Plain filename - Note that this overwrites *argv! */
	  if (wipefile (file[i], qname, &s, &flags) < 0)
	    err = 1;
	}
    }

  /* Just on general principles, wipe s. */
  memset (&s, 0, sizeof s);

  exit (err);
}
/*
 * vim:sw=2:sts=2:
 */