Adding upstream version 8.32.upstream/8.32upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1279 insertions, 0 deletions

diff --git a/src/shred.c b/src/shred.c
new file mode 100644
index 0000000..fbbeddf
--- /dev/null
+++ b/src/shred.c
@@ -0,0 +1,1279 @@
+/* shred.c - overwrite files and devices to make it harder to recover data
+
+   Copyright (C) 1999-2020 Free Software Foundation, Inc.
+   Copyright (C) 1997, 1998, 1999 Colin Plumb.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+   Written by Colin Plumb.  */
+
+/*
+ * Do a more secure 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
+ * https://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 in a
+ * clever way to try to leave no trace of the original filename.
+ *
+ * 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 proper_name ("Colin Plumb")
+
+#include <config.h>
+
+#include <getopt.h>
+#include <stdio.h>
+#include <assert.h>
+#include <setjmp.h>
+#include <sys/types.h>
+#if defined __linux__ && HAVE_SYS_MTIO_H
+# include <sys/mtio.h>
+#endif
+
+#include "system.h"
+#include "argmatch.h"
+#include "xdectoint.h"
+#include "die.h"
+#include "error.h"
+#include "fcntl--.h"
+#include "human.h"
+#include "randint.h"
+#include "randread.h"
+#include "renameatu.h"
+#include "stat-size.h"
+
+/* Default number of times to overwrite.  */
+enum { DEFAULT_PASSES = 3 };
+
+/* How many seconds to wait before checking whether to output another
+   verbose output line.  */
+enum { VERBOSE_UPDATE = 5 };
+
+/* Sector size and corresponding mask, for recovering after write failures.
+   The size must be a power of 2.  */
+enum { SECTOR_SIZE = 512 };
+enum { SECTOR_MASK = SECTOR_SIZE - 1 };
+verify (0 < SECTOR_SIZE && (SECTOR_SIZE & SECTOR_MASK) == 0);
+
+enum remove_method
+{
+  remove_none = 0,      /* the default: only wipe data.  */
+  remove_unlink,        /* don't obfuscate name, just unlink.  */
+  remove_wipe,          /* obfuscate name before unlink.  */
+  remove_wipesync       /* obfuscate name, syncing each byte, before unlink.  */
+};
+
+static char const *const remove_args[] =
+{
+  "unlink", "wipe", "wipesync", NULL
+};
+
+static enum remove_method const remove_methods[] =
+{
+  remove_unlink, remove_wipe, remove_wipesync
+};
+
+struct Options
+{
+  bool force;		/* -f flag: chmod files if necessary */
+  size_t n_iterations;	/* -n flag: Number of iterations */
+  off_t size;		/* -s flag: size of file */
+  enum remove_method remove_file; /* -u flag: remove file after shredding */
+  bool verbose;		/* -v flag: Print progress */
+  bool exact;		/* -x flag: Do not round up file size */
+  bool zero_fill;	/* -z flag: Add a final zero pass */
+};
+
+/* For long options that have no equivalent short option, use a
+   non-character as a pseudo short option, starting with CHAR_MAX + 1.  */
+enum
+{
+  RANDOM_SOURCE_OPTION = CHAR_MAX + 1
+};
+
+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'},
+  {"random-source", required_argument, NULL, RANDOM_SOURCE_OPTION},
+  {"remove", optional_argument, NULL, 'u'},
+  {"verbose", no_argument, NULL, 'v'},
+  {"zero", no_argument, NULL, 'z'},
+  {GETOPT_HELP_OPTION_DECL},
+  {GETOPT_VERSION_OPTION_DECL},
+  {NULL, 0, NULL, 0}
+};
+
+void
+usage (int status)
+{
+  if (status != EXIT_SUCCESS)
+    emit_try_help ();
+  else
+    {
+      printf (_("Usage: %s [OPTION]... FILE...\n"), program_name);
+      fputs (_("\
+Overwrite the specified FILE(s) repeatedly, in order to make it harder\n\
+for even very expensive hardware probing to recover the data.\n\
+"), stdout);
+      fputs (_("\
+\n\
+If FILE is -, shred standard output.\n\
+"), stdout);
+
+      emit_mandatory_arg_note ();
+
+      printf (_("\
+  -f, --force    change permissions to allow writing if necessary\n\
+  -n, --iterations=N  overwrite N times instead of the default (%d)\n\
+      --random-source=FILE  get random bytes from FILE\n\
+  -s, --size=N   shred this many bytes (suffixes like K, M, G accepted)\n\
+"), DEFAULT_PASSES);
+      fputs (_("\
+  -u             deallocate and remove file after overwriting\n\
+      --remove[=HOW]  like -u but give control on HOW to delete;  See below\n\
+  -v, --verbose  show progress\n\
+  -x, --exact    do not round file sizes up to the next full block;\n\
+                   this is the default for non-regular files\n\
+  -z, --zero     add a final overwrite with zeros to hide shredding\n\
+"), stdout);
+      fputs (HELP_OPTION_DESCRIPTION, stdout);
+      fputs (VERSION_OPTION_DESCRIPTION, stdout);
+      fputs (_("\
+\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.\n\
+The optional HOW parameter indicates how to remove a directory entry:\n\
+'unlink' => use a standard unlink call.\n\
+'wipe' => also first obfuscate bytes in the name.\n\
+'wipesync' => also sync each obfuscated byte to disk.\n\
+The default mode is 'wipesync', but note it can be expensive.\n\
+\n\
+"), stdout);
+      fputs (_("\
+CAUTION: shred assumes the file system and hardware overwrite data in place.\n\
+Although this is common, many platforms operate otherwise.  Also, backups\n\
+and mirrors may contain unremovable copies that will let a shredded file\n\
+be recovered later.  See the GNU coreutils manual for details.\n\
+"), stdout);
+      emit_ancillary_info (PROGRAM_NAME);
+    }
+  exit (status);
+}
+
+/*
+ * Determine if pattern type is periodic or not.
+ */
+static bool
+periodic_pattern (int type)
+{
+  if (type <= 0)
+    return false;
+
+  unsigned char r[3];
+  unsigned int bits = type & 0xfff;
+
+  bits |= bits << 12;
+  r[0] = (bits >> 4) & 255;
+  r[1] = (bits >> 8) & 255;
+  r[2] = bits & 255;
+
+  return (r[0] != r[1]) || (r[0] != r[2]);
+}
+
+/*
+ * 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 int bits = type & 0xfff;
+
+  bits |= bits << 12;
+  r[0] = (bits >> 4) & 255;
+  r[1] = (bits >> 8) & 255;
+  r[2] = bits & 255;
+  for (i = 3; i <= size / 2; i *= 2)
+    memcpy (r + i, r, i);
+  if (i < size)
+    memcpy (r + i, r, size - i);
+
+  /* Invert the first bit of every sector. */
+  if (type & 0x1000)
+    for (i = 0; i < size; i += SECTOR_SIZE)
+      r[i] ^= 0x80;
+}
+
+/*
+ * 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);
+}
+
+/* Return true when it's ok to ignore an fsync or fdatasync
+   failure that set errno to ERRNO_VAL.  */
+static bool
+ignorable_sync_errno (int errno_val)
+{
+  return (errno_val == EINVAL
+          || errno_val == EBADF
+          /* HP-UX does this */
+          || errno_val == EISDIR);
+}
+
+/* Request that all data for FD be transferred to the corresponding
+   storage device.  QNAME is the file name (quoted for colons).
+   Report any errors found.  Return 0 on success, -1
+   (setting errno) on failure.  It is not an error if fdatasync and/or
+   fsync is not supported for this file, or if the file is not a
+   writable file descriptor.  */
+static int
+dosync (int fd, char const *qname)
+{
+  int err;
+
+#if HAVE_FDATASYNC
+  if (fdatasync (fd) == 0)
+    return 0;
+  err = errno;
+  if ( ! ignorable_sync_errno (err))
+    {
+      error (0, err, _("%s: fdatasync failed"), qname);
+      errno = err;
+      return -1;
+    }
+#endif
+
+  if (fsync (fd) == 0)
+    return 0;
+  err = errno;
+  if ( ! ignorable_sync_errno (err))
+    {
+      error (0, err, _("%s: fsync failed"), qname);
+      errno = err;
+      return -1;
+    }
+
+  sync ();
+  return 0;
+}
+
+/* Turn on or off direct I/O mode for file descriptor FD, if possible.
+   Try to turn it on if ENABLE is true.  Otherwise, try to turn it off.  */
+static void
+direct_mode (int fd, bool enable)
+{
+  if (O_DIRECT)
+    {
+      int fd_flags = fcntl (fd, F_GETFL);
+      if (0 < fd_flags)
+        {
+          int new_flags = (enable
+                           ? (fd_flags | O_DIRECT)
+                           : (fd_flags & ~O_DIRECT));
+          if (new_flags != fd_flags)
+            fcntl (fd, F_SETFL, new_flags);
+        }
+    }
+
+#if HAVE_DIRECTIO && defined DIRECTIO_ON && defined DIRECTIO_OFF
+  /* This is Solaris-specific.  */
+  directio (fd, enable ? DIRECTIO_ON : DIRECTIO_OFF);
+#endif
+}
+
+/* Rewind FD; its status is ST.  */
+static bool
+dorewind (int fd, struct stat const *st)
+{
+  if (S_ISCHR (st->st_mode))
+    {
+#if defined __linux__ && HAVE_SYS_MTIO_H
+      /* In the Linux kernel, lseek does not work on tape devices; it
+         returns a randomish value instead.  Try the low-level tape
+         rewind operation first.  */
+      struct mtop op;
+      op.mt_op = MTREW;
+      op.mt_count = 1;
+      if (ioctl (fd, MTIOCTOP, &op) == 0)
+        return true;
+#endif
+    }
+  off_t offset = lseek (fd, 0, SEEK_SET);
+  if (0 < offset)
+    errno = EINVAL;
+  return offset == 0;
+}
+
+/* By convention, negative sizes represent unknown values.  */
+
+static bool
+known (off_t size)
+{
+  return 0 <= size;
+}
+
+/*
+ * Do pass number K of N, writing *SIZEP bytes of the given pattern TYPE
+ * to the file descriptor FD.  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 with ENOSPC.
+ *
+ * Return 1 on write error, -1 on other error, 0 on success.
+ */
+static int
+dopass (int fd, struct stat const *st, char const *qname, off_t *sizep,
+        int type, struct randread_source *s,
+        unsigned long int k, unsigned long int n)
+{
+  off_t size = *sizep;
+  off_t offset;			/* Current file position */
+  time_t thresh IF_LINT ( = 0);	/* Time to maybe print next status update */
+  time_t now = 0;		/* Current time */
+  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 */
+
+  /* Fill pattern buffer.  Aligning it to a page so we can do direct I/O.  */
+  size_t page_size = getpagesize ();
+#define PERIODIC_OUTPUT_SIZE (60 * 1024)
+#define NONPERIODIC_OUTPUT_SIZE (64 * 1024)
+  verify (PERIODIC_OUTPUT_SIZE % 3 == 0);
+  size_t output_size = periodic_pattern (type)
+                       ? PERIODIC_OUTPUT_SIZE : NONPERIODIC_OUTPUT_SIZE;
+#define PAGE_ALIGN_SLOP (page_size - 1)                /* So directio works */
+#define FILLPATTERN_SIZE (((output_size + 2) / 3) * 3) /* Multiple of 3 */
+#define PATTERNBUF_SIZE (PAGE_ALIGN_SLOP + FILLPATTERN_SIZE)
+  void *fill_pattern_mem = xmalloc (PATTERNBUF_SIZE);
+  unsigned char *pbuf = ptr_align (fill_pattern_mem, page_size);
+
+  char pass_string[PASS_NAME_SIZE];	/* Name of current pass */
+  bool write_error = false;
+  bool other_error = false;
+
+  /* Printable previous offset into the file */
+  char previous_offset_buf[LONGEST_HUMAN_READABLE + 1];
+  char const *previous_human_offset IF_LINT ( = 0);
+
+  /* As a performance tweak, avoid direct I/O for small sizes,
+     as it's just a performance rather then security consideration,
+     and direct I/O can often be unsupported for small non aligned sizes.  */
+  bool try_without_directio = 0 < size && size < output_size;
+  if (! try_without_directio)
+    direct_mode (fd, true);
+
+  if (! dorewind (fd, st))
+    {
+      error (0, errno, _("%s: cannot rewind"), qname);
+      other_error = true;
+      goto free_pattern_mem;
+    }
+
+  /* Constant fill patterns need only be set up once. */
+  if (type >= 0)
+    {
+      lim = known (size) && size < FILLPATTERN_SIZE ? size : FILLPATTERN_SIZE;
+      fillpattern (type, pbuf, lim);
+      passname (pbuf, pass_string);
+    }
+  else
+    {
+      passname (0, pass_string);
+    }
+
+  /* Set position if first status update */
+  if (n)
+    {
+      error (0, 0, _("%s: pass %lu/%lu (%s)..."), qname, k, n, pass_string);
+      thresh = time (NULL) + VERBOSE_UPDATE;
+      previous_human_offset = "";
+    }
+
+  offset = 0;
+  while (true)
+    {
+      /* How much to write this time? */
+      lim = output_size;
+      if (known (size) && size - offset < output_size)
+        {
+          if (size < offset)
+            break;
+          lim = size - offset;
+          if (!lim)
+            break;
+        }
+      if (type < 0)
+        randread (s, pbuf, lim);
+      /* Loop to retry partial writes. */
+      for (soff = 0; soff < lim; soff += ssize)
+        {
+          ssize = write (fd, pbuf + soff, lim - soff);
+          if (0 < ssize)
+            assume (ssize <= lim - soff);
+          else
+            {
+              if (! known (size) && (ssize == 0 || errno == ENOSPC))
+                {
+                  /* We have found the end of the file.  */
+                  if (soff <= OFF_T_MAX - offset)
+                    *sizep = size = offset + soff;
+                  break;
+                }
+              else
+                {
+                  int errnum = errno;
+                  char buf[INT_BUFSIZE_BOUND (uintmax_t)];
+
+                  /* Retry without direct I/O since this may not be supported
+                     at all on some (file) systems, or with the current size.
+                     I.e., a specified --size that is not aligned, or when
+                     dealing with slop at the end of a file with --exact.  */
+                  if (! try_without_directio && errno == EINVAL)
+                    {
+                      direct_mode (fd, false);
+                      ssize = 0;
+                      try_without_directio = true;
+                      continue;
+                    }
+                  error (0, errnum, _("%s: error writing at offset %s"),
+                         qname, umaxtostr (offset + soff, buf));
+
+                  /* 'shred' is often used on bad media, before throwing it
+                     out.  Thus, it shouldn't give up on bad blocks.  This
+                     code works because lim is always a multiple of
+                     SECTOR_SIZE, except at the end.  This size constraint
+                     also enables direct I/O on some (file) systems.  */
+                  verify (PERIODIC_OUTPUT_SIZE % SECTOR_SIZE == 0);
+                  verify (NONPERIODIC_OUTPUT_SIZE % SECTOR_SIZE == 0);
+                  if (errnum == EIO && known (size)
+                      && (soff | SECTOR_MASK) < lim)
+                    {
+                      size_t soff1 = (soff | SECTOR_MASK) + 1;
+                      if (lseek (fd, offset + soff1, SEEK_SET) != -1)
+                        {
+                          /* Arrange to skip this block. */
+                          ssize = soff1 - soff;
+                          write_error = true;
+                          continue;
+                        }
+                      error (0, errno, _("%s: lseek failed"), qname);
+                    }
+                  other_error = true;
+                  goto free_pattern_mem;
+                }
+            }
+        }
+
+      /* Okay, we have written "soff" bytes. */
+
+      if (OFF_T_MAX - offset < soff)
+        {
+          error (0, 0, _("%s: file too large"), qname);
+          other_error = true;
+          goto free_pattern_mem;
+        }
+
+      offset += soff;
+
+      bool done = offset == size;
+
+      /* Time to print progress? */
+      if (n && ((done && *previous_human_offset)
+                || thresh <= (now = time (NULL))))
+        {
+          char offset_buf[LONGEST_HUMAN_READABLE + 1];
+          char size_buf[LONGEST_HUMAN_READABLE + 1];
+          int human_progress_opts = (human_autoscale | human_SI
+                                     | human_base_1024 | human_B);
+          char const *human_offset
+            = human_readable (offset, offset_buf,
+                              human_floor | human_progress_opts, 1, 1);
+
+          if (done || !STREQ (previous_human_offset, human_offset))
+            {
+              if (! known (size))
+                error (0, 0, _("%s: pass %lu/%lu (%s)...%s"),
+                       qname, k, n, pass_string, human_offset);
+              else
+                {
+                  uintmax_t off = offset;
+                  int percent = (size == 0
+                                 ? 100
+                                 : (off <= TYPE_MAXIMUM (uintmax_t) / 100
+                                    ? off * 100 / size
+                                    : off / (size / 100)));
+                  char const *human_size
+                    = human_readable (size, size_buf,
+                                      human_ceiling | human_progress_opts,
+                                      1, 1);
+                  if (done)
+                    human_offset = human_size;
+                  error (0, 0, _("%s: pass %lu/%lu (%s)...%s/%s %d%%"),
+                         qname, k, n, pass_string, human_offset, human_size,
+                         percent);
+                }
+
+              strcpy (previous_offset_buf, human_offset);
+              previous_human_offset = previous_offset_buf;
+              thresh = now + VERBOSE_UPDATE;
+
+              /*
+               * 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 (dosync (fd, qname) != 0)
+                {
+                  if (errno != EIO)
+                    {
+                      other_error = true;
+                      goto free_pattern_mem;
+                    }
+                  write_error = true;
+                }
+            }
+        }
+    }
+
+  /* Force what we just wrote to hit the media. */
+  if (dosync (fd, qname) != 0)
+    {
+      if (errno != EIO)
+        {
+          other_error = true;
+          goto free_pattern_mem;
+        }
+      write_error = true;
+    }
+
+free_pattern_mem:
+  free (fill_pattern_mem);
+
+  return other_error ? -1 : write_error;
+}
+
+/*
+ * 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 first 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 randint_source *s)
+{
+  size_t randpasses;
+  int const *p;
+  int *d;
+  size_t n;
+  size_t accum, top, swap;
+  int k;
+
+  if (!num)
+    return;
+
+  /* Stage 1: choose the passes to use */
+  p = patterns;
+  randpasses = 0;
+  d = dest;			/* Destination for generated pass list */
+  n = num;			/* Passes remaining to fill */
+
+  while (true)
+    {
+      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;
+              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 n of the k available */
+          do
+            {
+              if (n == (size_t) k || randint_choose (s, k) < n)
+                {
+                  *d++ = *p;
+                  n--;
+                }
+              p++;
+              k--;
+            }
+          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 + randint_choose (s, top - n);
+          k = dest[n];
+          dest[n] = dest[swap];
+          dest[swap] = k;
+        }
+      accum -= randpasses;
+    }
+  /* assert (top == num); */
+}
+
+/*
+ * The core routine to actually do the work.  This overwrites the first
+ * size bytes of the given fd.  Return true if successful.
+ */
+static bool
+do_wipefd (int fd, char const *qname, struct randint_source *s,
+           struct Options const *flags)
+{
+  size_t i;
+  struct stat st;
+  off_t size;		/* Size to write, size to read */
+  off_t i_size = 0;	/* For small files, initial size to overwrite inode */
+  unsigned long int n;	/* Number of passes for printing purposes */
+  int *passarray;
+  bool ok = true;
+  struct randread_source *rs;
+
+  n = 0;		/* dopass takes n == 0 to mean "don't print progress" */
+  if (flags->verbose)
+    n = flags->n_iterations + flags->zero_fill;
+
+  if (fstat (fd, &st))
+    {
+      error (0, errno, _("%s: fstat failed"), qname);
+      return false;
+    }
+
+  /* If we know that we can't possibly shred the file, give up now.
+     Otherwise, we may go into an 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 false;
+    }
+  else if (S_ISREG (st.st_mode) && st.st_size < 0)
+    {
+      error (0, 0, _("%s: file has negative size"), qname);
+      return false;
+    }
+
+  /* Allocate pass array */
+  passarray = xnmalloc (flags->n_iterations, sizeof *passarray);
+
+  size = flags->size;
+  if (size == -1)
+    {
+      if (S_ISREG (st.st_mode))
+        {
+          size = st.st_size;
+
+          if (! flags->exact)
+            {
+              /* Round up to the nearest block size to clear slack space.  */
+              off_t remainder = size % ST_BLKSIZE (st);
+              if (size && size < ST_BLKSIZE (st))
+                i_size = size;
+              if (remainder != 0)
+                {
+                  off_t size_incr = ST_BLKSIZE (st) - remainder;
+                  size += MIN (size_incr, OFF_T_MAX - size);
+                }
+            }
+        }
+      else
+        {
+          /* The behavior of lseek is unspecified, but in practice if
+             it returns a positive number that's the size of this
+             device.  */
+          size = lseek (fd, 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;
+            }
+        }
+    }
+  else if (S_ISREG (st.st_mode)
+           && st.st_size < MIN (ST_BLKSIZE (st), size))
+    i_size = st.st_size;
+
+  /* Schedule the passes in random order. */
+  genpattern (passarray, flags->n_iterations, s);
+
+  rs = randint_get_source (s);
+
+  while (true)
+    {
+      off_t pass_size;
+      unsigned long int pn = n;
+
+      if (i_size)
+        {
+          pass_size = i_size;
+          i_size = 0;
+          pn = 0;
+        }
+      else if (size)
+        {
+          pass_size = size;
+          size = 0;
+        }
+      /* TODO: consider handling tail packing by
+         writing the tail padding as a separate pass,
+         (that would not rewind).  */
+      else
+        break;
+
+      for (i = 0; i < flags->n_iterations + flags->zero_fill; i++)
+        {
+          int err = 0;
+          int type = i < flags->n_iterations ? passarray[i] : 0;
+
+          err = dopass (fd, &st, qname, &pass_size, type, rs, i + 1, pn);
+
+          if (err)
+            {
+              ok = false;
+              if (err < 0)
+                goto wipefd_out;
+            }
+        }
+    }
+
+  /* Now deallocate the data.  The effect of ftruncate is specified
+     on regular files and shared memory objects (also directories, but
+     they are not possible here); don't worry about errors reported
+     for other file types.  */
+
+  if (flags->remove_file && ftruncate (fd, 0) != 0
+      && (S_ISREG (st.st_mode) || S_TYPEISSHM (&st)))
+    {
+      error (0, errno, _("%s: error truncating"), qname);
+      ok = false;
+      goto wipefd_out;
+    }
+
+wipefd_out:
+  free (passarray);
+  return ok;
+}
+
+/* A wrapper with a little more checking for fds on the command line */
+static bool
+wipefd (int fd, char const *qname, struct randint_source *s,
+        struct Options const *flags)
+{
+  int fd_flags = fcntl (fd, F_GETFL);
+
+  if (fd_flags < 0)
+    {
+      error (0, errno, _("%s: fcntl failed"), qname);
+      return false;
+    }
+  if (fd_flags & O_APPEND)
+    {
+      error (0, 0, _("%s: cannot shred append-only file descriptor"), qname);
+      return false;
+    }
+  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_.";
+
+/* Increment NAME (with LEN bytes).  NAME must be a big-endian base N
+   number with the digits taken from nameset.  Return true if successful.
+   Otherwise, (because NAME already has the greatest possible value)
+   return false.  */
+
+static bool
+incname (char *name, size_t len)
+{
+  while (len--)
+    {
+      char const *p = strchr (nameset, name[len]);
+
+      /* Given that NAME is composed of bytes from NAMESET,
+         P will never be NULL here.  */
+      assert (p);
+
+      /* If this character has a successor, use it.  */
+      if (p[1])
+        {
+          name[len] = p[1];
+          return true;
+        }
+
+      /* Otherwise, set this digit to 0 and increment the prefix.  */
+      name[len] = nameset[0];
+    }
+
+  return false;
+}
+
+/*
+ * Repeatedly rename a file with shorter and shorter names,
+ * to obliterate all traces of the file name (and length) 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 and/or fsync on it.  This is non-standard, so 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
+ * file system with synchronous metadata updates, this is unnecessary.
+ */
+static bool
+wipename (char *oldname, char const *qoldname, struct Options const *flags)
+{
+  char *newname = xstrdup (oldname);
+  char *base = last_component (newname);
+  char *dir = dir_name (newname);
+  char *qdir = xstrdup (quotef (dir));
+  bool first = true;
+  bool ok = true;
+  int dir_fd = -1;
+
+  if (flags->remove_file == remove_wipesync)
+    dir_fd = open (dir, O_RDONLY | O_DIRECTORY | O_NOCTTY | O_NONBLOCK);
+
+  if (flags->verbose)
+    error (0, 0, _("%s: removing"), qoldname);
+
+  if (flags->remove_file != remove_unlink)
+    for (size_t len = base_len (base); len != 0; len--)
+      {
+        memset (base, nameset[0], len);
+        base[len] = 0;
+        bool rename_ok;
+        while (! (rename_ok = (renameatu (AT_FDCWD, oldname, AT_FDCWD, newname,
+                                          RENAME_NOREPLACE)
+                               == 0))
+               && errno == EEXIST && incname (base, len))
+          continue;
+        if (rename_ok)
+          {
+            if (0 <= dir_fd && dosync (dir_fd, qdir) != 0)
+              ok = false;
+            if (flags->verbose)
+              {
+                /* People seem to understand this better than talking
+                   about renaming OLDNAME.  NEWNAME doesn't need
+                   quoting because we picked it.  OLDNAME needs to be
+                   quoted only the first time.  */
+                char const *old = first ? qoldname : oldname;
+                error (0, 0,
+                       _("%s: renamed to %s"), old, newname);
+                first = false;
+              }
+            memcpy (oldname + (base - newname), base, len + 1);
+          }
+      }
+
+  if (unlink (oldname) != 0)
+    {
+      error (0, errno, _("%s: failed to remove"), qoldname);
+      ok = false;
+    }
+  else if (flags->verbose)
+    error (0, 0, _("%s: removed"), qoldname);
+  if (0 <= dir_fd)
+    {
+      if (dosync (dir_fd, qdir) != 0)
+        ok = false;
+      if (close (dir_fd) != 0)
+        {
+          error (0, errno, _("%s: failed to close"), qdir);
+          ok = false;
+        }
+    }
+  free (newname);
+  free (dir);
+  free (qdir);
+  return ok;
+}
+
+/*
+ * 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 bool
+wipefile (char *name, char const *qname,
+          struct randint_source *s, struct Options const *flags)
+{
+  bool ok;
+  int fd;
+
+  fd = open (name, O_WRONLY | O_NOCTTY | O_BINARY);
+  if (fd < 0
+      && (errno == EACCES && flags->force)
+      && chmod (name, S_IWUSR) == 0)
+    fd = open (name, O_WRONLY | O_NOCTTY | O_BINARY);
+  if (fd < 0)
+    {
+      error (0, errno, _("%s: failed to open for writing"), qname);
+      return false;
+    }
+
+  ok = do_wipefd (fd, qname, s, flags);
+  if (close (fd) != 0)
+    {
+      error (0, errno, _("%s: failed to close"), qname);
+      ok = false;
+    }
+  if (ok && flags->remove_file)
+    ok = wipename (name, qname, flags);
+  return ok;
+}
+
+
+/* Buffers for random data.  */
+static struct randint_source *randint_source;
+
+/* Just on general principles, wipe buffers containing information
+   that may be related to the possibly-pseudorandom values used during
+   shredding.  */
+static void
+clear_random_data (void)
+{
+  randint_all_free (randint_source);
+}
+
+
+int
+main (int argc, char **argv)
+{
+  bool ok = true;
+  struct Options flags = { 0, };
+  char **file;
+  int n_files;
+  int c;
+  int i;
+  char const *random_source = NULL;
+
+  initialize_main (&argc, &argv);
+  set_program_name (argv[0]);
+  setlocale (LC_ALL, "");
+  bindtextdomain (PACKAGE, LOCALEDIR);
+  textdomain (PACKAGE);
+
+  atexit (close_stdout);
+
+  flags.n_iterations = DEFAULT_PASSES;
+  flags.size = -1;
+
+  while ((c = getopt_long (argc, argv, "fn:s:uvxz", long_opts, NULL)) != -1)
+    {
+      switch (c)
+        {
+        case 'f':
+          flags.force = true;
+          break;
+
+        case 'n':
+          flags.n_iterations = xdectoumax (optarg, 0,
+                                           MIN (ULONG_MAX,
+                                                SIZE_MAX / sizeof (int)), "",
+                                           _("invalid number of passes"), 0);
+          break;
+
+        case RANDOM_SOURCE_OPTION:
+          if (random_source && !STREQ (random_source, optarg))
+            die (EXIT_FAILURE, 0, _("multiple random sources specified"));
+          random_source = optarg;
+          break;
+
+        case 'u':
+          if (optarg == NULL)
+            flags.remove_file = remove_wipesync;
+          else
+            flags.remove_file = XARGMATCH ("--remove", optarg,
+                                           remove_args, remove_methods);
+          break;
+
+        case 's':
+          flags.size = xnumtoumax (optarg, 0, 0, OFF_T_MAX, "cbBkKMGTPEZY0",
+                                   _("invalid file size"), 0);
+          break;
+
+        case 'v':
+          flags.verbose = true;
+          break;
+
+        case 'x':
+          flags.exact = true;
+          break;
+
+        case 'z':
+          flags.zero_fill = true;
+          break;
+
+        case_GETOPT_HELP_CHAR;
+
+        case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
+
+        default:
+          usage (EXIT_FAILURE);
+        }
+    }
+
+  file = argv + optind;
+  n_files = argc - optind;
+
+  if (n_files == 0)
+    {
+      error (0, 0, _("missing file operand"));
+      usage (EXIT_FAILURE);
+    }
+
+  randint_source = randint_all_new (random_source, SIZE_MAX);
+  if (! randint_source)
+    die (EXIT_FAILURE, errno, "%s", quotef (random_source));
+  atexit (clear_random_data);
+
+  for (i = 0; i < n_files; i++)
+    {
+      char *qname = xstrdup (quotef (file[i]));
+      if (STREQ (file[i], "-"))
+        {
+          ok &= wipefd (STDOUT_FILENO, qname, randint_source, &flags);
+        }
+      else
+        {
+          /* Plain filename - Note that this overwrites *argv! */
+          ok &= wipefile (file[i], qname, randint_source, &flags);
+        }
+      free (qname);
+    }
+
+  return ok ? EXIT_SUCCESS : EXIT_FAILURE;
+}
+/*
+ * vim:sw=2:sts=2:
+ */