coreutils/shred.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Copyright (C) 2017 Denys Vlasenko <vda.linux@googlemail.com>
   4  *
   5  * Licensed under GPLv2, see file LICENSE in this source tree.
   6  */
   7 //config:config SHRED
   8 //config:       bool "shred (5.5 kb)"
   9 //config:       default y
  10 //config:       help
  11 //config:       Overwrite a file to hide its contents, and optionally delete it
  12
  13 //applet:IF_SHRED(APPLET(shred, BB_DIR_USR_BIN, BB_SUID_DROP))
  14
  15 //kbuild:lib-$(CONFIG_SHRED) += shred.o
  16
  17 //usage:#define shred_trivial_usage
  18 //usage:       "[-fuz] [-n N] [-s SIZE] FILE..."
  19 //usage:#define shred_full_usage "\n\n"
  20 //usage:       "Overwrite/delete FILEs\n"
  21 //usage:     "\n        -f      Chmod to ensure writability"
  22 //usage:     "\n        -s SIZE Size to write"
  23 //usage:     "\n        -n N    Overwrite N times (default 3)"
  24 //usage:     "\n        -z      Final overwrite with zeros"
  25 //usage:     "\n        -u      Remove file"
  26 //-x (exact: don't round up to 4k) and -v (verbose) are accepted but have no effect
  27
  28 /* shred (GNU coreutils) 8.25:
  29 -f, --force             change permissions to allow writing if necessary
  30 -u                      truncate and remove file after overwriting
  31 -z, --zero              add a final overwrite with zeros to hide shredding
  32 -n, --iterations=N      overwrite N times instead of the default (3)
  33 -v, --verbose           show progress
  34 -x, --exact             do not round file sizes up to the next full block; this is the default for non-regular files
  35 --random-source=FILE    get random bytes from FILE
  36 -s, --size=N            shred this many bytes (suffixes like K, M, G accepted)
  37 --remove[=HOW]          like -u but give control on HOW to delete;  See below
  38 */
  39
  40 #include "libbb.h"
  41
  42 int shred_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  43 int shred_main(int argc UNUSED_PARAM, char **argv)
  44 {
  45         char *opt_s;
  46         int rand_fd = rand_fd; /* for compiler */
  47         int zero_fd;
  48         unsigned num_iter = 3;
  49         unsigned opt;
  50         enum {
  51                 OPT_f = (1 << 0),
  52                 OPT_u = (1 << 1),
  53                 OPT_z = (1 << 2),
  54                 OPT_n = (1 << 3),
  55                 OPT_v = (1 << 4),
  56                 OPT_x = (1 << 5),
  57                 OPT_s = (1 << 6),
  58         };
  59
  60         opt = getopt32(argv, "^" "fuzn:+vxs:" "\0" "-1"/*min 1 arg*/, &num_iter, &opt_s);
  61         argv += optind;
  62
  63         zero_fd = xopen("/dev/zero", O_RDONLY);
  64         if (num_iter != 0)
  65                 rand_fd = xopen("/dev/urandom", O_RDONLY);
  66
  67         for (;;) {
  68                 struct stat sb;
  69                 const char *fname;
  70                 unsigned i;
  71                 int fd;
  72
  73                 fname = *argv++;
  74                 if (!fname)
  75                         break;
  76                 fd = -1;
  77                 if (opt & OPT_f) {
  78                         fd = open(fname, O_WRONLY);
  79                         if (fd < 0)
  80                                 chmod(fname, 0666);
  81                 }
  82                 if (fd < 0)
  83                         fd = xopen(fname, O_WRONLY);
  84
  85                 if (fstat(fd, &sb) == 0 && sb.st_size > 0) {
  86                         off_t size = sb.st_size;
  87
  88                         if (opt & OPT_s) {
  89                                 size = BB_STRTOOFF(opt_s, NULL, 0); /* accepts oct/hex */
  90                                 if (errno || size < 0) bb_show_usage();
  91                         }
  92
  93                         for (i = 0; i < num_iter; i++) {
  94                                 bb_copyfd_size(rand_fd, fd, size);
  95                                 fdatasync(fd);
  96                                 xlseek(fd, 0, SEEK_SET);
  97                         }
  98                         if (opt & OPT_z) {
  99                                 bb_copyfd_size(zero_fd, fd, size);
 100                                 fdatasync(fd);
 101                         }
 102                 }
 103                 if (opt & OPT_u) {
 104                         ftruncate(fd, 0);
 105                         xunlink(fname);
 106                 }
 107                 xclose(fd);
 108         }
 109
 110         return EXIT_SUCCESS;
 111 }