LXR busybox/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 (4.9 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
  42int shred_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  43int 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}
 112