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      1 /* shred.c - Overwrite a file to securely delete
      2  *
      3  * Copyright 2014 Rob Landley <rob (at) landley.net>
      4  *
      5  * No standard
      6 
      7 USE_SHRED(NEWTOY(shred, "<1zxus#<1n#<1o#<0f", TOYFLAG_USR|TOYFLAG_BIN))
      8 
      9 config SHRED
     10   bool "shred"
     11   default y
     12   help
     13     usage: shred [-fuz] [-n COUNT] [-s SIZE] FILE...
     14 
     15     Securely delete a file by overwriting its contents with random data.
     16 
     17     -f		Force (chmod if necessary)
     18     -n COUNT	Random overwrite iterations (default 1)
     19     -o OFFSET	Start at OFFSET
     20     -s SIZE		Use SIZE instead of detecting file size
     21     -u		Unlink (actually delete file when done)
     22     -x		Use exact size (default without -s rounds up to next 4k)
     23     -z		Zero at end
     24 
     25     Note: data journaling filesystems render this command useless, you must
     26     overwrite all free space (fill up disk) to erase old data on those.
     27 */
     28 
     29 #define FOR_shred
     30 #include "toys.h"
     31 
     32 GLOBALS(
     33   long o, n, s;
     34 )
     35 
     36 void shred_main(void)
     37 {
     38   char **try;
     39 
     40   if (!(toys.optflags & FLAG_n)) TT.n++;
     41 
     42   // We don't use loopfiles() here because "-" isn't stdin, and want to
     43   // respond to files we can't open via chmod.
     44 
     45   for (try = toys.optargs; *try; try++) {
     46     off_t pos = 0, len = TT.s;
     47     int fd = open(*try, O_RDWR), iter = 0, throw;
     48 
     49     // do -f chmod if necessary
     50     if (fd == -1 && (toys.optflags & FLAG_f)) {
     51       chmod(*try, 0600);
     52       fd = open(*try, O_RDWR);
     53     }
     54     if (fd == -1) {
     55       perror_msg_raw(*try);
     56       continue;
     57     }
     58 
     59     // determine length
     60     if (!len) len = fdlength(fd);
     61     if (len<1) {
     62       error_msg("%s: needs -s", *try);
     63       close(fd);
     64       continue;
     65     }
     66 
     67     // Loop through, writing to this file
     68     for (;;) {
     69       // Advance to next -n or -z?
     70 
     71       if (pos >= len) {
     72         pos = -1;
     73         if (++iter == TT.n && (toys.optargs && FLAG_z)) {
     74           memset(toybuf, 0, sizeof(toybuf));
     75           continue;
     76         }
     77         if (iter >= TT.n) break;
     78       }
     79 
     80       if (pos < TT.o) {
     81         if (TT.o != lseek(fd, TT.o, SEEK_SET)) {
     82           perror_msg_raw(*try);
     83           break;
     84         }
     85         pos = TT.o;
     86       }
     87 
     88       // Determine length, read random data if not zeroing, write.
     89 
     90       throw = sizeof(toybuf);
     91       if (toys.optflags & FLAG_x)
     92         if (len-pos < throw) throw = len-pos;
     93 
     94       if (iter != TT.n) xgetrandom(toybuf, throw, 0);
     95       if (throw != writeall(fd, toybuf, throw)) perror_msg_raw(*try);
     96       pos += throw;
     97     }
     98     if (toys.optflags & FLAG_u)
     99       if (unlink(*try)) perror_msg("unlink '%s'", *try);
    100   }
    101 }
    102