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/* shred.c - Overwrite a file to securely delete
*
* Copyright 2014 Rob Landley <rob@landley.net>
*
* No standard
USE_SHRED(NEWTOY(shred, "<1zxus#<1n#<1o#<0f", TOYFLAG_USR|TOYFLAG_BIN))
config SHRED
bool "shred"
default y
help
usage: shred [-fuxz] [-n COUNT] [-o OFFSET] [-s SIZE] FILE...
Securely delete a file by overwriting its contents with random data.
-f Force (chmod if necessary)
-n COUNT Random overwrite iterations (default 1)
-o OFFSET Start at OFFSET
-s SIZE Use SIZE instead of detecting file size
-u Unlink (actually delete file when done)
-x Use exact size (default without -s rounds up to next 4k)
-z Zero at end
Note: data journaling filesystems render this command useless, you must
overwrite all free space (fill up disk) to erase old data on those.
*/
#define FOR_shred
#include "toys.h"
GLOBALS(
long o, n, s;
)
void shred_main(void)
{
char **try;
if (!FLAG(n)) TT.n++;
// We don't use loopfiles() here because "-" isn't stdin, and want to
// respond to files we can't open via chmod.
for (try = toys.optargs; *try; try++) {
off_t pos = 0, len = TT.s;
int fd = open(*try, O_RDWR), iter = 0, throw;
// do -f chmod if necessary
if (fd == -1 && FLAG(f)) {
chmod(*try, 0600);
fd = open(*try, O_RDWR);
}
if (fd == -1) {
perror_msg_raw(*try);
continue;
}
// determine length
if (!len) len = fdlength(fd);
if (len<1) {
error_msg("%s: needs -s", *try);
close(fd);
continue;
}
// Loop through, writing to this file
for (;;) {
// Advance to next -n or -z?
if (pos >= len) {
pos = -1;
if (++iter == TT.n && FLAG(z)) {
memset(toybuf, 0, sizeof(toybuf));
continue;
}
if (iter >= TT.n) break;
}
if (pos < TT.o) {
if (TT.o != lseek(fd, TT.o, SEEK_SET)) {
perror_msg_raw(*try);
break;
}
pos = TT.o;
}
// Determine length, read random data if not zeroing, write.
throw = sizeof(toybuf);
if (FLAG(x) && len-pos < throw) throw = len-pos;
if (iter != TT.n) xgetrandom(toybuf, throw, 0);
if (throw != writeall(fd, toybuf, throw)) perror_msg_raw(*try);
pos += throw;
}
if (FLAG(u) && unlink(*try)) perror_msg("unlink '%s'", *try);
}
}
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