micro-utils/coreutils/shred.c

#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>

#define RAND_SOURCE "/dev/urandom"

unsigned int f_flag;
unsigned int u_flag;
unsigned int z_flag;
unsigned int n_loops;

int shred(int rand_fd, int fd) {
	/* Get size */
	off_t size = lseek(fd, 0, SEEK_END);
	if (size <= 0)
		return 1;

	void *buf = mmap(NULL, size, PROT_WRITE, MAP_SHARED, fd, 0);
	if (buf == MAP_FAILED) {
		fprintf(stderr, "shred: mmap: %s\n", strerror(errno));
		return 1;
	}

	for (unsigned int n = 0; n < n_loops; n++) {
		read(rand_fd, buf, size);
		fsync(fd);
	}

	if (z_flag)
		memset(buf, 0, size);

	if (munmap(buf, size)) {
		fprintf(stderr, "shred: munmap: %s\n", strerror(errno));
		return 1;
	}

	return 0;
}

int main(int argc, char **argv) {
	n_loops = 3;

	int opt;
	while ((opt = getopt(argc, argv, "fuzn:")) != -1) {
		switch (opt) {
			case 'f':
				f_flag = 1;
				break;

			case 'u':
				u_flag = 1;
				break;

			case 'z':
				z_flag = 1;
				break;

			case 'n':
				n_loops = atoi(optarg);
				break;

			default:
				printf("shred [file1 file2...]\n\t[-n N Overwrite N times, default 3]\n\t[-z Final overwrite with zeros]\n\t[-u Remove file] [-f Chmod to ensure writability]\n");
				return 0;
		}
	}

	argv += optind;
	argc -= optind;
	if (argc == 0) {
		fprintf(stderr, "shred: missing operand\n");
		return 1;
	}

	int rand_fd = open(RAND_SOURCE, O_RDONLY);
	if (rand_fd < 0) {
		fprintf(stderr, "shred: %s: %s\n", RAND_SOURCE, strerror(errno));
		return 1;
	}

	for (int i = 0; i < argc; i++) {
		int fd = open(argv[i], O_RDWR);
		if (fd < 0) {
			fprintf(stderr, "shred: %s is %s\n", argv[i], strerror(errno));
			continue;
		}

		shred(rand_fd, fd);
		fsync(fd);
		close(fd);

		if (f_flag) {
			if (chmod(argv[i], 0) < 0)
				fprintf(stderr, "shred: %s is %s\n", argv[i], strerror(errno));
		}

		if (u_flag) {
			if (unlink(argv[i]) < 0)
				fprintf(stderr, "shred: %s is %s\n", argv[i], strerror(errno));
		}
	}

	close(rand_fd);
	return 0;
}