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author | Lars Wirzenius <liw@liw.fi> | 2009-01-27 15:23:41 +0200 |
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committer | Lars Wirzenius <liw@liw.fi> | 2009-01-27 15:23:41 +0200 |
commit | a71f4cce9ad601767102109afb4fed6dd7f7b95f (patch) | |
tree | 88ee7567b80ce418e6dfc240169aaabddcc3aa33 | |
parent | bf794a16f1ea5d78994b9cff7ba8be91ae2bdf6c (diff) | |
parent | fde4d951bc38301e94ad336c73835e7108704dbc (diff) | |
download | extrautils-a71f4cce9ad601767102109afb4fed6dd7f7b95f.tar.gz |
Merged branch to implement corrupt(1).
-rw-r--r-- | Makefile | 4 | ||||
-rw-r--r-- | corrupt.1 | 32 | ||||
-rw-r--r-- | corrupt.c | 177 |
3 files changed, 212 insertions, 1 deletions
@@ -4,9 +4,11 @@ sharedir = $(prefix)/share mandir = $(sharedir)/man man1dir = $(mandir)/man1 -progs = isascii +progs = isascii corrupt scripts = total +CFLAGS = -Wall -O2 --std=gnu99 + all: $(progs) install: all diff --git a/corrupt.1 b/corrupt.1 new file mode 100644 index 0000000..593a0e3 --- /dev/null +++ b/corrupt.1 @@ -0,0 +1,32 @@ +.\" corrupt.1 - manual page for the corrupt command +.\" Copyright (C) 2009 Lars Wirzenius +.\" +.\" This program is free software: you can redistribute it and/or modify +.\" it under the terms of the GNU General Public License as published by +.\" the Free Software Foundation, either version 3 of the License, or +.\" (at your option) any later version. +.\" +.\" This program is distributed in the hope that it will be useful, +.\" but WITHOUT ANY WARRANTY; without even the implied warranty of +.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +.\" GNU General Public License for more details. +.\" +.\" You should have received a copy of the GNU General Public License +.\" along with this program. If not, see <http://www.gnu.org/licenses/>. +.\" +.TH CORRUPT 1 +.SH NAME +corrupt \- modify files by randomly changing bits +.SH SYNOPSIS +.BR corrupt +[\fB-n\fR \fIBITS\fR] +[\fB--bits\fR \fIBITS\fR] +.IR file ... +.SH DESCRIPTION +.B corrupt +modifies files by toggling a randomly chosen bit. +.SH OPTIONS +.TP +.BR -n " \fIBITS\fR, " --bits " \fIBITS\fR" +Set the number of bits to modify. +Default is one bit. diff --git a/corrupt.c b/corrupt.c new file mode 100644 index 0000000..0d29453 --- /dev/null +++ b/corrupt.c @@ -0,0 +1,177 @@ +/* + * Copyright (C) 2009 Lars Wirzenius + * + * This program is free software: you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation, either version 3 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ + + +#define _LARGEFILE64_SOURCE +#define _GNU_SOURCE + +#include <errno.h> +#include <limits.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <time.h> +#include <sys/types.h> +#include <sys/stat.h> +#include <fcntl.h> +#include <unistd.h> +#include <getopt.h> + + +/* Number of bits to corrupt. */ +static int num_bits = 1; + + +/* Choose a random integer in [0..n-1]. */ +static long choose(long n) +{ + if (n == 0) + return 0; + + long buckets = (RAND_MAX + 1L) / n; + long max = buckets * n; + long r; + + do { + r = random(); + } while (r >= max); + return r / buckets; +} + + +static int seek(const char *filename, int fd, off_t offset) +{ + if (lseek(fd, offset, SEEK_SET) == (off_t) -1) { + fprintf(stderr, "Can't seek in %s: %s", filename, strerror(errno)); + return -1; + } + return 0; +} + + +static int corrupt_one_bit(const char *filename, int fd, struct stat st) +{ + long offset; + long bit; + unsigned char byte; + + offset = choose(st.st_size); + bit = choose(CHAR_BIT); + + if (seek(filename, fd, offset) == -1) + return -1; + if (read(fd, &byte, 1) == -1) { + fprintf(stderr, "Can't read %s: %s", filename, strerror(errno)); + return -1; + } + + /* This is where we toggle the bit. */ + unsigned mask = 1 << bit; // All zeroes, except for the interesting bit. + unsigned interesting = byte & mask; // Only the interesting bit can be 1. + unsigned toggled = interesting ^ mask; // Interesting bit has been toggled. + unsigned others = byte & (~mask); // Interesting bit is 0. + byte = others | toggled; + + /* Now write it back. */ + if (seek(filename, fd, offset) == -1) + return -1; + if (write(fd, &byte, 1) != 1) { + fprintf(stderr, "Can't write %s: %s", filename, strerror(errno)); + return -1; + } + + return 0; +} + + +static int corrupt(const char *filename) +{ + int fd; + struct stat st; + + fd = open(filename, O_RDWR | O_LARGEFILE); + if (fd == -1) { + fprintf(stderr, "Can't open %s: %s\n", filename, strerror(errno)); + return -1; + } + + if (fstat(fd, &st) == -1) { + fprintf(stderr, "Can't find length of %s: %s", filename, + strerror(errno)); + return -1; + } + + for (int i = 0; i < num_bits; ++i) + if (corrupt_one_bit(filename, fd, st) == -1) + return -1; + + if (close(fd) == -1) { + fprintf(stderr, "Can't close %s: %s", filename, strerror(errno)); + return -1; + } + + return 0; +} + + +static int parse_args(int argc, char **argv) +{ + const char optstring[] = "n:"; + const struct option longopts[] = { + { "bits", required_argument, NULL, 'n' }, + { 0 }, + }; + char *endptr; + + for (;;) { + int opt = getopt_long(argc, argv, optstring, longopts, NULL); + switch (opt) { + case -1: + return optind; + + case 'n': + num_bits = strtol(optarg, &endptr, 10); + if (*endptr != '\0') { + fprintf(stderr, "Invalid number of bits: %s\n", optarg); + exit(1); + } + break; + + default: + case '?': + exit(1); + } + } +} + + +int main(int argc, char **argv) +{ + int exit_code; + int i; + + i = parse_args(argc, argv); + if (i == -1) + return 1; + + srandom(time(NULL) + getpid()); + exit_code = 0; + for (; i < argc; ++i) + if (corrupt(argv[i]) == -1) + exit_code = 1; + return exit_code; +} |