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-rw-r--r--Makefile4
-rw-r--r--corrupt.125
-rw-r--r--corrupt.c118
3 files changed, 146 insertions, 1 deletions
diff --git a/Makefile b/Makefile
index 20a7bc9..45087a0 100644
--- a/Makefile
+++ b/Makefile
@@ -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..f9b1338
--- /dev/null
+++ b/corrupt.1
@@ -0,0 +1,25 @@
+.\" 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
+.IR file ...
+.SH DESCRIPTION
+.B corrupt
+modifies files by toggling a randomly chosen bit.
diff --git a/corrupt.c b/corrupt.c
new file mode 100644
index 0000000..f8c5cd2
--- /dev/null
+++ b/corrupt.c
@@ -0,0 +1,118 @@
+/*
+ * 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
+
+#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>
+
+
+/* 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 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;
+ }
+
+ long offset = choose(st.st_size);
+ long bit = choose(CHAR_BIT);
+ printf("%s: offset=%ld bit=%ld\n", filename, offset, bit);
+
+ if (lseek(fd, offset, SEEK_SET) == (off_t) -1) {
+ fprintf(stderr, "Can't seek in %s: %s", filename, strerror(errno));
+ return -1;
+ }
+
+ unsigned char byte;
+ 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 (lseek(fd, offset, SEEK_SET) == (off_t) -1) {
+ fprintf(stderr, "Can't seek in %s: %s", filename, strerror(errno));
+ return -1;
+ }
+ if (write(fd, &byte, 1) != 1) {
+ fprintf(stderr, "Can't write %s: %s", filename, strerror(errno));
+ return -1;
+ }
+
+ if (close(fd) == -1) {
+ fprintf(stderr, "Can't close %s: %s", filename, strerror(errno));
+ return -1;
+ }
+
+ return 0;
+}
+
+
+int main(int argc, char **argv)
+{
+ int exit_code;
+
+ srandom(time(NULL) + getpid());
+ exit_code = 0;
+ for (int i = 1; i < argc; ++i)
+ if (corrupt(argv[i]) == -1)
+ exit_code = 1;
+ return exit_code;
+}