1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
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;
}
|
