1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2020 Peter Holm <[email protected]>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29 /*
30 * Flip one or more bits in a file.
31 */
32
33 #include <sys/types.h>
34 #include <sys/stat.h>
35
36 #include <err.h>
37 #include <fcntl.h>
38 #include <stdio.h>
39 #include <stdlib.h>
40 #include <string.h>
41 #include <unistd.h>
42
43 extern char *optarg;
44 extern int optind;
45
46 static long
random_long(long mi,long ma)47 random_long(long mi, long ma)
48 {
49 return (arc4random() % (ma - mi + 1) + mi);
50 }
51
52 static void
flip(void * ap,size_t len)53 flip(void *ap, size_t len)
54 {
55 unsigned char *cp;
56 int byte;
57 unsigned char bit, buf, mask, old __unused;
58
59 cp = (unsigned char *)ap;
60 byte = random_long(0, len - 1);
61 bit = random_long(0,7);
62 mask = ~(1 << bit);
63 buf = cp[byte];
64 old = cp[byte];
65 buf = (buf & mask) | (~buf & ~mask);
66 cp[byte] = buf;
67 #if defined(DEBUG)
68 printf("Change %2x to %2x at %d by flipping bit %d\n",
69 old, buf, byte, bit);
70 #endif
71 }
72
73 static void
trash(char * c)74 trash(char *c)
75 {
76 if (arc4random() % 2 == 1)
77 *c = 0;
78 else
79 arc4random_buf(c, sizeof(c));
80 }
81
82 int
main(int argc,char * argv[])83 main(int argc, char *argv[])
84 {
85 struct stat st;
86 off_t pos;
87 size_t size;
88 int fd, i, times;
89 char c;
90
91 times = 1;
92 size = 0;
93 while ((c = getopt(argc, argv, "n:s:")) != -1) {
94 switch (c) {
95 case 'n':
96 times = atoi(optarg);
97 break;
98 case 's':
99 size = atol(optarg);
100 break;
101 case '?':
102 default:
103 fprintf(stderr,
104 "Usage: %s [ -n <num> <file>]\n",
105 argv[0]);
106 exit(1);
107 }
108 }
109 argc -= optind;
110 argv += optind;
111
112 if (argc != 1) {
113 fprintf(stderr, "Missing file name\n");
114 exit(1);
115 }
116
117 if ((fd = open(argv[0], O_RDWR)) == -1)
118 err(1, "open(%s)", argv[0]);
119
120 if (size == 0) {
121 if (fstat(fd, &st) == -1)
122 err(1, "stat %s", argv[0]);
123 if ((st.st_mode & S_IFREG) == 0)
124 errx(1, "%s must be a regular file\n", argv[0]);
125 size = st.st_size;
126 }
127
128 for (i = 0; i < times; i++) {
129 pos = arc4random() % size;
130 if (lseek(fd, pos, SEEK_SET) == -1)
131 err(1, "lseek()");
132 if (read(fd, &c, 1) != 1)
133 err(1, "read()");
134 if (arc4random() % 100 < 98)
135 flip(&c, 1);
136 else
137 trash(&c);
138 if (lseek(fd, pos, SEEK_SET) == -1)
139 err(1, "lseek()");
140 if (write(fd, &c, 1) != 1)
141 err(1, "write()");
142 }
143
144 return (0);
145 }
146