1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2020 Peter Holm <pho@FreeBSD.org>
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 c, fd, i, times;
89
90 times = 1;
91 size = 0;
92 while ((c = getopt(argc, argv, "n:s:")) != -1) {
93 switch (c) {
94 case 'n':
95 times = atoi(optarg);
96 break;
97 case 's':
98 size = atol(optarg);
99 break;
100 case '?':
101 default:
102 fprintf(stderr,
103 "Usage: %s [ -n <num> <file>]\n",
104 argv[0]);
105 exit(1);
106 }
107 }
108 argc -= optind;
109 argv += optind;
110
111 if (argc != 1) {
112 fprintf(stderr, "Missing file name\n");
113 exit(1);
114 }
115
116 if ((fd = open(argv[0], O_RDWR)) == -1)
117 err(1, "open(%s)", argv[0]);
118
119 if (size == 0) {
120 if (fstat(fd, &st) == -1)
121 err(1, "stat %s", argv[0]);
122 if ((st.st_mode & S_IFREG) == 0)
123 errx(1, "%s must be a regular file\n", argv[0]);
124 size = st.st_size;
125 }
126
127 for (i = 0; i < times; i++) {
128 char ch;
129
130 pos = arc4random() % size;
131 if (lseek(fd, pos, SEEK_SET) == -1)
132 err(1, "lseek()");
133 if (read(fd, &ch, 1) != 1)
134 err(1, "read()");
135 if (arc4random() % 100 < 98)
136 flip(&ch, 1);
137 else
138 trash(&ch);
139 if (lseek(fd, pos, SEEK_SET) == -1)
140 err(1, "lseek()");
141 if (write(fd, &ch, 1) != 1)
142 err(1, "write()");
143 }
144
145 return (0);
146 }
147