src/xorimage.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * xorimage.c - partially based on OpenWrt's addpattern.c
   4  */
   5
   6
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <string.h>
  10 #include <stdbool.h>
  11 #include <stdint.h>
  12 #include <unistd.h>
  13 #include <sys/stat.h>
  14
  15 static char default_pattern[] = "12345678";
  16 static int is_hex_pattern;
  17
  18
  19 int xor_data(void *data, size_t len, const void *pattern, int p_len, int p_off)
  20 {
  21         const uint8_t *key = pattern;
  22         uint8_t *d = data;
  23
  24         while (len--) {
  25                 *d ^= key[p_off];
  26                 d++;
  27                 p_off = (p_off + 1) % p_len;
  28         }
  29         return p_off;
  30 }
  31
  32
  33 void usage(void) __attribute__ (( __noreturn__ ));
  34
  35 void usage(void)
  36 {
  37         fprintf(stderr, "Usage: xorimage [-i infile] [-o outfile] [-p <pattern>] [-x]\n");
  38         exit(EXIT_FAILURE);
  39 }
  40
  41
  42 int main(int argc, char **argv)
  43 {
  44         char buf[1024]; /* keep this at 1k or adjust garbage calc below */
  45         FILE *in = stdin;
  46         FILE *out = stdout;
  47         char *ifn = NULL;
  48         char *ofn = NULL;
  49         const char *pattern = default_pattern;
  50         char hex_pattern[128];
  51         unsigned int hex_buf;
  52         int c;
  53         size_t n;
  54         int p_len, p_off = 0;
  55
  56         while ((c = getopt(argc, argv, "i:o:p:xh")) != -1) {
  57                 switch (c) {
  58                         case 'i':
  59                                 ifn = optarg;
  60                                 break;
  61                         case 'o':
  62                                 ofn = optarg;
  63                                 break;
  64                         case 'p':
  65                                 pattern = optarg;
  66                                 break;
  67                         case 'x':
  68                                 is_hex_pattern = true;
  69                                 break;
  70                         case 'h':
  71                         default:
  72                                 usage();
  73                 }
  74         }
  75
  76         if (optind != argc || optind == 1) {
  77                 fprintf(stderr, "illegal arg \"%s\"\n", argv[optind]);
  78                 usage();
  79         }
  80
  81         if (ifn && !(in = fopen(ifn, "r"))) {
  82                 fprintf(stderr, "can not open \"%s\" for reading\n", ifn);
  83                 usage();
  84         }
  85
  86         if (ofn && !(out = fopen(ofn, "w"))) {
  87                 fprintf(stderr, "can not open \"%s\" for writing\n", ofn);
  88                 usage();
  89         }
  90
  91         p_len = strlen(pattern);
  92
  93         if (p_len == 0) {
  94                 fprintf(stderr, "pattern cannot be empty\n");
  95                 usage();
  96         }
  97
  98         if (is_hex_pattern) {
  99                 int i;
 100
 101                 if ((p_len / 2) > sizeof(hex_pattern)) {
 102                         fprintf(stderr, "provided hex pattern is too long\n");
 103                         usage();
 104                 }
 105
 106                 if (p_len % 2 != 0) {
 107                         fprintf(stderr, "the number of characters (hex) is incorrect\n");
 108                         usage();
 109                 }
 110
 111                 for (i = 0; i < (p_len / 2); i++) {
 112                         if (sscanf(pattern + (i * 2), "%2x", &hex_buf) < 0) {
 113                                 fprintf(stderr, "invalid hex digit around %d\n", i * 2);
 114                                 usage();
 115                         }
 116                         hex_pattern[i] = (char)hex_buf;
 117                 }
 118         }
 119
 120         while ((n = fread(buf, 1, sizeof(buf), in)) > 0) {
 121                 if (n < sizeof(buf)) {
 122                         if (ferror(in)) {
 123                         FREAD_ERROR:
 124                                 fprintf(stderr, "fread error\n");
 125                                 return EXIT_FAILURE;
 126                         }
 127                 }
 128
 129                 if (is_hex_pattern) {
 130                         p_off = xor_data(buf, n, hex_pattern, (p_len / 2),
 131                                          p_off);
 132                 } else {
 133                         p_off = xor_data(buf, n, pattern, p_len, p_off);
 134                 }
 135
 136                 if (!fwrite(buf, n, 1, out)) {
 137                 FWRITE_ERROR:
 138                         fprintf(stderr, "fwrite error\n");
 139                         return EXIT_FAILURE;
 140                 }
 141         }
 142
 143         if (ferror(in)) {
 144                 goto FREAD_ERROR;
 145         }
 146
 147         if (fflush(out)) {
 148                 goto FWRITE_ERROR;
 149         }
 150
 151         fclose(in);
 152         fclose(out);
 153
 154         return EXIT_SUCCESS;
 155 }