├── Makefile
├── README.md
└── main.c


/Makefile:
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1 | all: main.c
2 | 	gcc main.c -o modex
3 | 


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/README.md:
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1 | patch the DEX crc in ODEX files
2 | 


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/main.c:
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  1 | /*
  2 |  *  mod_odex by Collin Mulliner <collinATmulliner.org>
  3 |  *  - patch the DEX crc in ODEX files
  4 |  *  license: GPLv3
  5 |  *  http://www.mulliner.org/android/
  6 |  */
  7 | 
  8 | #include <stdio.h>
  9 | #include <stdlib.h>
 10 | #include <stdint.h>
 11 | #include <sys/mman.h>
 12 | #include <sys/types.h>
 13 | #include <sys/stat.h>
 14 | #include <fcntl.h>
 15 | #include <string.h>
 16 | #include <unistd.h>
 17 | 
 18 | #define DEBUG 1
 19 | 
 20 | struct oat_header_t
 21 | {
 22 | 	char magic[4];
 23 | 	char version[4];
 24 | 	uint32_t adler32_checksum;
 25 | 	uint32_t instruction_set;
 26 | 	uint32_t instruction_set_features;
 27 | 	uint32_t dex_file_count;
 28 | 	uint32_t data[11]; // this seams to change deppening on the oat version (11 = 064)
 29 | 	uint32_t key_value_store_size;
 30 | 	// unsigned char key_value_store;
 31 | };
 32 | 
 33 | // not used, just to remember the structure
 34 | /*
 35 | struct oat_dex_file_header_t
 36 | {
 37 | 	uint32_t dex_file_location_size;
 38 | 	char dex_file_location[1];
 39 | 	uint32_t dex_file_location_checksum;
 40 | 	uint32_t dex_file_pointer;
 41 | 	// classes_offsets
 42 | };
 43 | */
 44 | 
 45 | void parse_oat_dex_file_header(unsigned char *data, int count, uint32_t oldcrc, uint32_t newcrc)
 46 | {
 47 | 	// this is the name of the apk once it gets installed on the device
 48 | 	char baseapk[] = {"base.apk"};
 49 | 	unsigned char *dp = data;
 50 | 	int c = count;
 51 | 	char name_tmp[128];
 52 | 
 53 | 	while (c > 0) {
 54 | 		if (memcmp(dp, baseapk, 8) == 0) {
 55 | 			uint32_t *namelen = (uint32_t*) (dp - 4);
 56 | 			printf("classes len: %d\n", *namelen);
 57 | 			memcpy(name_tmp, dp, *namelen);
 58 | 			name_tmp[*namelen] = 0;
 59 | 			printf("classes: %s\n", name_tmp);
 60 | 			uint32_t *crc32 = (uint32_t*)(dp + *namelen);
 61 | 			printf("classes crc32: %.8X\n", *crc32);
 62 | 
 63 | 			if (oldcrc != 0 && newcrc != 0) {
 64 | 				if (*crc32 == oldcrc) {
 65 | 					*crc32 = newcrc;
 66 | 					printf("!classes crc32: %.8X\n", *crc32);
 67 | 				}
 68 | 			}
 69 | 
 70 | 			c--;
 71 | 			dp += *namelen + 8;
 72 | 		}
 73 | 		dp++;
 74 | 	}
 75 | }
 76 | 
 77 | void parse_odex(unsigned char *odex, uint32_t oldcrc, uint32_t newcrc)
 78 | {
 79 | 	struct oat_header_t *oat = (struct oat_header_t*) odex;
 80 | 	printf("%c%c%c%c\n", oat->magic[0],oat->magic[1],oat->magic[2],oat->magic[3]);
 81 | 	printf("dex file count: %d\n", oat->dex_file_count);
 82 | 	printf("key_value_store_size: %d\n", oat->key_value_store_size);
 83 | 	
 84 | 	// find key value store
 85 | 	char *kvs = odex + sizeof(struct oat_header_t);
 86 | 	printf("kvs[0]: %s\n", kvs);
 87 | 	
 88 | 	parse_oat_dex_file_header(kvs + oat->key_value_store_size, oat->dex_file_count, oldcrc, newcrc);
 89 | }
 90 | 
 91 | int main(int argc, char **argv)
 92 | {
 93 | 	if (argc == 1) {
 94 | 		printf("%s: file_name.odex [oldcrc:newcrc]\n\tif CRCs are provided the oldcrc will be replaced with the newcrc\n", argv[0]);
 95 | 		exit(0);
 96 | 	}
 97 | 
 98 | 	struct stat fs;
 99 | 	int fp = open(argv[1], O_RDWR);
100 | 	fstat(fp, &fs);
101 | 	void *dex = mmap(0, fs.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fp, 0);
102 | 
103 | 	uint32_t oldcrc = 0;
104 | 	uint32_t newcrc = 0;
105 | 
106 | 	if (argc == 3) {
107 | 		if (strlen(argv[2]) == 17) {
108 | 			argv[2][8] = 0;
109 | 			oldcrc = strtol(&argv[2][0], 0, 16);
110 | 			newcrc = strtol(&argv[2][9], 0, 16);
111 | 			printf("old crc: %.8X  new crc: %.8X\n", oldcrc, newcrc);
112 | 		}
113 | 	}
114 | 
115 | 	// search (e.g. oat/odex files)
116 | 	char dexid[] = {'o','a','t', '\n'};
117 | 	unsigned char *d = (unsigned char*)dex;
118 | 	for (uint32_t i = 0; i < fs.st_size; i++) {
119 | 		if (memcmp(d, dexid, 4) == 0) {
120 | 			printf("%s\n", d);
121 | 			printf("offset = %d\n", i);
122 | 			break;
123 | 		}
124 | 		d++;
125 | 	}
126 | 
127 | 	parse_odex((unsigned char*)d, oldcrc, newcrc);
128 | 
129 | 	munmap(dex, fs.st_size);
130 | 	close(fp);
131 | }
132 | 


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