1 /* 2 * Copyright (C) 2008 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include "common.h" 18 #include "verifier.h" 19 #include "ui.h" 20 21 #include "mincrypt/rsa.h" 22 #include "mincrypt/sha.h" 23 24 #include <string.h> 25 #include <stdio.h> 26 #include <errno.h> 27 28 extern RecoveryUI* ui; 29 30 // Look for an RSA signature embedded in the .ZIP file comment given 31 // the path to the zip. Verify it matches one of the given public 32 // keys. 33 // 34 // Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered 35 // or no key matches the signature). 36 37 int verify_file(const char* path, const RSAPublicKey *pKeys, unsigned int numKeys) { 38 ui->SetProgress(0.0); 39 40 FILE* f = fopen(path, "rb"); 41 if (f == NULL) { 42 LOGE("failed to open %s (%s)\n", path, strerror(errno)); 43 return VERIFY_FAILURE; 44 } 45 46 // An archive with a whole-file signature will end in six bytes: 47 // 48 // (2-byte signature start) $ff $ff (2-byte comment size) 49 // 50 // (As far as the ZIP format is concerned, these are part of the 51 // archive comment.) We start by reading this footer, this tells 52 // us how far back from the end we have to start reading to find 53 // the whole comment. 54 55 #define FOOTER_SIZE 6 56 57 if (fseek(f, -FOOTER_SIZE, SEEK_END) != 0) { 58 LOGE("failed to seek in %s (%s)\n", path, strerror(errno)); 59 fclose(f); 60 return VERIFY_FAILURE; 61 } 62 63 unsigned char footer[FOOTER_SIZE]; 64 if (fread(footer, 1, FOOTER_SIZE, f) != FOOTER_SIZE) { 65 LOGE("failed to read footer from %s (%s)\n", path, strerror(errno)); 66 fclose(f); 67 return VERIFY_FAILURE; 68 } 69 70 if (footer[2] != 0xff || footer[3] != 0xff) { 71 fclose(f); 72 return VERIFY_FAILURE; 73 } 74 75 size_t comment_size = footer[4] + (footer[5] << 8); 76 size_t signature_start = footer[0] + (footer[1] << 8); 77 LOGI("comment is %d bytes; signature %d bytes from end\n", 78 comment_size, signature_start); 79 80 if (signature_start - FOOTER_SIZE < RSANUMBYTES) { 81 // "signature" block isn't big enough to contain an RSA block. 82 LOGE("signature is too short\n"); 83 fclose(f); 84 return VERIFY_FAILURE; 85 } 86 87 #define EOCD_HEADER_SIZE 22 88 89 // The end-of-central-directory record is 22 bytes plus any 90 // comment length. 91 size_t eocd_size = comment_size + EOCD_HEADER_SIZE; 92 93 if (fseek(f, -eocd_size, SEEK_END) != 0) { 94 LOGE("failed to seek in %s (%s)\n", path, strerror(errno)); 95 fclose(f); 96 return VERIFY_FAILURE; 97 } 98 99 // Determine how much of the file is covered by the signature. 100 // This is everything except the signature data and length, which 101 // includes all of the EOCD except for the comment length field (2 102 // bytes) and the comment data. 103 size_t signed_len = ftell(f) + EOCD_HEADER_SIZE - 2; 104 105 unsigned char* eocd = (unsigned char*)malloc(eocd_size); 106 if (eocd == NULL) { 107 LOGE("malloc for EOCD record failed\n"); 108 fclose(f); 109 return VERIFY_FAILURE; 110 } 111 if (fread(eocd, 1, eocd_size, f) != eocd_size) { 112 LOGE("failed to read eocd from %s (%s)\n", path, strerror(errno)); 113 fclose(f); 114 return VERIFY_FAILURE; 115 } 116 117 // If this is really is the EOCD record, it will begin with the 118 // magic number $50 $4b $05 $06. 119 if (eocd[0] != 0x50 || eocd[1] != 0x4b || 120 eocd[2] != 0x05 || eocd[3] != 0x06) { 121 LOGE("signature length doesn't match EOCD marker\n"); 122 fclose(f); 123 return VERIFY_FAILURE; 124 } 125 126 size_t i; 127 for (i = 4; i < eocd_size-3; ++i) { 128 if (eocd[i ] == 0x50 && eocd[i+1] == 0x4b && 129 eocd[i+2] == 0x05 && eocd[i+3] == 0x06) { 130 // if the sequence $50 $4b $05 $06 appears anywhere after 131 // the real one, minzip will find the later (wrong) one, 132 // which could be exploitable. Fail verification if 133 // this sequence occurs anywhere after the real one. 134 LOGE("EOCD marker occurs after start of EOCD\n"); 135 fclose(f); 136 return VERIFY_FAILURE; 137 } 138 } 139 140 #define BUFFER_SIZE 4096 141 142 SHA_CTX ctx; 143 SHA_init(&ctx); 144 unsigned char* buffer = (unsigned char*)malloc(BUFFER_SIZE); 145 if (buffer == NULL) { 146 LOGE("failed to alloc memory for sha1 buffer\n"); 147 fclose(f); 148 return VERIFY_FAILURE; 149 } 150 151 double frac = -1.0; 152 size_t so_far = 0; 153 fseek(f, 0, SEEK_SET); 154 while (so_far < signed_len) { 155 size_t size = BUFFER_SIZE; 156 if (signed_len - so_far < size) size = signed_len - so_far; 157 if (fread(buffer, 1, size, f) != size) { 158 LOGE("failed to read data from %s (%s)\n", path, strerror(errno)); 159 fclose(f); 160 return VERIFY_FAILURE; 161 } 162 SHA_update(&ctx, buffer, size); 163 so_far += size; 164 double f = so_far / (double)signed_len; 165 if (f > frac + 0.02 || size == so_far) { 166 ui->SetProgress(f); 167 frac = f; 168 } 169 } 170 fclose(f); 171 free(buffer); 172 173 const uint8_t* sha1 = SHA_final(&ctx); 174 for (i = 0; i < numKeys; ++i) { 175 // The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that 176 // the signing tool appends after the signature itself. 177 if (RSA_verify(pKeys+i, eocd + eocd_size - 6 - RSANUMBYTES, 178 RSANUMBYTES, sha1)) { 179 LOGI("whole-file signature verified against key %d\n", i); 180 free(eocd); 181 return VERIFY_SUCCESS; 182 } else { 183 LOGI("failed to verify against key %d\n", i); 184 } 185 } 186 free(eocd); 187 LOGE("failed to verify whole-file signature\n"); 188 return VERIFY_FAILURE; 189 } 190 191 // Reads a file containing one or more public keys as produced by 192 // DumpPublicKey: this is an RSAPublicKey struct as it would appear 193 // as a C source literal, eg: 194 // 195 // "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}" 196 // 197 // For key versions newer than the original 2048-bit e=3 keys 198 // supported by Android, the string is preceded by a version 199 // identifier, eg: 200 // 201 // "v2 {64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}" 202 // 203 // (Note that the braces and commas in this example are actual 204 // characters the parser expects to find in the file; the ellipses 205 // indicate more numbers omitted from this example.) 206 // 207 // The file may contain multiple keys in this format, separated by 208 // commas. The last key must not be followed by a comma. 209 // 210 // Returns NULL if the file failed to parse, or if it contain zero keys. 211 RSAPublicKey* 212 load_keys(const char* filename, int* numKeys) { 213 RSAPublicKey* out = NULL; 214 *numKeys = 0; 215 216 FILE* f = fopen(filename, "r"); 217 if (f == NULL) { 218 LOGE("opening %s: %s\n", filename, strerror(errno)); 219 goto exit; 220 } 221 222 { 223 int i; 224 bool done = false; 225 while (!done) { 226 ++*numKeys; 227 out = (RSAPublicKey*)realloc(out, *numKeys * sizeof(RSAPublicKey)); 228 RSAPublicKey* key = out + (*numKeys - 1); 229 230 char start_char; 231 if (fscanf(f, " %c", &start_char) != 1) goto exit; 232 if (start_char == '{') { 233 // a version 1 key has no version specifier. 234 key->exponent = 3; 235 } else if (start_char == 'v') { 236 int version; 237 if (fscanf(f, "%d {", &version) != 1) goto exit; 238 if (version == 2) { 239 key->exponent = 65537; 240 } else { 241 goto exit; 242 } 243 } 244 245 if (fscanf(f, " %i , 0x%x , { %u", 246 &(key->len), &(key->n0inv), &(key->n[0])) != 3) { 247 goto exit; 248 } 249 if (key->len != RSANUMWORDS) { 250 LOGE("key length (%d) does not match expected size\n", key->len); 251 goto exit; 252 } 253 for (i = 1; i < key->len; ++i) { 254 if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit; 255 } 256 if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit; 257 for (i = 1; i < key->len; ++i) { 258 if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit; 259 } 260 fscanf(f, " } } "); 261 262 // if the line ends in a comma, this file has more keys. 263 switch (fgetc(f)) { 264 case ',': 265 // more keys to come. 266 break; 267 268 case EOF: 269 done = true; 270 break; 271 272 default: 273 LOGE("unexpected character between keys\n"); 274 goto exit; 275 } 276 277 LOGI("read key e=%d\n", key->exponent); 278 } 279 } 280 281 fclose(f); 282 return out; 283 284 exit: 285 if (f) fclose(f); 286 free(out); 287 *numKeys = 0; 288 return NULL; 289 } 290
