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 20 #include "mincrypt/rsa.h" 21 #include "mincrypt/sha.h" 22 23 #include <string.h> 24 #include <stdio.h> 25 #include <errno.h> 26 27 // Look for an RSA signature embedded in the .ZIP file comment given 28 // the path to the zip. Verify it matches one of the given public 29 // keys. 30 // 31 // Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered 32 // or no key matches the signature). 33 34 int verify_file(const char* path, const RSAPublicKey *pKeys, unsigned int numKeys) { 35 ui_set_progress(0.0); 36 37 FILE* f = fopen(path, "rb"); 38 if (f == NULL) { 39 LOGE("failed to open %s (%s)\n", path, strerror(errno)); 40 return VERIFY_FAILURE; 41 } 42 43 // An archive with a whole-file signature will end in six bytes: 44 // 45 // (2-byte signature start) $ff $ff (2-byte comment size) 46 // 47 // (As far as the ZIP format is concerned, these are part of the 48 // archive comment.) We start by reading this footer, this tells 49 // us how far back from the end we have to start reading to find 50 // the whole comment. 51 52 #define FOOTER_SIZE 6 53 54 if (fseek(f, -FOOTER_SIZE, SEEK_END) != 0) { 55 LOGE("failed to seek in %s (%s)\n", path, strerror(errno)); 56 fclose(f); 57 return VERIFY_FAILURE; 58 } 59 60 unsigned char footer[FOOTER_SIZE]; 61 if (fread(footer, 1, FOOTER_SIZE, f) != FOOTER_SIZE) { 62 LOGE("failed to read footer from %s (%s)\n", path, strerror(errno)); 63 fclose(f); 64 return VERIFY_FAILURE; 65 } 66 67 if (footer[2] != 0xff || footer[3] != 0xff) { 68 fclose(f); 69 return VERIFY_FAILURE; 70 } 71 72 int comment_size = footer[4] + (footer[5] << 8); 73 int signature_start = footer[0] + (footer[1] << 8); 74 LOGI("comment is %d bytes; signature %d bytes from end\n", 75 comment_size, signature_start); 76 77 if (signature_start - FOOTER_SIZE < RSANUMBYTES) { 78 // "signature" block isn't big enough to contain an RSA block. 79 LOGE("signature is too short\n"); 80 fclose(f); 81 return VERIFY_FAILURE; 82 } 83 84 #define EOCD_HEADER_SIZE 22 85 86 // The end-of-central-directory record is 22 bytes plus any 87 // comment length. 88 size_t eocd_size = comment_size + EOCD_HEADER_SIZE; 89 90 if (fseek(f, -eocd_size, SEEK_END) != 0) { 91 LOGE("failed to seek in %s (%s)\n", path, strerror(errno)); 92 fclose(f); 93 return VERIFY_FAILURE; 94 } 95 96 // Determine how much of the file is covered by the signature. 97 // This is everything except the signature data and length, which 98 // includes all of the EOCD except for the comment length field (2 99 // bytes) and the comment data. 100 size_t signed_len = ftell(f) + EOCD_HEADER_SIZE - 2; 101 102 unsigned char* eocd = malloc(eocd_size); 103 if (eocd == NULL) { 104 LOGE("malloc for EOCD record failed\n"); 105 fclose(f); 106 return VERIFY_FAILURE; 107 } 108 if (fread(eocd, 1, eocd_size, f) != eocd_size) { 109 LOGE("failed to read eocd from %s (%s)\n", path, strerror(errno)); 110 fclose(f); 111 return VERIFY_FAILURE; 112 } 113 114 // If this is really is the EOCD record, it will begin with the 115 // magic number $50 $4b $05 $06. 116 if (eocd[0] != 0x50 || eocd[1] != 0x4b || 117 eocd[2] != 0x05 || eocd[3] != 0x06) { 118 LOGE("signature length doesn't match EOCD marker\n"); 119 fclose(f); 120 return VERIFY_FAILURE; 121 } 122 123 int i; 124 for (i = 4; i < eocd_size-3; ++i) { 125 if (eocd[i ] == 0x50 && eocd[i+1] == 0x4b && 126 eocd[i+2] == 0x05 && eocd[i+3] == 0x06) { 127 // if the sequence $50 $4b $05 $06 appears anywhere after 128 // the real one, minzip will find the later (wrong) one, 129 // which could be exploitable. Fail verification if 130 // this sequence occurs anywhere after the real one. 131 LOGE("EOCD marker occurs after start of EOCD\n"); 132 fclose(f); 133 return VERIFY_FAILURE; 134 } 135 } 136 137 #define BUFFER_SIZE 4096 138 139 SHA_CTX ctx; 140 SHA_init(&ctx); 141 unsigned char* buffer = malloc(BUFFER_SIZE); 142 if (buffer == NULL) { 143 LOGE("failed to alloc memory for sha1 buffer\n"); 144 fclose(f); 145 return VERIFY_FAILURE; 146 } 147 148 double frac = -1.0; 149 size_t so_far = 0; 150 fseek(f, 0, SEEK_SET); 151 while (so_far < signed_len) { 152 int size = BUFFER_SIZE; 153 if (signed_len - so_far < size) size = signed_len - so_far; 154 if (fread(buffer, 1, size, f) != size) { 155 LOGE("failed to read data from %s (%s)\n", path, strerror(errno)); 156 fclose(f); 157 return VERIFY_FAILURE; 158 } 159 SHA_update(&ctx, buffer, size); 160 so_far += size; 161 double f = so_far / (double)signed_len; 162 if (f > frac + 0.02 || size == so_far) { 163 ui_set_progress(f); 164 frac = f; 165 } 166 } 167 fclose(f); 168 free(buffer); 169 170 const uint8_t* sha1 = SHA_final(&ctx); 171 for (i = 0; i < numKeys; ++i) { 172 // The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that 173 // the signing tool appends after the signature itself. 174 if (RSA_verify(pKeys+i, eocd + eocd_size - 6 - RSANUMBYTES, 175 RSANUMBYTES, sha1)) { 176 LOGI("whole-file signature verified against key %d\n", i); 177 free(eocd); 178 return VERIFY_SUCCESS; 179 } 180 } 181 free(eocd); 182 LOGE("failed to verify whole-file signature\n"); 183 return VERIFY_FAILURE; 184 } 185
