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 "install/verifier.h"
18
19 #include <errno.h>
20 #include <stdio.h>
21 #include <stdlib.h>
22 #include <string.h>
23
24 #include <algorithm>
25 #include <functional>
26 #include <memory>
27 #include <vector>
28
29 #include <android-base/logging.h>
30 #include <openssl/bio.h>
31 #include <openssl/bn.h>
32 #include <openssl/ecdsa.h>
33 #include <openssl/evp.h>
34 #include <openssl/obj_mac.h>
35 #include <openssl/pem.h>
36 #include <openssl/rsa.h>
37 #include <ziparchive/zip_archive.h>
38
39 #include "otautil/print_sha1.h"
40 #include "private/asn1_decoder.h"
41
42 /*
43 * Simple version of PKCS#7 SignedData extraction. This extracts the
44 * signature OCTET STRING to be used for signature verification.
45 *
46 * For full details, see http://www.ietf.org/rfc/rfc3852.txt
47 *
48 * The PKCS#7 structure looks like:
49 *
50 * SEQUENCE (ContentInfo)
51 * OID (ContentType)
52 * [0] (content)
53 * SEQUENCE (SignedData)
54 * INTEGER (version CMSVersion)
55 * SET (DigestAlgorithmIdentifiers)
56 * SEQUENCE (EncapsulatedContentInfo)
57 * [0] (CertificateSet OPTIONAL)
58 * [1] (RevocationInfoChoices OPTIONAL)
59 * SET (SignerInfos)
60 * SEQUENCE (SignerInfo)
61 * INTEGER (CMSVersion)
62 * SEQUENCE (SignerIdentifier)
63 * SEQUENCE (DigestAlgorithmIdentifier)
64 * SEQUENCE (SignatureAlgorithmIdentifier)
65 * OCTET STRING (SignatureValue)
66 */
read_pkcs7(const uint8_t * pkcs7_der,size_t pkcs7_der_len,std::vector<uint8_t> * sig_der)67 static bool read_pkcs7(const uint8_t* pkcs7_der, size_t pkcs7_der_len,
68 std::vector<uint8_t>* sig_der) {
69 CHECK(sig_der != nullptr);
70 sig_der->clear();
71
72 asn1_context ctx(pkcs7_der, pkcs7_der_len);
73
74 std::unique_ptr<asn1_context> pkcs7_seq(ctx.asn1_sequence_get());
75 if (pkcs7_seq == nullptr || !pkcs7_seq->asn1_sequence_next()) {
76 return false;
77 }
78
79 std::unique_ptr<asn1_context> signed_data_app(pkcs7_seq->asn1_constructed_get());
80 if (signed_data_app == nullptr) {
81 return false;
82 }
83
84 std::unique_ptr<asn1_context> signed_data_seq(signed_data_app->asn1_sequence_get());
85 if (signed_data_seq == nullptr || !signed_data_seq->asn1_sequence_next() ||
86 !signed_data_seq->asn1_sequence_next() || !signed_data_seq->asn1_sequence_next() ||
87 !signed_data_seq->asn1_constructed_skip_all()) {
88 return false;
89 }
90
91 std::unique_ptr<asn1_context> sig_set(signed_data_seq->asn1_set_get());
92 if (sig_set == nullptr) {
93 return false;
94 }
95
96 std::unique_ptr<asn1_context> sig_seq(sig_set->asn1_sequence_get());
97 if (sig_seq == nullptr || !sig_seq->asn1_sequence_next() || !sig_seq->asn1_sequence_next() ||
98 !sig_seq->asn1_sequence_next() || !sig_seq->asn1_sequence_next()) {
99 return false;
100 }
101
102 const uint8_t* sig_der_ptr;
103 size_t sig_der_length;
104 if (!sig_seq->asn1_octet_string_get(&sig_der_ptr, &sig_der_length)) {
105 return false;
106 }
107
108 sig_der->resize(sig_der_length);
109 std::copy(sig_der_ptr, sig_der_ptr + sig_der_length, sig_der->begin());
110 return true;
111 }
112
verify_file(VerifierInterface * package,const std::vector<Certificate> & keys)113 int verify_file(VerifierInterface* package, const std::vector<Certificate>& keys) {
114 CHECK(package);
115 package->SetProgress(0.0);
116
117 // An archive with a whole-file signature will end in six bytes:
118 //
119 // (2-byte signature start) $ff $ff (2-byte comment size)
120 //
121 // (As far as the ZIP format is concerned, these are part of the archive comment.) We start by
122 // reading this footer, this tells us how far back from the end we have to start reading to find
123 // the whole comment.
124
125 #define FOOTER_SIZE 6
126 uint64_t length = package->GetPackageSize();
127
128 if (length < FOOTER_SIZE) {
129 LOG(ERROR) << "not big enough to contain footer";
130 return VERIFY_FAILURE;
131 }
132
133 uint8_t footer[FOOTER_SIZE];
134 if (!package->ReadFullyAtOffset(footer, FOOTER_SIZE, length - FOOTER_SIZE)) {
135 LOG(ERROR) << "Failed to read footer";
136 return VERIFY_FAILURE;
137 }
138
139 if (footer[2] != 0xff || footer[3] != 0xff) {
140 LOG(ERROR) << "footer is wrong";
141 return VERIFY_FAILURE;
142 }
143
144 size_t comment_size = footer[4] + (footer[5] << 8);
145 size_t signature_start = footer[0] + (footer[1] << 8);
146 LOG(INFO) << "comment is " << comment_size << " bytes; signature is " << signature_start
147 << " bytes from end";
148
149 if (signature_start > comment_size) {
150 LOG(ERROR) << "signature start: " << signature_start
151 << " is larger than comment size: " << comment_size;
152 return VERIFY_FAILURE;
153 }
154
155 if (signature_start <= FOOTER_SIZE) {
156 LOG(ERROR) << "Signature start is in the footer";
157 return VERIFY_FAILURE;
158 }
159
160 #define EOCD_HEADER_SIZE 22
161
162 // The end-of-central-directory record is 22 bytes plus any comment length.
163 size_t eocd_size = comment_size + EOCD_HEADER_SIZE;
164
165 if (length < eocd_size) {
166 LOG(ERROR) << "not big enough to contain EOCD";
167 return VERIFY_FAILURE;
168 }
169
170 // Determine how much of the file is covered by the signature. This is everything except the
171 // signature data and length, which includes all of the EOCD except for the comment length field
172 // (2 bytes) and the comment data.
173 uint64_t signed_len = length - eocd_size + EOCD_HEADER_SIZE - 2;
174
175 uint8_t eocd[eocd_size];
176 if (!package->ReadFullyAtOffset(eocd, eocd_size, length - eocd_size)) {
177 LOG(ERROR) << "Failed to read EOCD of " << eocd_size << " bytes";
178 return VERIFY_FAILURE;
179 }
180
181 // If this is really is the EOCD record, it will begin with the magic number $50 $4b $05 $06.
182 if (eocd[0] != 0x50 || eocd[1] != 0x4b || eocd[2] != 0x05 || eocd[3] != 0x06) {
183 LOG(ERROR) << "signature length doesn't match EOCD marker";
184 return VERIFY_FAILURE;
185 }
186
187 for (size_t i = 4; i < eocd_size - 3; ++i) {
188 if (eocd[i] == 0x50 && eocd[i + 1] == 0x4b && eocd[i + 2] == 0x05 && eocd[i + 3] == 0x06) {
189 // If the sequence $50 $4b $05 $06 appears anywhere after the real one, libziparchive will
190 // find the later (wrong) one, which could be exploitable. Fail the verification if this
191 // sequence occurs anywhere after the real one.
192 LOG(ERROR) << "EOCD marker occurs after start of EOCD";
193 return VERIFY_FAILURE;
194 }
195 }
196
197 bool need_sha1 = false;
198 bool need_sha256 = false;
199 for (const auto& key : keys) {
200 switch (key.hash_len) {
201 case SHA_DIGEST_LENGTH:
202 need_sha1 = true;
203 break;
204 case SHA256_DIGEST_LENGTH:
205 need_sha256 = true;
206 break;
207 }
208 }
209
210 SHA_CTX sha1_ctx;
211 SHA256_CTX sha256_ctx;
212 SHA1_Init(&sha1_ctx);
213 SHA256_Init(&sha256_ctx);
214
215 std::vector<HasherUpdateCallback> hashers;
216 if (need_sha1) {
217 hashers.emplace_back(
218 std::bind(&SHA1_Update, &sha1_ctx, std::placeholders::_1, std::placeholders::_2));
219 }
220 if (need_sha256) {
221 hashers.emplace_back(
222 std::bind(&SHA256_Update, &sha256_ctx, std::placeholders::_1, std::placeholders::_2));
223 }
224
225 double frac = -1.0;
226 uint64_t so_far = 0;
227 while (so_far < signed_len) {
228 // On a Nexus 5X, experiment showed 16MiB beat 1MiB by 6% faster for a 1196MiB full OTA and
229 // 60% for an 89MiB incremental OTA. http://b/28135231.
230 uint64_t read_size = std::min<uint64_t>(signed_len - so_far, 16 * MiB);
231 package->UpdateHashAtOffset(hashers, so_far, read_size);
232 so_far += read_size;
233
234 double f = so_far / static_cast<double>(signed_len);
235 if (f > frac + 0.02 || read_size == so_far) {
236 package->SetProgress(f);
237 frac = f;
238 }
239 }
240
241 uint8_t sha1[SHA_DIGEST_LENGTH];
242 SHA1_Final(sha1, &sha1_ctx);
243 uint8_t sha256[SHA256_DIGEST_LENGTH];
244 SHA256_Final(sha256, &sha256_ctx);
245
246 const uint8_t* signature = eocd + eocd_size - signature_start;
247 size_t signature_size = signature_start - FOOTER_SIZE;
248
249 LOG(INFO) << "signature (offset: " << std::hex << (length - signature_start)
250 << ", length: " << signature_size << "): " << print_hex(signature, signature_size);
251
252 std::vector<uint8_t> sig_der;
253 if (!read_pkcs7(signature, signature_size, &sig_der)) {
254 LOG(ERROR) << "Could not find signature DER block";
255 return VERIFY_FAILURE;
256 }
257
258 // Check to make sure at least one of the keys matches the signature. Since any key can match,
259 // we need to try each before determining a verification failure has happened.
260 size_t i = 0;
261 for (const auto& key : keys) {
262 const uint8_t* hash;
263 int hash_nid;
264 switch (key.hash_len) {
265 case SHA_DIGEST_LENGTH:
266 hash = sha1;
267 hash_nid = NID_sha1;
268 break;
269 case SHA256_DIGEST_LENGTH:
270 hash = sha256;
271 hash_nid = NID_sha256;
272 break;
273 default:
274 continue;
275 }
276
277 // The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that the signing tool appends
278 // after the signature itself.
279 if (key.key_type == Certificate::KEY_TYPE_RSA) {
280 if (!RSA_verify(hash_nid, hash, key.hash_len, sig_der.data(), sig_der.size(),
281 key.rsa.get())) {
282 LOG(INFO) << "failed to verify against RSA key " << i;
283 continue;
284 }
285
286 LOG(INFO) << "whole-file signature verified against RSA key " << i;
287 return VERIFY_SUCCESS;
288 } else if (key.key_type == Certificate::KEY_TYPE_EC && key.hash_len == SHA256_DIGEST_LENGTH) {
289 if (!ECDSA_verify(0, hash, key.hash_len, sig_der.data(), sig_der.size(), key.ec.get())) {
290 LOG(INFO) << "failed to verify against EC key " << i;
291 continue;
292 }
293
294 LOG(INFO) << "whole-file signature verified against EC key " << i;
295 return VERIFY_SUCCESS;
296 } else {
297 LOG(INFO) << "Unknown key type " << key.key_type;
298 }
299 i++;
300 }
301
302 if (need_sha1) {
303 LOG(INFO) << "SHA-1 digest: " << print_hex(sha1, SHA_DIGEST_LENGTH);
304 }
305 if (need_sha256) {
306 LOG(INFO) << "SHA-256 digest: " << print_hex(sha256, SHA256_DIGEST_LENGTH);
307 }
308 LOG(ERROR) << "failed to verify whole-file signature";
309 return VERIFY_FAILURE;
310 }
311
IterateZipEntriesAndSearchForKeys(const ZipArchiveHandle & handle)312 static std::vector<Certificate> IterateZipEntriesAndSearchForKeys(const ZipArchiveHandle& handle) {
313 void* cookie;
314 int32_t iter_status = StartIteration(handle, &cookie, "", "x509.pem");
315 if (iter_status != 0) {
316 LOG(ERROR) << "Failed to iterate over entries in the certificate zipfile: "
317 << ErrorCodeString(iter_status);
318 return {};
319 }
320
321 std::vector<Certificate> result;
322
323 std::string_view name;
324 ZipEntry64 entry;
325 while ((iter_status = Next(cookie, &entry, &name)) == 0) {
326 if (entry.uncompressed_length > std::numeric_limits<size_t>::max()) {
327 LOG(ERROR) << "Failed to extract " << name
328 << " because's uncompressed size exceeds size of address space. "
329 << entry.uncompressed_length;
330 return {};
331 }
332 std::vector<uint8_t> pem_content(entry.uncompressed_length);
333 if (int32_t extract_status =
334 ExtractToMemory(handle, &entry, pem_content.data(), pem_content.size());
335 extract_status != 0) {
336 LOG(ERROR) << "Failed to extract " << name;
337 return {};
338 }
339
340 Certificate cert(0, Certificate::KEY_TYPE_RSA, nullptr, nullptr);
341 // Aborts the parsing if we fail to load one of the key file.
342 if (!LoadCertificateFromBuffer(pem_content, &cert)) {
343 LOG(ERROR) << "Failed to load keys from " << name;
344 return {};
345 }
346
347 result.emplace_back(std::move(cert));
348 }
349
350 if (iter_status != -1) {
351 LOG(ERROR) << "Error while iterating over zip entries: " << ErrorCodeString(iter_status);
352 return {};
353 }
354
355 return result;
356 }
357
LoadKeysFromZipfile(const std::string & zip_name)358 std::vector<Certificate> LoadKeysFromZipfile(const std::string& zip_name) {
359 ZipArchiveHandle handle;
360 if (int32_t open_status = OpenArchive(zip_name.c_str(), &handle); open_status != 0) {
361 LOG(ERROR) << "Failed to open " << zip_name << ": " << ErrorCodeString(open_status);
362 return {};
363 }
364
365 std::vector<Certificate> result = IterateZipEntriesAndSearchForKeys(handle);
366 CloseArchive(handle);
367 return result;
368 }
369
CheckRSAKey(const std::unique_ptr<RSA,RSADeleter> & rsa)370 bool CheckRSAKey(const std::unique_ptr<RSA, RSADeleter>& rsa) {
371 if (!rsa) {
372 return false;
373 }
374
375 const BIGNUM* out_n;
376 const BIGNUM* out_e;
377 RSA_get0_key(rsa.get(), &out_n, &out_e, nullptr /* private exponent */);
378 auto modulus_bits = BN_num_bits(out_n);
379 if (modulus_bits != 2048 && modulus_bits != 4096) {
380 LOG(ERROR) << "Modulus should be 2048 or 4096 bits long, actual: " << modulus_bits;
381 return false;
382 }
383
384 BN_ULONG exponent = BN_get_word(out_e);
385 if (exponent != 3 && exponent != 65537) {
386 LOG(ERROR) << "Public exponent should be 3 or 65537, actual: " << exponent;
387 return false;
388 }
389
390 return true;
391 }
392
CheckECKey(const std::unique_ptr<EC_KEY,ECKEYDeleter> & ec_key)393 bool CheckECKey(const std::unique_ptr<EC_KEY, ECKEYDeleter>& ec_key) {
394 if (!ec_key) {
395 return false;
396 }
397
398 const EC_GROUP* ec_group = EC_KEY_get0_group(ec_key.get());
399 if (!ec_group) {
400 LOG(ERROR) << "Failed to get the ec_group from the ec_key";
401 return false;
402 }
403 auto degree = EC_GROUP_get_degree(ec_group);
404 if (degree != 256) {
405 LOG(ERROR) << "Field size of the ec key should be 256 bits long, actual: " << degree;
406 return false;
407 }
408
409 return true;
410 }
411
LoadCertificateFromBuffer(const std::vector<uint8_t> & pem_content,Certificate * cert)412 bool LoadCertificateFromBuffer(const std::vector<uint8_t>& pem_content, Certificate* cert) {
413 std::unique_ptr<BIO, decltype(&BIO_free)> content(
414 BIO_new_mem_buf(pem_content.data(), pem_content.size()), BIO_free);
415
416 std::unique_ptr<X509, decltype(&X509_free)> x509(
417 PEM_read_bio_X509(content.get(), nullptr, nullptr, nullptr), X509_free);
418 if (!x509) {
419 LOG(ERROR) << "Failed to read x509 certificate";
420 return false;
421 }
422
423 int nid = X509_get_signature_nid(x509.get());
424 switch (nid) {
425 // SignApk has historically accepted md5WithRSA certificates, but treated them as
426 // sha1WithRSA anyway. Continue to do so for backwards compatibility.
427 case NID_md5WithRSA:
428 case NID_md5WithRSAEncryption:
429 case NID_sha1WithRSA:
430 case NID_sha1WithRSAEncryption:
431 cert->hash_len = SHA_DIGEST_LENGTH;
432 break;
433 case NID_sha256WithRSAEncryption:
434 case NID_ecdsa_with_SHA256:
435 cert->hash_len = SHA256_DIGEST_LENGTH;
436 break;
437 default:
438 LOG(ERROR) << "Unrecognized signature nid " << OBJ_nid2ln(nid);
439 return false;
440 }
441
442 std::unique_ptr<EVP_PKEY, decltype(&EVP_PKEY_free)> public_key(X509_get_pubkey(x509.get()),
443 EVP_PKEY_free);
444 if (!public_key) {
445 LOG(ERROR) << "Failed to extract the public key from x509 certificate";
446 return false;
447 }
448
449 int key_type = EVP_PKEY_id(public_key.get());
450 if (key_type == EVP_PKEY_RSA) {
451 cert->key_type = Certificate::KEY_TYPE_RSA;
452 cert->ec.reset();
453 cert->rsa.reset(EVP_PKEY_get1_RSA(public_key.get()));
454 if (!cert->rsa || !CheckRSAKey(cert->rsa)) {
455 LOG(ERROR) << "Failed to validate the rsa key info from public key";
456 return false;
457 }
458 } else if (key_type == EVP_PKEY_EC) {
459 cert->key_type = Certificate::KEY_TYPE_EC;
460 cert->rsa.reset();
461 cert->ec.reset(EVP_PKEY_get1_EC_KEY(public_key.get()));
462 if (!cert->ec || !CheckECKey(cert->ec)) {
463 LOG(ERROR) << "Failed to validate the ec key info from the public key";
464 return false;
465 }
466 } else {
467 LOG(ERROR) << "Unrecognized public key type " << OBJ_nid2ln(key_type);
468 return false;
469 }
470
471 return true;
472 }
473