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Diffstat (limited to 'otautil/verifier.cpp')
| -rw-r--r-- | otautil/verifier.cpp | 472 |
1 files changed, 472 insertions, 0 deletions
diff --git a/otautil/verifier.cpp b/otautil/verifier.cpp new file mode 100644 index 000000000..92b9faf29 --- /dev/null +++ b/otautil/verifier.cpp @@ -0,0 +1,472 @@ +/* + * Copyright (C) 2008 The Android Open Source Project + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#include "otautil/verifier.h" + +#include <errno.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> + +#include <algorithm> +#include <functional> +#include <memory> +#include <vector> + +#include <android-base/logging.h> +#include <openssl/bio.h> +#include <openssl/bn.h> +#include <openssl/ecdsa.h> +#include <openssl/evp.h> +#include <openssl/obj_mac.h> +#include <openssl/pem.h> +#include <openssl/rsa.h> +#include <ziparchive/zip_archive.h> + +#include "otautil/print_sha1.h" +#include "private/asn1_decoder.h" + +/* + * Simple version of PKCS#7 SignedData extraction. This extracts the + * signature OCTET STRING to be used for signature verification. + * + * For full details, see http://www.ietf.org/rfc/rfc3852.txt + * + * The PKCS#7 structure looks like: + * + * SEQUENCE (ContentInfo) + * OID (ContentType) + * [0] (content) + * SEQUENCE (SignedData) + * INTEGER (version CMSVersion) + * SET (DigestAlgorithmIdentifiers) + * SEQUENCE (EncapsulatedContentInfo) + * [0] (CertificateSet OPTIONAL) + * [1] (RevocationInfoChoices OPTIONAL) + * SET (SignerInfos) + * SEQUENCE (SignerInfo) + * INTEGER (CMSVersion) + * SEQUENCE (SignerIdentifier) + * SEQUENCE (DigestAlgorithmIdentifier) + * SEQUENCE (SignatureAlgorithmIdentifier) + * OCTET STRING (SignatureValue) + */ +static bool read_pkcs7(const uint8_t* pkcs7_der, size_t pkcs7_der_len, + std::vector<uint8_t>* sig_der) { + CHECK(sig_der != nullptr); + sig_der->clear(); + + asn1_context ctx(pkcs7_der, pkcs7_der_len); + + std::unique_ptr<asn1_context> pkcs7_seq(ctx.asn1_sequence_get()); + if (pkcs7_seq == nullptr || !pkcs7_seq->asn1_sequence_next()) { + return false; + } + + std::unique_ptr<asn1_context> signed_data_app(pkcs7_seq->asn1_constructed_get()); + if (signed_data_app == nullptr) { + return false; + } + + std::unique_ptr<asn1_context> signed_data_seq(signed_data_app->asn1_sequence_get()); + if (signed_data_seq == nullptr || !signed_data_seq->asn1_sequence_next() || + !signed_data_seq->asn1_sequence_next() || !signed_data_seq->asn1_sequence_next() || + !signed_data_seq->asn1_constructed_skip_all()) { + return false; + } + + std::unique_ptr<asn1_context> sig_set(signed_data_seq->asn1_set_get()); + if (sig_set == nullptr) { + return false; + } + + std::unique_ptr<asn1_context> sig_seq(sig_set->asn1_sequence_get()); + if (sig_seq == nullptr || !sig_seq->asn1_sequence_next() || !sig_seq->asn1_sequence_next() || + !sig_seq->asn1_sequence_next() || !sig_seq->asn1_sequence_next()) { + return false; + } + + const uint8_t* sig_der_ptr; + size_t sig_der_length; + if (!sig_seq->asn1_octet_string_get(&sig_der_ptr, &sig_der_length)) { + return false; + } + + sig_der->resize(sig_der_length); + std::copy(sig_der_ptr, sig_der_ptr + sig_der_length, sig_der->begin()); + return true; +} + +int verify_file(VerifierInterface* package, const std::vector<Certificate>& keys) { + CHECK(package); + package->SetProgress(0.0); + + // An archive with a whole-file signature will end in six bytes: + // + // (2-byte signature start) $ff $ff (2-byte comment size) + // + // (As far as the ZIP format is concerned, these are part of the archive comment.) We start by + // reading this footer, this tells us how far back from the end we have to start reading to find + // the whole comment. + +#define FOOTER_SIZE 6 + uint64_t length = package->GetPackageSize(); + + if (length < FOOTER_SIZE) { + LOG(ERROR) << "not big enough to contain footer"; + return VERIFY_FAILURE; + } + + uint8_t footer[FOOTER_SIZE]; + if (!package->ReadFullyAtOffset(footer, FOOTER_SIZE, length - FOOTER_SIZE)) { + LOG(ERROR) << "Failed to read footer"; + return VERIFY_FAILURE; + } + + if (footer[2] != 0xff || footer[3] != 0xff) { + LOG(ERROR) << "footer is wrong"; + return VERIFY_FAILURE; + } + + size_t comment_size = footer[4] + (footer[5] << 8); + size_t signature_start = footer[0] + (footer[1] << 8); + LOG(INFO) << "comment is " << comment_size << " bytes; signature is " << signature_start + << " bytes from end"; + + if (signature_start > comment_size) { + LOG(ERROR) << "signature start: " << signature_start + << " is larger than comment size: " << comment_size; + return VERIFY_FAILURE; + } + + if (signature_start <= FOOTER_SIZE) { + LOG(ERROR) << "Signature start is in the footer"; + return VERIFY_FAILURE; + } + +#define EOCD_HEADER_SIZE 22 + + // The end-of-central-directory record is 22 bytes plus any comment length. + size_t eocd_size = comment_size + EOCD_HEADER_SIZE; + + if (length < eocd_size) { + LOG(ERROR) << "not big enough to contain EOCD"; + return VERIFY_FAILURE; + } + + // Determine how much of the file is covered by the signature. This is everything except the + // signature data and length, which includes all of the EOCD except for the comment length field + // (2 bytes) and the comment data. + uint64_t signed_len = length - eocd_size + EOCD_HEADER_SIZE - 2; + + uint8_t eocd[eocd_size]; + if (!package->ReadFullyAtOffset(eocd, eocd_size, length - eocd_size)) { + LOG(ERROR) << "Failed to read EOCD of " << eocd_size << " bytes"; + return VERIFY_FAILURE; + } + + // If this is really is the EOCD record, it will begin with the magic number $50 $4b $05 $06. + if (eocd[0] != 0x50 || eocd[1] != 0x4b || eocd[2] != 0x05 || eocd[3] != 0x06) { + LOG(ERROR) << "signature length doesn't match EOCD marker"; + return VERIFY_FAILURE; + } + + for (size_t i = 4; i < eocd_size - 3; ++i) { + if (eocd[i] == 0x50 && eocd[i + 1] == 0x4b && eocd[i + 2] == 0x05 && eocd[i + 3] == 0x06) { + // If the sequence $50 $4b $05 $06 appears anywhere after the real one, libziparchive will + // find the later (wrong) one, which could be exploitable. Fail the verification if this + // sequence occurs anywhere after the real one. + LOG(ERROR) << "EOCD marker occurs after start of EOCD"; + return VERIFY_FAILURE; + } + } + + bool need_sha1 = false; + bool need_sha256 = false; + for (const auto& key : keys) { + switch (key.hash_len) { + case SHA_DIGEST_LENGTH: + need_sha1 = true; + break; + case SHA256_DIGEST_LENGTH: + need_sha256 = true; + break; + } + } + + SHA_CTX sha1_ctx; + SHA256_CTX sha256_ctx; + SHA1_Init(&sha1_ctx); + SHA256_Init(&sha256_ctx); + + std::vector<HasherUpdateCallback> hashers; + if (need_sha1) { + hashers.emplace_back( + std::bind(&SHA1_Update, &sha1_ctx, std::placeholders::_1, std::placeholders::_2)); + } + if (need_sha256) { + hashers.emplace_back( + std::bind(&SHA256_Update, &sha256_ctx, std::placeholders::_1, std::placeholders::_2)); + } + + double frac = -1.0; + uint64_t so_far = 0; + while (so_far < signed_len) { + // On a Nexus 5X, experiment showed 16MiB beat 1MiB by 6% faster for a 1196MiB full OTA and + // 60% for an 89MiB incremental OTA. http://b/28135231. + uint64_t read_size = std::min<uint64_t>(signed_len - so_far, 16 * MiB); + package->UpdateHashAtOffset(hashers, so_far, read_size); + so_far += read_size; + + double f = so_far / static_cast<double>(signed_len); + if (f > frac + 0.02 || read_size == so_far) { + package->SetProgress(f); + frac = f; + } + } + + uint8_t sha1[SHA_DIGEST_LENGTH]; + SHA1_Final(sha1, &sha1_ctx); + uint8_t sha256[SHA256_DIGEST_LENGTH]; + SHA256_Final(sha256, &sha256_ctx); + + const uint8_t* signature = eocd + eocd_size - signature_start; + size_t signature_size = signature_start - FOOTER_SIZE; + + LOG(INFO) << "signature (offset: " << std::hex << (length - signature_start) + << ", length: " << signature_size << "): " << print_hex(signature, signature_size); + + std::vector<uint8_t> sig_der; + if (!read_pkcs7(signature, signature_size, &sig_der)) { + LOG(ERROR) << "Could not find signature DER block"; + return VERIFY_FAILURE; + } + + // Check to make sure at least one of the keys matches the signature. Since any key can match, + // we need to try each before determining a verification failure has happened. + size_t i = 0; + for (const auto& key : keys) { + const uint8_t* hash; + int hash_nid; + switch (key.hash_len) { + case SHA_DIGEST_LENGTH: + hash = sha1; + hash_nid = NID_sha1; + break; + case SHA256_DIGEST_LENGTH: + hash = sha256; + hash_nid = NID_sha256; + break; + default: + continue; + } + + // The 6 bytes is the "(signature_start) $ff $ff (comment_size)" that the signing tool appends + // after the signature itself. + if (key.key_type == Certificate::KEY_TYPE_RSA) { + if (!RSA_verify(hash_nid, hash, key.hash_len, sig_der.data(), sig_der.size(), + key.rsa.get())) { + LOG(INFO) << "failed to verify against RSA key " << i; + continue; + } + + LOG(INFO) << "whole-file signature verified against RSA key " << i; + return VERIFY_SUCCESS; + } else if (key.key_type == Certificate::KEY_TYPE_EC && key.hash_len == SHA256_DIGEST_LENGTH) { + if (!ECDSA_verify(0, hash, key.hash_len, sig_der.data(), sig_der.size(), key.ec.get())) { + LOG(INFO) << "failed to verify against EC key " << i; + continue; + } + + LOG(INFO) << "whole-file signature verified against EC key " << i; + return VERIFY_SUCCESS; + } else { + LOG(INFO) << "Unknown key type " << key.key_type; + } + i++; + } + + if (need_sha1) { + LOG(INFO) << "SHA-1 digest: " << print_hex(sha1, SHA_DIGEST_LENGTH); + } + if (need_sha256) { + LOG(INFO) << "SHA-256 digest: " << print_hex(sha256, SHA256_DIGEST_LENGTH); + } + LOG(ERROR) << "failed to verify whole-file signature"; + return VERIFY_FAILURE; +} + +static std::vector<Certificate> IterateZipEntriesAndSearchForKeys(const ZipArchiveHandle& handle) { + void* cookie; + int32_t iter_status = StartIteration(handle, &cookie, "", "x509.pem"); + if (iter_status != 0) { + LOG(ERROR) << "Failed to iterate over entries in the certificate zipfile: " + << ErrorCodeString(iter_status); + return {}; + } + + std::vector<Certificate> result; + + std::string_view name; + ZipEntry64 entry; + while ((iter_status = Next(cookie, &entry, &name)) == 0) { + if (entry.uncompressed_length > std::numeric_limits<size_t>::max()) { + LOG(ERROR) << "Failed to extract " << name + << " because's uncompressed size exceeds size of address space. " + << entry.uncompressed_length; + return {}; + } + std::vector<uint8_t> pem_content(entry.uncompressed_length); + if (int32_t extract_status = + ExtractToMemory(handle, &entry, pem_content.data(), pem_content.size()); + extract_status != 0) { + LOG(ERROR) << "Failed to extract " << name; + return {}; + } + + Certificate cert(0, Certificate::KEY_TYPE_RSA, nullptr, nullptr); + // Aborts the parsing if we fail to load one of the key file. + if (!LoadCertificateFromBuffer(pem_content, &cert)) { + LOG(ERROR) << "Failed to load keys from " << name; + return {}; + } + + result.emplace_back(std::move(cert)); + } + + if (iter_status != -1) { + LOG(ERROR) << "Error while iterating over zip entries: " << ErrorCodeString(iter_status); + return {}; + } + + return result; +} + +std::vector<Certificate> LoadKeysFromZipfile(const std::string& zip_name) { + ZipArchiveHandle handle; + if (int32_t open_status = OpenArchive(zip_name.c_str(), &handle); open_status != 0) { + LOG(ERROR) << "Failed to open " << zip_name << ": " << ErrorCodeString(open_status); + return {}; + } + + std::vector<Certificate> result = IterateZipEntriesAndSearchForKeys(handle); + CloseArchive(handle); + return result; +} + +bool CheckRSAKey(const std::unique_ptr<RSA, RSADeleter>& rsa) { + if (!rsa) { + return false; + } + + const BIGNUM* out_n; + const BIGNUM* out_e; + RSA_get0_key(rsa.get(), &out_n, &out_e, nullptr /* private exponent */); + auto modulus_bits = BN_num_bits(out_n); + if (modulus_bits != 2048 && modulus_bits != 4096) { + LOG(ERROR) << "Modulus should be 2048 or 4096 bits long, actual: " << modulus_bits; + return false; + } + + BN_ULONG exponent = BN_get_word(out_e); + if (exponent != 3 && exponent != 65537) { + LOG(ERROR) << "Public exponent should be 3 or 65537, actual: " << exponent; + return false; + } + + return true; +} + +bool CheckECKey(const std::unique_ptr<EC_KEY, ECKEYDeleter>& ec_key) { + if (!ec_key) { + return false; + } + + const EC_GROUP* ec_group = EC_KEY_get0_group(ec_key.get()); + if (!ec_group) { + LOG(ERROR) << "Failed to get the ec_group from the ec_key"; + return false; + } + auto degree = EC_GROUP_get_degree(ec_group); + if (degree != 256) { + LOG(ERROR) << "Field size of the ec key should be 256 bits long, actual: " << degree; + return false; + } + + return true; +} + +bool LoadCertificateFromBuffer(const std::vector<uint8_t>& pem_content, Certificate* cert) { + std::unique_ptr<BIO, decltype(&BIO_free)> content( + BIO_new_mem_buf(pem_content.data(), pem_content.size()), BIO_free); + + std::unique_ptr<X509, decltype(&X509_free)> x509( + PEM_read_bio_X509(content.get(), nullptr, nullptr, nullptr), X509_free); + if (!x509) { + LOG(ERROR) << "Failed to read x509 certificate"; + return false; + } + + int nid = X509_get_signature_nid(x509.get()); + switch (nid) { + // SignApk has historically accepted md5WithRSA certificates, but treated them as + // sha1WithRSA anyway. Continue to do so for backwards compatibility. + case NID_md5WithRSA: + case NID_md5WithRSAEncryption: + case NID_sha1WithRSA: + case NID_sha1WithRSAEncryption: + cert->hash_len = SHA_DIGEST_LENGTH; + break; + case NID_sha256WithRSAEncryption: + case NID_ecdsa_with_SHA256: + cert->hash_len = SHA256_DIGEST_LENGTH; + break; + default: + LOG(ERROR) << "Unrecognized signature nid " << OBJ_nid2ln(nid); + return false; + } + + std::unique_ptr<EVP_PKEY, decltype(&EVP_PKEY_free)> public_key(X509_get_pubkey(x509.get()), + EVP_PKEY_free); + if (!public_key) { + LOG(ERROR) << "Failed to extract the public key from x509 certificate"; + return false; + } + + int key_type = EVP_PKEY_id(public_key.get()); + if (key_type == EVP_PKEY_RSA) { + cert->key_type = Certificate::KEY_TYPE_RSA; + cert->ec.reset(); + cert->rsa.reset(EVP_PKEY_get1_RSA(public_key.get())); + if (!cert->rsa || !CheckRSAKey(cert->rsa)) { + LOG(ERROR) << "Failed to validate the rsa key info from public key"; + return false; + } + } else if (key_type == EVP_PKEY_EC) { + cert->key_type = Certificate::KEY_TYPE_EC; + cert->rsa.reset(); + cert->ec.reset(EVP_PKEY_get1_EC_KEY(public_key.get())); + if (!cert->ec || !CheckECKey(cert->ec)) { + LOG(ERROR) << "Failed to validate the ec key info from the public key"; + return false; + } + } else { + LOG(ERROR) << "Unrecognized public key type " << OBJ_nid2ln(key_type); + return false; + } + + return true; +} |