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;
+}