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platform_system_security/keystore-engine/android_engine.cpp
David Benjamin dc4d142303 Replace custom BoringSSL scopers with bssl::UniquePtr. 
BoringSSL already provides C++ scopers.

Test: mma
Change-Id: I34d4ec36fc0b51750560be0886768a83fe69fbf5
2019-08-08 13:13:54 -04:00

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/* Copyright 2014 The Android Open Source Project
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
#define LOG_TAG "keystore-engine"
#include <pthread.h>
#include <sys/socket.h>
#include <stdarg.h>
#include <string.h>
#include <unistd.h>
#include <log/log.h>
#include <openssl/bn.h>
#include <openssl/ec.h>
#include <openssl/ec_key.h>
#include <openssl/ecdsa.h>
#include <openssl/engine.h>
#include <openssl/evp.h>
#include <openssl/rsa.h>
#include <openssl/x509.h>
#include <memory>
#ifndef BACKEND_WIFI_HIDL
#include "keystore_backend_binder.h"
#else
#include "keystore_backend_hidl.h"
#endif
namespace {
KeystoreBackend *g_keystore_backend;
void ensure_keystore_engine();
/* key_id_dup is called when one of the RSA or EC_KEY objects is duplicated. */
int key_id_dup(CRYPTO_EX_DATA* /* to */,
const CRYPTO_EX_DATA* /* from */,
void** from_d,
int /* index */,
long /* argl */,
void* /* argp */) {
char *key_id = reinterpret_cast<char *>(*from_d);
if (key_id != nullptr) {
*from_d = strdup(key_id);
}
return 1;
}
/* key_id_free is called when one of the RSA, DSA or EC_KEY object is freed. */
void key_id_free(void* /* parent */,
void* ptr,
CRYPTO_EX_DATA* /* ad */,
int /* index */,
long /* argl */,
void* /* argp */) {
char *key_id = reinterpret_cast<char *>(ptr);
free(key_id);
}
/* Many OpenSSL APIs take ownership of an argument on success but don't free
* the argument on failure. This means we need to tell our scoped pointers when
* we've transferred ownership, without triggering a warning by not using the
* result of release(). */
#define OWNERSHIP_TRANSFERRED(obj) auto _dummy __attribute__((unused)) = (obj).release()
const char* rsa_get_key_id(const RSA* rsa);
/* rsa_private_transform takes a big-endian integer from |in|, calculates the
* d'th power of it, modulo the RSA modulus, and writes the result as a
* big-endian integer to |out|. Both |in| and |out| are |len| bytes long. It
* returns one on success and zero otherwise. */
int rsa_private_transform(RSA *rsa, uint8_t *out, const uint8_t *in, size_t len) {
ALOGV("rsa_private_transform(%p, %p, %p, %u)", rsa, out, in, (unsigned) len);
ensure_keystore_engine();
const char *key_id = rsa_get_key_id(rsa);
if (key_id == nullptr) {
ALOGE("key had no key_id!");
return 0;
}
uint8_t* reply = nullptr;
size_t reply_len;
int32_t ret = g_keystore_backend->sign(key_id, in, len, &reply, &reply_len);
if (ret < 0) {
ALOGW("There was an error during rsa_decrypt: could not connect");
return 0;
} else if (ret != 0) {
ALOGW("Error during sign from keystore: %d", ret);
return 0;
} else if (reply_len == 0 || reply == nullptr) {
ALOGW("No valid signature returned");
return 0;
}
if (reply_len > len) {
/* The result of the RSA operation can never be larger than the size of
* the modulus so we assume that the result has extra zeros on the
* left. This provides attackers with an oracle, but there's nothing
* that we can do about it here. */
ALOGW("Reply len %zu greater than expected %zu", reply_len, len);
memcpy(out, &reply[reply_len - len], len);
} else if (reply_len < len) {
/* If the Keystore implementation returns a short value we assume that
* it's because it removed leading zeros from the left side. This is
* bad because it provides attackers with an oracle but we cannot do
* anything about a broken Keystore implementation here. */
ALOGW("Reply len %zu lesser than expected %zu", reply_len, len);
memset(out, 0, len);
memcpy(out + len - reply_len, &reply[0], reply_len);
} else {
memcpy(out, &reply[0], len);
}
ALOGV("rsa=%p keystore_rsa_priv_dec successful", rsa);
return 1;
}
const char* ecdsa_get_key_id(const EC_KEY* ec_key);
/* ecdsa_sign signs |digest_len| bytes from |digest| with |ec_key| and writes
* the resulting signature (an ASN.1 encoded blob) to |sig|. It returns one on
* success and zero otherwise. */
static int ecdsa_sign(const uint8_t* digest, size_t digest_len, uint8_t* sig,
unsigned int* sig_len, EC_KEY* ec_key) {
ALOGV("ecdsa_sign(%p, %u, %p)", digest, (unsigned) digest_len, ec_key);
ensure_keystore_engine();
const char *key_id = ecdsa_get_key_id(ec_key);
if (key_id == nullptr) {
ALOGE("key had no key_id!");
return 0;
}
size_t ecdsa_size = ECDSA_size(ec_key);
uint8_t* reply = nullptr;
size_t reply_len;
int32_t ret = g_keystore_backend->sign(
key_id, digest, digest_len, &reply, &reply_len);
if (ret < 0) {
ALOGW("There was an error during ecdsa_sign: could not connect");
return 0;
} else if (reply_len == 0 || reply == nullptr) {
ALOGW("No valid signature returned");
return 0;
} else if (reply_len > ecdsa_size) {
ALOGW("Signature is too large");
return 0;
}
// Reviewer: should't sig_len be checked here? Or is it just assumed that it is at least ecdsa_size?
memcpy(sig, &reply[0], reply_len);
*sig_len = reply_len;
ALOGV("ecdsa_sign(%p, %u, %p) => success", digest, (unsigned)digest_len,
ec_key);
return 1;
}
/* KeystoreEngine is a BoringSSL ENGINE that implements RSA and ECDSA by
* forwarding the requested operations to Keystore. */
class KeystoreEngine {
public:
KeystoreEngine()
: rsa_index_(RSA_get_ex_new_index(0 /* argl */,
nullptr /* argp */,
nullptr /* new_func */,
key_id_dup,
key_id_free)),
ec_key_index_(EC_KEY_get_ex_new_index(0 /* argl */,
nullptr /* argp */,
nullptr /* new_func */,
key_id_dup,
key_id_free)),
engine_(ENGINE_new()) {
memset(&rsa_method_, 0, sizeof(rsa_method_));
rsa_method_.common.is_static = 1;
rsa_method_.private_transform = rsa_private_transform;
rsa_method_.flags = RSA_FLAG_OPAQUE;
ENGINE_set_RSA_method(engine_, &rsa_method_, sizeof(rsa_method_));
memset(&ecdsa_method_, 0, sizeof(ecdsa_method_));
ecdsa_method_.common.is_static = 1;
ecdsa_method_.sign = ecdsa_sign;
ecdsa_method_.flags = ECDSA_FLAG_OPAQUE;
ENGINE_set_ECDSA_method(engine_, &ecdsa_method_, sizeof(ecdsa_method_));
}
int rsa_ex_index() const { return rsa_index_; }
int ec_key_ex_index() const { return ec_key_index_; }
const ENGINE* engine() const { return engine_; }
private:
const int rsa_index_;
const int ec_key_index_;
RSA_METHOD rsa_method_;
ECDSA_METHOD ecdsa_method_;
ENGINE* const engine_;
};
pthread_once_t g_keystore_engine_once = PTHREAD_ONCE_INIT;
KeystoreEngine *g_keystore_engine;
/* init_keystore_engine is called to initialize |g_keystore_engine|. This
* should only be called by |pthread_once|. */
void init_keystore_engine() {
g_keystore_engine = new KeystoreEngine;
#ifndef BACKEND_WIFI_HIDL
g_keystore_backend = new KeystoreBackendBinder;
#else
g_keystore_backend = new KeystoreBackendHidl;
#endif
}
/* ensure_keystore_engine ensures that |g_keystore_engine| is pointing to a
* valid |KeystoreEngine| object and creates one if not. */
void ensure_keystore_engine() {
pthread_once(&g_keystore_engine_once, init_keystore_engine);
}
const char* rsa_get_key_id(const RSA* rsa) {
return reinterpret_cast<char*>(
RSA_get_ex_data(rsa, g_keystore_engine->rsa_ex_index()));
}
const char* ecdsa_get_key_id(const EC_KEY* ec_key) {
return reinterpret_cast<char*>(
EC_KEY_get_ex_data(ec_key, g_keystore_engine->ec_key_ex_index()));
}
/* wrap_rsa returns an |EVP_PKEY| that contains an RSA key where the public
* part is taken from |public_rsa| and the private operations are forwarded to
* KeyStore and operate on the key named |key_id|. */
static EVP_PKEY *wrap_rsa(const char *key_id, const RSA *public_rsa) {
bssl::UniquePtr<RSA> rsa(RSA_new_method(g_keystore_engine->engine()));
if (rsa.get() == nullptr) {
return nullptr;
}
char *key_id_copy = strdup(key_id);
if (key_id_copy == nullptr) {
return nullptr;
}
if (!RSA_set_ex_data(rsa.get(), g_keystore_engine->rsa_ex_index(),
key_id_copy)) {
free(key_id_copy);
return nullptr;
}
rsa->n = BN_dup(public_rsa->n);
rsa->e = BN_dup(public_rsa->e);
if (rsa->n == nullptr || rsa->e == nullptr) {
return nullptr;
}
bssl::UniquePtr<EVP_PKEY> result(EVP_PKEY_new());
if (result.get() == nullptr ||
!EVP_PKEY_assign_RSA(result.get(), rsa.get())) {
return nullptr;
}
OWNERSHIP_TRANSFERRED(rsa);
return result.release();
}
/* wrap_ecdsa returns an |EVP_PKEY| that contains an ECDSA key where the public
* part is taken from |public_rsa| and the private operations are forwarded to
* KeyStore and operate on the key named |key_id|. */
static EVP_PKEY *wrap_ecdsa(const char *key_id, const EC_KEY *public_ecdsa) {
bssl::UniquePtr<EC_KEY> ec(EC_KEY_new_method(g_keystore_engine->engine()));
if (ec.get() == nullptr) {
return nullptr;
}
if (!EC_KEY_set_group(ec.get(), EC_KEY_get0_group(public_ecdsa)) ||
!EC_KEY_set_public_key(ec.get(), EC_KEY_get0_public_key(public_ecdsa))) {
return nullptr;
}
char *key_id_copy = strdup(key_id);
if (key_id_copy == nullptr) {
return nullptr;
}
if (!EC_KEY_set_ex_data(ec.get(), g_keystore_engine->ec_key_ex_index(),
key_id_copy)) {
free(key_id_copy);
return nullptr;
}
bssl::UniquePtr<EVP_PKEY> result(EVP_PKEY_new());
if (result.get() == nullptr ||
!EVP_PKEY_assign_EC_KEY(result.get(), ec.get())) {
return nullptr;
}
OWNERSHIP_TRANSFERRED(ec);
return result.release();
}
} /* anonymous namespace */
extern "C" {
EVP_PKEY* EVP_PKEY_from_keystore(const char* key_id) __attribute__((visibility("default")));
/* EVP_PKEY_from_keystore returns an |EVP_PKEY| that contains either an RSA or
* ECDSA key where the public part of the key reflects the value of the key
* named |key_id| in Keystore and the private operations are forwarded onto
* KeyStore. */
EVP_PKEY* EVP_PKEY_from_keystore(const char* key_id) {
ALOGV("EVP_PKEY_from_keystore(\"%s\")", key_id);
ensure_keystore_engine();
uint8_t *pubkey = nullptr;
size_t pubkey_len;
int32_t ret = g_keystore_backend->get_pubkey(key_id, &pubkey, &pubkey_len);
if (ret < 0) {
ALOGW("could not contact keystore");
return nullptr;
} else if (ret != 0 || pubkey == nullptr) {
ALOGW("keystore reports error: %d", ret);
return nullptr;
}
const uint8_t *inp = pubkey;
bssl::UniquePtr<EVP_PKEY> pkey(d2i_PUBKEY(nullptr, &inp, pubkey_len));
if (pkey.get() == nullptr) {
ALOGW("Cannot convert pubkey");
return nullptr;
}
EVP_PKEY *result;
switch (EVP_PKEY_type(pkey->type)) {
case EVP_PKEY_RSA: {
bssl::UniquePtr<RSA> public_rsa(EVP_PKEY_get1_RSA(pkey.get()));
result = wrap_rsa(key_id, public_rsa.get());
break;
}
case EVP_PKEY_EC: {
bssl::UniquePtr<EC_KEY> public_ecdsa(EVP_PKEY_get1_EC_KEY(pkey.get()));
result = wrap_ecdsa(key_id, public_ecdsa.get());
break;
}
default:
ALOGE("Unsupported key type %d", EVP_PKEY_type(pkey->type));
result = nullptr;
}
return result;
}
} // extern "C"
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