KeyUtil.cpp - SHIFTPHONES/android_system_vold - Gitiles

 /*
  * Copyright (C) 2016 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 "KeyUtil.h"

 #include <iomanip>
 #include <sstream>
 #include <string>

 #include <fcntl.h>
 #include <linux/fscrypt.h>
 #include <openssl/sha.h>
 #include <sys/ioctl.h>

 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/properties.h>
 #include <keyutils.h>

 #include "KeyStorage.h"
 #include "Utils.h"

 namespace android {
 namespace vold {

 using android::fscrypt::EncryptionOptions;
 using android::fscrypt::EncryptionPolicy;

 const KeyGeneration neverGen() {
     return KeyGeneration{0, false, false};
 }

 static bool randomKey(size_t size, KeyBuffer* key) {
     *key = KeyBuffer(size);
     if (ReadRandomBytes(key->size(), key->data()) != 0) {
         // TODO status_t plays badly with PLOG, fix it.
         LOG(ERROR) << "Random read failed";
         return false;
     }
     return true;
 }

 bool generateStorageKey(const KeyGeneration& gen, KeyBuffer* key) {
     if (!gen.allow_gen) {
         LOG(ERROR) << "Generating storage key not allowed";
         return false;
     }
     if (gen.use_hw_wrapped_key) {
         if (gen.keysize != FSCRYPT_MAX_KEY_SIZE) {
             LOG(ERROR) << "Cannot generate a wrapped key " << gen.keysize << " bytes long";
             return false;
         }
         LOG(DEBUG) << "Generating wrapped storage key";
         return generateWrappedStorageKey(key);
     } else {
         LOG(DEBUG) << "Generating standard storage key";
         return randomKey(gen.keysize, key);
     }
 }

 static bool isFsKeyringSupportedImpl() {
     android::base::unique_fd fd(open("/data", O_RDONLY | O_DIRECTORY | O_CLOEXEC));

     // FS_IOC_ADD_ENCRYPTION_KEY with a NULL argument will fail with ENOTTY if
     // the ioctl isn't supported.  Otherwise it will fail with another error
     // code such as EFAULT.
     //
     // Note that there's no need to check for FS_IOC_REMOVE_ENCRYPTION_KEY,
     // since it's guaranteed to be available if FS_IOC_ADD_ENCRYPTION_KEY is.
     // There's also no need to check for support on external volumes separately
     // from /data, since either the kernel supports the ioctls on all
     // fscrypt-capable filesystems or it doesn't.
     errno = 0;
     (void)ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, NULL);
     if (errno == ENOTTY) {
         LOG(INFO) << "Kernel doesn't support FS_IOC_ADD_ENCRYPTION_KEY.  Falling back to "
                      "session keyring";
         return false;
     }
     if (errno != EFAULT) {
         PLOG(WARNING) << "Unexpected error from FS_IOC_ADD_ENCRYPTION_KEY";
     }
     LOG(DEBUG) << "Detected support for FS_IOC_ADD_ENCRYPTION_KEY";
     android::base::SetProperty("ro.crypto.uses_fs_ioc_add_encryption_key", "true");
     return true;
 }

 // Return true if the kernel supports the ioctls to add/remove fscrypt keys
 // directly to/from the filesystem.
 bool isFsKeyringSupported(void) {
     static bool supported = isFsKeyringSupportedImpl();
     return supported;
 }

 // Get raw keyref - used to make keyname and to pass to ioctl
 static std::string generateKeyRef(const uint8_t* key, int length) {
     SHA512_CTX c;

     SHA512_Init(&c);
     SHA512_Update(&c, key, length);
     unsigned char key_ref1[SHA512_DIGEST_LENGTH];
     SHA512_Final(key_ref1, &c);

     SHA512_Init(&c);
     SHA512_Update(&c, key_ref1, SHA512_DIGEST_LENGTH);
     unsigned char key_ref2[SHA512_DIGEST_LENGTH];
     SHA512_Final(key_ref2, &c);

     static_assert(FSCRYPT_KEY_DESCRIPTOR_SIZE <= SHA512_DIGEST_LENGTH,
                   "Hash too short for descriptor");
     return std::string((char*)key_ref2, FSCRYPT_KEY_DESCRIPTOR_SIZE);
 }

 static bool fillKey(const KeyBuffer& key, fscrypt_key* fs_key) {
     if (key.size() != FSCRYPT_MAX_KEY_SIZE) {
         LOG(ERROR) << "Wrong size key " << key.size();
         return false;
     }
     static_assert(FSCRYPT_MAX_KEY_SIZE == sizeof(fs_key->raw), "Mismatch of max key sizes");
     fs_key->mode = 0;  // unused by kernel
     memcpy(fs_key->raw, key.data(), key.size());
     fs_key->size = key.size();
     return true;
 }

 static char const* const NAME_PREFIXES[] = {"ext4", "f2fs", "fscrypt", nullptr};

 static std::string keyrefstring(const std::string& raw_ref) {
     std::ostringstream o;
     for (unsigned char i : raw_ref) {
         o << std::hex << std::setw(2) << std::setfill('0') << (int)i;
     }
     return o.str();
 }

 static std::string buildLegacyKeyName(const std::string& prefix, const std::string& raw_ref) {
     return prefix + ":" + keyrefstring(raw_ref);
 }

 // Get the ID of the keyring we store all fscrypt keys in when the kernel is too
 // old to support FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY.
 static bool fscryptKeyring(key_serial_t* device_keyring) {
     *device_keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "fscrypt", 0);
     if (*device_keyring == -1) {
         PLOG(ERROR) << "Unable to find device keyring";
         return false;
     }
     return true;
 }

 // Add an encryption key of type "logon" to the global session keyring.
 static bool installKeyLegacy(const KeyBuffer& key, const std::string& raw_ref) {
     // Place fscrypt_key into automatically zeroing buffer.
     KeyBuffer fsKeyBuffer(sizeof(fscrypt_key));
     fscrypt_key& fs_key = *reinterpret_cast<fscrypt_key*>(fsKeyBuffer.data());

     if (!fillKey(key, &fs_key)) return false;
     key_serial_t device_keyring;
     if (!fscryptKeyring(&device_keyring)) return false;
     for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
         auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
         key_serial_t key_id =
             add_key("logon", ref.c_str(), (void*)&fs_key, sizeof(fs_key), device_keyring);
         if (key_id == -1) {
             PLOG(ERROR) << "Failed to insert key into keyring " << device_keyring;
             return false;
         }
         LOG(DEBUG) << "Added key " << key_id << " (" << ref << ") to keyring " << device_keyring
                    << " in process " << getpid();
     }
     return true;
 }

 // Installs fscrypt-provisioning key into session level kernel keyring.
 // This allows for the given key to be installed back into filesystem keyring.
 // For more context see reloadKeyFromSessionKeyring.
 static bool installProvisioningKey(const KeyBuffer& key, const std::string& ref,
                                    const fscrypt_key_specifier& key_spec) {
     key_serial_t device_keyring;
     if (!fscryptKeyring(&device_keyring)) return false;

     // Place fscrypt_provisioning_key_payload into automatically zeroing buffer.
     KeyBuffer buf(sizeof(fscrypt_provisioning_key_payload) + key.size(), 0);
     fscrypt_provisioning_key_payload& provisioning_key =
             *reinterpret_cast<fscrypt_provisioning_key_payload*>(buf.data());
     memcpy(provisioning_key.raw, key.data(), key.size());
     provisioning_key.type = key_spec.type;

     key_serial_t key_id = add_key("fscrypt-provisioning", ref.c_str(), (void*)&provisioning_key,
                                   buf.size(), device_keyring);
     if (key_id == -1) {
         PLOG(ERROR) << "Failed to insert fscrypt-provisioning key for " << ref
                     << " into session keyring";
         return false;
     }
     LOG(DEBUG) << "Added fscrypt-provisioning key for " << ref << " to session keyring";
     return true;
 }

 // Build a struct fscrypt_key_specifier for use in the key management ioctls.
 static bool buildKeySpecifier(fscrypt_key_specifier* spec, const EncryptionPolicy& policy) {
     switch (policy.options.version) {
         case 1:
             if (policy.key_raw_ref.size() != FSCRYPT_KEY_DESCRIPTOR_SIZE) {
                 LOG(ERROR) << "Invalid key specifier size for v1 encryption policy: "
                            << policy.key_raw_ref.size();
                 return false;
             }
             spec->type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
             memcpy(spec->u.descriptor, policy.key_raw_ref.c_str(), FSCRYPT_KEY_DESCRIPTOR_SIZE);
             return true;
         case 2:
             if (policy.key_raw_ref.size() != FSCRYPT_KEY_IDENTIFIER_SIZE) {
                 LOG(ERROR) << "Invalid key specifier size for v2 encryption policy: "
                            << policy.key_raw_ref.size();
                 return false;
             }
             spec->type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
             memcpy(spec->u.identifier, policy.key_raw_ref.c_str(), FSCRYPT_KEY_IDENTIFIER_SIZE);
             return true;
         default:
             LOG(ERROR) << "Invalid encryption policy version: " << policy.options.version;
             return false;
     }
 }

 // Installs key into keyring of a filesystem mounted on |mountpoint|.
 //
 // It's callers responsibility to fill key specifier, and either arg->raw or arg->key_id.
 //
 // In case arg->key_spec.type equals to FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER
 // arg->key_spec.u.identifier will be populated with raw key reference generated
 // by kernel.
 //
 // For documentation on difference between arg->raw and arg->key_id see
 // https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#fs-ioc-add-encryption-key
 static bool installFsKeyringKey(const std::string& mountpoint, const EncryptionOptions& options,
                                 fscrypt_add_key_arg* arg) {
     if (options.use_hw_wrapped_key) arg->__flags |= __FSCRYPT_ADD_KEY_FLAG_HW_WRAPPED;

     android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
     if (fd == -1) {
         PLOG(ERROR) << "Failed to open " << mountpoint << " to install key";
         return false;
     }

     if (ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, arg) != 0) {
         PLOG(ERROR) << "Failed to install fscrypt key to " << mountpoint;
         return false;
     }

     return true;
 }

 bool installKey(const std::string& mountpoint, const EncryptionOptions& options,
                 const KeyBuffer& key, EncryptionPolicy* policy) {
     policy->options = options;
     // Put the fscrypt_add_key_arg in an automatically-zeroing buffer, since we
     // have to copy the raw key into it.
     KeyBuffer arg_buf(sizeof(struct fscrypt_add_key_arg) + key.size(), 0);
     struct fscrypt_add_key_arg* arg = (struct fscrypt_add_key_arg*)arg_buf.data();

     // Initialize the "key specifier", which is like a name for the key.
     switch (options.version) {
         case 1:
             // A key for a v1 policy is specified by an arbitrary 8-byte
             // "descriptor", which must be provided by userspace.  We use the
             // first 8 bytes from the double SHA-512 of the key itself.
             if (options.use_hw_wrapped_key) {
                 /* When wrapped key is supported, only the first 32 bytes are
                    the same per boot. The second 32 bytes can change as the ephemeral
                    key is different. */
                 policy->key_raw_ref = generateKeyRef((const uint8_t*)key.data(), key.size()/2);
             } else {
                 policy->key_raw_ref = generateKeyRef((const uint8_t*)key.data(), key.size());
             }
             if (!isFsKeyringSupported()) {
                 return installKeyLegacy(key, policy->key_raw_ref);
             }
             if (!buildKeySpecifier(&arg->key_spec, *policy)) {
                 return false;
             }
             break;
         case 2:
             // A key for a v2 policy is specified by an 16-byte "identifier",
             // which is a cryptographic hash of the key itself which the kernel
             // computes and returns.  Any user-provided value is ignored; we
             // just need to set the specifier type to indicate that we're adding
             // this type of key.
             arg->key_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
             break;
         default:
             LOG(ERROR) << "Invalid encryption policy version: " << options.version;
             return false;
     }

     arg->raw_size = key.size();
     memcpy(arg->raw, key.data(), key.size());

     if (!installFsKeyringKey(mountpoint, options, arg)) return false;

     if (arg->key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
         // Retrieve the key identifier that the kernel computed.
         policy->key_raw_ref =
                 std::string((char*)arg->key_spec.u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
     }
     std::string ref = keyrefstring(policy->key_raw_ref);
     LOG(DEBUG) << "Installed fscrypt key with ref " << ref << " to " << mountpoint;

     if (!installProvisioningKey(key, ref, arg->key_spec)) return false;
     return true;
 }

 // Remove an encryption key of type "logon" from the global session keyring.
 static bool evictKeyLegacy(const std::string& raw_ref) {
     key_serial_t device_keyring;
     if (!fscryptKeyring(&device_keyring)) return false;
     bool success = true;
     for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
         auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
         auto key_serial = keyctl_search(device_keyring, "logon", ref.c_str(), 0);

         // Unlink the key from the keyring.  Prefer unlinking to revoking or
         // invalidating, since unlinking is actually no less secure currently, and
         // it avoids bugs in certain kernel versions where the keyring key is
         // referenced from places it shouldn't be.
         if (keyctl_unlink(key_serial, device_keyring) != 0) {
             PLOG(ERROR) << "Failed to unlink key with serial " << key_serial << " ref " << ref;
             success = false;
         } else {
             LOG(DEBUG) << "Unlinked key with serial " << key_serial << " ref " << ref;
         }
     }
     return success;
 }

 static bool evictProvisioningKey(const std::string& ref) {
     key_serial_t device_keyring;
     if (!fscryptKeyring(&device_keyring)) {
         return false;
     }

     auto key_serial = keyctl_search(device_keyring, "fscrypt-provisioning", ref.c_str(), 0);
     if (key_serial == -1 && errno != ENOKEY) {
         PLOG(ERROR) << "Error searching session keyring for fscrypt-provisioning key for " << ref;
         return false;
     }

     if (key_serial != -1 && keyctl_unlink(key_serial, device_keyring) != 0) {
         PLOG(ERROR) << "Failed to unlink fscrypt-provisioning key for " << ref
                     << " from session keyring";
         return false;
     }
     return true;
 }

 bool evictKey(const std::string& mountpoint, const EncryptionPolicy& policy) {
     if (policy.options.version == 1 && !isFsKeyringSupported()) {
         return evictKeyLegacy(policy.key_raw_ref);
     }

     android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
     if (fd == -1) {
         PLOG(ERROR) << "Failed to open " << mountpoint << " to evict key";
         return false;
     }

     struct fscrypt_remove_key_arg arg;
     memset(&arg, 0, sizeof(arg));

     if (!buildKeySpecifier(&arg.key_spec, policy)) {
         return false;
     }

     std::string ref = keyrefstring(policy.key_raw_ref);

     if (ioctl(fd, FS_IOC_REMOVE_ENCRYPTION_KEY, &arg) != 0) {
         PLOG(ERROR) << "Failed to evict fscrypt key with ref " << ref << " from " << mountpoint;
         return false;
     }

     LOG(DEBUG) << "Evicted fscrypt key with ref " << ref << " from " << mountpoint;
     if (arg.removal_status_flags & FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS) {
         // Should never happen because keys are only added/removed as root.
         LOG(ERROR) << "Unexpected case: key with ref " << ref << " is still added by other users!";
     } else if (arg.removal_status_flags & FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY) {
         LOG(ERROR) << "Files still open after removing key with ref " << ref
                    << ".  These files were not locked!";
     }

     if (!evictProvisioningKey(ref)) return false;
     return true;
 }

 bool retrieveOrGenerateKey(const std::string& key_path, const std::string& tmp_path,
                            const KeyAuthentication& key_authentication, const KeyGeneration& gen,
                            KeyBuffer* key) {
     if (pathExists(key_path)) {
         LOG(DEBUG) << "Key exists, using: " << key_path;
         if (!retrieveKey(key_path, key_authentication, key)) return false;
     } else {
         if (!gen.allow_gen) {
             LOG(ERROR) << "No key found in " << key_path;
             return false;
         }
         LOG(INFO) << "Creating new key in " << key_path;
         if (!generateStorageKey(gen, key)) return false;
         if (!storeKeyAtomically(key_path, tmp_path, key_authentication, *key)) return false;
     }
     return true;
 }

 bool reloadKeyFromSessionKeyring(const std::string& mountpoint, const EncryptionPolicy& policy) {
     key_serial_t device_keyring;
     if (!fscryptKeyring(&device_keyring)) {
         return false;
     }

     std::string ref = keyrefstring(policy.key_raw_ref);
     auto key_serial = keyctl_search(device_keyring, "fscrypt-provisioning", ref.c_str(), 0);
     if (key_serial == -1) {
         PLOG(ERROR) << "Failed to find fscrypt-provisioning key for " << ref
                     << " in session keyring";
         return false;
     }

     LOG(DEBUG) << "Installing fscrypt-provisioning key for " << ref << " back into " << mountpoint
                << " fs-keyring";

     struct fscrypt_add_key_arg arg;
     memset(&arg, 0, sizeof(arg));
     if (!buildKeySpecifier(&arg.key_spec, policy)) return false;
     arg.key_id = key_serial;
     if (!installFsKeyringKey(mountpoint, policy.options, &arg)) return false;

     return true;
 }

 }  // namespace vold
 }  // namespace android
	/*
	* Copyright (C) 2016 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 "KeyUtil.h"

	#include <iomanip>
	#include <sstream>
	#include <string>

	#include <fcntl.h>
	#include <linux/fscrypt.h>
	#include <openssl/sha.h>
	#include <sys/ioctl.h>

	#include <android-base/file.h>
	#include <android-base/logging.h>
	#include <android-base/properties.h>
	#include <keyutils.h>

	#include "KeyStorage.h"
	#include "Utils.h"

	namespace android {
	namespace vold {

	using android::fscrypt::EncryptionOptions;
	using android::fscrypt::EncryptionPolicy;

	const KeyGeneration neverGen() {
	return KeyGeneration{0, false, false};
	}

	static bool randomKey(size_t size, KeyBuffer* key) {
	*key = KeyBuffer(size);
	if (ReadRandomBytes(key->size(), key->data()) != 0) {
	// TODO status_t plays badly with PLOG, fix it.
	LOG(ERROR) << "Random read failed";
	return false;
	}
	return true;
	}

	bool generateStorageKey(const KeyGeneration& gen, KeyBuffer* key) {
	if (!gen.allow_gen) {
	LOG(ERROR) << "Generating storage key not allowed";
	return false;
	}
	if (gen.use_hw_wrapped_key) {
	if (gen.keysize != FSCRYPT_MAX_KEY_SIZE) {
	LOG(ERROR) << "Cannot generate a wrapped key " << gen.keysize << " bytes long";
	return false;
	}
	LOG(DEBUG) << "Generating wrapped storage key";
	return generateWrappedStorageKey(key);
	} else {
	LOG(DEBUG) << "Generating standard storage key";
	return randomKey(gen.keysize, key);
	}
	}

	static bool isFsKeyringSupportedImpl() {
	android::base::unique_fd fd(open("/data", O_RDONLY \| O_DIRECTORY \| O_CLOEXEC));

	// FS_IOC_ADD_ENCRYPTION_KEY with a NULL argument will fail with ENOTTY if
	// the ioctl isn't supported. Otherwise it will fail with another error
	// code such as EFAULT.
	//
	// Note that there's no need to check for FS_IOC_REMOVE_ENCRYPTION_KEY,
	// since it's guaranteed to be available if FS_IOC_ADD_ENCRYPTION_KEY is.
	// There's also no need to check for support on external volumes separately
	// from /data, since either the kernel supports the ioctls on all
	// fscrypt-capable filesystems or it doesn't.
	errno = 0;
	(void)ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, NULL);
	if (errno == ENOTTY) {
	LOG(INFO) << "Kernel doesn't support FS_IOC_ADD_ENCRYPTION_KEY. Falling back to "
	"session keyring";
	return false;
	}
	if (errno != EFAULT) {
	PLOG(WARNING) << "Unexpected error from FS_IOC_ADD_ENCRYPTION_KEY";
	}
	LOG(DEBUG) << "Detected support for FS_IOC_ADD_ENCRYPTION_KEY";
	android::base::SetProperty("ro.crypto.uses_fs_ioc_add_encryption_key", "true");
	return true;
	}

	// Return true if the kernel supports the ioctls to add/remove fscrypt keys
	// directly to/from the filesystem.
	bool isFsKeyringSupported(void) {
	static bool supported = isFsKeyringSupportedImpl();
	return supported;
	}

	// Get raw keyref - used to make keyname and to pass to ioctl
	static std::string generateKeyRef(const uint8_t* key, int length) {
	SHA512_CTX c;

	SHA512_Init(&c);
	SHA512_Update(&c, key, length);
	unsigned char key_ref1[SHA512_DIGEST_LENGTH];
	SHA512_Final(key_ref1, &c);

	SHA512_Init(&c);
	SHA512_Update(&c, key_ref1, SHA512_DIGEST_LENGTH);
	unsigned char key_ref2[SHA512_DIGEST_LENGTH];
	SHA512_Final(key_ref2, &c);

	static_assert(FSCRYPT_KEY_DESCRIPTOR_SIZE <= SHA512_DIGEST_LENGTH,
	"Hash too short for descriptor");
	return std::string((char*)key_ref2, FSCRYPT_KEY_DESCRIPTOR_SIZE);
	}

	static bool fillKey(const KeyBuffer& key, fscrypt_key* fs_key) {
	if (key.size() != FSCRYPT_MAX_KEY_SIZE) {
	LOG(ERROR) << "Wrong size key " << key.size();
	return false;
	}
	static_assert(FSCRYPT_MAX_KEY_SIZE == sizeof(fs_key->raw), "Mismatch of max key sizes");
	fs_key->mode = 0; // unused by kernel
	memcpy(fs_key->raw, key.data(), key.size());
	fs_key->size = key.size();
	return true;
	}

	static char const* const NAME_PREFIXES[] = {"ext4", "f2fs", "fscrypt", nullptr};

	static std::string keyrefstring(const std::string& raw_ref) {
	std::ostringstream o;
	for (unsigned char i : raw_ref) {
	o << std::hex << std::setw(2) << std::setfill('0') << (int)i;
	}
	return o.str();
	}

	static std::string buildLegacyKeyName(const std::string& prefix, const std::string& raw_ref) {
	return prefix + ":" + keyrefstring(raw_ref);
	}

	// Get the ID of the keyring we store all fscrypt keys in when the kernel is too
	// old to support FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY.
	static bool fscryptKeyring(key_serial_t* device_keyring) {
	*device_keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "fscrypt", 0);
	if (*device_keyring == -1) {
	PLOG(ERROR) << "Unable to find device keyring";
	return false;
	}
	return true;
	}

	// Add an encryption key of type "logon" to the global session keyring.
	static bool installKeyLegacy(const KeyBuffer& key, const std::string& raw_ref) {
	// Place fscrypt_key into automatically zeroing buffer.
	KeyBuffer fsKeyBuffer(sizeof(fscrypt_key));
	fscrypt_key& fs_key = reinterpret_cast<fscrypt_key>(fsKeyBuffer.data());

	if (!fillKey(key, &fs_key)) return false;
	key_serial_t device_keyring;
	if (!fscryptKeyring(&device_keyring)) return false;
	for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
	auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
	key_serial_t key_id =
	add_key("logon", ref.c_str(), (void*)&fs_key, sizeof(fs_key), device_keyring);
	if (key_id == -1) {
	PLOG(ERROR) << "Failed to insert key into keyring " << device_keyring;
	return false;
	}
	LOG(DEBUG) << "Added key " << key_id << " (" << ref << ") to keyring " << device_keyring
	<< " in process " << getpid();
	}
	return true;
	}

	// Installs fscrypt-provisioning key into session level kernel keyring.
	// This allows for the given key to be installed back into filesystem keyring.
	// For more context see reloadKeyFromSessionKeyring.
	static bool installProvisioningKey(const KeyBuffer& key, const std::string& ref,
	const fscrypt_key_specifier& key_spec) {
	key_serial_t device_keyring;
	if (!fscryptKeyring(&device_keyring)) return false;

	// Place fscrypt_provisioning_key_payload into automatically zeroing buffer.
	KeyBuffer buf(sizeof(fscrypt_provisioning_key_payload) + key.size(), 0);
	fscrypt_provisioning_key_payload& provisioning_key =
	reinterpret_cast<fscrypt_provisioning_key_payload>(buf.data());
	memcpy(provisioning_key.raw, key.data(), key.size());
	provisioning_key.type = key_spec.type;

	key_serial_t key_id = add_key("fscrypt-provisioning", ref.c_str(), (void*)&provisioning_key,
	buf.size(), device_keyring);
	if (key_id == -1) {
	PLOG(ERROR) << "Failed to insert fscrypt-provisioning key for " << ref
	<< " into session keyring";
	return false;
	}
	LOG(DEBUG) << "Added fscrypt-provisioning key for " << ref << " to session keyring";
	return true;
	}

	// Build a struct fscrypt_key_specifier for use in the key management ioctls.
	static bool buildKeySpecifier(fscrypt_key_specifier* spec, const EncryptionPolicy& policy) {
	switch (policy.options.version) {
	case 1:
	if (policy.key_raw_ref.size() != FSCRYPT_KEY_DESCRIPTOR_SIZE) {
	LOG(ERROR) << "Invalid key specifier size for v1 encryption policy: "
	<< policy.key_raw_ref.size();
	return false;
	}
	spec->type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
	memcpy(spec->u.descriptor, policy.key_raw_ref.c_str(), FSCRYPT_KEY_DESCRIPTOR_SIZE);
	return true;
	case 2:
	if (policy.key_raw_ref.size() != FSCRYPT_KEY_IDENTIFIER_SIZE) {
	LOG(ERROR) << "Invalid key specifier size for v2 encryption policy: "
	<< policy.key_raw_ref.size();
	return false;
	}
	spec->type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
	memcpy(spec->u.identifier, policy.key_raw_ref.c_str(), FSCRYPT_KEY_IDENTIFIER_SIZE);
	return true;
	default:
	LOG(ERROR) << "Invalid encryption policy version: " << policy.options.version;
	return false;
	}
	}

	// Installs key into keyring of a filesystem mounted on \|mountpoint\|.
	//
	// It's callers responsibility to fill key specifier, and either arg->raw or arg->key_id.
	//
	// In case arg->key_spec.type equals to FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER
	// arg->key_spec.u.identifier will be populated with raw key reference generated
	// by kernel.
	//
	// For documentation on difference between arg->raw and arg->key_id see
	// https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#fs-ioc-add-encryption-key
	static bool installFsKeyringKey(const std::string& mountpoint, const EncryptionOptions& options,
	fscrypt_add_key_arg* arg) {
	if (options.use_hw_wrapped_key) arg->__flags \|= __FSCRYPT_ADD_KEY_FLAG_HW_WRAPPED;

	android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY \| O_DIRECTORY \| O_CLOEXEC));
	if (fd == -1) {
	PLOG(ERROR) << "Failed to open " << mountpoint << " to install key";
	return false;
	}

	if (ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, arg) != 0) {
	PLOG(ERROR) << "Failed to install fscrypt key to " << mountpoint;
	return false;
	}

	return true;
	}

	bool installKey(const std::string& mountpoint, const EncryptionOptions& options,
	const KeyBuffer& key, EncryptionPolicy* policy) {
	policy->options = options;
	// Put the fscrypt_add_key_arg in an automatically-zeroing buffer, since we
	// have to copy the raw key into it.
	KeyBuffer arg_buf(sizeof(struct fscrypt_add_key_arg) + key.size(), 0);
	struct fscrypt_add_key_arg* arg = (struct fscrypt_add_key_arg*)arg_buf.data();

	// Initialize the "key specifier", which is like a name for the key.
	switch (options.version) {
	case 1:
	// A key for a v1 policy is specified by an arbitrary 8-byte
	// "descriptor", which must be provided by userspace. We use the
	// first 8 bytes from the double SHA-512 of the key itself.
	if (options.use_hw_wrapped_key) {
	/* When wrapped key is supported, only the first 32 bytes are
	the same per boot. The second 32 bytes can change as the ephemeral
	key is different. */
	policy->key_raw_ref = generateKeyRef((const uint8_t*)key.data(), key.size()/2);
	} else {
	policy->key_raw_ref = generateKeyRef((const uint8_t*)key.data(), key.size());
	}
	if (!isFsKeyringSupported()) {
	return installKeyLegacy(key, policy->key_raw_ref);
	}
	if (!buildKeySpecifier(&arg->key_spec, *policy)) {
	return false;
	}
	break;
	case 2:
	// A key for a v2 policy is specified by an 16-byte "identifier",
	// which is a cryptographic hash of the key itself which the kernel
	// computes and returns. Any user-provided value is ignored; we
	// just need to set the specifier type to indicate that we're adding
	// this type of key.
	arg->key_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
	break;
	default:
	LOG(ERROR) << "Invalid encryption policy version: " << options.version;
	return false;
	}

	arg->raw_size = key.size();
	memcpy(arg->raw, key.data(), key.size());

	if (!installFsKeyringKey(mountpoint, options, arg)) return false;

	if (arg->key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
	// Retrieve the key identifier that the kernel computed.
	policy->key_raw_ref =
	std::string((char*)arg->key_spec.u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
	}
	std::string ref = keyrefstring(policy->key_raw_ref);
	LOG(DEBUG) << "Installed fscrypt key with ref " << ref << " to " << mountpoint;

	if (!installProvisioningKey(key, ref, arg->key_spec)) return false;
	return true;
	}

	// Remove an encryption key of type "logon" from the global session keyring.
	static bool evictKeyLegacy(const std::string& raw_ref) {
	key_serial_t device_keyring;
	if (!fscryptKeyring(&device_keyring)) return false;
	bool success = true;
	for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
	auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
	auto key_serial = keyctl_search(device_keyring, "logon", ref.c_str(), 0);

	// Unlink the key from the keyring. Prefer unlinking to revoking or
	// invalidating, since unlinking is actually no less secure currently, and
	// it avoids bugs in certain kernel versions where the keyring key is
	// referenced from places it shouldn't be.
	if (keyctl_unlink(key_serial, device_keyring) != 0) {
	PLOG(ERROR) << "Failed to unlink key with serial " << key_serial << " ref " << ref;
	success = false;
	} else {
	LOG(DEBUG) << "Unlinked key with serial " << key_serial << " ref " << ref;
	}
	}
	return success;
	}

	static bool evictProvisioningKey(const std::string& ref) {
	key_serial_t device_keyring;
	if (!fscryptKeyring(&device_keyring)) {
	return false;
	}

	auto key_serial = keyctl_search(device_keyring, "fscrypt-provisioning", ref.c_str(), 0);
	if (key_serial == -1 && errno != ENOKEY) {
	PLOG(ERROR) << "Error searching session keyring for fscrypt-provisioning key for " << ref;
	return false;
	}

	if (key_serial != -1 && keyctl_unlink(key_serial, device_keyring) != 0) {
	PLOG(ERROR) << "Failed to unlink fscrypt-provisioning key for " << ref
	<< " from session keyring";
	return false;
	}
	return true;
	}

	bool evictKey(const std::string& mountpoint, const EncryptionPolicy& policy) {
	if (policy.options.version == 1 && !isFsKeyringSupported()) {
	return evictKeyLegacy(policy.key_raw_ref);
	}

	android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY \| O_DIRECTORY \| O_CLOEXEC));
	if (fd == -1) {
	PLOG(ERROR) << "Failed to open " << mountpoint << " to evict key";
	return false;
	}

	struct fscrypt_remove_key_arg arg;
	memset(&arg, 0, sizeof(arg));

	if (!buildKeySpecifier(&arg.key_spec, policy)) {
	return false;
	}

	std::string ref = keyrefstring(policy.key_raw_ref);

	if (ioctl(fd, FS_IOC_REMOVE_ENCRYPTION_KEY, &arg) != 0) {
	PLOG(ERROR) << "Failed to evict fscrypt key with ref " << ref << " from " << mountpoint;
	return false;
	}

	LOG(DEBUG) << "Evicted fscrypt key with ref " << ref << " from " << mountpoint;
	if (arg.removal_status_flags & FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS) {
	// Should never happen because keys are only added/removed as root.
	LOG(ERROR) << "Unexpected case: key with ref " << ref << " is still added by other users!";
	} else if (arg.removal_status_flags & FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY) {
	LOG(ERROR) << "Files still open after removing key with ref " << ref
	<< ". These files were not locked!";
	}

	if (!evictProvisioningKey(ref)) return false;
	return true;
	}

	bool retrieveOrGenerateKey(const std::string& key_path, const std::string& tmp_path,
	const KeyAuthentication& key_authentication, const KeyGeneration& gen,
	KeyBuffer* key) {
	if (pathExists(key_path)) {
	LOG(DEBUG) << "Key exists, using: " << key_path;
	if (!retrieveKey(key_path, key_authentication, key)) return false;
	} else {
	if (!gen.allow_gen) {
	LOG(ERROR) << "No key found in " << key_path;
	return false;
	}
	LOG(INFO) << "Creating new key in " << key_path;
	if (!generateStorageKey(gen, key)) return false;
	if (!storeKeyAtomically(key_path, tmp_path, key_authentication, *key)) return false;
	}
	return true;
	}

	bool reloadKeyFromSessionKeyring(const std::string& mountpoint, const EncryptionPolicy& policy) {
	key_serial_t device_keyring;
	if (!fscryptKeyring(&device_keyring)) {
	return false;
	}

	std::string ref = keyrefstring(policy.key_raw_ref);
	auto key_serial = keyctl_search(device_keyring, "fscrypt-provisioning", ref.c_str(), 0);
	if (key_serial == -1) {
	PLOG(ERROR) << "Failed to find fscrypt-provisioning key for " << ref
	<< " in session keyring";
	return false;
	}

	LOG(DEBUG) << "Installing fscrypt-provisioning key for " << ref << " back into " << mountpoint
	<< " fs-keyring";

	struct fscrypt_add_key_arg arg;
	memset(&arg, 0, sizeof(arg));
	if (!buildKeySpecifier(&arg.key_spec, policy)) return false;
	arg.key_id = key_serial;
	if (!installFsKeyringKey(mountpoint, policy.options, &arg)) return false;

	return true;
	}

	} // namespace vold
	} // namespace android