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512 lines
20 KiB
512 lines
20 KiB
/*
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* Copyright (C) 2016 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "KeyUtil.h"
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#include <iomanip>
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#include <sstream>
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#include <string>
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#include <thread>
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#include <fcntl.h>
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#include <linux/fscrypt.h>
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#include <openssl/sha.h>
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#include <sys/ioctl.h>
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#include <android-base/file.h>
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#include <android-base/logging.h>
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#include <android-base/properties.h>
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#include <keyutils.h>
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#include "KeyStorage.h"
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#include "Utils.h"
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namespace android {
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namespace vold {
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// This must be acquired before calling fscrypt ioctls that operate on keys.
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// This prevents race conditions between evicting and reinstalling keys.
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static std::mutex fscrypt_keyring_mutex;
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const KeyGeneration neverGen() {
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return KeyGeneration{0, false, false};
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}
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static bool randomKey(size_t size, KeyBuffer* key) {
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*key = KeyBuffer(size);
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if (ReadRandomBytes(key->size(), key->data()) != 0) {
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// TODO status_t plays badly with PLOG, fix it.
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LOG(ERROR) << "Random read failed";
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return false;
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}
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return true;
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}
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bool generateStorageKey(const KeyGeneration& gen, KeyBuffer* key) {
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if (!gen.allow_gen) return false;
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if (gen.use_hw_wrapped_key) {
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if (gen.keysize != FSCRYPT_MAX_KEY_SIZE) {
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LOG(ERROR) << "Cannot generate a wrapped key " << gen.keysize << " bytes long";
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return false;
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}
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LOG(DEBUG) << "Generating wrapped storage key";
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return generateWrappedStorageKey(key);
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} else {
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LOG(DEBUG) << "Generating standard storage key";
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return randomKey(gen.keysize, key);
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}
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}
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static bool isFsKeyringSupportedImpl() {
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android::base::unique_fd fd(open("/data", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
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// FS_IOC_ADD_ENCRYPTION_KEY with a NULL argument will fail with ENOTTY if
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// the ioctl isn't supported. Otherwise it will fail with another error
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// code such as EFAULT.
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//
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// Note that there's no need to check for FS_IOC_REMOVE_ENCRYPTION_KEY,
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// since it's guaranteed to be available if FS_IOC_ADD_ENCRYPTION_KEY is.
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// There's also no need to check for support on external volumes separately
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// from /data, since either the kernel supports the ioctls on all
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// fscrypt-capable filesystems or it doesn't.
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errno = 0;
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(void)ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, NULL);
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if (errno == ENOTTY) {
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LOG(INFO) << "Kernel doesn't support FS_IOC_ADD_ENCRYPTION_KEY. Falling back to "
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"session keyring";
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return false;
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}
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if (errno != EFAULT) {
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PLOG(WARNING) << "Unexpected error from FS_IOC_ADD_ENCRYPTION_KEY";
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}
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LOG(DEBUG) << "Detected support for FS_IOC_ADD_ENCRYPTION_KEY";
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android::base::SetProperty("ro.crypto.uses_fs_ioc_add_encryption_key", "true");
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return true;
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}
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// Return true if the kernel supports the ioctls to add/remove fscrypt keys
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// directly to/from the filesystem.
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bool isFsKeyringSupported(void) {
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static bool supported = isFsKeyringSupportedImpl();
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return supported;
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}
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// Get raw keyref - used to make keyname and to pass to ioctl
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static std::string generateKeyRef(const uint8_t* key, int length) {
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SHA512_CTX c;
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SHA512_Init(&c);
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SHA512_Update(&c, key, length);
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unsigned char key_ref1[SHA512_DIGEST_LENGTH];
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SHA512_Final(key_ref1, &c);
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SHA512_Init(&c);
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SHA512_Update(&c, key_ref1, SHA512_DIGEST_LENGTH);
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unsigned char key_ref2[SHA512_DIGEST_LENGTH];
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SHA512_Final(key_ref2, &c);
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static_assert(FSCRYPT_KEY_DESCRIPTOR_SIZE <= SHA512_DIGEST_LENGTH,
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"Hash too short for descriptor");
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return std::string((char*)key_ref2, FSCRYPT_KEY_DESCRIPTOR_SIZE);
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}
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static bool fillKey(const KeyBuffer& key, fscrypt_key* fs_key) {
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if (key.size() != FSCRYPT_MAX_KEY_SIZE) {
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LOG(ERROR) << "Wrong size key " << key.size();
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return false;
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}
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static_assert(FSCRYPT_MAX_KEY_SIZE == sizeof(fs_key->raw), "Mismatch of max key sizes");
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fs_key->mode = 0; // unused by kernel
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memcpy(fs_key->raw, key.data(), key.size());
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fs_key->size = key.size();
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return true;
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}
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static char const* const NAME_PREFIXES[] = {"ext4", "f2fs", "fscrypt", nullptr};
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static std::string keyrefstring(const std::string& raw_ref) {
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std::ostringstream o;
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for (unsigned char i : raw_ref) {
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o << std::hex << std::setw(2) << std::setfill('0') << (int)i;
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}
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return o.str();
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}
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static std::string buildLegacyKeyName(const std::string& prefix, const std::string& raw_ref) {
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return prefix + ":" + keyrefstring(raw_ref);
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}
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// Get the ID of the keyring we store all fscrypt keys in when the kernel is too
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// old to support FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY.
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static bool fscryptKeyring(key_serial_t* device_keyring) {
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*device_keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "fscrypt", 0);
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if (*device_keyring == -1) {
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PLOG(ERROR) << "Unable to find device keyring";
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return false;
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}
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return true;
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}
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// Add an encryption key of type "logon" to the global session keyring.
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static bool installKeyLegacy(const KeyBuffer& key, const std::string& raw_ref) {
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// Place fscrypt_key into automatically zeroing buffer.
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KeyBuffer fsKeyBuffer(sizeof(fscrypt_key));
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fscrypt_key& fs_key = *reinterpret_cast<fscrypt_key*>(fsKeyBuffer.data());
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if (!fillKey(key, &fs_key)) return false;
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key_serial_t device_keyring;
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if (!fscryptKeyring(&device_keyring)) return false;
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for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
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auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
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key_serial_t key_id =
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add_key("logon", ref.c_str(), (void*)&fs_key, sizeof(fs_key), device_keyring);
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if (key_id == -1) {
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PLOG(ERROR) << "Failed to insert key into keyring " << device_keyring;
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return false;
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}
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LOG(DEBUG) << "Added key " << key_id << " (" << ref << ") to keyring " << device_keyring
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<< " in process " << getpid();
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}
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return true;
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}
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// Installs fscrypt-provisioning key into session level kernel keyring.
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// This allows for the given key to be installed back into filesystem keyring.
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// For more context see reloadKeyFromSessionKeyring.
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static bool installProvisioningKey(const KeyBuffer& key, const std::string& ref,
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const fscrypt_key_specifier& key_spec) {
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key_serial_t device_keyring;
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if (!fscryptKeyring(&device_keyring)) return false;
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// Place fscrypt_provisioning_key_payload into automatically zeroing buffer.
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KeyBuffer buf(sizeof(fscrypt_provisioning_key_payload) + key.size(), 0);
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fscrypt_provisioning_key_payload& provisioning_key =
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*reinterpret_cast<fscrypt_provisioning_key_payload*>(buf.data());
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memcpy(provisioning_key.raw, key.data(), key.size());
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provisioning_key.type = key_spec.type;
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key_serial_t key_id = add_key("fscrypt-provisioning", ref.c_str(), (void*)&provisioning_key,
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buf.size(), device_keyring);
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if (key_id == -1) {
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PLOG(ERROR) << "Failed to insert fscrypt-provisioning key for " << ref
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<< " into session keyring";
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return false;
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}
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LOG(DEBUG) << "Added fscrypt-provisioning key for " << ref << " to session keyring";
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return true;
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}
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// Build a struct fscrypt_key_specifier for use in the key management ioctls.
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static bool buildKeySpecifier(fscrypt_key_specifier* spec, const EncryptionPolicy& policy) {
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switch (policy.options.version) {
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case 1:
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if (policy.key_raw_ref.size() != FSCRYPT_KEY_DESCRIPTOR_SIZE) {
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LOG(ERROR) << "Invalid key specifier size for v1 encryption policy: "
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<< policy.key_raw_ref.size();
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return false;
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}
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spec->type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
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memcpy(spec->u.descriptor, policy.key_raw_ref.c_str(), FSCRYPT_KEY_DESCRIPTOR_SIZE);
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return true;
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case 2:
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if (policy.key_raw_ref.size() != FSCRYPT_KEY_IDENTIFIER_SIZE) {
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LOG(ERROR) << "Invalid key specifier size for v2 encryption policy: "
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<< policy.key_raw_ref.size();
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return false;
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}
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spec->type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
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memcpy(spec->u.identifier, policy.key_raw_ref.c_str(), FSCRYPT_KEY_IDENTIFIER_SIZE);
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return true;
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default:
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LOG(ERROR) << "Invalid encryption policy version: " << policy.options.version;
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return false;
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}
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}
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// Installs key into keyring of a filesystem mounted on |mountpoint|.
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//
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// It's callers responsibility to fill key specifier, and either arg->raw or arg->key_id.
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//
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// In case arg->key_spec.type equals to FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER
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// arg->key_spec.u.identifier will be populated with raw key reference generated
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// by kernel.
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//
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// For documentation on difference between arg->raw and arg->key_id see
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// https://www.kernel.org/doc/html/latest/filesystems/fscrypt.html#fs-ioc-add-encryption-key
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static bool installFsKeyringKey(const std::string& mountpoint, const EncryptionOptions& options,
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fscrypt_add_key_arg* arg) {
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if (options.use_hw_wrapped_key) arg->__flags |= __FSCRYPT_ADD_KEY_FLAG_HW_WRAPPED;
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android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
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if (fd == -1) {
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PLOG(ERROR) << "Failed to open " << mountpoint << " to install key";
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return false;
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}
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if (ioctl(fd, FS_IOC_ADD_ENCRYPTION_KEY, arg) != 0) {
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PLOG(ERROR) << "Failed to install fscrypt key to " << mountpoint;
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return false;
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}
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return true;
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}
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bool installKey(const std::string& mountpoint, const EncryptionOptions& options,
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const KeyBuffer& key, EncryptionPolicy* policy) {
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const std::lock_guard<std::mutex> lock(fscrypt_keyring_mutex);
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policy->options = options;
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// Put the fscrypt_add_key_arg in an automatically-zeroing buffer, since we
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// have to copy the raw key into it.
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KeyBuffer arg_buf(sizeof(struct fscrypt_add_key_arg) + key.size(), 0);
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struct fscrypt_add_key_arg* arg = (struct fscrypt_add_key_arg*)arg_buf.data();
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// Initialize the "key specifier", which is like a name for the key.
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switch (options.version) {
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case 1:
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// A key for a v1 policy is specified by an arbitrary 8-byte
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// "descriptor", which must be provided by userspace. We use the
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// first 8 bytes from the double SHA-512 of the key itself.
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policy->key_raw_ref = generateKeyRef((const uint8_t*)key.data(), key.size());
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if (!isFsKeyringSupported()) {
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return installKeyLegacy(key, policy->key_raw_ref);
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}
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if (!buildKeySpecifier(&arg->key_spec, *policy)) {
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return false;
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}
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break;
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case 2:
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// A key for a v2 policy is specified by an 16-byte "identifier",
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// which is a cryptographic hash of the key itself which the kernel
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// computes and returns. Any user-provided value is ignored; we
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// just need to set the specifier type to indicate that we're adding
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// this type of key.
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arg->key_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
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break;
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default:
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LOG(ERROR) << "Invalid encryption policy version: " << options.version;
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return false;
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}
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arg->raw_size = key.size();
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memcpy(arg->raw, key.data(), key.size());
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if (!installFsKeyringKey(mountpoint, options, arg)) return false;
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if (arg->key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
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// Retrieve the key identifier that the kernel computed.
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policy->key_raw_ref =
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std::string((char*)arg->key_spec.u.identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
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}
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std::string ref = keyrefstring(policy->key_raw_ref);
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LOG(DEBUG) << "Installed fscrypt key with ref " << ref << " to " << mountpoint;
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if (!installProvisioningKey(key, ref, arg->key_spec)) return false;
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return true;
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}
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// Remove an encryption key of type "logon" from the global session keyring.
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static bool evictKeyLegacy(const std::string& raw_ref) {
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key_serial_t device_keyring;
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if (!fscryptKeyring(&device_keyring)) return false;
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bool success = true;
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for (char const* const* name_prefix = NAME_PREFIXES; *name_prefix != nullptr; name_prefix++) {
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auto ref = buildLegacyKeyName(*name_prefix, raw_ref);
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auto key_serial = keyctl_search(device_keyring, "logon", ref.c_str(), 0);
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// Unlink the key from the keyring. Prefer unlinking to revoking or
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// invalidating, since unlinking is actually no less secure currently, and
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// it avoids bugs in certain kernel versions where the keyring key is
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// referenced from places it shouldn't be.
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if (keyctl_unlink(key_serial, device_keyring) != 0) {
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PLOG(ERROR) << "Failed to unlink key with serial " << key_serial << " ref " << ref;
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success = false;
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} else {
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LOG(DEBUG) << "Unlinked key with serial " << key_serial << " ref " << ref;
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}
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}
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return success;
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}
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static bool evictProvisioningKey(const std::string& ref) {
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key_serial_t device_keyring;
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if (!fscryptKeyring(&device_keyring)) {
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return false;
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}
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auto key_serial = keyctl_search(device_keyring, "fscrypt-provisioning", ref.c_str(), 0);
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if (key_serial == -1 && errno != ENOKEY) {
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PLOG(ERROR) << "Error searching session keyring for fscrypt-provisioning key for " << ref;
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return false;
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}
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if (key_serial != -1 && keyctl_unlink(key_serial, device_keyring) != 0) {
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PLOG(ERROR) << "Failed to unlink fscrypt-provisioning key for " << ref
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<< " from session keyring";
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return false;
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}
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return true;
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}
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static void waitForBusyFiles(const struct fscrypt_key_specifier key_spec, const std::string ref,
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const std::string mountpoint) {
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android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
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if (fd == -1) {
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PLOG(ERROR) << "Failed to open " << mountpoint << " to evict key";
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return;
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}
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std::chrono::milliseconds wait_time(3200);
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std::chrono::milliseconds total_wait_time(0);
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while (wait_time <= std::chrono::milliseconds(51200)) {
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total_wait_time += wait_time;
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std::this_thread::sleep_for(wait_time);
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const std::lock_guard<std::mutex> lock(fscrypt_keyring_mutex);
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struct fscrypt_get_key_status_arg get_arg;
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memset(&get_arg, 0, sizeof(get_arg));
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get_arg.key_spec = key_spec;
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if (ioctl(fd, FS_IOC_GET_ENCRYPTION_KEY_STATUS, &get_arg) != 0) {
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PLOG(ERROR) << "Failed to get status for fscrypt key with ref " << ref << " from "
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<< mountpoint;
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return;
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}
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if (get_arg.status != FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED) {
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LOG(DEBUG) << "Key status changed, cancelling busy file cleanup for key with ref "
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<< ref << ".";
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return;
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}
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struct fscrypt_remove_key_arg remove_arg;
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memset(&remove_arg, 0, sizeof(remove_arg));
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remove_arg.key_spec = key_spec;
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if (ioctl(fd, FS_IOC_REMOVE_ENCRYPTION_KEY, &remove_arg) != 0) {
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PLOG(ERROR) << "Failed to clean up busy files for fscrypt key with ref " << ref
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<< " from " << mountpoint;
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return;
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}
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if (remove_arg.removal_status_flags & FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS) {
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// Should never happen because keys are only added/removed as root.
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LOG(ERROR) << "Unexpected case: key with ref " << ref
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<< " is still added by other users!";
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} else if (!(remove_arg.removal_status_flags &
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FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY)) {
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LOG(INFO) << "Successfully cleaned up busy files for key with ref " << ref
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<< ". After waiting " << total_wait_time.count() << "ms.";
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return;
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}
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LOG(WARNING) << "Files still open after waiting " << total_wait_time.count()
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<< "ms. Key with ref " << ref << " still has unlocked files!";
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wait_time *= 2;
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}
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LOG(ERROR) << "Waiting for files to close never completed. Files using key with ref " << ref
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<< " were not locked!";
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}
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bool evictKey(const std::string& mountpoint, const EncryptionPolicy& policy) {
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const std::lock_guard<std::mutex> lock(fscrypt_keyring_mutex);
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if (policy.options.version == 1 && !isFsKeyringSupported()) {
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return evictKeyLegacy(policy.key_raw_ref);
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}
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android::base::unique_fd fd(open(mountpoint.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
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if (fd == -1) {
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PLOG(ERROR) << "Failed to open " << mountpoint << " to evict key";
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return false;
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}
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struct fscrypt_remove_key_arg arg;
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memset(&arg, 0, sizeof(arg));
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if (!buildKeySpecifier(&arg.key_spec, policy)) {
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return false;
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}
|
|
|
|
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(WARNING)
|
|
<< "Files still open after removing key with ref " << ref
|
|
<< ". These files were not locked! Punting busy file clean up to worker thread.";
|
|
// Processes are killed asynchronously in ActivityManagerService due to performance issues
|
|
// with synchronous kills. If there were busy files they will probably be killed soon. Wait
|
|
// for them asynchronously.
|
|
std::thread busyFilesThread(waitForBusyFiles, arg.key_spec, ref, mountpoint);
|
|
busyFilesThread.detach();
|
|
}
|
|
|
|
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
|