decrypt: AOSP 10 requires the use of fscrypt
fscrypt aosp doc: https://source.android.com/security/encryption/file-based
kernel fscrypt doc: https://www.kernel.org/doc/html/v4.18/filesystems/fscrypt.html
This commit implements the ability for TWRP to use fscrypt to decrypt
files on the fscrypt implementation. It has been implemented mostly
in a new successor library to e4crypt called libtwrpfscrypt. Most of the
code was ported from AOSP vold.
Notable updates include:
- updated policy storage by libtar
- lookup of fbe policies by libtwrpfscrypt
- threaded keystore operations
Big thanks to Dees_Troy for the initial trailblazing
of encryption in TWRP.
Change-Id: I69cd2eba3693a9914e00213d4943229635d0cdae
diff --git a/crypto/fscrypt/KeyUtil.cpp b/crypto/fscrypt/KeyUtil.cpp
new file mode 100755
index 0000000..91d6b37
--- /dev/null
+++ b/crypto/fscrypt/KeyUtil.cpp
@@ -0,0 +1,191 @@
+/*
+ * 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 <linux/fs.h>
+#include <iomanip>
+#include <sstream>
+#include <string>
+
+#include <openssl/sha.h>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <keyutils.h>
+
+#include "KeyStorage.h"
+#include "Utils.h"
+
+namespace android {
+namespace vold {
+
+constexpr int FS_AES_256_XTS_KEY_SIZE = 64;
+
+bool randomKey(KeyBuffer* key) {
+ *key = KeyBuffer(FS_AES_256_XTS_KEY_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;
+}
+
+// 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(FS_KEY_DESCRIPTOR_SIZE <= SHA512_DIGEST_LENGTH, "Hash too short for descriptor");
+ return std::string((char*)key_ref2, FS_KEY_DESCRIPTOR_SIZE);
+}
+
+static bool fillKey(const KeyBuffer& key, fscrypt_key* fs_key) {
+ if (key.size() != FS_AES_256_XTS_KEY_SIZE) {
+ LOG(ERROR) << "Wrong size key " << key.size();
+ return false;
+ }
+ static_assert(FS_AES_256_XTS_KEY_SIZE <= sizeof(fs_key->raw), "Key too long!");
+ fs_key->mode = FS_ENCRYPTION_MODE_AES_256_XTS;
+ fs_key->size = key.size();
+ memset(fs_key->raw, 0, sizeof(fs_key->raw));
+ memcpy(fs_key->raw, key.data(), key.size());
+ return true;
+}
+
+static char const* const NAME_PREFIXES[] = {"ext4", "f2fs", "fscrypt", nullptr};
+
+static std::string keyname(const std::string& prefix, const std::string& raw_ref) {
+ std::ostringstream o;
+ o << prefix << ":";
+ for (unsigned char i : raw_ref) {
+ o << std::hex << std::setw(2) << std::setfill('0') << (int)i;
+ }
+ return o.str();
+}
+
+// Get the keyring we store all keys in
+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;
+}
+
+// Install password into global keyring
+// Return raw key reference for use in policy
+bool installKey(const KeyBuffer& key, 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;
+ *raw_ref = generateKeyRef(fs_key.raw, fs_key.size);
+ 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 = keyname(*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;
+}
+
+bool evictKey(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 = keyname(*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;
+}
+
+bool retrieveAndInstallKey(bool create_if_absent, const KeyAuthentication& key_authentication,
+ const std::string& key_path, const std::string& tmp_path,
+ std::string* key_ref) {
+ KeyBuffer key;
+ if (pathExists(key_path)) {
+ LOG(DEBUG) << "Key exists, using: " << key_path;
+ if (!retrieveKey(key_path, key_authentication, &key)) return false;
+ } else {
+ if (!create_if_absent) {
+ LOG(ERROR) << "No key found in " << key_path;
+ return false;
+ }
+ LOG(INFO) << "Creating new key in " << key_path;
+ if (!randomKey(&key)) return false;
+ if (!storeKeyAtomically(key_path, tmp_path, key_authentication, key)) return false;
+ }
+
+ if (!installKey(key, key_ref)) {
+ LOG(ERROR) << "Failed to install key in " << key_path;
+ return false;
+ }
+ return true;
+}
+
+bool retrieveKey(bool create_if_absent, const std::string& key_path, const std::string& tmp_path,
+ KeyBuffer* key, bool keepOld) {
+ LOG(ERROR) << "retreiveKey1";
+ if (pathExists(key_path)) {
+ LOG(ERROR) << "Key exists, using: " << key_path;
+ if (!retrieveKey(key_path, kEmptyAuthentication, key, keepOld)) return false;
+ } else {
+ if (!create_if_absent) {
+ LOG(ERROR) << "No key found in " << key_path;
+ return false;
+ }
+ LOG(ERROR) << "Creating new key in " << key_path;
+ if (!randomKey(key)) return false;
+ LOG(ERROR) << "retrieveKey1";
+ if (!storeKeyAtomically(key_path, tmp_path, kEmptyAuthentication, *key)) return false;
+ }
+ return true;
+}
+
+} // namespace vold
+} // namespace android