Refactor to lay the groundwork for metadata encryption

Bug: 26778031
Test: Angler, Marlin build and boot
Change-Id: Ic136dfe6195a650f7db76d3489f36da6a1929dc5

1 files changed, 167 insertions, 0 deletions

diff --git a/KeyUtil.cpp b/KeyUtil.cpp
new file mode 100644
index 0000000..37398e6
--- /dev/null
+++ b/KeyUtil.cpp
@@ -0,0 +1,167 @@
+/*
+ * 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 <ext4_utils/key_control.h>
+
+#include <openssl/sha.h>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+
+#include "KeyStorage.h"
+#include "Utils.h"
+
+namespace android {
+namespace vold {
+
+bool randomKey(std::string* key) {
+    if (ReadRandomBytes(EXT4_AES_256_XTS_KEY_SIZE, *key) != 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 char* 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(EXT4_KEY_DESCRIPTOR_SIZE <= SHA512_DIGEST_LENGTH,
+                  "Hash too short for descriptor");
+    return std::string((char*)key_ref2, EXT4_KEY_DESCRIPTOR_SIZE);
+}
+
+static bool fillKey(const std::string& key, ext4_encryption_key* ext4_key) {
+    if (key.size() != EXT4_AES_256_XTS_KEY_SIZE) {
+        LOG(ERROR) << "Wrong size key " << key.size();
+        return false;
+    }
+    static_assert(EXT4_AES_256_XTS_KEY_SIZE <= sizeof(ext4_key->raw), "Key too long!");
+    ext4_key->mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
+    ext4_key->size = key.size();
+    memset(ext4_key->raw, 0, sizeof(ext4_key->raw));
+    memcpy(ext4_key->raw, key.data(), key.size());
+    return true;
+}
+
+static std::string keyname(const std::string& raw_ref) {
+    std::ostringstream o;
+    o << "ext4:";
+    for (auto 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 e4cryptKeyring(key_serial_t* device_keyring) {
+    *device_keyring = keyctl_search(KEY_SPEC_SESSION_KEYRING, "keyring", "e4crypt", 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 std::string& key, std::string* raw_ref) {
+    ext4_encryption_key ext4_key;
+    if (!fillKey(key, &ext4_key)) return false;
+    *raw_ref = generateKeyRef(ext4_key.raw, ext4_key.size);
+    auto ref = keyname(*raw_ref);
+    key_serial_t device_keyring;
+    if (!e4cryptKeyring(&device_keyring)) return false;
+    key_serial_t key_id =
+        add_key("logon", ref.c_str(), (void*)&ext4_key, sizeof(ext4_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();
+
+    // *TODO* Remove this code when kernel is fixed - see b/28373400
+    // Kernel preserves caches across a key insertion with ext4ice, which leads
+    // to contradictory dirents
+    if (!android::base::WriteStringToFile("3", "/proc/sys/vm/drop_caches")) {
+        PLOG(ERROR) << "Failed to drop_caches";
+    }
+
+    return true;
+}
+
+bool evictKey(const std::string& raw_ref) {
+    auto ref = keyname(raw_ref);
+    key_serial_t device_keyring;
+    if (!e4cryptKeyring(&device_keyring)) return false;
+    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;
+        return false;
+    }
+    LOG(DEBUG) << "Unlinked key with serial " << key_serial << " ref " << ref;
+    return true;
+}
+
+bool retrieveAndInstallKey(bool create_if_absent, const std::string& key_path,
+                           const std::string& tmp_path, std::string* key_ref) {
+    std::string key;
+    if (pathExists(key_path)) {
+        LOG(DEBUG) << "Key exists, using: " << key_path;
+        if (!retrieveKey(key_path, kEmptyAuthentication, &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,
+                kEmptyAuthentication, key)) return false;
+    }
+
+    if (!installKey(key, key_ref)) {
+        LOG(ERROR) << "Failed to install key in " << key_path;
+        return false;
+    }
+    return true;
+}
+
+}  // namespace vold
+}  // namespace android