fsverity_init: refactor into library + binary

This is needed to import some of the functionality into first stage
init.

Bug: 199914227
Test: build
Change-Id: I0a78f62b1957404d7fe78c79151a1620834ea3a1
diff --git a/fsverity_init/main.cpp b/fsverity_init/main.cpp
new file mode 100644
index 0000000..3f75dca
--- /dev/null
+++ b/fsverity_init/main.cpp
@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2021 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 <string>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/properties.h>
+#include <fsverity_init.h>
+#include <log/log.h>
+#include <mini_keyctl_utils.h>
+
+int main(int argc, const char** argv) {
+    if (argc < 2) {
+        LOG(ERROR) << "Not enough arguments";
+        return -1;
+    }
+
+    key_serial_t keyring_id = android::GetKeyringId(".fs-verity");
+    if (keyring_id < 0) {
+        LOG(ERROR) << "Failed to find .fs-verity keyring id";
+        return -1;
+    }
+
+    const std::string_view command = argv[1];
+
+    if (command == "--load-verified-keys") {
+        LoadKeyFromVerifiedPartitions(keyring_id);
+    } else if (command == "--load-extra-key") {
+        if (argc != 3) {
+            LOG(ERROR) << "--load-extra-key requires <key_name> argument.";
+            return -1;
+        }
+        if (!LoadKeyFromStdin(keyring_id, argv[2])) {
+            return -1;
+        }
+    } else if (command == "--lock") {
+        // Requires files backed by fs-verity to be verified with a key in .fs-verity
+        // keyring.
+        if (!android::base::WriteStringToFile("1", "/proc/sys/fs/verity/require_signatures")) {
+            PLOG(ERROR) << "Failed to enforce fs-verity signature";
+        }
+
+        if (!android::base::GetBoolProperty("ro.debuggable", false)) {
+            if (keyctl_restrict_keyring(keyring_id, nullptr, nullptr) < 0) {
+                PLOG(ERROR) << "Cannot restrict .fs-verity keyring";
+            }
+        }
+    } else {
+        LOG(ERROR) << "Unknown argument(s).";
+        return -1;
+    }
+
+    return 0;
+}