fsverity_init/fsverity_init.cpp

/*
 * Copyright (C) 2019 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.
 */

#define LOG_TAG "fsverity_init"

#include <sys/types.h>

#include <filesystem>
#include <string>

#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/properties.h>
#include <android-base/strings.h>
#include <log/log.h>
#include <mini_keyctl_utils.h>

bool LoadKeyToKeyring(key_serial_t keyring_id, const char* desc, const char* data, size_t size) {
    key_serial_t key = add_key("asymmetric", desc, data, size, keyring_id);
    if (key < 0) {
        PLOG(ERROR) << "Failed to add key";
        return false;
    }
    return true;
}

void LoadKeyFromStdin(key_serial_t keyring_id, const char* keyname) {
    std::string content;
    if (!android::base::ReadFdToString(STDIN_FILENO, &content)) {
        LOG(ERROR) << "Failed to read key from stdin";
        return;
    }
    if (!LoadKeyToKeyring(keyring_id, keyname, content.c_str(), content.size())) {
        LOG(ERROR) << "Failed to load key from stdin";
    }
}

void LoadKeyFromFile(key_serial_t keyring_id, const char* keyname, const std::string& path) {
    std::string content;
    if (!android::base::ReadFileToString(path, &content)) {
        LOG(ERROR) << "Failed to read key from " << path;
        return;
    }
    if (!LoadKeyToKeyring(keyring_id, keyname, content.c_str(), content.size())) {
        LOG(ERROR) << "Failed to load key from " << path;
    }
}

void LoadKeyFromDirectory(key_serial_t keyring_id, const char* keyname, const char* dir) {
    if (!std::filesystem::exists(dir)) {
        return;
    }
    for (const auto& entry : std::filesystem::directory_iterator(dir)) {
        if (!android::base::EndsWithIgnoreCase(entry.path().c_str(), ".der")) continue;

        LoadKeyFromFile(keyring_id, keyname, entry.path());
    }
}

void LoadKeyFromVerifiedPartitions(key_serial_t keyring_id) {
    // NB: Directories need to be synced with FileIntegrityService.java in
    // frameworks/base.
    LoadKeyFromDirectory(keyring_id, "fsv_system", "/system/etc/security/fsverity");
    LoadKeyFromDirectory(keyring_id, "fsv_product", "/product/etc/security/fsverity");
}

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;
        }
        LoadKeyFromStdin(keyring_id, argv[2]);
    } 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;
}