ext4_utils/ext4_crypt_init_extensions.cpp

#define TAG "ext4_utils"

#include "ext4_crypt.h"

#include <string>
#include <fstream>
#include <iomanip>
#include <sstream>

#include <errno.h>
#include <sys/mount.h>
#include <sys/stat.h>

#include <cutils/klog.h>
#include <cutils/properties.h>
#include <cutils/sockets.h>
#include <poll.h>

#include "unencrypted_properties.h"

// ext4enc:TODO Include structure from somewhere sensible
// MUST be in sync with ext4_crypto.c in kernel
#define EXT4_MAX_KEY_SIZE 76
struct ext4_encryption_key {
        uint32_t mode;
        char raw[EXT4_MAX_KEY_SIZE];
        uint32_t size;
};

static const std::string keyring = "@s";
static const std::string arbitrary_sequence_number = "42";
static const int vold_command_timeout_ms = 10 * 1000;

static key_serial_t device_keyring = -1;

static std::string vold_command(std::string const& command)
{
    KLOG_INFO(TAG, "Running command %s\n", command.c_str());
    int sock = socket_local_client("vold",
                                   ANDROID_SOCKET_NAMESPACE_RESERVED,
                                   SOCK_STREAM);

    if (sock < 0) {
        KLOG_INFO(TAG, "Cannot open vold, failing command\n");
        return "";
    }

    class CloseSocket
    {
        int sock_;
    public:
        CloseSocket(int sock) : sock_(sock) {}
        ~CloseSocket() { close(sock_); }
    };

    CloseSocket cs(sock);

    // Use arbitrary sequence number. This should only be used when the
    // framework is down, so this is (mostly) OK.
    std::string actual_command = arbitrary_sequence_number + " " + command;
    if (write(sock, actual_command.c_str(), actual_command.size() + 1) < 0) {
        KLOG_ERROR(TAG, "Cannot write command\n");
        return "";
    }

    struct pollfd poll_sock = {sock, POLLIN, 0};

    int rc = poll(&poll_sock, 1, vold_command_timeout_ms);
    if (rc < 0) {
        KLOG_ERROR(TAG, "Error in poll %s\n", strerror(errno));
        return "";
    }
    if (!(poll_sock.revents & POLLIN)) {
        KLOG_ERROR(TAG, "Timeout\n");
        return "";
    }
    char buffer[4096];
    memset(buffer, 0, sizeof(buffer));
    rc = read(sock, buffer, sizeof(buffer));
    if (rc <= 0) {
        if (rc == 0) {
            KLOG_ERROR(TAG, "Lost connection to Vold - did it crash?\n");
        } else {
            KLOG_ERROR(TAG, "Error reading data (%s)\n", strerror(errno));
        }
        return "";
    }

    // We don't truly know that this is the correct result. However,
    // since this will only be used when the framework is down,
    // it should be OK unless someone is running vdc at the same time.
    // Worst case we force a reboot in the very rare synchronization
    // error
    return std::string(buffer, rc);
}

int e4crypt_create_device_key(const char* dir,
                              int ensure_dir_exists(const char*))
{
    // Make sure folder exists. Use make_dir to set selinux permissions.
    KLOG_INFO(TAG, "Creating test device key\n");
    UnencryptedProperties props(dir);
    if (ensure_dir_exists(props.GetPath().c_str())) {
        KLOG_ERROR(TAG, "Failed to create %s with error %s\n",
                   props.GetPath().c_str(), strerror(errno));
        return -1;
    }

    if (props.Get<std::string>(properties::key).empty()) {
        // Create new key since it doesn't already exist
        std::ifstream urandom("/dev/urandom", std::ifstream::binary);
        if (!urandom) {
            KLOG_ERROR(TAG, "Failed to open /dev/urandom\n");
            return -1;
        }

        // ext4enc:TODO Don't hardcode 32
        std::string key_material(32, '\0');
        urandom.read(&key_material[0], key_material.length());
        if (!urandom) {
            KLOG_ERROR(TAG, "Failed to read random bytes\n");
            return -1;
        }

        if (!props.Set(properties::key, key_material)) {
            KLOG_ERROR(TAG, "Failed to write key material\n");
            return -1;
        }
    }

    if (!props.Remove(properties::ref)) {
        KLOG_ERROR(TAG, "Failed to remove key ref\n");
        return -1;
    }

    return 0;
}

int e4crypt_install_keyring()
{
    device_keyring = add_key("keyring",
                             "e4crypt",
                             0,
                             0,
                             KEY_SPEC_SESSION_KEYRING);

    if (device_keyring == -1) {
        KLOG_ERROR(TAG, "Failed to create keyring\n");
        return -1;
    }

    KLOG_INFO(TAG, "Keyring created wth id %d in process %d\n",
              device_keyring, getpid());

    // ext4enc:TODO set correct permissions
    long result = keyctl_setperm(device_keyring, 0x3f3f3f3f);
    if (result) {
        KLOG_ERROR(TAG, "KEYCTL_SETPERM failed with error %ld\n", result);
        return -1;
    }

    return 0;
}

int e4crypt_install_key(const char* dir)
{
    UnencryptedProperties props(dir);
    auto key = props.Get<std::string>(properties::key);

    // Get password to decrypt as needed
    if (e4crypt_non_default_key(dir)) {
        std::string result = vold_command("cryptfs getpw");
        // result is either
        // 200 0 -1
        // or
        // 200 0 {{sensitive}} 0001020304
        // where 0001020304 is hex encoding of password
        std::istringstream i(result);
        std::string bit;
        i >> bit;
        if (bit != "200") {
            KLOG_ERROR(TAG, "Expecting 200\n");
            return -1;
        }

        i >> bit;
        if (bit != arbitrary_sequence_number) {
            KLOG_ERROR(TAG, "Expecting %s\n", arbitrary_sequence_number.c_str());
            return -1;
        }

        i >> bit;
        if (bit != "{{sensitive}}") {
            KLOG_INFO(TAG, "Not encrypted\n");
            return -1;
        }

        i >> bit;
    }

    // Add key to keyring
    ext4_encryption_key ext4_key = {0, {0}, 0};
    if (key.length() > sizeof(ext4_key.raw)) {
        KLOG_ERROR(TAG, "Key too long\n");
        return -1;
    }

    ext4_key.mode = 0;
    memcpy(ext4_key.raw, &key[0], key.length());
    ext4_key.size = key.length();

    // ext4enc:TODO Use better reference not 1234567890
    key_serial_t key_id = add_key("logon", "ext4-key:1234567890",
                                  (void*)&ext4_key, sizeof(ext4_key),
                                  device_keyring);

    if (key_id == -1) {
        KLOG_ERROR(TAG, "Failed to insert key into keyring with error %s\n",
                   strerror(errno));
        return -1;
    }

    KLOG_INFO(TAG, "Added key %d to keyring %d in process %d\n",
              key_id, device_keyring, getpid());

    // ext4enc:TODO set correct permissions
    long result = keyctl_setperm(key_id, 0x3f3f3f3f);
    if (result) {
        KLOG_ERROR(TAG, "KEYCTL_SETPERM failed with error %ld\n", result);
        return -1;
    }

    // Save reference to key so we can set policy later
    if (!props.Set(properties::ref, "ext4-key:1234567890")) {
        KLOG_ERROR(TAG, "Cannot save key reference\n");
        return -1;
    }

    return 0;
}

int e4crypt_set_directory_policy(const char* dir)
{
    // Only set policy on first level /data directories
    // To make this less restrictive, consider using a policy file.
    // However this is overkill for as long as the policy is simply
    // to apply a global policy to all /data folders created via makedir
    if (!dir || strncmp(dir, "/data/", 6) || strchr(dir + 6, '/')) {
        return 0;
    }

    UnencryptedProperties props("/data");
    std::string ref = props.Get<std::string>(properties::ref);
    std::string policy = keyring + "." + ref;
    KLOG_INFO(TAG, "Setting policy %s\n", policy.c_str());
    int result = do_policy_set(dir, policy.c_str());
    if (result) {
        KLOG_ERROR(TAG, "Setting policy on %s failed!\n", dir);
        return -1;
    }

    return 0;
}