/*
* Example of LUKS2 kesylot handler (EXAMPLE)
*
* Copyright (C) 2016-2020 Milan Broz <gmazyland@gmail.com>
*
* Use:
* - generate LUKS device
* - store passphrase used in previous step remotely (single line w/o \r\n)
* - add new token using this example
* - activate device by token
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <json-c/json.h>
#include <libssh/libssh.h>
#include <libssh/sftp.h>
#include "libcryptsetup.h"
#define TOKEN_NUM 0
#define PASSWORD_LENGTH 8192
typedef int (*password_cb_func) (char **password);
static json_object *get_token_jobj(struct crypt_device *cd, int token)
{
const char *json_slot;
/* libcryptsetup API call */
if (crypt_token_json_get(cd, token, &json_slot))
return NULL;
return json_tokener_parse(json_slot);
}
static int download_remote_password(struct crypt_device *cd, ssh_session ssh,
const char *path, char **password,
size_t *password_len)
{
char *pass;
size_t pass_len;
int r;
sftp_attributes sftp_attr = NULL;
sftp_session sftp = NULL;
sftp_file file = NULL;
sftp = sftp_new(ssh);
if (!sftp) {
crypt_log(cd, CRYPT_LOG_ERROR, "Cannot create sftp session: ");
r = SSH_FX_FAILURE;
goto out;
}
r = sftp_init(sftp);
if (r != SSH_OK) {
crypt_log(cd, CRYPT_LOG_ERROR, "Cannot init sftp session: ");
goto out;
}
file = sftp_open(sftp, path, O_RDONLY, 0);
if (!file) {
crypt_log(cd, CRYPT_LOG_ERROR, "Cannot create sftp session: ");
r = SSH_FX_FAILURE;
goto out;
}
sftp_attr = sftp_fstat(file);
if (!sftp_attr) {
crypt_log(cd, CRYPT_LOG_ERROR, "Cannot stat sftp file: ");
r = SSH_FX_FAILURE;
goto out;
}
pass_len = sftp_attr->size > PASSWORD_LENGTH ? PASSWORD_LENGTH : sftp_attr->size;
pass = malloc(pass_len);
if (!pass) {
crypt_log(cd, CRYPT_LOG_ERROR, "Not enough memory.\n");
r = SSH_FX_FAILURE;
goto out;
}
r = sftp_read(file, pass, pass_len);
if (r < 0 || (size_t)r != pass_len) {
crypt_log(cd, CRYPT_LOG_ERROR, "Cannot read remote key: ");
r = SSH_FX_FAILURE;
goto out;
}
*password = pass;
*password_len = pass_len;
r = SSH_OK;
out:
if (r != SSH_OK) {
crypt_log(cd, CRYPT_LOG_ERROR, ssh_get_error(ssh));
crypt_log(cd, CRYPT_LOG_ERROR, "\n");
free(pass);
}
if (sftp_attr)
sftp_attributes_free(sftp_attr);
if (file)
sftp_close(file);
if (sftp)
sftp_free(sftp);
return r == SSH_OK ? 0 : -EINVAL;
}
static ssh_session ssh_session_init(struct crypt_device *cd,
const char *host,
const char *user)
{
int r, port = 22;
ssh_session ssh = ssh_new();
if (!ssh)
return NULL;
ssh_options_set(ssh, SSH_OPTIONS_HOST, host);
ssh_options_set(ssh, SSH_OPTIONS_USER, user);
ssh_options_set(ssh, SSH_OPTIONS_PORT, &port);
crypt_log(cd, CRYPT_LOG_NORMAL, "Initiating ssh session.\n");
r = ssh_connect(ssh);
if (r != SSH_OK) {
crypt_log(cd, CRYPT_LOG_ERROR, "Connection failed: ");
goto out;
}
r = ssh_is_server_known(ssh);
if (r != SSH_SERVER_KNOWN_OK) {
crypt_log(cd, CRYPT_LOG_ERROR, "Server not known: ");
r = SSH_AUTH_ERROR;
goto out;
}
r = SSH_OK;
/* initialise list of authentication methods. yes, according to official libssh docs... */
ssh_userauth_none(ssh, NULL);
out:
if (r != SSH_OK) {
crypt_log(cd, CRYPT_LOG_ERROR, ssh_get_error(ssh));
crypt_log(cd, CRYPT_LOG_ERROR, "\n");
ssh_disconnect(ssh);
ssh_free(ssh);
ssh = NULL;
}
return ssh;
}
static void ssh_session_close(ssh_session ssh)
{
if (ssh) {
ssh_disconnect(ssh);
ssh_free(ssh);
}
}
static int _public_key_auth(struct crypt_device *cd, ssh_session ssh)
{
int r;
ssh_key pkey = NULL;
crypt_log(cd, CRYPT_LOG_DEBUG, "Trying public key authentication method.\n");
if (!(ssh_userauth_list(ssh, NULL) & SSH_AUTH_METHOD_PUBLICKEY)) {
crypt_log(cd, CRYPT_LOG_ERROR, "Public key auth method not allowed on host.\n");
return SSH_AUTH_ERROR;
}
r = ssh_pki_import_privkey_file("/home/user/.ssh/id_rsa", NULL, NULL, NULL, &pkey);
if (r != SSH_OK) {
crypt_log(cd, CRYPT_LOG_ERROR, "Failed to import private key\n");
return r;
}
r = ssh_userauth_try_publickey(ssh, NULL, pkey);
if (r == SSH_AUTH_SUCCESS) {
crypt_log(cd, CRYPT_LOG_DEBUG, "Public key method accepted.\n");
r = ssh_userauth_publickey(ssh, NULL, pkey);
}
ssh_key_free(pkey);
if (r != SSH_AUTH_SUCCESS) {
crypt_log(cd, CRYPT_LOG_ERROR, "Public key authentication error: ");
crypt_log(cd, CRYPT_LOG_ERROR, ssh_get_error(ssh));
crypt_log(cd, CRYPT_LOG_ERROR, "\n");
}
return r;
}
static int _password_auth(struct crypt_device *cd, ssh_session ssh, password_cb_func pcb)
{
int r = SSH_AUTH_ERROR;
char *ssh_password = NULL;
if (!(ssh_userauth_list(ssh, NULL) & SSH_AUTH_METHOD_PASSWORD)) {
crypt_log(cd, CRYPT_LOG_ERROR, "Password auth method not allowed on host.\n");
return r;
}
if (pcb(&ssh_password)) {
crypt_log(cd, CRYPT_LOG_ERROR, "Failed to process password.\n");
return r;
}
r = ssh_userauth_password(ssh, NULL, ssh_password);
free(ssh_password);
if (r != SSH_AUTH_SUCCESS) {
crypt_log(cd, CRYPT_LOG_ERROR, "Password authentication error: ");
crypt_log(cd, CRYPT_LOG_ERROR, ssh_get_error(ssh));
crypt_log(cd, CRYPT_LOG_ERROR, "\n");
}
return r;
}
static int SSHTEST_token_open(struct crypt_device *cd,
int token,
char **password,
size_t *password_len,
void *usrptr)
{
int r;
json_object *jobj_server, *jobj_user, *jobj_path, *jobj_token;
ssh_session ssh;
password_cb_func pcb = usrptr; /* custom password callback */
jobj_token = get_token_jobj(cd, token);
json_object_object_get_ex(jobj_token, "ssh_server", &jobj_server);
json_object_object_get_ex(jobj_token, "ssh_user", &jobj_user);
json_object_object_get_ex(jobj_token, "ssh_path", &jobj_path);
ssh = ssh_session_init(cd, json_object_get_string(jobj_server),
json_object_get_string(jobj_user));
if (!ssh)
return -EINVAL;
r = _public_key_auth(cd, ssh);
/* try password method fallback. superficial example use case for an usrptr */
if (r != SSH_AUTH_SUCCESS && pcb) {
crypt_log(cd, CRYPT_LOG_DEBUG, "Trying password method instead.\n");
r = _password_auth(cd, ssh, pcb);
}
if (r == SSH_AUTH_SUCCESS)
r = download_remote_password(cd, ssh, json_object_get_string(jobj_path),
password, password_len);
ssh_session_close(ssh);
return r ? -EINVAL : r;
}
const crypt_token_handler SSHTEST_token = {
.name = "sshkeytest",
.open = SSHTEST_token_open,
};
static int token_add(const char *device, const char *server,
const char *user, const char *path)
{
struct crypt_device *cd = NULL;
json_object *jobj = NULL, *jobj_keyslots;
int r;
r = crypt_token_register(&SSHTEST_token);
if (r < 0)
return EXIT_FAILURE;
r = crypt_init(&cd, device);
if (r < 0)
return EXIT_FAILURE;
r = crypt_load(cd, CRYPT_LUKS2, NULL);
if (r < 0) {
crypt_free(cd);
return EXIT_FAILURE;
}
jobj = json_object_new_object();
json_object_object_add(jobj, "type", json_object_new_string(SSHTEST_token.name)); /* mandatory */
jobj_keyslots = json_object_new_array();
json_object_array_add(jobj_keyslots, json_object_new_string("0")); /* assign to first keyslot only */
json_object_object_add(jobj, "keyslots", jobj_keyslots); /* mandatory array field (may be empty and assigned later */
/* custom metadata */
json_object_object_add(jobj, "ssh_server", json_object_new_string(server));
json_object_object_add(jobj, "ssh_user", json_object_new_string(user));
json_object_object_add(jobj, "ssh_path", json_object_new_string(path));
/* libcryptsetup API call */
r = crypt_token_json_set(cd, TOKEN_NUM, json_object_to_json_string_ext(jobj, JSON_C_TO_STRING_PLAIN));
crypt_free(cd);
json_object_put(jobj);
return EXIT_SUCCESS;
}
/* naive implementation of password prompt. Yes it will print out the password on input :) */
static int ssh_password_callback(char **ssh_password)
{
ssize_t i;
char *pass = malloc(512);
if (!pass)
return -ENOMEM;
fprintf(stdout, "Host asks for password:\n");
i = read(STDIN_FILENO, pass, 512);
if (i > 0) {
pass[i-1] = '\0';
i = 0;
} else if (i == 0) { /* EOF */
*pass = '\0';
i = -1;
}
if (!i)
*ssh_password = pass;
else
free(pass);
return i;
}
static int open_by_token(const char *device, const char *name)
{
struct crypt_device *cd = NULL;
int r;
r = crypt_token_register(&SSHTEST_token);
if (r < 0)
return EXIT_FAILURE;
r = crypt_init(&cd, device);
if (r < 0)
return EXIT_FAILURE;
r = crypt_load(cd, CRYPT_LUKS2, NULL);
if (r < 0) {
crypt_free(cd);
return EXIT_FAILURE;
}
r = crypt_activate_by_token(cd, name, TOKEN_NUM, ssh_password_callback, 0);
crypt_free(cd);
return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
}
static void keyslot_help(void)
{
printf("Use parameters:\n add device server user path\n"
" open device name\n");
exit(1);
}
int main(int argc, char *argv[])
{
crypt_set_debug_level(CRYPT_LOG_DEBUG);
/* Adding slot to device */
if (argc == 6 && !strcmp("add", argv[1]))
return token_add(argv[2], argv[3], argv[4], argv[5]);
/* Key check without activation */
if (argc == 3 && !strcmp("open", argv[1]))
return open_by_token(argv[2], NULL);
/* Key check with activation (requires root) */
if (argc == 4 && !strcmp("open", argv[1]))
return open_by_token(argv[2], argv[3]);
keyslot_help();
return 1;
}