libssh/examples/samplesshd-kbdint.c

/* This is a sample implementation of a libssh based SSH server */
/*
Copyright 2003-2011 Aris Adamantiadis

This file is part of the SSH Library

You are free to copy this file, modify it in any way, consider it being public
domain. This does not apply to the rest of the library though, but it is
allowed to cut-and-paste working code from this file to any license of
program.
The goal is to show the API in action. It's not a reference on how terminal
clients must be made or how a client should react.
*/

#include "config.h"

#include <libssh/libssh.h>
#include <libssh/server.h>

#ifdef HAVE_ARGP_H
#include <argp.h>
#endif
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <stdbool.h>

#ifndef BUF_SIZE
#define BUF_SIZE 2048
#endif

#define SSHD_USER "libssh"
#define SSHD_PASSWORD "libssh"

#ifndef KEYS_FOLDER
#ifdef _WIN32
#define KEYS_FOLDER
#else
#define KEYS_FOLDER "/etc/ssh/"
#endif
#endif

static int port = 22;
static bool authenticated = false;

#ifdef WITH_PCAP
static const char *pcap_file = "debug.server.pcap";
static ssh_pcap_file pcap;

static void set_pcap(ssh_session session){
	if(!pcap_file)
		return;
	pcap=ssh_pcap_file_new();
	if(ssh_pcap_file_open(pcap,pcap_file) == SSH_ERROR){
		printf("Error opening pcap file\n");
		ssh_pcap_file_free(pcap);
		pcap=NULL;
		return;
	}
	ssh_set_pcap_file(session,pcap);
}

static void cleanup_pcap(void) {
	ssh_pcap_file_free(pcap);
	pcap=NULL;
}
#endif


static int auth_password(const char *user, const char *password)
{
    int cmp;

    cmp = strcmp(user, SSHD_USER);
    if (cmp != 0) {
        return 0;
    }
    cmp = strcmp(password, SSHD_PASSWORD);
    if (cmp != 0) {
        return 0;
    }

    authenticated = true;
    return 1; // authenticated
}
#ifdef HAVE_ARGP_H
const char *argp_program_version = "libssh server example "
  SSH_STRINGIFY(LIBSSH_VERSION);
const char *argp_program_bug_address = "<libssh@libssh.org>";

/* Program documentation. */
static char doc[] = "libssh -- a Secure Shell protocol implementation";

/* A description of the arguments we accept. */
static char args_doc[] = "BINDADDR";

/* The options we understand. */
static struct argp_option options[] = {
  {
    .name  = "port",
    .key   = 'p',
    .arg   = "PORT",
    .flags = 0,
    .doc   = "Set the port to bind.",
    .group = 0
  },
  {
    .name  = "hostkey",
    .key   = 'k',
    .arg   = "FILE",
    .flags = 0,
    .doc   = "Set the host key.",
    .group = 0
  },
  {
    .name  = "dsakey",
    .key   = 'd',
    .arg   = "FILE",
    .flags = 0,
    .doc   = "Set the dsa key.",
    .group = 0
  },
  {
    .name  = "rsakey",
    .key   = 'r',
    .arg   = "FILE",
    .flags = 0,
    .doc   = "Set the rsa key.",
    .group = 0
  },
  {
    .name  = "verbose",
    .key   = 'v',
    .arg   = NULL,
    .flags = 0,
    .doc   = "Get verbose output.",
    .group = 0
  },
  {NULL, 0, 0, 0, NULL, 0}
};

/* Parse a single option. */
static error_t parse_opt (int key, char *arg, struct argp_state *state) {
  /* Get the input argument from argp_parse, which we
   * know is a pointer to our arguments structure.
   */
  ssh_bind sshbind = state->input;

  switch (key) {
    case 'p':
      ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_BINDPORT_STR, arg);
      port = atoi(arg);
      break;
    case 'd':
      ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_DSAKEY, arg);
      break;
    case 'k':
      ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_HOSTKEY, arg);
      break;
    case 'r':
      ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_RSAKEY, arg);
      break;
    case 'v':
      ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_LOG_VERBOSITY_STR, "3");
      break;
    case ARGP_KEY_ARG:
      if (state->arg_num >= 1) {
        /* Too many arguments. */
        argp_usage (state);
      }
      ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_BINDADDR, arg);
      break;
    case ARGP_KEY_END:
      if (state->arg_num < 1) {
        /* Not enough arguments. */
        argp_usage (state);
      }
      break;
    default:
      return ARGP_ERR_UNKNOWN;
  }

  return 0;
}

/* Our argp parser. */
static struct argp argp = {options, parse_opt, args_doc, doc, NULL, NULL, NULL};
#endif /* HAVE_ARGP_H */

static const char *name;
static const char *instruction;
static const char *prompts[2];
static char echo[] = { 1, 0 };

static int kbdint_check_response(ssh_session session) {
    int count;

    count = ssh_userauth_kbdint_getnanswers(session);
    if(count != 2) {
        instruction = "Something weird happened :(";
        return 0;
    }
    if(strcasecmp("Arthur Dent",
                        ssh_userauth_kbdint_getanswer(session, 0)) != 0) {
        instruction = "OK, this is not YOUR name, "
                                        "but it's a reference to the HGTG...";
        prompts[0] = "The main character's full name: ";
        return 0;
    }
    if(strcmp("42", ssh_userauth_kbdint_getanswer(session, 1)) != 0) {
        instruction = "Make an effort !!! What is the Answer to the Ultimate "
                            "Question of Life, the Universe, and Everything ?";
        prompts[1] = "Answer to the Ultimate Question of Life, the Universe, "
                            "and Everything: ";
        return 0;
    }

    authenticated = true;
    return 1;
}

static int authenticate(ssh_session session) {
    ssh_message message;

    name = "\n\nKeyboard-Interactive Fancy Authentication\n";
    instruction = "Please enter your real name and your password";
    prompts[0] = "Real name: ";
    prompts[1] = "Password: ";

    do {
        message=ssh_message_get(session);
        if(!message)
            break;
        switch(ssh_message_type(message)){
            case SSH_REQUEST_AUTH:
                switch(ssh_message_subtype(message)){
                    case SSH_AUTH_METHOD_PASSWORD:
                        printf("User %s wants to auth with pass %s\n",
                               ssh_message_auth_user(message),
                               ssh_message_auth_password(message));
                        if(auth_password(ssh_message_auth_user(message),
                           ssh_message_auth_password(message))){
                               ssh_message_auth_reply_success(message,0);
                               ssh_message_free(message);
                               return 1;
                           }
                        ssh_message_auth_set_methods(message,
                                                SSH_AUTH_METHOD_PASSWORD |
                                                SSH_AUTH_METHOD_INTERACTIVE);
                        // not authenticated, send default message
                        ssh_message_reply_default(message);
                        break;

                    case SSH_AUTH_METHOD_INTERACTIVE:
                        if(!ssh_message_auth_kbdint_is_response(message)) {
                            printf("User %s wants to auth with kbdint\n",
                                   ssh_message_auth_user(message));
                            ssh_message_auth_interactive_request(message, name,
                                                    instruction, 2, prompts, echo);
                        } else {
                            if(kbdint_check_response(session)) {
                                ssh_message_auth_reply_success(message,0);
                                ssh_message_free(message);
                                return 1;
                            }
                            ssh_message_auth_set_methods(message,
                                                    SSH_AUTH_METHOD_PASSWORD |
                                                    SSH_AUTH_METHOD_INTERACTIVE);
                            ssh_message_reply_default(message);
                        }
                        break;
                    case SSH_AUTH_METHOD_NONE:
                    default:
                        printf("User %s wants to auth with unknown auth %d\n",
                               ssh_message_auth_user(message),
                               ssh_message_subtype(message));
                        ssh_message_auth_set_methods(message,
                                                SSH_AUTH_METHOD_PASSWORD |
                                                SSH_AUTH_METHOD_INTERACTIVE);
                        ssh_message_reply_default(message);
                        break;
                }
                break;
            default:
                ssh_message_auth_set_methods(message,
                                                SSH_AUTH_METHOD_PASSWORD |
                                                SSH_AUTH_METHOD_INTERACTIVE);
                ssh_message_reply_default(message);
        }
        ssh_message_free(message);
    } while (1);
    return 0;
}

int main(int argc, char **argv){
    ssh_session session;
    ssh_bind sshbind;
    ssh_message message;
    ssh_channel chan=0;
    char buf[BUF_SIZE];
    int auth=0;
    int shell=0;
    int i;
    int r;

    sshbind=ssh_bind_new();
    session=ssh_new();

    ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_DSAKEY,
                                            KEYS_FOLDER "ssh_host_dsa_key");
    ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_RSAKEY,
                                            KEYS_FOLDER "ssh_host_rsa_key");

#ifdef HAVE_ARGP_H
    /*
     * Parse our arguments; every option seen by parse_opt will
     * be reflected in arguments.
     */
    argp_parse (&argp, argc, argv, 0, 0, sshbind);
#else
    (void) argc;
    (void) argv;
#endif
#ifdef WITH_PCAP
    set_pcap(session);
#endif

    if(ssh_bind_listen(sshbind)<0){
        printf("Error listening to socket: %s\n", ssh_get_error(sshbind));
        return 1;
    }
    printf("Started sample libssh sshd on port %d\n", port);
    printf("You can login as the user %s with the password %s\n", SSHD_USER,
                                                            SSHD_PASSWORD);
    r = ssh_bind_accept(sshbind, session);
    if(r==SSH_ERROR){
      printf("Error accepting a connection: %s\n", ssh_get_error(sshbind));
      return 1;
    }
    if (ssh_handle_key_exchange(session)) {
        printf("ssh_handle_key_exchange: %s\n", ssh_get_error(session));
        return 1;
    }

    /* proceed to authentication */
    auth = authenticate(session);
    if (!auth || !authenticated) {
        printf("Authentication error: %s\n", ssh_get_error(session));
        ssh_disconnect(session);
        return 1;
    }


    /* wait for a channel session */
    do {
        message = ssh_message_get(session);
        if(message){
            if(ssh_message_type(message) == SSH_REQUEST_CHANNEL_OPEN &&
                    ssh_message_subtype(message) == SSH_CHANNEL_SESSION) {
                chan = ssh_message_channel_request_open_reply_accept(message);
                ssh_message_free(message);
                break;
            } else {
                ssh_message_reply_default(message);
                ssh_message_free(message);
            }
        } else {
            break;
        }
    } while(!chan);

    if(!chan) {
        printf("Error: cleint did not ask for a channel session (%s)\n",
                                                    ssh_get_error(session));
        ssh_finalize();
        return 1;
    }


    /* wait for a shell */
    do {
        message = ssh_message_get(session);
        if(message != NULL) {
            if(ssh_message_type(message) == SSH_REQUEST_CHANNEL &&
                    ssh_message_subtype(message) == SSH_CHANNEL_REQUEST_SHELL) {
                shell = 1;
                ssh_message_channel_request_reply_success(message);
                ssh_message_free(message);
                break;
            }
            ssh_message_reply_default(message);
            ssh_message_free(message);
        } else {
            break;
        }
    } while(!shell);

    if(!shell) {
        printf("Error: No shell requested (%s)\n", ssh_get_error(session));
        return 1;
    }


    printf("it works !\n");
    do{
        i=ssh_channel_read(chan,buf, sizeof(buf), 0);
        if(i>0) {
            if(*buf == '' || *buf == '')
                    break;
            if(i == 1 && *buf == '\r')
                ssh_channel_write(chan, "\r\n", 2);
            else
                ssh_channel_write(chan, buf, i);
            if (write(1,buf,i) < 0) {
                printf("error writing to buffer\n");
                return 1;
            }
        }
    } while (i>0);
    ssh_channel_close(chan);
    ssh_disconnect(session);
    ssh_bind_free(sshbind);
#ifdef WITH_PCAP
    cleanup_pcap();
#endif
    ssh_finalize();
    return 0;
}