libssh/libssh/server.c

/*
 * server.c - functions for creating a SSH server
 *
 * This file is part of the SSH Library
 *
 * Copyright (c) 2004-2005 by Aris Adamantiadis
 *
 * The SSH Library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 *
 * The SSH Library 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 Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the SSH Library; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 *
 * vim: ts=2 sw=2 et cindent
 */

/**
 * \defgroup ssh_server SSH Server
 * \addtogroup ssh_server
 * @{
 */

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#include "libssh/priv.h"
#include "libssh/libssh.h"
#include "libssh/server.h"
#include "libssh/ssh2.h"

#ifdef _WIN32

#include <winsock2.h>
#define SOCKOPT_TYPE_ARG4 char

/* We need to provide hstrerror. Not we can't call the parameter h_errno because it's #defined */
inline char *hstrerror(int h_errno_val) {
  static char text[50] = {0};

  snprintf(text, sizeof(text), "gethostbyname error %d\n", h_errno_val);

  return text;
}
#else /* _WIN32 */

#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#define SOCKOPT_TYPE_ARG4 int

#endif /* _WIN32 */

/* TODO FIXME: must use getaddrinfo */
static socket_t bind_socket(SSH_BIND *ssh_bind, const char *hostname,
    int port) {
  struct sockaddr_in myaddr;
  struct hostent *hp=NULL;
  socket_t s;
  int opt = 1;

  s = socket(PF_INET, SOCK_STREAM, 0);
  if (s < 0) {
    ssh_set_error(ssh_bind, SSH_FATAL, "%s", strerror(errno));
    return -1;
  }

#ifdef HAVE_GETHOSTBYNAME
  hp = gethostbyname(hostname);
#endif

  if (hp == NULL) {
    ssh_set_error(ssh_bind, SSH_FATAL,
        "Resolving %s: %s", hostname, hstrerror(h_errno));
    close(s);
    return -1;
  }

  memset(&myaddr, 0, sizeof(myaddr));
  memcpy(&myaddr.sin_addr, hp->h_addr, hp->h_length);
  myaddr.sin_family = hp->h_addrtype;
  myaddr.sin_port = htons(port);

  if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (char *)&opt, sizeof(opt)) < 0) {
    ssh_set_error(ssh_bind, SSH_FATAL,
        "Setting socket options failed: %s", hstrerror(h_errno));
    close(s);
    return -1;
  }

  if (bind(s, (struct sockaddr *) &myaddr, sizeof(myaddr)) < 0) {
    ssh_set_error(ssh_bind, SSH_FATAL, "Binding to %s:%d: %s",
        hostname,
        port,
        strerror(errno));
    close(s);
    return -1;
  }

  return s;
}

SSH_BIND *ssh_bind_new(void) {
  SSH_BIND *ptr;

  ptr = malloc(sizeof(SSH_BIND));
  if (ptr == NULL) {
    return NULL;
  }
  ZERO_STRUCTP(ptr);
  ptr->bindfd = -1;

  return ptr;
}

void ssh_bind_set_options(SSH_BIND *ssh_bind, SSH_OPTIONS *options) {
  ssh_bind->options = options;
}

int ssh_bind_listen(SSH_BIND *ssh_bind) {
  const char *host;
  int fd;

  if (ssh_bind->options == NULL) {
    return -1;
  }

  if (ssh_socket_init() < 0) {
    return -1;
  }

  host = ssh_bind->options->bindaddr;
  if (host == NULL) {
    host = "0.0.0.0";
  }

  fd = bind_socket(ssh_bind, host, ssh_bind->options->bindport);
  if (fd < 0) {
    return -1;
  }
  ssh_bind->bindfd = fd;

  if (listen(fd, 10) < 0) {
    ssh_set_error(ssh_bind, SSH_FATAL,
        "Listening to socket %d: %s",
        fd, strerror(errno));
    close(fd);
    return -1;
  }

  return 0;
}

void ssh_bind_set_blocking(SSH_BIND *ssh_bind, int blocking) {
  ssh_bind->blocking = blocking ? 1 : 0;
}

int ssh_bind_get_fd(SSH_BIND *ssh_bind) {
  return ssh_bind->bindfd;
}

void ssh_bind_fd_toaccept(SSH_BIND *ssh_bind) {
  ssh_bind->toaccept = 1;
}

SSH_SESSION *ssh_bind_accept(SSH_BIND *ssh_bind) {
  SSH_SESSION *session;
  PRIVATE_KEY *dsa = NULL;
  PRIVATE_KEY *rsa = NULL;
  int fd = -1;

  if (ssh_bind->bindfd < 0) {
    ssh_set_error(ssh_bind, SSH_FATAL,
        "Can't accept new clients on a not bound socket.");
    return NULL;
  }

  if (ssh_bind->options->dsakey == NULL || ssh_bind->options->rsakey == NULL) {
    ssh_set_error(ssh_bind, SSH_FATAL,
        "DSA or RSA host key file must be set before accept()");
    return NULL;
  }

  if (ssh_bind->options->dsakey) {
    dsa = _privatekey_from_file(ssh_bind, ssh_bind->options->dsakey, TYPE_DSS);
    if (dsa == NULL) {
      return NULL;
    }
  }

  if (ssh_bind->options->rsakey) {
    rsa = _privatekey_from_file(ssh_bind, ssh_bind->options->rsakey, TYPE_RSA);
    if (rsa == NULL) {
      privatekey_free(dsa);
      return NULL;
    }
  }

  fd = accept(ssh_bind->bindfd, NULL, NULL);
  if (fd < 0) {
    ssh_set_error(ssh_bind, SSH_FATAL,
        "Accepting a new connection: %s",
        strerror(errno));
    privatekey_free(dsa);
    privatekey_free(rsa);
    return NULL;
  }

  session = ssh_new();
  if (session == NULL) {
    ssh_set_error(ssh_bind, SSH_FATAL, "Not enough space");
    privatekey_free(dsa);
    privatekey_free(rsa);
    return NULL;
  }
  session->server = 1;
  session->version = 2;
  session->options = ssh_options_copy(ssh_bind->options);
  if (session->options == NULL) {
    ssh_set_error(ssh_bind, SSH_FATAL, "No space left");
    privatekey_free(dsa);
    privatekey_free(rsa);
    ssh_cleanup(session);
    return NULL;
  }

  ssh_socket_free(session->socket);
  session->socket = ssh_socket_new(session);
  if (session->socket == NULL) {
    privatekey_free(dsa);
    privatekey_free(rsa);
    ssh_cleanup(session);
    return NULL;
  }
  ssh_socket_set_fd(session->socket,fd);
  session->dsa_key = dsa;
  session->rsa_key = rsa;

  return session;
}

void ssh_bind_free(SSH_BIND *ssh_bind){
    if(ssh_bind->bindfd>=0)
        close(ssh_bind->bindfd);
    ssh_bind->bindfd=-1;
    if(ssh_bind->options)
    	ssh_options_free(ssh_bind->options);
    free(ssh_bind);
}

extern char *supported_methods[];

static int server_set_kex(SSH_SESSION * session) {
    KEX *server = &session->server_kex;
    SSH_OPTIONS *options = session->options;
    int i, j;
    char *wanted;
    memset(server,0,sizeof(KEX));
    // the program might ask for a specific cookie to be sent. useful for server
    //   debugging
    if (options->wanted_cookie)
        memcpy(server->cookie, options->wanted_cookie, 16);
    else
        ssh_get_random(server->cookie, 16,0);
    if (session->dsa_key && session->rsa_key) {
      if (ssh_options_set_wanted_algos(options, SSH_HOSTKEYS, "ssh-dss,ssh-rsa") < 0) {
        return -1;
      }
    } else {
      if (session->dsa_key) {
        if (ssh_options_set_wanted_algos(options, SSH_HOSTKEYS, "ssh-dss") < 0) {
          return -1;
        }
      } else {
        if (ssh_options_set_wanted_algos(options, SSH_HOSTKEYS, "ssh-rsa") < 0) {
          return -1;
        }
      }
    }
    server->methods = malloc(10 * sizeof(char **));
    if (server->methods == NULL) {
      return -1;
    }
    for (i = 0; i < 10; i++) {
        if (!(wanted = options->wanted_methods[i]))
            wanted = supported_methods[i];
        server->methods[i] = strdup(wanted);
        if (server->methods[i] == NULL) {
          for (j = i - 1; j <= 0; j--) {
            SAFE_FREE(server->methods[j]);
          }
          SAFE_FREE(server->methods);
          return -1;
        }
    }
    return 0;
}

static int dh_handshake_server(SSH_SESSION *session){
    STRING *e,*f,*pubkey,*sign;
    PUBLIC_KEY *pub;
    PRIVATE_KEY *prv;
    BUFFER *buf=buffer_new();
    if (packet_wait(session, SSH2_MSG_KEXDH_INIT, 1) != SSH_OK)
        return -1;
    e=buffer_get_ssh_string(session->in_buffer);
    if(!e){
        ssh_set_error(session,SSH_FATAL,"No e number in client request");
        return -1;
    }
    if (dh_import_e(session, e) < 0) {
      ssh_set_error(session,SSH_FATAL,"Cannot import e number");
      return -1;
    }
    free(e);
    if (dh_generate_y(session) < 0) {
      ssh_set_error(session,SSH_FATAL,"Could not create y number");
      return -1;
    }
    if (dh_generate_f(session) < 0) {
      ssh_set_error(session,SSH_FATAL,"Could not create f number");
      return -1;
    }
    f=dh_get_f(session);
    switch(session->hostkeys){
        case TYPE_DSS:
            prv=session->dsa_key;
            break;
        case TYPE_RSA:
            prv=session->rsa_key;
            break;
        default:
            prv=NULL;
    }
    pub=publickey_from_privatekey(prv);
    pubkey=publickey_to_string(pub);
    publickey_free(pub);
    dh_import_pubkey(session,pubkey);
    if (dh_build_k(session) < 0) {
      return -1;
    }
    if (make_sessionid(session) != SSH_OK) {
      return -1;
    }
    sign=ssh_sign_session_id(session,prv);
    buffer_free(buf);
    /* free private keys as they should not be readable past this point */
    if(session->rsa_key){
        privatekey_free(session->rsa_key);
        session->rsa_key=NULL;
    }
    if(session->dsa_key){
        privatekey_free(session->dsa_key);
        session->dsa_key=NULL;
    }
    buffer_add_u8(session->out_buffer,SSH2_MSG_KEXDH_REPLY);
    buffer_add_ssh_string(session->out_buffer,pubkey);
    buffer_add_ssh_string(session->out_buffer,f);
    buffer_add_ssh_string(session->out_buffer,sign);
    free(sign);
    packet_send(session);
    free(f);
    buffer_add_u8(session->out_buffer,SSH2_MSG_NEWKEYS);
    packet_send(session);
    ssh_log(session, SSH_LOG_PACKET, "SSH_MSG_NEWKEYS sent");

    packet_wait(session,SSH2_MSG_NEWKEYS,1);
    ssh_log(session, SSH_LOG_PACKET, "Got SSH_MSG_NEWKEYS");
    if (generate_session_keys(session) < 0) {
      return -1;
    }
    /* once we got SSH2_MSG_NEWKEYS we can switch next_crypto and current_crypto */
    if(session->current_crypto)
        crypto_free(session->current_crypto);
    /* XXX later, include a function to change keys */
    session->current_crypto=session->next_crypto;
    session->next_crypto = crypto_new();
    if (session->next_crypto == NULL) {
      return -1;
    }
    return 0;
}
/* do the banner and key exchange */
int ssh_accept(SSH_SESSION *session){
    ssh_send_banner(session,1);
    if (ssh_crypto_init() < 0) {
      return -1;
    }
    session->alive=1;
    session->clientbanner=ssh_get_banner(session);
    if (server_set_kex(session) < 0) {
      return -1;
    }
    ssh_send_kex(session,1);
    if(ssh_get_kex(session,1) < 0) {
        return -1;
    }
    ssh_list_kex(session, &session->client_kex);
    crypt_set_algorithms_server(session);
    if(dh_handshake_server(session))
        return -1;
    session->connected=1;
    return 0;
}
/** @}
 */