inetutils/libinetutils/shishi.c

/* shishi.c -- functions to use kerberos V with shishi
  Copyright (C) 2005-2025 Free Software Foundation, Inc.

  This file is part of GNU Inetutils.

  GNU Inetutils 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 3 of the License, or (at
  your option) any later version.

  GNU Inetutils 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, see `http://www.gnu.org/licenses/'. */

#include <config.h>

#ifdef SHISHI
# include <string.h>
# include <stdlib.h>
# include <errno.h>
# include <shishi.h>
# include <syslog.h>
# include <unistd.h>
# include <shishi_def.h>

/* shishi authentication, client side */
int
shishi_auth (Shishi **handle, int verbose, char **cname,
	     const char *sname, int sock, char *cmd,
	     unsigned short port, Shishi_key **enckey, const char *realm)
{
  Shishi_ap *ap;
  Shishi_tkt *tkt;
  Shishi_tkts_hint hint;
  Shishi *h;

  int rc;
  char *out, *p;
  size_t outlen;
  int krb5len, msglen;
  char *tmpserver;
  char auth;
  /* KERBEROS 5 SENDAUTH MESSAGE */
  char krb5sendauth[] = "KRB5_SENDAUTH_V1.0";
  /* PROTOCOL VERSION */
  char krb5sendclient[] = "KCMDV0.2";
  /* to store error msg sent by server */
  char errormsg[101];
  char cksumdata[101];

  if (!shishi_check_version (SHISHI_VERSION))
    {
      fprintf (stderr, "shishi_check_version() failed:\n"
	       "Header file incompatible with shared library.\n");
      return SHISHI_INVALID_ARGUMENT;
    }

  rc = shishi_init (handle);
  if (rc != SHISHI_OK)
    {
      fprintf (stderr,
	       "error initializing shishi: %s\n", shishi_strerror (rc));
      return rc;
    }

  if (realm)
    shishi_realm_default_set (*handle, realm);

  h = *handle;

  if (!*cname)
    *cname = (char *) shishi_principal_default (h);

  /* size of KRB5 auth message */
  krb5len = strlen (krb5sendauth) + 1;
  msglen = htonl (krb5len);
  write (sock, &msglen, sizeof (int));
  /* KRB5 authentication message */
  write (sock, krb5sendauth, krb5len);
  /* size of client message */
  krb5len = strlen (krb5sendclient) + 1;
  msglen = htonl (krb5len);
  write (sock, &msglen, sizeof (int));
  /* KRB5 client message */
  write (sock, krb5sendclient, krb5len);

  /* get answer from server 0 = ok, 1 = error with message */
  read (sock, &auth, 1);
  if (auth)
    {
      ssize_t n;

      errormsg[0] = '\0';
      n = read (sock, errormsg, sizeof (errormsg) - 1);

      if (n >= 0 && n < (ssize_t) sizeof (errormsg))
	errormsg[n] = '\0';
      else
	errormsg[sizeof (errormsg) - 1] = '\0';

      fprintf (stderr, "Error during server authentication : %s\n", errormsg);
      return SHISHI_VERIFY_FAILED;
    }

  if (verbose)
    {
      printf ("Client: %s\n", *cname);
      printf ("Server: %s\n", sname);
    }

  /* Get a ticket for the server. */

  memset (&hint, 0, sizeof (hint));

  tmpserver = malloc (strlen (SERVICE) + strlen (sname) + 2);
  if (!tmpserver)
    {
      perror ("shishi_auth()");
      return SHISHI_TOO_SMALL_BUFFER;
    }

  p = strchr (sname, '/');
  if (p && (p != sname))
    strcpy (tmpserver, sname);	/* Non-empty prefix.  */
  else
    sprintf (tmpserver, "%s/%s", SERVICE, sname + (p ? 1 : 0));

  /* Retrieve realm assigned to this server as per configuration,
   * unless an explicit domain was passed in the call.
   */
  if (!realm)
    {
      if (!p)
	p = (char *) sname;
      else if (*p == '/')
	++p;

      shishi_realm_default_set (h, shishi_realm_for_server (h, p));
    }

  hint.client = (char *) *cname;
  hint.server = (char *) tmpserver;

  tkt = shishi_tkts_get (shishi_tkts_default (h), &hint);
  if (!tkt)
    {
      fprintf (stderr, "cannot find ticket for \"%s@%s\"\n",
	       tmpserver, shishi_realm_default (h));
      free (tmpserver);
      return SHISHI_INVALID_TICKET;
    }

  free (tmpserver);

  if (verbose)
    shishi_tkt_pretty_print (tkt, stderr);

  /* Create Authentication context */

  rc = shishi_ap_tktoptions (h, &ap, tkt, SHISHI_APOPTIONS_MUTUAL_REQUIRED);
  if (rc != SHISHI_OK)
    {
      fprintf (stderr, "cannot create authentication context\n");
      return rc;
    }


  /* checksum = port: terminal name */

  snprintf (cksumdata, sizeof (cksumdata) - 1,
	    "%u:%s%s", ntohs (port), cmd, *cname);

  /* add checksum to authenticator */

  shishi_ap_authenticator_cksumdata_set (ap, cksumdata, strlen (cksumdata));
  /* To be compatible with MIT rlogind */
  shishi_ap_authenticator_cksumtype_set (ap, SHISHI_RSA_MD5);

  /* create der encoded AP-REQ */

  rc = shishi_ap_req_der (ap, &out, &outlen);
  if (rc != SHISHI_OK)
    {
      fprintf (stderr, "cannot build authentication request: %s\n",
	       shishi_strerror (rc));

      return rc;
    }

  if (verbose)
    shishi_authenticator_print (h, stderr, shishi_ap_authenticator (ap));

  /* extract subkey if present from ap exchange for secure connection */

  if (enckey)
    shishi_authenticator_get_subkey (h, shishi_ap_authenticator (ap), enckey);

  /* send size of AP-REQ to the server */

  msglen = outlen;
  msglen = htonl (msglen);
  write (sock, (char *) &msglen, sizeof (int));

  /* send AP-REQ to the server */

  write (sock, out, outlen);

  /* read response from server - what ? */

  read (sock, &rc, sizeof (rc));
  if (rc)
    return SHISHI_APREP_VERIFY_FAILED;

  /* For mutual authentication, wait for server reply. */

  if (shishi_apreq_mutual_required_p (h, shishi_ap_req (ap)))
    {
      if (verbose)
	printf ("Waiting for server to authenticate itself...\n");

      /* read size of the AP-REP */

      read (sock, (char *) &msglen, sizeof (int));

      /* read AP-REP */
      outlen = ntohl (msglen);
      outlen = read (sock, out, outlen);

      rc = shishi_ap_rep_verify_der (ap, out, outlen);
      if (rc == SHISHI_OK)
	{
	  if (verbose)
	    printf ("AP-REP verification OK...\n");
	}
      else
	{
	  if (rc == SHISHI_APREP_VERIFY_FAILED)
	    fprintf (stderr, "AP-REP verification failed...\n");
	  else
	    fprintf (stderr, "AP-REP verification error: %s\n",
		     shishi_strerror (rc));
	  return rc;
	}

      /* The server is authenticated. */
      if (verbose)
	printf ("Server authenticated.\n");
    }

  /* We are now authenticated. */
  if (verbose)
    printf ("User authenticated.\n");

  return SHISHI_OK;

}

/*
 * XXX: Is this ever needed?
 *
static void
senderror (int s, char type, char *buf)
{
  write (s, &type, sizeof (char));
  write (s, buf, strlen (buf));
}
*/

/* shishi authentication, server side */
int
get_auth (int infd, Shishi **handle, Shishi_ap **ap,
	  Shishi_key **enckey, const char **err_msg, int *protoversion,
	  int *cksumtype, char **cksum, size_t *cksumlen, char *srvname)
{
  Shishi_key *key;
  char *out;
  size_t outlen;
  char *buf;
  int buflen;
  int len;
  int rc;
  int error;
  /* KERBEROS 5 SENDAUTH MESSAGE */
  char krb5sendauth[] = "KRB5_SENDAUTH_V1.0";
  /* PROTOCOL VERSION */
  char krb5kcmd1[] = "KCMDV0.1";
  char krb5kcmd2[] = "KCMDV0.2";
  char *servername, *server = NULL, *realm = NULL;

  *err_msg = NULL;
  /* Get key for the server. */

  if (!shishi_check_version (SHISHI_VERSION))
    {
      *err_msg =
	"shishi_check_version() failed: header file incompatible with shared library.";
      return SHISHI_INVALID_ARGUMENT;
    }

  rc = shishi_init_server (handle);
  if (rc != SHISHI_OK)
    return rc;

  if (srvname && *srvname)
    {
      rc = shishi_parse_name (*handle, srvname, &server, &realm);
      if (rc != SHISHI_OK)
	{
	  *err_msg = shishi_strerror (rc);
	  return rc;
	}
    }

  if (server && *server)
    {
      char *p;

      servername = malloc (sizeof (SERVICE) + strlen (server) + 2);
      if (!servername)
	{
	  *err_msg = "Not enough memory";
	  return SHISHI_TOO_SMALL_BUFFER;
	}

      p = strchr (server, '/');
      if (p && (p != server))
	sprintf (servername, "%s", server);	/* Non-empty prefix.  */
      else
	sprintf (servername, "%s/%s", SERVICE, server + (p ? 1 : 0));	/* Remove initial slash.  */
    }
  else
    servername = shishi_server_for_local_service (*handle, SERVICE);

  if (realm && *realm)
    shishi_realm_default_set (*handle, realm);

  free (server);
  free (realm);

  /* Enable use of `~/.k5login'.  */
  if (shishi_check_version ("1.0.2"))	/* Faulty in version 1.0.1.  */
    {
      rc = shishi_cfg_authorizationtype_set (*handle, "k5login basic");
      if (rc != SHISHI_OK)
	{
	  *err_msg = shishi_error (*handle);
	  return rc;
	}
    }

  key = shishi_hostkeys_for_serverrealm (*handle, servername,
					 shishi_realm_default (*handle));
  free (servername);
  if (!key)
    {
      *err_msg = shishi_error (*handle);
      return SHISHI_INVALID_KEY;
    }

  /* Read Kerberos 5 sendauth message */
  rc = read (infd, &len, sizeof (int));
  if (rc != sizeof (int))
    {
      *err_msg = "Error reading message size";
      return SHISHI_IO_ERROR;
    }

  buflen = ntohl (len);
  buf = malloc (buflen);
  if (!buf)
    {
      *err_msg = "Not enough memory";
      return SHISHI_TOO_SMALL_BUFFER;
    }

  rc = read (infd, buf, buflen);
  if (rc != buflen)
    {
      *err_msg = "Error reading authentication message";
      return SHISHI_IO_ERROR;
    }

  len = strlen (krb5sendauth);
  rc = strncmp (buf, krb5sendauth, buflen >= len ? len : buflen);
  if (rc)
    {
      *err_msg = "Invalid authentication type";
      /* Authentication type is wrong.  */
      write (infd, "\001", 1);
      return SHISHI_VERIFY_FAILED;
    }

  free (buf);

  /* Read protocol version */
  rc = read (infd, &len, sizeof (int));
  if (rc != sizeof (int))
    {
      *err_msg = "Error reading protocol message size";
      return SHISHI_IO_ERROR;
    }
  buflen = ntohl (len);
  buf = malloc (buflen);
  if (!buf)
    {
      *err_msg = "Not enough memory";
      return SHISHI_TOO_SMALL_BUFFER;
    }

  rc = read (infd, buf, buflen);
  if (rc != buflen)
    {
      *err_msg = "Error reading protocol message";
      return SHISHI_IO_ERROR;
    }

  len = strlen (krb5kcmd1);
  rc = strncmp (buf, krb5kcmd1, buflen >= len ? len : buflen);
  if (rc)
    {
      len = strlen (krb5kcmd2);
      rc = strncmp (buf, krb5kcmd2, buflen >= len ? len : buflen);
      if (rc)
	{
	  *err_msg = "Protocol version not supported";
	  /* Protocol version is wrong.  */
	  write (infd, "\002", 1);
	  return SHISHI_VERIFY_FAILED;
	}
      *protoversion = 2;
    }
  else
    *protoversion = 1;

  free (buf);

  /* Authentication type is ok */

  write (infd, "\0", 1);

  /* Read Authentication request from client */

  rc = read (infd, &len, sizeof (int));
  if (rc != sizeof (int))
    {
      *err_msg = "Error reading authentication request size";
      return SHISHI_IO_ERROR;
    }

  buflen = ntohl (len);
  buf = malloc (buflen);
  if (!buf)
    {
      *err_msg = "Not enough memory";
      return SHISHI_TOO_SMALL_BUFFER;
    }

  rc = read (infd, buf, buflen);
  if (rc != buflen)
    {
      *err_msg = "Error reading authentication request";
      return SHISHI_IO_ERROR;
    }

  /* Create Authentication context */

  rc = shishi_ap_nosubkey (*handle, ap);
  if (rc != SHISHI_OK)
    return rc;

  /* Store request in context */

  rc = shishi_ap_req_der_set (*ap, buf, buflen);
  if (rc != SHISHI_OK)
    return rc;

  free (buf);

  /* Process authentication request */

  rc = shishi_ap_req_process (*ap, key);
  if (rc != SHISHI_OK)
    return rc;

# ifdef ENCRYPTION

  /* extract subkey if present from ap exchange for secure connection */
  if (*protoversion == 2)
    {
      *enckey = NULL;
      shishi_authenticator_get_subkey (*handle,
				       shishi_ap_authenticator (*ap), enckey);
    }

# endif

  /* Get authenticator checksum */
  rc = shishi_authenticator_cksum (*handle,
				   shishi_ap_authenticator (*ap),
				   cksumtype, cksum, cksumlen);
  if (rc != SHISHI_OK)
    return rc;

  /* User is authenticated.  */
  error = 0;
  write (infd, &error, sizeof (int));

  /* Authenticate ourself to client, if requested.  */

  if (shishi_apreq_mutual_required_p (*handle, shishi_ap_req (*ap)))
    {
      int len;

      rc = shishi_ap_rep_der (*ap, &out, &outlen);
      if (rc != SHISHI_OK)
	return rc;

      len = outlen;
      len = htonl (len);
      rc = write (infd, &len, sizeof (len));
      if (rc != sizeof (int))
	{
	  *err_msg = "Error sending AP-REP";
	  free (out);
	  return SHISHI_IO_ERROR;
	}

      rc = write (infd, out, ntohl (len));
      if (rc != (int) ntohl (len))
	{
	  *err_msg = "Error sending AP-REP";
	  free (out);
	  return SHISHI_IO_ERROR;
	}

      free (out);

      /* We are authenticated to client */
    }

# ifdef ENCRYPTION
  if (*protoversion == 1)
    {
      Shishi_tkt *tkt;

      tkt = shishi_ap_tkt (*ap);
      if (tkt == NULL)
	{
	  *err_msg = "Could not get tkt from AP-REQ";
	  return SHISHI_INVALID_TICKET;
	}

      rc = shishi_encticketpart_get_key (*handle,
					 shishi_tkt_encticketpart (tkt),
					 enckey);
      if (rc != SHISHI_OK)
	return rc;
    }
# endif

  return SHISHI_OK;
}

# ifdef ENCRYPTION

/* read encrypted data on socket */
int
readenc (Shishi *h, int sock, char *buf, int *len, shishi_ivector *iv,
	 Shishi_key *enckey, int proto)
{
  char *out;
  char *outbis;

  int rc;
  int val;
  size_t outlen;
  int dlen = 0, blocksize, enctype, hashsize;

  /* read size of message */
  read (sock, &dlen, sizeof (int));

  dlen = ntohl (dlen);
  /* if 0 put read size to 0 */
  if (!dlen)
    {
      *len = dlen;
      return SHISHI_OK;
    }

  if (proto == 1)
    *len = dlen;

  /* convert size to encryption size */
  enctype = shishi_key_type (enckey);

  blocksize = shishi_cipher_blocksize (enctype);
  hashsize =
    shishi_checksum_cksumlen (shishi_cipher_defaultcksumtype (enctype));

  switch (enctype)
    {
    case SHISHI_AES128_CTS_HMAC_SHA1_96:
    case SHISHI_AES256_CTS_HMAC_SHA1_96:
      dlen += 4 + hashsize + blocksize;
      break;
    case SHISHI_ARCFOUR_HMAC:
    case SHISHI_ARCFOUR_HMAC_EXP:
      dlen += 4 + 8 + blocksize - 1;
      dlen /= blocksize;
      dlen *= blocksize;
      dlen += hashsize;
      break;
    case SHISHI_DES3_CBC_HMAC_SHA1_KD:
      dlen += 4 + 2 * blocksize - 1;
      dlen /= blocksize;
      dlen *= blocksize;
      dlen += hashsize;
      break;
    case SHISHI_DES_CBC_CRC:
      dlen += 2 * blocksize - 1;
      if (proto == 2)
	dlen += 4;
      dlen += hashsize;
      dlen /= blocksize;
      dlen *= blocksize;
      break;
    default:
      dlen += blocksize - 1;
      if (proto == 2)
	dlen += 4;
      dlen += hashsize;
      dlen /= blocksize;
      dlen *= blocksize;
      break;
    }

  /* read encrypted data */
  outbis = malloc (dlen);
  if (outbis == NULL)
    {
      perror ("readenc()");
      return 1;
    }

  rc = read (sock, outbis, dlen);
  if (rc != dlen)
    {
      fprintf (stderr, "Error during read socket\n");
      free (outbis);
      return 1;
    }

  if (proto == 1)
    {
      rc =
	shishi_decrypt (h, enckey, iv->keyusage, outbis, dlen, &out, &outlen);
      if (rc != SHISHI_OK)
	{
	  fprintf (stderr, "decryption error\n");
	  free (outbis);
	  return 1;
	}

      val = 0;
    }
  else
    {
      rc = shishi_crypto_decrypt (iv->ctx, outbis, dlen, &out, &outlen);
      if (rc != SHISHI_OK)
	{
	  fprintf (stderr, "decryption error\n");
	  free (outbis);
	  return 1;
	}

      /* in KCMDV0.2 first 4 bytes of decrypted data = len of data */
      *len = ntohl (*((int *) out));
      val = sizeof (int);
    }

  memset (buf, 0, SHISHI_ENCRYPT_BUFLEN);

  /* copy decrypted data to output */
  memcpy (buf, out + val, outlen - val);

  free (out);
  free (outbis);

  return SHISHI_OK;
}

/* write encrypted data to socket */
int
writeenc (Shishi *h, int sock, char *buf, int wlen, int *len,
	  shishi_ivector *iv, Shishi_key *enckey, int proto)
{
  char *out;
  char *bufbis;

  int rc;
  int dlen;
  size_t outlen;

  dlen = wlen;
  dlen = htonl (dlen);

  /* data to encrypt = size + data */
  if (proto == 2)
    {
      bufbis = malloc (wlen + sizeof (int));
      if (!bufbis)
	{
	  perror ("writeenc");
	  return 1;
	}
      memcpy (bufbis, (char *) &dlen, sizeof (int));
      memcpy (bufbis + sizeof (int), buf, wlen);

      /* encrypt it */
      rc =
	shishi_crypto_encrypt (iv->ctx, bufbis, wlen + sizeof (int), &out,
			       &outlen);
    }
  else
    {
      bufbis = malloc (wlen);
      if (!bufbis)
	{
	  perror ("bufbis");
	  return 1;
	}
      memcpy (bufbis, buf, wlen);

      /* data to encrypt = size + data */
      rc =
	shishi_encrypt (h, enckey, iv->keyusage, bufbis, wlen, &out, &outlen);
    }

  if (rc != SHISHI_OK)
    {
      fprintf (stderr, "decryption error\n");
      free (bufbis);
      return 1;
    }

  free (bufbis);

  /* data to send = original size + encrypted data */
  /* send it */
  write (sock, &dlen, sizeof (int));
  write (sock, out, outlen);

  *len = wlen;

  free (out);

  return SHISHI_OK;


}
# endif/* ENCRYPTION */
#endif