Server-Side Application

The source code for the server-side program, gss_server, is provided in the following example.

Example B-2 Complete Code Listing for gss-server.c Sample Program

/*
 * Copyright 1994 by OpenVision Technologies, Inc.
 * 
 * Permission to use, copy, modify, distribute, and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appears in all copies and
 * that both that copyright notice and this permission notice appear in
 * supporting documentation, and that the name of OpenVision not be used
 * in advertising or publicity pertaining to distribution of the software
 * without specific, written prior permission. OpenVision makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 * 
 * OPENVISION DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL OPENVISION BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
 * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
 * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

#if !defined(lint) && !defined(__CODECENTER__)
static char *rcsid = \
"$Header: /cvs/krbdev/krb5/src/appl/gss-sample/gss-server.c, \
    v 1.21 1998/12/22 \
04:10:08 tytso Exp $";
#endif

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <netinet/in.h>
#include <unistd.h>
#include <stdlib.h>
#include <ctype.h>

#include <gssapi/gssapi.h>
#include <gssapi/gssapi_ext.h>
#include <gss-misc.h>

#include <string.h>

void usage()
{
     fprintf(stderr, "Usage: gss-server [-port port] [-verbose]\n");
     fprintf(stderr, "       [-inetd] [-logfile file] [service_name]\n");
     exit(1);
}

FILE *log;

int verbose = 0;

/*
 * Function: server_acquire_creds
 *
 * Purpose: imports a service name and acquires credentials for it
 *
 * Arguments:
 *
 *      service_name    (r) the ASCII service name
 *      server_creds    (w) the GSS-API service credentials
 *
 * Returns: 0 on success, -1 on failure
 *
 * Effects:
 *
 * The service name is imported with gss_import_name, and service
 * credentials are acquired with gss_acquire_cred.  If either operation
 * fails, an error message is displayed and -1 is returned; otherwise,
 * 0 is returned.
 */
int server_acquire_creds(service_name, server_creds)
     char *service_name;
     gss_cred_id_t *server_creds;
{
     gss_buffer_desc name_buf;
     gss_name_t server_name;
     OM_uint32 maj_stat, min_stat;

     name_buf.value = service_name;
     name_buf.length = strlen(name_buf.value) + 1;
     maj_stat = gss_import_name(&min_stat, &name_buf, 
         (gss_OID) GSS_C_NT_HOSTBASED_SERVICE, &server_name);
     if (maj_stat != GSS_S_COMPLETE) {
         display_status("importing name", maj_stat, min_stat);
         return -1;
     }

     maj_stat = gss_acquire_cred(&min_stat, server_name, 0,
                                 GSS_C_NULL_OID_SET, GSS_C_ACCEPT,
                                 server_creds, NULL, NULL);
     if (maj_stat != GSS_S_COMPLETE) {
          display_status("acquiring credentials", maj_stat, min_stat);
          return -1;
     }

     (void) gss_release_name(&min_stat, &server_name);

     return 0;
}

/*
 * Function: server_establish_context
 *
 * Purpose: establishes a GSS-API context as a specified service with
 * an incoming client, and returns the context handle and associated
 * client name
 *
 * Arguments:
 *
 *      s               (r) an established TCP connection to the client
 *      service_creds   (r) server credentials, from gss_acquire_cred
 *      context         (w) the established GSS-API context
 *      client_name     (w) the client's ASCII name
 *
 * Returns: 0 on success, -1 on failure
 *
 * Effects:
 *
 * Any valid client request is accepted.  If a context is established,
 * its handle is returned in context and the client name is returned
 * in client_name and 0 is returned.  If unsuccessful, an error
 * message is displayed and -1 is returned.
 */
int server_establish_context(s, server_creds, context, client_name, \
     ret_flags)

     int s;
     gss_cred_id_t server_creds;
     gss_ctx_id_t *context;
     gss_buffer_t client_name;
     OM_uint32 *ret_flags;
{
     gss_buffer_desc send_tok, recv_tok;
     gss_name_t client;
     gss_OID doid;
     OM_uint32 maj_stat, min_stat, acc_sec_min_stat;
     gss_buffer_desc    oid_name;

     *context = GSS_C_NO_CONTEXT;
     
     do {
          if (recv_token(s, &recv_tok) < 0)
               return -1;

          if (verbose && log) {
              fprintf(log, "Received token (size=%d): \n", recv_tok.length);
              print_token(&recv_tok);
          }

          maj_stat =
               gss_accept_sec_context(&acc_sec_min_stat,
                                      context,
                                      server_creds,
                                      &recv_tok,
                                      GSS_C_NO_CHANNEL_BINDINGS,
                                      &client,
                                      &doid,
                                      &send_tok,
                                      ret_flags,
                                      NULL,     /* ignore time_rec */
                                      NULL);    /* ignore del_cred_handle */

          (void) gss_release_buffer(&min_stat, &recv_tok);

          if (send_tok.length != 0) {
              if (verbose && log) {
                  fprintf(log,
                          "Sending accept_sec_context token (size=%d):\n",
                          send_tok.length);
                  print_token(&send_tok);
              }
              if (send_token(s, &send_tok) < 0) {
                  fprintf(log, "failure sending token\n");
                  return -1;
              }

              (void) gss_release_buffer(&min_stat, &send_tok);
          }
          if (maj_stat!=GSS_S_COMPLETE && maj_stat!=GSS_S_CONTINUE_NEEDED) {
              display_status("accepting context", maj_stat,
                              acc_sec_min_stat);
              if (*context == GSS_C_NO_CONTEXT)
                       gss_delete_sec_context(&min_stat, context,
                                              GSS_C_NO_BUFFER);
              return -1;
          }

          if (verbose && log) {
              if (maj_stat == GSS_S_CONTINUE_NEEDED)
                  fprintf(log, "continue needed...\n");
              else
                  fprintf(log, "\n");
              fflush(log);
          }
     } while (maj_stat == GSS_S_CONTINUE_NEEDED);

     /* display the flags */
     display_ctx_flags(*ret_flags);

     if (verbose && log) {
         maj_stat = gss_oid_to_str(&min_stat, doid, &oid_name);
         if (maj_stat != GSS_S_COMPLETE) {
             display_status("converting oid->string", maj_stat, min_stat);
             return -1;
         }
         fprintf(log, "Accepted connection using mechanism OID %.*s.\n",
                 (int) oid_name.length, (char *) oid_name.value);
         (void) gss_release_buffer(&min_stat, &oid_name);
     }

     maj_stat = gss_display_name(&min_stat, client, client_name, &doid);
     if (maj_stat != GSS_S_COMPLETE) {
          display_status("displaying name", maj_stat, min_stat);
          return -1;
     }
     maj_stat = gss_release_name(&min_stat, &client);
     if (maj_stat != GSS_S_COMPLETE) {
          display_status("releasing name", maj_stat, min_stat);
          return -1;
     }
     return 0;
}

/*
 * Function: create_socket
 *
 * Purpose: Opens a listening TCP socket.
 *
 * Arguments:
 *
 *      port            (r) the port number on which to listen
 *
 * Returns: the listening socket file descriptor, or -1 on failure
 *
 * Effects:
 *
 * A listening socket on the specified port is created and returned.
 * On error, an error message is displayed and -1 is returned.
 */
int create_socket(port)
     u_short port;
{
     struct sockaddr_in saddr;
     int s;
     int on = 1;
     
     saddr.sin_family = AF_INET;
     saddr.sin_port = htons(port);
     saddr.sin_addr.s_addr = INADDR_ANY;

     if ((s = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
          perror("creating socket");
          return -1;
     }
     /* Let the socket be reused right away */
     (void) setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (char *)&on, 
          sizeof(on));
     if (bind(s, (struct sockaddr *) &saddr, sizeof(saddr)) < 0) {
          perror("binding socket");
          (void) close(s);
          return -1;
     }
     if (listen(s, 5) < 0) {
          perror("listening on socket");
          (void) close(s);
          return -1;
     }
     return s;
}

static float timeval_subtract(tv1, tv2)
        struct timeval *tv1, *tv2;
{
        return ((tv1->tv_sec - tv2->tv_sec) +
                ((float) (tv1->tv_usec - tv2->tv_usec)) / 1000000);
}

/*
 * Yes, yes, this isn't the best place for doing this test.
 * DO NOT REMOVE THIS UNTIL A BETTER TEST HAS BEEN WRITTEN, THOUGH.
 *                                      -TYT
 */
int test_import_export_context(context)
        gss_ctx_id_t *context;
{
        OM_uint32       min_stat, maj_stat;
        gss_buffer_desc context_token, copied_token;
        struct timeval tm1, tm2;

        /*
         * Attempt to save and then restore the context.
         */
        gettimeofday(&tm1, (struct timezone *)0);
        maj_stat = gss_export_sec_context(&min_stat, context, \
            &context_token);
        if (maj_stat != GSS_S_COMPLETE) {
                display_status("exporting context", maj_stat, min_stat);
                return 1;
        }
        gettimeofday(&tm2, (struct timezone *)0);
        if (verbose && log)
                fprintf(log, "Exported context: %d bytes, %7.4f seconds\n",
                        context_token.length, timeval_subtract(&tm2, &tm1));
        copied_token.length = context_token.length;
        copied_token.value = malloc(context_token.length);
        if (copied_token.value == 0) {
            fprintf(log, "Couldn't allocate memory to copy context \
                token.\n");
            return 1;
        }
        memcpy(copied_token.value, context_token.value, \
            copied_token.length);
        maj_stat = gss_import_sec_context(&min_stat, &copied_token, \
            context);
        if (maj_stat != GSS_S_COMPLETE) {
                display_status("importing context", maj_stat, min_stat);
                return 1;
        }
        free(copied_token.value);
        gettimeofday(&tm1, (struct timezone *)0);
        if (verbose && log)
                fprintf(log, "Importing context: %7.4f seconds\n",
                        timeval_subtract(&tm1, &tm2));
        (void) gss_release_buffer(&min_stat, &context_token);
        return 0;
}

/*
 * Function: sign_server
 *
 * Purpose: Performs the "sign" service.
 *
 * Arguments:
 *
 *      s               (r) a TCP socket on which a connection has been
 *                      accept()ed
 *      service_name    (r) the ASCII name of the GSS-API service to
 *                      establish a context as
 * 
 * Returns: -1 on error
 *
 * Effects:
 *
 * sign_server establishes a context, and performs a single sign request.
 *
 * A sign request is a single GSS-API sealed token.  The token is
 * unsealed and a signature block, produced with gss_sign, is returned
 * to the sender.  The context is then destroyed and the connection
 * closed.
 *
 * If any error occurs, -1 is returned.
 */
int sign_server(s, server_creds)
     int s;
     gss_cred_id_t server_creds;
{
     gss_buffer_desc client_name, xmit_buf, msg_buf;
     gss_ctx_id_t context;
     OM_uint32 maj_stat, min_stat;
     int i, conf_state, ret_flags;
     char       *cp;
     
     /* Establish a context with the client */
     if (server_establish_context(s, server_creds, &context,
                                  &client_name, &ret_flags) < 0)
        return(-1);
          
     printf("Accepted connection: \"%.*s\"\n",
            (int) client_name.length, (char *) client_name.value);
     (void) gss_release_buffer(&min_stat, &client_name);

     for (i=0; i < 3; i++)
             if (test_import_export_context(&context))
                     return -1;

     /* Receive the sealed message token */
     if (recv_token(s, &xmit_buf) < 0)
        return(-1);
          
     if (verbose && log) {
        fprintf(log, "Sealed message token:\n");
        print_token(&xmit_buf);
     }

     maj_stat = gss_unwrap(&min_stat, context, &xmit_buf, &msg_buf,
                           &conf_state, (gss_qop_t *) NULL);
     if (maj_stat != GSS_S_COMPLETE) {
        display_status("unsealing message", maj_stat, min_stat);
        return(-1);
     } else if (! conf_state) {
        fprintf(stderr, "Warning!  Message not encrypted.\n");
     }

     (void) gss_release_buffer(&min_stat, &xmit_buf);

     fprintf(log, "Received message: ");
     cp = msg_buf.value;
     if ((isprint(cp[0]) || isspace(cp[0])) &&
         (isprint(cp[1]) || isspace(cp[1]))) {
        fprintf(log, "\"%.*s\"\n", msg_buf.length, msg_buf.value);
     } else {
        printf("\n");
        print_token(&msg_buf);
     }
          
     /* Produce a signature block for the message */
     maj_stat = gss_get_mic(&min_stat, context, GSS_C_QOP_DEFAULT,
                            &msg_buf, &xmit_buf);
     if (maj_stat != GSS_S_COMPLETE) {
        display_status("signing message", maj_stat, min_stat);
        return(-1);
     }

     (void) gss_release_buffer(&min_stat, &msg_buf);

     /* Send the signature block to the client */
     if (send_token(s, &xmit_buf) < 0)
        return(-1);

     (void) gss_release_buffer(&min_stat, &xmit_buf);

     /* Delete context */
     maj_stat = gss_delete_sec_context(&min_stat, &context, NULL);
     if (maj_stat != GSS_S_COMPLETE) {
        display_status("deleting context", maj_stat, min_stat);
        return(-1);
     }

     fflush(log);

     return(0);
}

int
main(argc, argv)
     int argc;
     char **argv;
{
     char *service_name;
     gss_cred_id_t server_creds;
     OM_uint32 min_stat;
     u_short port = 4444;
     int s;
     int once = 0;
     int do_inetd = 0;

     log = stdout;
     display_file = stdout;
     argc--; argv++;
     while (argc) {
          if (strcmp(*argv, "-port") == 0) {
               argc--; argv++;
               if (!argc) usage();
               port = atoi(*argv);
          } else if (strcmp(*argv, "-verbose") == 0) {
              verbose = 1;
          } else if (strcmp(*argv, "-once") == 0) {
              once = 1;
          } else if (strcmp(*argv, "-inetd") == 0) {
              do_inetd = 1;
          } else if (strcmp(*argv, "-logfile") == 0) {
              argc--; argv++;
              if (!argc) usage();
              log = fopen(*argv, "a");
              display_file = log;
              if (!log) {
                  perror(*argv);
                  exit(1);
              }
          } else
               break;
          argc--; argv++;
     }
     if (argc != 1)
          usage();

     if ((*argv)[0] == '-')
          usage();

     service_name = *argv;

     if (server_acquire_creds(service_name, &server_creds) < 0)
         return -1;
     
     if (do_inetd) {
         close(1);
         close(2);

         sign_server(0, server_creds);
         close(0);
     } else {
         int stmp;

         if ((stmp = create_socket(port)) >= 0) {
             do {
                 /* Accept a TCP connection */
                 if ((s = accept(stmp, NULL, 0)) < 0) {
                     perror("accepting connection");
                     continue;
                 }
                 /* this return value is not checked, because there's
                    not really anything to do if it fails */
                 sign_server(s, server_creds);
                 close(s);
             } while (!once);

             close(stmp);
         }
     }

     (void) gss_release_cred(&min_stat, &server_creds);

     /*NOTREACHED*/
     (void) close(s);
     return 0;
}