auth-krb4.c

   1 /*
   2  *    Dug Song <dugsong@UMICH.EDU>
   3  *    Kerberos v4 authentication and ticket-passing routines.
   4  */
   5
   6 #include "includes.h"
   7 #include "packet.h"
   8 #include "xmalloc.h"
   9 #include "ssh.h"
  10 #include "servconf.h"
  11
  12 RCSID("$OpenBSD: auth-krb4.c,v 1.17 2000/08/28 03:50:54 deraadt Exp $");
  13
  14 #ifdef KRB4
  15 char *ticket = NULL;
  16
  17 extern ServerOptions options;
  18
  19 /*
  20  * try krb4 authentication,
  21  * return 1 on success, 0 on failure, -1 if krb4 is not available
  22  */
  23
  24 int
  25 auth_krb4_password(struct passwd * pw, const char *password)
  26 {
  27         AUTH_DAT adata;
  28         KTEXT_ST tkt;
  29         struct hostent *hp;
  30         unsigned long faddr;
  31         char localhost[MAXHOSTNAMELEN];
  32         char phost[INST_SZ];
  33         char realm[REALM_SZ];
  34         int r;
  35
  36         /*
  37          * Try Kerberos password authentication only for non-root
  38          * users and only if Kerberos is installed.
  39          */
  40         if (pw->pw_uid != 0 && krb_get_lrealm(realm, 1) == KSUCCESS) {
  41
  42                 /* Set up our ticket file. */
  43                 if (!krb4_init(pw->pw_uid)) {
  44                         log("Couldn't initialize Kerberos ticket file for %s!",
  45                             pw->pw_name);
  46                         goto kerberos_auth_failure;
  47                 }
  48                 /* Try to get TGT using our password. */
  49                 r = krb_get_pw_in_tkt((char *) pw->pw_name, "",
  50                     realm, "krbtgt", realm,
  51                     DEFAULT_TKT_LIFE, (char *) password);
  52                 if (r != INTK_OK) {
  53                         packet_send_debug("Kerberos V4 password "
  54                             "authentication for %s failed: %s",
  55                             pw->pw_name, krb_err_txt[r]);
  56                         goto kerberos_auth_failure;
  57                 }
  58                 /* Successful authentication. */
  59                 chown(tkt_string(), pw->pw_uid, pw->pw_gid);
  60
  61                 /*
  62                  * Now that we have a TGT, try to get a local
  63                  * "rcmd" ticket to ensure that we are not talking
  64                  * to a bogus Kerberos server.
  65                  */
  66                 (void) gethostname(localhost, sizeof(localhost));
  67                 (void) strlcpy(phost, (char *) krb_get_phost(localhost),
  68                     INST_SZ);
  69                 r = krb_mk_req(&tkt, KRB4_SERVICE_NAME, phost, realm, 33);
  70
  71                 if (r == KSUCCESS) {
  72                         if (!(hp = gethostbyname(localhost))) {
  73                                 log("Couldn't get local host address!");
  74                                 goto kerberos_auth_failure;
  75                         }
  76                         memmove((void *) &faddr, (void *) hp->h_addr,
  77                             sizeof(faddr));
  78
  79                         /* Verify our "rcmd" ticket. */
  80                         r = krb_rd_req(&tkt, KRB4_SERVICE_NAME, phost,
  81                             faddr, &adata, "");
  82                         if (r == RD_AP_UNDEC) {
  83                                 /*
  84                                  * Probably didn't have a srvtab on
  85                                  * localhost. Disallow login.
  86                                  */
  87                                 log("Kerberos V4 TGT for %s unverifiable, "
  88                                     "no srvtab installed? krb_rd_req: %s",
  89                                     pw->pw_name, krb_err_txt[r]);
  90                                 goto kerberos_auth_failure;
  91                         } else if (r != KSUCCESS) {
  92                                 log("Kerberos V4 %s ticket unverifiable: %s",
  93                                     KRB4_SERVICE_NAME, krb_err_txt[r]);
  94                                 goto kerberos_auth_failure;
  95                         }
  96                 } else if (r == KDC_PR_UNKNOWN) {
  97                         /*
  98                          * Disallow login if no rcmd service exists, and
  99                          * log the error.
 100                          */
 101                         log("Kerberos V4 TGT for %s unverifiable: %s; %s.%s "
 102                             "not registered, or srvtab is wrong?", pw->pw_name,
 103                         krb_err_txt[r], KRB4_SERVICE_NAME, phost);
 104                         goto kerberos_auth_failure;
 105                 } else {
 106                         /*
 107                          * TGT is bad, forget it. Possibly spoofed!
 108                          */
 109                         packet_send_debug("WARNING: Kerberos V4 TGT "
 110                             "possibly spoofed for %s: %s",
 111                             pw->pw_name, krb_err_txt[r]);
 112                         goto kerberos_auth_failure;
 113                 }
 114
 115                 /* Authentication succeeded. */
 116                 return 1;
 117
 118 kerberos_auth_failure:
 119                 krb4_cleanup_proc(NULL);
 120
 121                 if (!options.kerberos_or_local_passwd)
 122                         return 0;
 123         } else {
 124                 /* Logging in as root or no local Kerberos realm. */
 125                 packet_send_debug("Unable to authenticate to Kerberos.");
 126         }
 127         /* Fall back to ordinary passwd authentication. */
 128         return -1;
 129 }
 130
 131 void
 132 krb4_cleanup_proc(void *ignore)
 133 {
 134         debug("krb4_cleanup_proc called");
 135         if (ticket) {
 136                 (void) dest_tkt();
 137                 xfree(ticket);
 138                 ticket = NULL;
 139         }
 140 }
 141
 142 int
 143 krb4_init(uid_t uid)
 144 {
 145         static int cleanup_registered = 0;
 146         const char *tkt_root = TKT_ROOT;
 147         struct stat st;
 148         int fd;
 149
 150         if (!ticket) {
 151                 /* Set unique ticket string manually since we're still root. */
 152                 ticket = xmalloc(MAXPATHLEN);
 153 #ifdef AFS
 154                 if (lstat("/ticket", &st) != -1)
 155                         tkt_root = "/ticket/";
 156 #endif /* AFS */
 157                 snprintf(ticket, MAXPATHLEN, "%s%u_%d", tkt_root, uid, getpid());
 158                 (void) krb_set_tkt_string(ticket);
 159         }
 160         /* Register ticket cleanup in case of fatal error. */
 161         if (!cleanup_registered) {
 162                 fatal_add_cleanup(krb4_cleanup_proc, NULL);
 163                 cleanup_registered = 1;
 164         }
 165         /* Try to create our ticket file. */
 166         if ((fd = mkstemp(ticket)) != -1) {
 167                 close(fd);
 168                 return 1;
 169         }
 170         /* Ticket file exists - make sure user owns it (just passed ticket). */
 171         if (lstat(ticket, &st) != -1) {
 172                 if (st.st_mode == (S_IFREG | S_IRUSR | S_IWUSR) &&
 173                     st.st_uid == uid)
 174                         return 1;
 175         }
 176         /* Failure - cancel cleanup function, leaving bad ticket for inspection. */
 177         log("WARNING: bad ticket file %s", ticket);
 178         fatal_remove_cleanup(krb4_cleanup_proc, NULL);
 179         cleanup_registered = 0;
 180         xfree(ticket);
 181         ticket = NULL;
 182
 183         return 0;
 184 }
 185
 186 int
 187 auth_krb4(const char *server_user, KTEXT auth, char **client)
 188 {
 189         AUTH_DAT adat = {0};
 190         KTEXT_ST reply;
 191         char instance[INST_SZ];
 192         int r, s;
 193         socklen_t slen;
 194         u_int cksum;
 195         Key_schedule schedule;
 196         struct sockaddr_in local, foreign;
 197
 198         s = packet_get_connection_in();
 199
 200         slen = sizeof(local);
 201         memset(&local, 0, sizeof(local));
 202         if (getsockname(s, (struct sockaddr *) & local, &slen) < 0)
 203                 debug("getsockname failed: %.100s", strerror(errno));
 204         slen = sizeof(foreign);
 205         memset(&foreign, 0, sizeof(foreign));
 206         if (getpeername(s, (struct sockaddr *) & foreign, &slen) < 0) {
 207                 debug("getpeername failed: %.100s", strerror(errno));
 208                 fatal_cleanup();
 209         }
 210         instance[0] = '*';
 211         instance[1] = 0;
 212
 213         /* Get the encrypted request, challenge, and session key. */
 214         if ((r = krb_rd_req(auth, KRB4_SERVICE_NAME, instance, 0, &adat, ""))) {
 215                 packet_send_debug("Kerberos V4 krb_rd_req: %.100s", krb_err_txt[r]);
 216                 return 0;
 217         }
 218         des_key_sched((des_cblock *) adat.session, schedule);
 219
 220         *client = xmalloc(MAX_K_NAME_SZ);
 221         (void) snprintf(*client, MAX_K_NAME_SZ, "%s%s%s@%s", adat.pname,
 222             *adat.pinst ? "." : "", adat.pinst, adat.prealm);
 223
 224         /* Check ~/.klogin authorization now. */
 225         if (kuserok(&adat, (char *) server_user) != KSUCCESS) {
 226                 packet_send_debug("Kerberos V4 .klogin authorization failed!");
 227                 log("Kerberos V4 .klogin authorization failed for %s to account %s",
 228                     *client, server_user);
 229                 xfree(*client);
 230                 return 0;
 231         }
 232         /* Increment the checksum, and return it encrypted with the
 233            session key. */
 234         cksum = adat.checksum + 1;
 235         cksum = htonl(cksum);
 236
 237         /* If we can't successfully encrypt the checksum, we send back an
 238            empty message, admitting our failure. */
 239         if ((r = krb_mk_priv((u_char *) & cksum, reply.dat, sizeof(cksum) + 1,
 240             schedule, &adat.session, &local, &foreign)) < 0) {
 241                 packet_send_debug("Kerberos V4 mk_priv: (%d) %s", r, krb_err_txt[r]);
 242                 reply.dat[0] = 0;
 243                 reply.length = 0;
 244         } else
 245                 reply.length = r;
 246
 247         /* Clear session key. */
 248         memset(&adat.session, 0, sizeof(&adat.session));
 249
 250         packet_start(SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 251         packet_put_string((char *) reply.dat, reply.length);
 252         packet_send();
 253         packet_write_wait();
 254         return 1;
 255 }
 256 #endif /* KRB4 */
 257
 258 #ifdef AFS
 259 int
 260 auth_kerberos_tgt(struct passwd *pw, const char *string)
 261 {
 262         CREDENTIALS creds;
 263
 264         if (!radix_to_creds(string, &creds)) {
 265                 log("Protocol error decoding Kerberos V4 tgt");
 266                 packet_send_debug("Protocol error decoding Kerberos V4 tgt");
 267                 goto auth_kerberos_tgt_failure;
 268         }
 269         if (strncmp(creds.service, "", 1) == 0) /* backward compatibility */
 270                 strlcpy(creds.service, "krbtgt", sizeof creds.service);
 271
 272         if (strcmp(creds.service, "krbtgt")) {
 273                 log("Kerberos V4 tgt (%s%s%s@%s) rejected for %s", creds.pname,
 274                     creds.pinst[0] ? "." : "", creds.pinst, creds.realm,
 275                     pw->pw_name);
 276                 packet_send_debug("Kerberos V4 tgt (%s%s%s@%s) rejected for %s",
 277                     creds.pname, creds.pinst[0] ? "." : "", creds.pinst,
 278                     creds.realm, pw->pw_name);
 279                 goto auth_kerberos_tgt_failure;
 280         }
 281         if (!krb4_init(pw->pw_uid))
 282                 goto auth_kerberos_tgt_failure;
 283
 284         if (in_tkt(creds.pname, creds.pinst) != KSUCCESS)
 285                 goto auth_kerberos_tgt_failure;
 286
 287         if (save_credentials(creds.service, creds.instance, creds.realm,
 288             creds.session, creds.lifetime, creds.kvno,
 289             &creds.ticket_st, creds.issue_date) != KSUCCESS) {
 290                 packet_send_debug("Kerberos V4 tgt refused: couldn't save credentials");
 291                 goto auth_kerberos_tgt_failure;
 292         }
 293         /* Successful authentication, passed all checks. */
 294         chown(tkt_string(), pw->pw_uid, pw->pw_gid);
 295
 296         packet_send_debug("Kerberos V4 tgt accepted (%s.%s@%s, %s%s%s@%s)",
 297             creds.service, creds.instance, creds.realm, creds.pname,
 298             creds.pinst[0] ? "." : "", creds.pinst, creds.realm);
 299         memset(&creds, 0, sizeof(creds));
 300         packet_start(SSH_SMSG_SUCCESS);
 301         packet_send();
 302         packet_write_wait();
 303         return 1;
 304
 305 auth_kerberos_tgt_failure:
 306         krb4_cleanup_proc(NULL);
 307         memset(&creds, 0, sizeof(creds));
 308         packet_start(SSH_SMSG_FAILURE);
 309         packet_send();
 310         packet_write_wait();
 311         return 0;
 312 }
 313
 314 int
 315 auth_afs_token(struct passwd *pw, const char *token_string)
 316 {
 317         CREDENTIALS creds;
 318         uid_t uid = pw->pw_uid;
 319
 320         if (!radix_to_creds(token_string, &creds)) {
 321                 log("Protocol error decoding AFS token");
 322                 packet_send_debug("Protocol error decoding AFS token");
 323                 packet_start(SSH_SMSG_FAILURE);
 324                 packet_send();
 325                 packet_write_wait();
 326                 return 0;
 327         }
 328         if (strncmp(creds.service, "", 1) == 0) /* backward compatibility */
 329                 strlcpy(creds.service, "afs", sizeof creds.service);
 330
 331         if (strncmp(creds.pname, "AFS ID ", 7) == 0)
 332                 uid = atoi(creds.pname + 7);
 333
 334         if (kafs_settoken(creds.realm, uid, &creds)) {
 335                 log("AFS token (%s@%s) rejected for %s", creds.pname, creds.realm,
 336                     pw->pw_name);
 337                 packet_send_debug("AFS token (%s@%s) rejected for %s", creds.pname,
 338                     creds.realm, pw->pw_name);
 339                 memset(&creds, 0, sizeof(creds));
 340                 packet_start(SSH_SMSG_FAILURE);
 341                 packet_send();
 342                 packet_write_wait();
 343                 return 0;
 344         }
 345         packet_send_debug("AFS token accepted (%s@%s, %s@%s)", creds.service,
 346             creds.realm, creds.pname, creds.realm);
 347         memset(&creds, 0, sizeof(creds));
 348         packet_start(SSH_SMSG_SUCCESS);
 349         packet_send();
 350         packet_write_wait();
 351         return 1;
 352 }
 353 #endif /* AFS */