crypto/openssh/auth2-pubkey.c

   1 /* $OpenBSD: auth2-pubkey.c,v 1.55 2016/01/27 00:53:12 djm Exp $ */
   2 /*
   3  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "includes.h"
  27
  28 #include <sys/types.h>
  29 #include <sys/stat.h>
  30 #include <sys/wait.h>
  31
  32 #include <errno.h>
  33 #include <fcntl.h>
  34 #ifdef HAVE_PATHS_H
  35 # include <paths.h>
  36 #endif
  37 #include <pwd.h>
  38 #include <signal.h>
  39 #include <stdio.h>
  40 #include <stdarg.h>
  41 #include <string.h>
  42 #include <time.h>
  43 #include <unistd.h>
  44 #include <limits.h>
  45
  46 #include "xmalloc.h"
  47 #include "ssh.h"
  48 #include "ssh2.h"
  49 #include "packet.h"
  50 #include "buffer.h"
  51 #include "log.h"
  52 #include "misc.h"
  53 #include "servconf.h"
  54 #include "compat.h"
  55 #include "key.h"
  56 #include "hostfile.h"
  57 #include "auth.h"
  58 #include "pathnames.h"
  59 #include "uidswap.h"
  60 #include "auth-options.h"
  61 #include "canohost.h"
  62 #ifdef GSSAPI
  63 #include "ssh-gss.h"
  64 #endif
  65 #include "monitor_wrap.h"
  66 #include "authfile.h"
  67 #include "match.h"
  68 #include "ssherr.h"
  69 #include "channels.h" /* XXX for session.h */
  70 #include "session.h" /* XXX for child_set_env(); refactor? */
  71
  72 /* import */
  73 extern ServerOptions options;
  74 extern u_char *session_id2;
  75 extern u_int session_id2_len;
  76
  77 static int
  78 userauth_pubkey(Authctxt *authctxt)
  79 {
  80         Buffer b;
  81         Key *key = NULL;
  82         char *pkalg, *userstyle, *fp = NULL;
  83         u_char *pkblob, *sig;
  84         u_int alen, blen, slen;
  85         int have_sig, pktype;
  86         int authenticated = 0;
  87
  88         if (!authctxt->valid) {
  89                 debug2("%s: disabled because of invalid user", __func__);
  90                 return 0;
  91         }
  92         have_sig = packet_get_char();
  93         if (datafellows & SSH_BUG_PKAUTH) {
  94                 debug2("%s: SSH_BUG_PKAUTH", __func__);
  95                 /* no explicit pkalg given */
  96                 pkblob = packet_get_string(&blen);
  97                 buffer_init(&b);
  98                 buffer_append(&b, pkblob, blen);
  99                 /* so we have to extract the pkalg from the pkblob */
 100                 pkalg = buffer_get_string(&b, &alen);
 101                 buffer_free(&b);
 102         } else {
 103                 pkalg = packet_get_string(&alen);
 104                 pkblob = packet_get_string(&blen);
 105         }
 106         pktype = key_type_from_name(pkalg);
 107         if (pktype == KEY_UNSPEC) {
 108                 /* this is perfectly legal */
 109                 logit("%s: unsupported public key algorithm: %s",
 110                     __func__, pkalg);
 111                 goto done;
 112         }
 113         key = key_from_blob(pkblob, blen);
 114         if (key == NULL) {
 115                 error("%s: cannot decode key: %s", __func__, pkalg);
 116                 goto done;
 117         }
 118         if (key->type != pktype) {
 119                 error("%s: type mismatch for decoded key "
 120                     "(received %d, expected %d)", __func__, key->type, pktype);
 121                 goto done;
 122         }
 123         if (key_type_plain(key->type) == KEY_RSA &&
 124             (datafellows & SSH_BUG_RSASIGMD5) != 0) {
 125                 logit("Refusing RSA key because client uses unsafe "
 126                     "signature scheme");
 127                 goto done;
 128         }
 129         fp = sshkey_fingerprint(key, options.fingerprint_hash, SSH_FP_DEFAULT);
 130         if (auth2_userkey_already_used(authctxt, key)) {
 131                 logit("refusing previously-used %s key", key_type(key));
 132                 goto done;
 133         }
 134         if (match_pattern_list(sshkey_ssh_name(key),
 135             options.pubkey_key_types, 0) != 1) {
 136                 logit("%s: key type %s not in PubkeyAcceptedKeyTypes",
 137                     __func__, sshkey_ssh_name(key));
 138                 goto done;
 139         }
 140
 141         if (have_sig) {
 142                 debug3("%s: have signature for %s %s",
 143                     __func__, sshkey_type(key), fp);
 144                 sig = packet_get_string(&slen);
 145                 packet_check_eom();
 146                 buffer_init(&b);
 147                 if (datafellows & SSH_OLD_SESSIONID) {
 148                         buffer_append(&b, session_id2, session_id2_len);
 149                 } else {
 150                         buffer_put_string(&b, session_id2, session_id2_len);
 151                 }
 152                 /* reconstruct packet */
 153                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 154                 xasprintf(&userstyle, "%s%s%s", authctxt->user,
 155                     authctxt->style ? ":" : "",
 156                     authctxt->style ? authctxt->style : "");
 157                 buffer_put_cstring(&b, userstyle);
 158                 free(userstyle);
 159                 buffer_put_cstring(&b,
 160                     datafellows & SSH_BUG_PKSERVICE ?
 161                     "ssh-userauth" :
 162                     authctxt->service);
 163                 if (datafellows & SSH_BUG_PKAUTH) {
 164                         buffer_put_char(&b, have_sig);
 165                 } else {
 166                         buffer_put_cstring(&b, "publickey");
 167                         buffer_put_char(&b, have_sig);
 168                         buffer_put_cstring(&b, pkalg);
 169                 }
 170                 buffer_put_string(&b, pkblob, blen);
 171 #ifdef DEBUG_PK
 172                 buffer_dump(&b);
 173 #endif
 174                 pubkey_auth_info(authctxt, key, NULL);
 175
 176                 /* test for correct signature */
 177                 authenticated = 0;
 178                 if (PRIVSEP(user_key_allowed(authctxt->pw, key, 1)) &&
 179                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 180                     buffer_len(&b))) == 1) {
 181                         authenticated = 1;
 182                         /* Record the successful key to prevent reuse */
 183                         auth2_record_userkey(authctxt, key);
 184                         key = NULL; /* Don't free below */
 185                 }
 186                 buffer_free(&b);
 187                 free(sig);
 188         } else {
 189                 debug("%s: test whether pkalg/pkblob are acceptable for %s %s",
 190                     __func__, sshkey_type(key), fp);
 191                 packet_check_eom();
 192
 193                 /* XXX fake reply and always send PK_OK ? */
 194                 /*
 195                  * XXX this allows testing whether a user is allowed
 196                  * to login: if you happen to have a valid pubkey this
 197                  * message is sent. the message is NEVER sent at all
 198                  * if a user is not allowed to login. is this an
 199                  * issue? -markus
 200                  */
 201                 if (PRIVSEP(user_key_allowed(authctxt->pw, key, 0))) {
 202                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 203                         packet_put_string(pkalg, alen);
 204                         packet_put_string(pkblob, blen);
 205                         packet_send();
 206                         packet_write_wait();
 207                         authctxt->postponed = 1;
 208                 }
 209         }
 210         if (authenticated != 1)
 211                 auth_clear_options();
 212 done:
 213         debug2("%s: authenticated %d pkalg %s", __func__, authenticated, pkalg);
 214         if (key != NULL)
 215                 key_free(key);
 216         free(pkalg);
 217         free(pkblob);
 218         free(fp);
 219         return authenticated;
 220 }
 221
 222 void
 223 pubkey_auth_info(Authctxt *authctxt, const Key *key, const char *fmt, ...)
 224 {
 225         char *fp, *extra;
 226         va_list ap;
 227         int i;
 228
 229         extra = NULL;
 230         if (fmt != NULL) {
 231                 va_start(ap, fmt);
 232                 i = vasprintf(&extra, fmt, ap);
 233                 va_end(ap);
 234                 if (i < 0 || extra == NULL)
 235                         fatal("%s: vasprintf failed", __func__);
 236         }
 237
 238         if (key_is_cert(key)) {
 239                 fp = sshkey_fingerprint(key->cert->signature_key,
 240                     options.fingerprint_hash, SSH_FP_DEFAULT);
 241                 auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s",
 242                     key_type(key), key->cert->key_id,
 243                     (unsigned long long)key->cert->serial,
 244                     key_type(key->cert->signature_key),
 245                     fp == NULL ? "(null)" : fp,
 246                     extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
 247                 free(fp);
 248         } else {
 249                 fp = sshkey_fingerprint(key, options.fingerprint_hash,
 250                     SSH_FP_DEFAULT);
 251                 auth_info(authctxt, "%s %s%s%s", key_type(key),
 252                     fp == NULL ? "(null)" : fp,
 253                     extra == NULL ? "" : ", ", extra == NULL ? "" : extra);
 254                 free(fp);
 255         }
 256         free(extra);
 257 }
 258
 259 /*
 260  * Splits 's' into an argument vector. Handles quoted string and basic
 261  * escape characters (\\, \", \'). Caller must free the argument vector
 262  * and its members.
 263  */
 264 static int
 265 split_argv(const char *s, int *argcp, char ***argvp)
 266 {
 267         int r = SSH_ERR_INTERNAL_ERROR;
 268         int argc = 0, quote, i, j;
 269         char *arg, **argv = xcalloc(1, sizeof(*argv));
 270
 271         *argvp = NULL;
 272         *argcp = 0;
 273
 274         for (i = 0; s[i] != '\0'; i++) {
 275                 /* Skip leading whitespace */
 276                 if (s[i] == ' ' || s[i] == '\t')
 277                         continue;
 278
 279                 /* Start of a token */
 280                 quote = 0;
 281                 if (s[i] == '\\' &&
 282                     (s[i + 1] == '\'' || s[i + 1] == '\"' || s[i + 1] == '\\'))
 283                         i++;
 284                 else if (s[i] == '\'' || s[i] == '"')
 285                         quote = s[i++];
 286
 287                 argv = xreallocarray(argv, (argc + 2), sizeof(*argv));
 288                 arg = argv[argc++] = xcalloc(1, strlen(s + i) + 1);
 289                 argv[argc] = NULL;
 290
 291                 /* Copy the token in, removing escapes */
 292                 for (j = 0; s[i] != '\0'; i++) {
 293                         if (s[i] == '\\') {
 294                                 if (s[i + 1] == '\'' ||
 295                                     s[i + 1] == '\"' ||
 296                                     s[i + 1] == '\\') {
 297                                         i++; /* Skip '\' */
 298                                         arg[j++] = s[i];
 299                                 } else {
 300                                         /* Unrecognised escape */
 301                                         arg[j++] = s[i];
 302                                 }
 303                         } else if (quote == 0 && (s[i] == ' ' || s[i] == '\t'))
 304                                 break; /* done */
 305                         else if (quote != 0 && s[i] == quote)
 306                                 break; /* done */
 307                         else
 308                                 arg[j++] = s[i];
 309                 }
 310                 if (s[i] == '\0') {
 311                         if (quote != 0) {
 312                                 /* Ran out of string looking for close quote */
 313                                 r = SSH_ERR_INVALID_FORMAT;
 314                                 goto out;
 315                         }
 316                         break;
 317                 }
 318         }
 319         /* Success */
 320         *argcp = argc;
 321         *argvp = argv;
 322         argc = 0;
 323         argv = NULL;
 324         r = 0;
 325  out:
 326         if (argc != 0 && argv != NULL) {
 327                 for (i = 0; i < argc; i++)
 328                         free(argv[i]);
 329                 free(argv);
 330         }
 331         return r;
 332 }
 333
 334 /*
 335  * Reassemble an argument vector into a string, quoting and escaping as
 336  * necessary. Caller must free returned string.
 337  */
 338 static char *
 339 assemble_argv(int argc, char **argv)
 340 {
 341         int i, j, ws, r;
 342         char c, *ret;
 343         struct sshbuf *buf, *arg;
 344
 345         if ((buf = sshbuf_new()) == NULL || (arg = sshbuf_new()) == NULL)
 346                 fatal("%s: sshbuf_new failed", __func__);
 347
 348         for (i = 0; i < argc; i++) {
 349                 ws = 0;
 350                 sshbuf_reset(arg);
 351                 for (j = 0; argv[i][j] != '\0'; j++) {
 352                         r = 0;
 353                         c = argv[i][j];
 354                         switch (c) {
 355                         case ' ':
 356                         case '\t':
 357                                 ws = 1;
 358                                 r = sshbuf_put_u8(arg, c);
 359                                 break;
 360                         case '\\':
 361                         case '\'':
 362                         case '"':
 363                                 if ((r = sshbuf_put_u8(arg, '\\')) != 0)
 364                                         break;
 365                                 /* FALLTHROUGH */
 366                         default:
 367                                 r = sshbuf_put_u8(arg, c);
 368                                 break;
 369                         }
 370                         if (r != 0)
 371                                 fatal("%s: sshbuf_put_u8: %s",
 372                                     __func__, ssh_err(r));
 373                 }
 374                 if ((i != 0 && (r = sshbuf_put_u8(buf, ' ')) != 0) ||
 375                     (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0) ||
 376                     (r = sshbuf_putb(buf, arg)) != 0 ||
 377                     (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0))
 378                         fatal("%s: buffer error: %s", __func__, ssh_err(r));
 379         }
 380         if ((ret = malloc(sshbuf_len(buf) + 1)) == NULL)
 381                 fatal("%s: malloc failed", __func__);
 382         memcpy(ret, sshbuf_ptr(buf), sshbuf_len(buf));
 383         ret[sshbuf_len(buf)] = '\0';
 384         sshbuf_free(buf);
 385         sshbuf_free(arg);
 386         return ret;
 387 }
 388
 389 /*
 390  * Runs command in a subprocess. Returns pid on success and a FILE* to the
 391  * subprocess' stdout or 0 on failure.
 392  * NB. "command" is only used for logging.
 393  */
 394 static pid_t
 395 subprocess(const char *tag, struct passwd *pw, const char *command,
 396     int ac, char **av, FILE **child)
 397 {
 398         FILE *f;
 399         struct stat st;
 400         int devnull, p[2], i;
 401         pid_t pid;
 402         char *cp, errmsg[512];
 403         u_int envsize;
 404         char **child_env;
 405
 406         *child = NULL;
 407
 408         debug3("%s: %s command \"%s\" running as %s", __func__,
 409             tag, command, pw->pw_name);
 410
 411         /* Verify the path exists and is safe-ish to execute */
 412         if (*av[0] != '/') {
 413                 error("%s path is not absolute", tag);
 414                 return 0;
 415         }
 416         temporarily_use_uid(pw);
 417         if (stat(av[0], &st) < 0) {
 418                 error("Could not stat %s \"%s\": %s", tag,
 419                     av[0], strerror(errno));
 420                 restore_uid();
 421                 return 0;
 422         }
 423         if (auth_secure_path(av[0], &st, NULL, 0,
 424             errmsg, sizeof(errmsg)) != 0) {
 425                 error("Unsafe %s \"%s\": %s", tag, av[0], errmsg);
 426                 restore_uid();
 427                 return 0;
 428         }
 429
 430         /*
 431          * Run the command; stderr is left in place, stdout is the
 432          * authorized_keys output.
 433          */
 434         if (pipe(p) != 0) {
 435                 error("%s: pipe: %s", tag, strerror(errno));
 436                 restore_uid();
 437                 return 0;
 438         }
 439
 440         /*
 441          * Don't want to call this in the child, where it can fatal() and
 442          * run cleanup_exit() code.
 443          */
 444         restore_uid();
 445
 446         switch ((pid = fork())) {
 447         case -1: /* error */
 448                 error("%s: fork: %s", tag, strerror(errno));
 449                 close(p[0]);
 450                 close(p[1]);
 451                 return 0;
 452         case 0: /* child */
 453                 /* Prepare a minimal environment for the child. */
 454                 envsize = 5;
 455                 child_env = xcalloc(sizeof(*child_env), envsize);
 456                 child_set_env(&child_env, &envsize, "PATH", _PATH_STDPATH);
 457                 child_set_env(&child_env, &envsize, "USER", pw->pw_name);
 458                 child_set_env(&child_env, &envsize, "LOGNAME", pw->pw_name);
 459                 child_set_env(&child_env, &envsize, "HOME", pw->pw_dir);
 460                 if ((cp = getenv("LANG")) != NULL)
 461                         child_set_env(&child_env, &envsize, "LANG", cp);
 462
 463                 for (i = 0; i < NSIG; i++)
 464                         signal(i, SIG_DFL);
 465
 466                 if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
 467                         error("%s: open %s: %s", tag, _PATH_DEVNULL,
 468                             strerror(errno));
 469                         _exit(1);
 470                 }
 471                 /* Keep stderr around a while longer to catch errors */
 472                 if (dup2(devnull, STDIN_FILENO) == -1 ||
 473                     dup2(p[1], STDOUT_FILENO) == -1) {
 474                         error("%s: dup2: %s", tag, strerror(errno));
 475                         _exit(1);
 476                 }
 477                 closefrom(STDERR_FILENO + 1);
 478
 479                 /* Don't use permanently_set_uid() here to avoid fatal() */
 480                 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
 481                         error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid,
 482                             strerror(errno));
 483                         _exit(1);
 484                 }
 485                 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
 486                         error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid,
 487                             strerror(errno));
 488                         _exit(1);
 489                 }
 490                 /* stdin is pointed to /dev/null at this point */
 491                 if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
 492                         error("%s: dup2: %s", tag, strerror(errno));
 493                         _exit(1);
 494                 }
 495
 496                 execve(av[0], av, child_env);
 497                 error("%s exec \"%s\": %s", tag, command, strerror(errno));
 498                 _exit(127);
 499         default: /* parent */
 500                 break;
 501         }
 502
 503         close(p[1]);
 504         if ((f = fdopen(p[0], "r")) == NULL) {
 505                 error("%s: fdopen: %s", tag, strerror(errno));
 506                 close(p[0]);
 507                 /* Don't leave zombie child */
 508                 kill(pid, SIGTERM);
 509                 while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
 510                         ;
 511                 return 0;
 512         }
 513         /* Success */
 514         debug3("%s: %s pid %ld", __func__, tag, (long)pid);
 515         *child = f;
 516         return pid;
 517 }
 518
 519 /* Returns 0 if pid exited cleanly, non-zero otherwise */
 520 static int
 521 exited_cleanly(pid_t pid, const char *tag, const char *cmd)
 522 {
 523         int status;
 524
 525         while (waitpid(pid, &status, 0) == -1) {
 526                 if (errno != EINTR) {
 527                         error("%s: waitpid: %s", tag, strerror(errno));
 528                         return -1;
 529                 }
 530         }
 531         if (WIFSIGNALED(status)) {
 532                 error("%s %s exited on signal %d", tag, cmd, WTERMSIG(status));
 533                 return -1;
 534         } else if (WEXITSTATUS(status) != 0) {
 535                 error("%s %s failed, status %d", tag, cmd, WEXITSTATUS(status));
 536                 return -1;
 537         }
 538         return 0;
 539 }
 540
 541 static int
 542 match_principals_option(const char *principal_list, struct sshkey_cert *cert)
 543 {
 544         char *result;
 545         u_int i;
 546
 547         /* XXX percent_expand() sequences for authorized_principals? */
 548
 549         for (i = 0; i < cert->nprincipals; i++) {
 550                 if ((result = match_list(cert->principals[i],
 551                     principal_list, NULL)) != NULL) {
 552                         debug3("matched principal from key options \"%.100s\"",
 553                             result);
 554                         free(result);
 555                         return 1;
 556                 }
 557         }
 558         return 0;
 559 }
 560
 561 static int
 562 process_principals(FILE *f, char *file, struct passwd *pw,
 563     struct sshkey_cert *cert)
 564 {
 565         char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
 566         u_long linenum = 0;
 567         u_int i;
 568
 569         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 570                 /* Skip leading whitespace. */
 571                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 572                         ;
 573                 /* Skip blank and comment lines. */
 574                 if ((ep = strchr(cp, '#')) != NULL)
 575                         *ep = '\0';
 576                 if (!*cp || *cp == '\n')
 577                         continue;
 578                 /* Trim trailing whitespace. */
 579                 ep = cp + strlen(cp) - 1;
 580                 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
 581                         *ep-- = '\0';
 582                 /*
 583                  * If the line has internal whitespace then assume it has
 584                  * key options.
 585                  */
 586                 line_opts = NULL;
 587                 if ((ep = strrchr(cp, ' ')) != NULL ||
 588                     (ep = strrchr(cp, '\t')) != NULL) {
 589                         for (; *ep == ' ' || *ep == '\t'; ep++)
 590                                 ;
 591                         line_opts = cp;
 592                         cp = ep;
 593                 }
 594                 for (i = 0; i < cert->nprincipals; i++) {
 595                         if (strcmp(cp, cert->principals[i]) == 0) {
 596                                 debug3("%s:%lu: matched principal \"%.100s\"",
 597                                     file == NULL ? "(command)" : file,
 598                                     linenum, cert->principals[i]);
 599                                 if (auth_parse_options(pw, line_opts,
 600                                     file, linenum) != 1)
 601                                         continue;
 602                                 return 1;
 603                         }
 604                 }
 605         }
 606         return 0;
 607 }
 608
 609 static int
 610 match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert)
 611 {
 612         FILE *f;
 613         int success;
 614
 615         temporarily_use_uid(pw);
 616         debug("trying authorized principals file %s", file);
 617         if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
 618                 restore_uid();
 619                 return 0;
 620         }
 621         success = process_principals(f, file, pw, cert);
 622         fclose(f);
 623         restore_uid();
 624         return success;
 625 }
 626
 627 /*
 628  * Checks whether principal is allowed in output of command.
 629  * returns 1 if the principal is allowed or 0 otherwise.
 630  */
 631 static int
 632 match_principals_command(struct passwd *user_pw, struct sshkey_cert *cert)
 633 {
 634         FILE *f = NULL;
 635         int ok, found_principal = 0;
 636         struct passwd *pw;
 637         int i, ac = 0, uid_swapped = 0;
 638         pid_t pid;
 639         char *tmp, *username = NULL, *command = NULL, **av = NULL;
 640         void (*osigchld)(int);
 641
 642         if (options.authorized_principals_command == NULL)
 643                 return 0;
 644         if (options.authorized_principals_command_user == NULL) {
 645                 error("No user for AuthorizedPrincipalsCommand specified, "
 646                     "skipping");
 647                 return 0;
 648         }
 649
 650         /*
 651          * NB. all returns later this function should go via "out" to
 652          * ensure the original SIGCHLD handler is restored properly.
 653          */
 654         osigchld = signal(SIGCHLD, SIG_DFL);
 655
 656         /* Prepare and verify the user for the command */
 657         username = percent_expand(options.authorized_principals_command_user,
 658             "u", user_pw->pw_name, (char *)NULL);
 659         pw = getpwnam(username);
 660         if (pw == NULL) {
 661                 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
 662                     username, strerror(errno));
 663                 goto out;
 664         }
 665
 666         /* Turn the command into an argument vector */
 667         if (split_argv(options.authorized_principals_command, &ac, &av) != 0) {
 668                 error("AuthorizedPrincipalsCommand \"%s\" contains "
 669                     "invalid quotes", command);
 670                 goto out;
 671         }
 672         if (ac == 0) {
 673                 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
 674                     command);
 675                 goto out;
 676         }
 677         for (i = 1; i < ac; i++) {
 678                 tmp = percent_expand(av[i],
 679                     "u", user_pw->pw_name,
 680                     "h", user_pw->pw_dir,
 681                     (char *)NULL);
 682                 if (tmp == NULL)
 683                         fatal("%s: percent_expand failed", __func__);
 684                 free(av[i]);
 685                 av[i] = tmp;
 686         }
 687         /* Prepare a printable command for logs, etc. */
 688         command = assemble_argv(ac, av);
 689
 690         if ((pid = subprocess("AuthorizedPrincipalsCommand", pw, command,
 691             ac, av, &f)) == 0)
 692                 goto out;
 693
 694         uid_swapped = 1;
 695         temporarily_use_uid(pw);
 696
 697         ok = process_principals(f, NULL, pw, cert);
 698
 699         if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command) != 0)
 700                 goto out;
 701
 702         /* Read completed successfully */
 703         found_principal = ok;
 704  out:
 705         if (f != NULL)
 706                 fclose(f);
 707         signal(SIGCHLD, osigchld);
 708         for (i = 0; i < ac; i++)
 709                 free(av[i]);
 710         free(av);
 711         if (uid_swapped)
 712                 restore_uid();
 713         free(command);
 714         free(username);
 715         return found_principal;
 716 }
 717 /*
 718  * Checks whether key is allowed in authorized_keys-format file,
 719  * returns 1 if the key is allowed or 0 otherwise.
 720  */
 721 static int
 722 check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw)
 723 {
 724         char line[SSH_MAX_PUBKEY_BYTES];
 725         const char *reason;
 726         int found_key = 0;
 727         u_long linenum = 0;
 728         Key *found;
 729         char *fp;
 730
 731         found_key = 0;
 732
 733         found = NULL;
 734         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 735                 char *cp, *key_options = NULL;
 736                 if (found != NULL)
 737                         key_free(found);
 738                 found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
 739                 auth_clear_options();
 740
 741                 /* Skip leading whitespace, empty and comment lines. */
 742                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 743                         ;
 744                 if (!*cp || *cp == '\n' || *cp == '#')
 745                         continue;
 746
 747                 if (key_read(found, &cp) != 1) {
 748                         /* no key?  check if there are options for this key */
 749                         int quoted = 0;
 750                         debug2("user_key_allowed: check options: '%s'", cp);
 751                         key_options = cp;
 752                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 753                                 if (*cp == '\\' && cp[1] == '"')
 754                                         cp++;   /* Skip both */
 755                                 else if (*cp == '"')
 756                                         quoted = !quoted;
 757                         }
 758                         /* Skip remaining whitespace. */
 759                         for (; *cp == ' ' || *cp == '\t'; cp++)
 760                                 ;
 761                         if (key_read(found, &cp) != 1) {
 762                                 debug2("user_key_allowed: advance: '%s'", cp);
 763                                 /* still no key?  advance to next line*/
 764                                 continue;
 765                         }
 766                 }
 767                 if (key_is_cert(key)) {
 768                         if (!key_equal(found, key->cert->signature_key))
 769                                 continue;
 770                         if (auth_parse_options(pw, key_options, file,
 771                             linenum) != 1)
 772                                 continue;
 773                         if (!key_is_cert_authority)
 774                                 continue;
 775                         if ((fp = sshkey_fingerprint(found,
 776                             options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 777                                 continue;
 778                         debug("matching CA found: file %s, line %lu, %s %s",
 779                             file, linenum, key_type(found), fp);
 780                         /*
 781                          * If the user has specified a list of principals as
 782                          * a key option, then prefer that list to matching
 783                          * their username in the certificate principals list.
 784                          */
 785                         if (authorized_principals != NULL &&
 786                             !match_principals_option(authorized_principals,
 787                             key->cert)) {
 788                                 reason = "Certificate does not contain an "
 789                                     "authorized principal";
 790  fail_reason:
 791                                 free(fp);
 792                                 error("%s", reason);
 793                                 auth_debug_add("%s", reason);
 794                                 continue;
 795                         }
 796                         if (key_cert_check_authority(key, 0, 0,
 797                             authorized_principals == NULL ? pw->pw_name : NULL,
 798                             &reason) != 0)
 799                                 goto fail_reason;
 800                         if (auth_cert_options(key, pw) != 0) {
 801                                 free(fp);
 802                                 continue;
 803                         }
 804                         verbose("Accepted certificate ID \"%s\" (serial %llu) "
 805                             "signed by %s CA %s via %s", key->cert->key_id,
 806                             (unsigned long long)key->cert->serial,
 807                             key_type(found), fp, file);
 808                         free(fp);
 809                         found_key = 1;
 810                         break;
 811                 } else if (key_equal(found, key)) {
 812                         if (auth_parse_options(pw, key_options, file,
 813                             linenum) != 1)
 814                                 continue;
 815                         if (key_is_cert_authority)
 816                                 continue;
 817                         if ((fp = sshkey_fingerprint(found,
 818                             options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 819                                 continue;
 820                         debug("matching key found: file %s, line %lu %s %s",
 821                             file, linenum, key_type(found), fp);
 822                         free(fp);
 823                         found_key = 1;
 824                         break;
 825                 }
 826         }
 827         if (found != NULL)
 828                 key_free(found);
 829         if (!found_key)
 830                 debug2("key not found");
 831         return found_key;
 832 }
 833
 834 /* Authenticate a certificate key against TrustedUserCAKeys */
 835 static int
 836 user_cert_trusted_ca(struct passwd *pw, Key *key)
 837 {
 838         char *ca_fp, *principals_file = NULL;
 839         const char *reason;
 840         int ret = 0, found_principal = 0, use_authorized_principals;
 841
 842         if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
 843                 return 0;
 844
 845         if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
 846             options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 847                 return 0;
 848
 849         if (sshkey_in_file(key->cert->signature_key,
 850             options.trusted_user_ca_keys, 1, 0) != 0) {
 851                 debug2("%s: CA %s %s is not listed in %s", __func__,
 852                     key_type(key->cert->signature_key), ca_fp,
 853                     options.trusted_user_ca_keys);
 854                 goto out;
 855         }
 856         /*
 857          * If AuthorizedPrincipals is in use, then compare the certificate
 858          * principals against the names in that file rather than matching
 859          * against the username.
 860          */
 861         if ((principals_file = authorized_principals_file(pw)) != NULL) {
 862                 if (match_principals_file(principals_file, pw, key->cert))
 863                         found_principal = 1;
 864         }
 865         /* Try querying command if specified */
 866         if (!found_principal && match_principals_command(pw, key->cert))
 867                 found_principal = 1;
 868         /* If principals file or command is specified, then require a match */
 869         use_authorized_principals = principals_file != NULL ||
 870             options.authorized_principals_command != NULL;
 871         if (!found_principal && use_authorized_principals) {
 872                 reason = "Certificate does not contain an authorized principal";
 873  fail_reason:
 874                 error("%s", reason);
 875                 auth_debug_add("%s", reason);
 876                 goto out;
 877         }
 878         if (key_cert_check_authority(key, 0, 1,
 879             use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
 880                 goto fail_reason;
 881         if (auth_cert_options(key, pw) != 0)
 882                 goto out;
 883
 884         verbose("Accepted certificate ID \"%s\" (serial %llu) signed by "
 885             "%s CA %s via %s", key->cert->key_id,
 886             (unsigned long long)key->cert->serial,
 887             key_type(key->cert->signature_key), ca_fp,
 888             options.trusted_user_ca_keys);
 889         ret = 1;
 890
 891  out:
 892         free(principals_file);
 893         free(ca_fp);
 894         return ret;
 895 }
 896
 897 /*
 898  * Checks whether key is allowed in file.
 899  * returns 1 if the key is allowed or 0 otherwise.
 900  */
 901 static int
 902 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 903 {
 904         FILE *f;
 905         int found_key = 0;
 906
 907         /* Temporarily use the user's uid. */
 908         temporarily_use_uid(pw);
 909
 910         debug("trying public key file %s", file);
 911         if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
 912                 found_key = check_authkeys_file(f, file, key, pw);
 913                 fclose(f);
 914         }
 915
 916         restore_uid();
 917         return found_key;
 918 }
 919
 920 /*
 921  * Checks whether key is allowed in output of command.
 922  * returns 1 if the key is allowed or 0 otherwise.
 923  */
 924 static int
 925 user_key_command_allowed2(struct passwd *user_pw, Key *key)
 926 {
 927         FILE *f = NULL;
 928         int r, ok, found_key = 0;
 929         struct passwd *pw;
 930         int i, uid_swapped = 0, ac = 0;
 931         pid_t pid;
 932         char *username = NULL, *key_fp = NULL, *keytext = NULL;
 933         char *tmp, *command = NULL, **av = NULL;
 934         void (*osigchld)(int);
 935
 936         if (options.authorized_keys_command == NULL)
 937                 return 0;
 938         if (options.authorized_keys_command_user == NULL) {
 939                 error("No user for AuthorizedKeysCommand specified, skipping");
 940                 return 0;
 941         }
 942
 943         /*
 944          * NB. all returns later this function should go via "out" to
 945          * ensure the original SIGCHLD handler is restored properly.
 946          */
 947         osigchld = signal(SIGCHLD, SIG_DFL);
 948
 949         /* Prepare and verify the user for the command */
 950         username = percent_expand(options.authorized_keys_command_user,
 951             "u", user_pw->pw_name, (char *)NULL);
 952         pw = getpwnam(username);
 953         if (pw == NULL) {
 954                 error("AuthorizedKeysCommandUser \"%s\" not found: %s",
 955                     username, strerror(errno));
 956                 goto out;
 957         }
 958
 959         /* Prepare AuthorizedKeysCommand */
 960         if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash,
 961             SSH_FP_DEFAULT)) == NULL) {
 962                 error("%s: sshkey_fingerprint failed", __func__);
 963                 goto out;
 964         }
 965         if ((r = sshkey_to_base64(key, &keytext)) != 0) {
 966                 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r));
 967                 goto out;
 968         }
 969
 970         /* Turn the command into an argument vector */
 971         if (split_argv(options.authorized_keys_command, &ac, &av) != 0) {
 972                 error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
 973                     command);
 974                 goto out;
 975         }
 976         if (ac == 0) {
 977                 error("AuthorizedKeysCommand \"%s\" yielded no arguments",
 978                     command);
 979                 goto out;
 980         }
 981         for (i = 1; i < ac; i++) {
 982                 tmp = percent_expand(av[i],
 983                     "u", user_pw->pw_name,
 984                     "h", user_pw->pw_dir,
 985                     "t", sshkey_ssh_name(key),
 986                     "f", key_fp,
 987                     "k", keytext,
 988                     (char *)NULL);
 989                 if (tmp == NULL)
 990                         fatal("%s: percent_expand failed", __func__);
 991                 free(av[i]);
 992                 av[i] = tmp;
 993         }
 994         /* Prepare a printable command for logs, etc. */
 995         command = assemble_argv(ac, av);
 996
 997         /*
 998          * If AuthorizedKeysCommand was run without arguments
 999          * then fall back to the old behaviour of passing the
1000          * target username as a single argument.
1001          */
1002         if (ac == 1) {
1003                 av = xreallocarray(av, ac + 2, sizeof(*av));
1004                 av[1] = xstrdup(user_pw->pw_name);
1005                 av[2] = NULL;
1006                 /* Fix up command too, since it is used in log messages */
1007                 free(command);
1008                 xasprintf(&command, "%s %s", av[0], av[1]);
1009         }
1010
1011         if ((pid = subprocess("AuthorizedKeysCommand", pw, command,
1012             ac, av, &f)) == 0)
1013                 goto out;
1014
1015         uid_swapped = 1;
1016         temporarily_use_uid(pw);
1017
1018         ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
1019
1020         if (exited_cleanly(pid, "AuthorizedKeysCommand", command) != 0)
1021                 goto out;
1022
1023         /* Read completed successfully */
1024         found_key = ok;
1025  out:
1026         if (f != NULL)
1027                 fclose(f);
1028         signal(SIGCHLD, osigchld);
1029         for (i = 0; i < ac; i++)
1030                 free(av[i]);
1031         free(av);
1032         if (uid_swapped)
1033                 restore_uid();
1034         free(command);
1035         free(username);
1036         free(key_fp);
1037         free(keytext);
1038         return found_key;
1039 }
1040
1041 /*
1042  * Check whether key authenticates and authorises the user.
1043  */
1044 int
1045 user_key_allowed(struct passwd *pw, Key *key, int auth_attempt)
1046 {
1047         u_int success, i;
1048         char *file;
1049
1050         if (auth_key_is_revoked(key))
1051                 return 0;
1052         if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
1053                 return 0;
1054
1055         success = user_cert_trusted_ca(pw, key);
1056         if (success)
1057                 return success;
1058
1059         success = user_key_command_allowed2(pw, key);
1060         if (success > 0)
1061                 return success;
1062
1063         for (i = 0; !success && i < options.num_authkeys_files; i++) {
1064
1065                 if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
1066                         continue;
1067                 file = expand_authorized_keys(
1068                     options.authorized_keys_files[i], pw);
1069
1070                 success = user_key_allowed2(pw, key, file);
1071                 free(file);
1072         }
1073
1074         return success;
1075 }
1076
1077 /* Records a public key in the list of previously-successful keys */
1078 void
1079 auth2_record_userkey(Authctxt *authctxt, struct sshkey *key)
1080 {
1081         struct sshkey **tmp;
1082
1083         if (authctxt->nprev_userkeys >= INT_MAX ||
1084             (tmp = reallocarray(authctxt->prev_userkeys,
1085             authctxt->nprev_userkeys + 1, sizeof(*tmp))) == NULL)
1086                 fatal("%s: reallocarray failed", __func__);
1087         authctxt->prev_userkeys = tmp;
1088         authctxt->prev_userkeys[authctxt->nprev_userkeys] = key;
1089         authctxt->nprev_userkeys++;
1090 }
1091
1092 /* Checks whether a key has already been used successfully for authentication */
1093 int
1094 auth2_userkey_already_used(Authctxt *authctxt, struct sshkey *key)
1095 {
1096         u_int i;
1097
1098         for (i = 0; i < authctxt->nprev_userkeys; i++) {
1099                 if (sshkey_equal_public(key, authctxt->prev_userkeys[i])) {
1100                         return 1;
1101                 }
1102         }
1103         return 0;
1104 }
1105
1106 Authmethod method_pubkey = {
1107         "publickey",
1108         userauth_pubkey,
1109         &options.pubkey_authentication
1110 };