crypto/openssh/ssh_api.c

   1 /* $OpenBSD: ssh_api.c,v 1.27 2021/04/03 06:18:41 djm Exp $ */
   2 /*
   3  * Copyright (c) 2012 Markus Friedl.  All rights reserved.
   4  *
   5  * Permission to use, copy, modify, and distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  16  */
  17
  18 #include "includes.h"
  19
  20 #include <sys/types.h>
  21
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24
  25 #include "ssh_api.h"
  26 #include "compat.h"
  27 #include "log.h"
  28 #include "authfile.h"
  29 #include "sshkey.h"
  30 #include "misc.h"
  31 #include "ssh2.h"
  32 #include "version.h"
  33 #include "myproposal.h"
  34 #include "ssherr.h"
  35 #include "sshbuf.h"
  36
  37 #include "openbsd-compat/openssl-compat.h"
  38
  39 #include <string.h>
  40
  41 int     _ssh_exchange_banner(struct ssh *);
  42 int     _ssh_send_banner(struct ssh *, struct sshbuf *);
  43 int     _ssh_read_banner(struct ssh *, struct sshbuf *);
  44 int     _ssh_order_hostkeyalgs(struct ssh *);
  45 int     _ssh_verify_host_key(struct sshkey *, struct ssh *);
  46 struct sshkey *_ssh_host_public_key(int, int, struct ssh *);
  47 struct sshkey *_ssh_host_private_key(int, int, struct ssh *);
  48 int     _ssh_host_key_sign(struct ssh *, struct sshkey *, struct sshkey *,
  49     u_char **, size_t *, const u_char *, size_t, const char *);
  50
  51 /*
  52  * stubs for the server side implementation of kex.
  53  * disable privsep so our stubs will never be called.
  54  */
  55 int     use_privsep = 0;
  56 int     mm_sshkey_sign(struct sshkey *, u_char **, u_int *,
  57     const u_char *, u_int, const char *, const char *, const char *, u_int);
  58
  59 #ifdef WITH_OPENSSL
  60 DH      *mm_choose_dh(int, int, int);
  61 #endif
  62
  63 int
  64 mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp,
  65     const u_char *data, u_int datalen, const char *alg,
  66     const char *sk_provider, const char *sk_pin, u_int compat)
  67 {
  68         return (-1);
  69 }
  70
  71 #ifdef WITH_OPENSSL
  72 DH *
  73 mm_choose_dh(int min, int nbits, int max)
  74 {
  75         return (NULL);
  76 }
  77 #endif
  78
  79 /* API */
  80
  81 int
  82 ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params)
  83 {
  84         char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
  85         struct ssh *ssh;
  86         char **proposal;
  87         static int called;
  88         int r;
  89
  90         if (!called) {
  91                 seed_rng();
  92                 called = 1;
  93         }
  94
  95         if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL)
  96                 return SSH_ERR_ALLOC_FAIL;
  97         if (is_server)
  98                 ssh_packet_set_server(ssh);
  99
 100         /* Initialize key exchange */
 101         proposal = kex_params ? kex_params->proposal : myproposal;
 102         if ((r = kex_ready(ssh, proposal)) != 0) {
 103                 ssh_free(ssh);
 104                 return r;
 105         }
 106         ssh->kex->server = is_server;
 107         if (is_server) {
 108 #ifdef WITH_OPENSSL
 109                 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server;
 110                 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server;
 111                 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server;
 112                 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server;
 113                 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server;
 114                 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
 115                 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
 116 # ifdef OPENSSL_HAS_ECC
 117                 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server;
 118 # endif
 119 #endif /* WITH_OPENSSL */
 120                 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server;
 121                 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_server;
 122                 ssh->kex->load_host_public_key=&_ssh_host_public_key;
 123                 ssh->kex->load_host_private_key=&_ssh_host_private_key;
 124                 ssh->kex->sign=&_ssh_host_key_sign;
 125         } else {
 126 #ifdef WITH_OPENSSL
 127                 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client;
 128                 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client;
 129                 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client;
 130                 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client;
 131                 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client;
 132                 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
 133                 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
 134 # ifdef OPENSSL_HAS_ECC
 135                 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
 136 # endif
 137 #endif /* WITH_OPENSSL */
 138                 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
 139                 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client;
 140                 ssh->kex->verify_host_key =&_ssh_verify_host_key;
 141         }
 142         *sshp = ssh;
 143         return 0;
 144 }
 145
 146 void
 147 ssh_free(struct ssh *ssh)
 148 {
 149         struct key_entry *k;
 150
 151         if (ssh == NULL)
 152                 return;
 153
 154         /*
 155          * we've only created the public keys variants in case we
 156          * are a acting as a server.
 157          */
 158         while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
 159                 TAILQ_REMOVE(&ssh->public_keys, k, next);
 160                 if (ssh->kex && ssh->kex->server)
 161                         sshkey_free(k->key);
 162                 free(k);
 163         }
 164         while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
 165                 TAILQ_REMOVE(&ssh->private_keys, k, next);
 166                 free(k);
 167         }
 168         ssh_packet_close(ssh);
 169         free(ssh);
 170 }
 171
 172 void
 173 ssh_set_app_data(struct ssh *ssh, void *app_data)
 174 {
 175         ssh->app_data = app_data;
 176 }
 177
 178 void *
 179 ssh_get_app_data(struct ssh *ssh)
 180 {
 181         return ssh->app_data;
 182 }
 183
 184 /* Returns < 0 on error, 0 otherwise */
 185 int
 186 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
 187 {
 188         struct sshkey *pubkey = NULL;
 189         struct key_entry *k = NULL, *k_prv = NULL;
 190         int r;
 191
 192         if (ssh->kex->server) {
 193                 if ((r = sshkey_from_private(key, &pubkey)) != 0)
 194                         return r;
 195                 if ((k = malloc(sizeof(*k))) == NULL ||
 196                     (k_prv = malloc(sizeof(*k_prv))) == NULL) {
 197                         free(k);
 198                         sshkey_free(pubkey);
 199                         return SSH_ERR_ALLOC_FAIL;
 200                 }
 201                 k_prv->key = key;
 202                 TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
 203
 204                 /* add the public key, too */
 205                 k->key = pubkey;
 206                 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
 207                 r = 0;
 208         } else {
 209                 if ((k = malloc(sizeof(*k))) == NULL)
 210                         return SSH_ERR_ALLOC_FAIL;
 211                 k->key = key;
 212                 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
 213                 r = 0;
 214         }
 215
 216         return r;
 217 }
 218
 219 int
 220 ssh_set_verify_host_key_callback(struct ssh *ssh,
 221     int (*cb)(struct sshkey *, struct ssh *))
 222 {
 223         if (cb == NULL || ssh->kex == NULL)
 224                 return SSH_ERR_INVALID_ARGUMENT;
 225
 226         ssh->kex->verify_host_key = cb;
 227
 228         return 0;
 229 }
 230
 231 int
 232 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
 233 {
 234         return sshbuf_put(ssh_packet_get_input(ssh), data, len);
 235 }
 236
 237 int
 238 ssh_packet_next(struct ssh *ssh, u_char *typep)
 239 {
 240         int r;
 241         u_int32_t seqnr;
 242         u_char type;
 243
 244         /*
 245          * Try to read a packet. Return SSH_MSG_NONE if no packet or not
 246          * enough data.
 247          */
 248         *typep = SSH_MSG_NONE;
 249         if (sshbuf_len(ssh->kex->client_version) == 0 ||
 250             sshbuf_len(ssh->kex->server_version) == 0)
 251                 return _ssh_exchange_banner(ssh);
 252         /*
 253          * If we enough data and a dispatch function then
 254          * call the function and get the next packet.
 255          * Otherwise return the packet type to the caller so it
 256          * can decide how to go on.
 257          *
 258          * We will only call the dispatch function for:
 259          *     20-29    Algorithm negotiation
 260          *     30-49    Key exchange method specific (numbers can be reused for
 261          *              different authentication methods)
 262          */
 263         for (;;) {
 264                 if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
 265                         return r;
 266                 if (type > 0 && type < DISPATCH_MAX &&
 267                     type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
 268                     ssh->dispatch[type] != NULL) {
 269                         if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
 270                                 return r;
 271                 } else {
 272                         *typep = type;
 273                         return 0;
 274                 }
 275         }
 276 }
 277
 278 const u_char *
 279 ssh_packet_payload(struct ssh *ssh, size_t *lenp)
 280 {
 281         return sshpkt_ptr(ssh, lenp);
 282 }
 283
 284 int
 285 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
 286 {
 287         int r;
 288
 289         if ((r = sshpkt_start(ssh, type)) != 0 ||
 290             (r = sshpkt_put(ssh, data, len)) != 0 ||
 291             (r = sshpkt_send(ssh)) != 0)
 292                 return r;
 293         return 0;
 294 }
 295
 296 const u_char *
 297 ssh_output_ptr(struct ssh *ssh, size_t *len)
 298 {
 299         struct sshbuf *output = ssh_packet_get_output(ssh);
 300
 301         *len = sshbuf_len(output);
 302         return sshbuf_ptr(output);
 303 }
 304
 305 int
 306 ssh_output_consume(struct ssh *ssh, size_t len)
 307 {
 308         return sshbuf_consume(ssh_packet_get_output(ssh), len);
 309 }
 310
 311 int
 312 ssh_output_space(struct ssh *ssh, size_t len)
 313 {
 314         return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
 315 }
 316
 317 int
 318 ssh_input_space(struct ssh *ssh, size_t len)
 319 {
 320         return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
 321 }
 322
 323 /* Read other side's version identification. */
 324 int
 325 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner)
 326 {
 327         struct sshbuf *input = ssh_packet_get_input(ssh);
 328         const char *mismatch = "Protocol mismatch.\r\n";
 329         const u_char *s = sshbuf_ptr(input);
 330         u_char c;
 331         char *cp = NULL, *remote_version = NULL;
 332         int r = 0, remote_major, remote_minor, expect_nl;
 333         size_t n, j;
 334
 335         for (j = n = 0;;) {
 336                 sshbuf_reset(banner);
 337                 expect_nl = 0;
 338                 for (;;) {
 339                         if (j >= sshbuf_len(input))
 340                                 return 0; /* insufficient data in input buf */
 341                         c = s[j++];
 342                         if (c == '\r') {
 343                                 expect_nl = 1;
 344                                 continue;
 345                         }
 346                         if (c == '\n')
 347                                 break;
 348                         if (expect_nl)
 349                                 goto bad;
 350                         if ((r = sshbuf_put_u8(banner, c)) != 0)
 351                                 return r;
 352                         if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN)
 353                                 goto bad;
 354                 }
 355                 if (sshbuf_len(banner) >= 4 &&
 356                     memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0)
 357                         break;
 358                 debug_f("%.*s", (int)sshbuf_len(banner),
 359                     sshbuf_ptr(banner));
 360                 /* Accept lines before banner only on client */
 361                 if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) {
 362   bad:
 363                         if ((r = sshbuf_put(ssh_packet_get_output(ssh),
 364                             mismatch, strlen(mismatch))) != 0)
 365                                 return r;
 366                         return SSH_ERR_NO_PROTOCOL_VERSION;
 367                 }
 368         }
 369         if ((r = sshbuf_consume(input, j)) != 0)
 370                 return r;
 371
 372         /* XXX remote version must be the same size as banner for sscanf */
 373         if ((cp = sshbuf_dup_string(banner)) == NULL ||
 374             (remote_version = calloc(1, sshbuf_len(banner))) == NULL) {
 375                 r = SSH_ERR_ALLOC_FAIL;
 376                 goto out;
 377         }
 378
 379         /*
 380          * Check that the versions match.  In future this might accept
 381          * several versions and set appropriate flags to handle them.
 382          */
 383         if (sscanf(cp, "SSH-%d.%d-%[^\n]\n",
 384             &remote_major, &remote_minor, remote_version) != 3) {
 385                 r = SSH_ERR_INVALID_FORMAT;
 386                 goto out;
 387         }
 388         debug("Remote protocol version %d.%d, remote software version %.100s",
 389             remote_major, remote_minor, remote_version);
 390
 391         compat_banner(ssh, remote_version);
 392         if  (remote_major == 1 && remote_minor == 99) {
 393                 remote_major = 2;
 394                 remote_minor = 0;
 395         }
 396         if (remote_major != 2)
 397                 r = SSH_ERR_PROTOCOL_MISMATCH;
 398
 399         debug("Remote version string %.100s", cp);
 400  out:
 401         free(cp);
 402         free(remote_version);
 403         return r;
 404 }
 405
 406 /* Send our own protocol version identification. */
 407 int
 408 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner)
 409 {
 410         char *cp;
 411         int r;
 412
 413         if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0)
 414                 return r;
 415         if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0)
 416                 return r;
 417         /* Remove trailing \r\n */
 418         if ((r = sshbuf_consume_end(banner, 2)) != 0)
 419                 return r;
 420         if ((cp = sshbuf_dup_string(banner)) == NULL)
 421                 return SSH_ERR_ALLOC_FAIL;
 422         debug("Local version string %.100s", cp);
 423         free(cp);
 424         return 0;
 425 }
 426
 427 int
 428 _ssh_exchange_banner(struct ssh *ssh)
 429 {
 430         struct kex *kex = ssh->kex;
 431         int r;
 432
 433         /*
 434          * if _ssh_read_banner() cannot parse a full version string
 435          * it will return NULL and we end up calling it again.
 436          */
 437
 438         r = 0;
 439         if (kex->server) {
 440                 if (sshbuf_len(ssh->kex->server_version) == 0)
 441                         r = _ssh_send_banner(ssh, ssh->kex->server_version);
 442                 if (r == 0 &&
 443                     sshbuf_len(ssh->kex->server_version) != 0 &&
 444                     sshbuf_len(ssh->kex->client_version) == 0)
 445                         r = _ssh_read_banner(ssh, ssh->kex->client_version);
 446         } else {
 447                 if (sshbuf_len(ssh->kex->server_version) == 0)
 448                         r = _ssh_read_banner(ssh, ssh->kex->server_version);
 449                 if (r == 0 &&
 450                     sshbuf_len(ssh->kex->server_version) != 0 &&
 451                     sshbuf_len(ssh->kex->client_version) == 0)
 452                         r = _ssh_send_banner(ssh, ssh->kex->client_version);
 453         }
 454         if (r != 0)
 455                 return r;
 456         /* start initial kex as soon as we have exchanged the banners */
 457         if (sshbuf_len(ssh->kex->server_version) != 0 &&
 458             sshbuf_len(ssh->kex->client_version) != 0) {
 459                 if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
 460                     (r = kex_send_kexinit(ssh)) != 0)
 461                         return r;
 462         }
 463         return 0;
 464 }
 465
 466 struct sshkey *
 467 _ssh_host_public_key(int type, int nid, struct ssh *ssh)
 468 {
 469         struct key_entry *k;
 470
 471         debug3_f("need %d", type);
 472         TAILQ_FOREACH(k, &ssh->public_keys, next) {
 473                 debug3_f("check %s", sshkey_type(k->key));
 474                 if (k->key->type == type &&
 475                     (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
 476                         return (k->key);
 477         }
 478         return (NULL);
 479 }
 480
 481 struct sshkey *
 482 _ssh_host_private_key(int type, int nid, struct ssh *ssh)
 483 {
 484         struct key_entry *k;
 485
 486         debug3_f("need %d", type);
 487         TAILQ_FOREACH(k, &ssh->private_keys, next) {
 488                 debug3_f("check %s", sshkey_type(k->key));
 489                 if (k->key->type == type &&
 490                     (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
 491                         return (k->key);
 492         }
 493         return (NULL);
 494 }
 495
 496 int
 497 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
 498 {
 499         struct key_entry *k;
 500
 501         debug3_f("need %s", sshkey_type(hostkey));
 502         TAILQ_FOREACH(k, &ssh->public_keys, next) {
 503                 debug3_f("check %s", sshkey_type(k->key));
 504                 if (sshkey_equal_public(hostkey, k->key))
 505                         return (0);     /* ok */
 506         }
 507         return (-1);    /* failed */
 508 }
 509
 510 /* offer hostkey algorithms in kexinit depending on registered keys */
 511 int
 512 _ssh_order_hostkeyalgs(struct ssh *ssh)
 513 {
 514         struct key_entry *k;
 515         char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
 516         char **proposal;
 517         size_t maxlen;
 518         int ktype, r;
 519
 520         /* XXX we de-serialize ssh->kex->my, modify it, and change it */
 521         if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
 522                 return r;
 523         orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
 524         if ((oavail = avail = strdup(orig)) == NULL) {
 525                 r = SSH_ERR_ALLOC_FAIL;
 526                 goto out;
 527         }
 528         maxlen = strlen(avail) + 1;
 529         if ((replace = calloc(1, maxlen)) == NULL) {
 530                 r = SSH_ERR_ALLOC_FAIL;
 531                 goto out;
 532         }
 533         *replace = '\0';
 534         while ((alg = strsep(&avail, ",")) && *alg != '\0') {
 535                 if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
 536                         continue;
 537                 TAILQ_FOREACH(k, &ssh->public_keys, next) {
 538                         if (k->key->type == ktype ||
 539                             (sshkey_is_cert(k->key) && k->key->type ==
 540                             sshkey_type_plain(ktype))) {
 541                                 if (*replace != '\0')
 542                                         strlcat(replace, ",", maxlen);
 543                                 strlcat(replace, alg, maxlen);
 544                                 break;
 545                         }
 546                 }
 547         }
 548         if (*replace != '\0') {
 549                 debug2_f("orig/%d    %s", ssh->kex->server, orig);
 550                 debug2_f("replace/%d %s", ssh->kex->server, replace);
 551                 free(orig);
 552                 proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
 553                 replace = NULL; /* owned by proposal */
 554                 r = kex_prop2buf(ssh->kex->my, proposal);
 555         }
 556  out:
 557         free(oavail);
 558         free(replace);
 559         kex_prop_free(proposal);
 560         return r;
 561 }
 562
 563 int
 564 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey,
 565     struct sshkey *pubkey, u_char **signature, size_t *slen,
 566     const u_char *data, size_t dlen, const char *alg)
 567 {
 568         return sshkey_sign(privkey, signature, slen, data, dlen,
 569             alg, NULL, NULL, ssh->compat);
 570 }