crypto/openssh/auth2-chall.c

   1 /* $OpenBSD: auth2-chall.c,v 1.54 2020/10/18 11:32:01 djm Exp $ */
   2 /*
   3  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
   4  * Copyright (c) 2001 Per Allansson.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #include "includes.h"
  28
  29 #include <sys/types.h>
  30
  31 #include <stdlib.h>
  32 #include <stdio.h>
  33 #include <string.h>
  34 #include <stdarg.h>
  35
  36 #include "xmalloc.h"
  37 #include "ssh2.h"
  38 #include "sshkey.h"
  39 #include "hostfile.h"
  40 #include "auth.h"
  41 #include "sshbuf.h"
  42 #include "packet.h"
  43 #include "dispatch.h"
  44 #include "ssherr.h"
  45 #include "log.h"
  46 #include "misc.h"
  47 #include "servconf.h"
  48
  49 /* import */
  50 extern ServerOptions options;
  51
  52 static int auth2_challenge_start(struct ssh *);
  53 static int send_userauth_info_request(struct ssh *);
  54 static int input_userauth_info_response(int, u_int32_t, struct ssh *);
  55
  56 #ifdef BSD_AUTH
  57 extern KbdintDevice bsdauth_device;
  58 #else
  59 #ifdef USE_PAM
  60 extern KbdintDevice sshpam_device;
  61 #endif
  62 #endif
  63
  64 KbdintDevice *devices[] = {
  65 #ifdef BSD_AUTH
  66         &bsdauth_device,
  67 #else
  68 #ifdef USE_PAM
  69         &sshpam_device,
  70 #endif
  71 #endif
  72         NULL
  73 };
  74
  75 typedef struct KbdintAuthctxt KbdintAuthctxt;
  76 struct KbdintAuthctxt
  77 {
  78         char *devices;
  79         void *ctxt;
  80         KbdintDevice *device;
  81         u_int nreq;
  82         u_int devices_done;
  83 };
  84
  85 #ifdef USE_PAM
  86 void
  87 remove_kbdint_device(const char *devname)
  88 {
  89         int i, j;
  90
  91         for (i = 0; devices[i] != NULL; i++)
  92                 if (strcmp(devices[i]->name, devname) == 0) {
  93                         for (j = i; devices[j] != NULL; j++)
  94                                 devices[j] = devices[j+1];
  95                         i--;
  96                 }
  97 }
  98 #endif
  99
 100 static KbdintAuthctxt *
 101 kbdint_alloc(const char *devs)
 102 {
 103         KbdintAuthctxt *kbdintctxt;
 104         struct sshbuf *b;
 105         int i, r;
 106
 107 #ifdef USE_PAM
 108         if (!options.use_pam)
 109                 remove_kbdint_device("pam");
 110 #endif
 111
 112         kbdintctxt = xcalloc(1, sizeof(KbdintAuthctxt));
 113         if (strcmp(devs, "") == 0) {
 114                 if ((b = sshbuf_new()) == NULL)
 115                         fatal_f("sshbuf_new failed");
 116                 for (i = 0; devices[i]; i++) {
 117                         if ((r = sshbuf_putf(b, "%s%s",
 118                             sshbuf_len(b) ? "," : "", devices[i]->name)) != 0)
 119                                 fatal_fr(r, "buffer error");
 120                 }
 121                 if ((kbdintctxt->devices = sshbuf_dup_string(b)) == NULL)
 122                         fatal_f("sshbuf_dup_string failed");
 123                 sshbuf_free(b);
 124         } else {
 125                 kbdintctxt->devices = xstrdup(devs);
 126         }
 127         debug("kbdint_alloc: devices '%s'", kbdintctxt->devices);
 128         kbdintctxt->ctxt = NULL;
 129         kbdintctxt->device = NULL;
 130         kbdintctxt->nreq = 0;
 131
 132         return kbdintctxt;
 133 }
 134 static void
 135 kbdint_reset_device(KbdintAuthctxt *kbdintctxt)
 136 {
 137         if (kbdintctxt->ctxt) {
 138                 kbdintctxt->device->free_ctx(kbdintctxt->ctxt);
 139                 kbdintctxt->ctxt = NULL;
 140         }
 141         kbdintctxt->device = NULL;
 142 }
 143 static void
 144 kbdint_free(KbdintAuthctxt *kbdintctxt)
 145 {
 146         if (kbdintctxt->device)
 147                 kbdint_reset_device(kbdintctxt);
 148         free(kbdintctxt->devices);
 149         freezero(kbdintctxt, sizeof(*kbdintctxt));
 150 }
 151 /* get next device */
 152 static int
 153 kbdint_next_device(Authctxt *authctxt, KbdintAuthctxt *kbdintctxt)
 154 {
 155         size_t len;
 156         char *t;
 157         int i;
 158
 159         if (kbdintctxt->device)
 160                 kbdint_reset_device(kbdintctxt);
 161         do {
 162                 len = kbdintctxt->devices ?
 163                     strcspn(kbdintctxt->devices, ",") : 0;
 164
 165                 if (len == 0)
 166                         break;
 167                 for (i = 0; devices[i]; i++) {
 168                         if ((kbdintctxt->devices_done & (1 << i)) != 0 ||
 169                             !auth2_method_allowed(authctxt,
 170                             "keyboard-interactive", devices[i]->name))
 171                                 continue;
 172                         if (strncmp(kbdintctxt->devices, devices[i]->name,
 173                             len) == 0) {
 174                                 kbdintctxt->device = devices[i];
 175                                 kbdintctxt->devices_done |= 1 << i;
 176                         }
 177                 }
 178                 t = kbdintctxt->devices;
 179                 kbdintctxt->devices = t[len] ? xstrdup(t+len+1) : NULL;
 180                 free(t);
 181                 debug2("kbdint_next_device: devices %s", kbdintctxt->devices ?
 182                     kbdintctxt->devices : "<empty>");
 183         } while (kbdintctxt->devices && !kbdintctxt->device);
 184
 185         return kbdintctxt->device ? 1 : 0;
 186 }
 187
 188 /*
 189  * try challenge-response, set authctxt->postponed if we have to
 190  * wait for the response.
 191  */
 192 int
 193 auth2_challenge(struct ssh *ssh, char *devs)
 194 {
 195         Authctxt *authctxt = ssh->authctxt;
 196         debug("auth2_challenge: user=%s devs=%s",
 197             authctxt->user ? authctxt->user : "<nouser>",
 198             devs ? devs : "<no devs>");
 199
 200         if (authctxt->user == NULL || !devs)
 201                 return 0;
 202         if (authctxt->kbdintctxt == NULL)
 203                 authctxt->kbdintctxt = kbdint_alloc(devs);
 204         return auth2_challenge_start(ssh);
 205 }
 206
 207 /* unregister kbd-int callbacks and context */
 208 void
 209 auth2_challenge_stop(struct ssh *ssh)
 210 {
 211         Authctxt *authctxt = ssh->authctxt;
 212         /* unregister callback */
 213         ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE, NULL);
 214         if (authctxt->kbdintctxt != NULL) {
 215                 kbdint_free(authctxt->kbdintctxt);
 216                 authctxt->kbdintctxt = NULL;
 217         }
 218 }
 219
 220 /* side effect: sets authctxt->postponed if a reply was sent*/
 221 static int
 222 auth2_challenge_start(struct ssh *ssh)
 223 {
 224         Authctxt *authctxt = ssh->authctxt;
 225         KbdintAuthctxt *kbdintctxt = authctxt->kbdintctxt;
 226
 227         debug2("auth2_challenge_start: devices %s",
 228             kbdintctxt->devices ?  kbdintctxt->devices : "<empty>");
 229
 230         if (kbdint_next_device(authctxt, kbdintctxt) == 0) {
 231                 auth2_challenge_stop(ssh);
 232                 return 0;
 233         }
 234         debug("auth2_challenge_start: trying authentication method '%s'",
 235             kbdintctxt->device->name);
 236
 237         if ((kbdintctxt->ctxt = kbdintctxt->device->init_ctx(authctxt)) == NULL) {
 238                 auth2_challenge_stop(ssh);
 239                 return 0;
 240         }
 241         if (send_userauth_info_request(ssh) == 0) {
 242                 auth2_challenge_stop(ssh);
 243                 return 0;
 244         }
 245         ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_INFO_RESPONSE,
 246             &input_userauth_info_response);
 247
 248         authctxt->postponed = 1;
 249         return 0;
 250 }
 251
 252 static int
 253 send_userauth_info_request(struct ssh *ssh)
 254 {
 255         Authctxt *authctxt = ssh->authctxt;
 256         KbdintAuthctxt *kbdintctxt;
 257         char *name, *instr, **prompts;
 258         u_int r, i, *echo_on;
 259
 260         kbdintctxt = authctxt->kbdintctxt;
 261         if (kbdintctxt->device->query(kbdintctxt->ctxt,
 262             &name, &instr, &kbdintctxt->nreq, &prompts, &echo_on))
 263                 return 0;
 264
 265         if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_INFO_REQUEST)) != 0 ||
 266             (r = sshpkt_put_cstring(ssh, name)) != 0 ||
 267             (r = sshpkt_put_cstring(ssh, instr)) != 0 ||
 268             (r = sshpkt_put_cstring(ssh, "")) != 0 ||   /* language not used */
 269             (r = sshpkt_put_u32(ssh, kbdintctxt->nreq)) != 0)
 270                 fatal_fr(r, "start packet");
 271         for (i = 0; i < kbdintctxt->nreq; i++) {
 272                 if ((r = sshpkt_put_cstring(ssh, prompts[i])) != 0 ||
 273                     (r = sshpkt_put_u8(ssh, echo_on[i])) != 0)
 274                         fatal_fr(r, "assemble packet");
 275         }
 276         if ((r = sshpkt_send(ssh)) != 0 ||
 277             (r = ssh_packet_write_wait(ssh)) != 0)
 278                 fatal_fr(r, "send packet");
 279
 280         for (i = 0; i < kbdintctxt->nreq; i++)
 281                 free(prompts[i]);
 282         free(prompts);
 283         free(echo_on);
 284         free(name);
 285         free(instr);
 286         return 1;
 287 }
 288
 289 static int
 290 input_userauth_info_response(int type, u_int32_t seq, struct ssh *ssh)
 291 {
 292         Authctxt *authctxt = ssh->authctxt;
 293         KbdintAuthctxt *kbdintctxt;
 294         int authenticated = 0, res;
 295         int r;
 296         u_int i, nresp;
 297         const char *devicename = NULL;
 298         char **response = NULL;
 299
 300         if (authctxt == NULL)
 301                 fatal_f("no authctxt");
 302         kbdintctxt = authctxt->kbdintctxt;
 303         if (kbdintctxt == NULL || kbdintctxt->ctxt == NULL)
 304                 fatal_f("no kbdintctxt");
 305         if (kbdintctxt->device == NULL)
 306                 fatal_f("no device");
 307
 308         authctxt->postponed = 0;        /* reset */
 309         if ((r = sshpkt_get_u32(ssh, &nresp)) != 0)
 310                 fatal_fr(r, "parse packet");
 311         if (nresp != kbdintctxt->nreq)
 312                 fatal_f("wrong number of replies");
 313         if (nresp > 100)
 314                 fatal_f("too many replies");
 315         if (nresp > 0) {
 316                 response = xcalloc(nresp, sizeof(char *));
 317                 for (i = 0; i < nresp; i++) {
 318                         if ((r = sshpkt_get_cstring(ssh, &response[i], NULL)) != 0)
 319                                 fatal_fr(r, "parse response");
 320                 }
 321         }
 322         if ((r = sshpkt_get_end(ssh)) != 0)
 323                 fatal_fr(r, "parse packet");
 324
 325         res = kbdintctxt->device->respond(kbdintctxt->ctxt, nresp, response);
 326
 327         for (i = 0; i < nresp; i++) {
 328                 explicit_bzero(response[i], strlen(response[i]));
 329                 free(response[i]);
 330         }
 331         free(response);
 332
 333         switch (res) {
 334         case 0:
 335                 /* Success! */
 336                 authenticated = authctxt->valid ? 1 : 0;
 337                 break;
 338         case 1:
 339                 /* Authentication needs further interaction */
 340                 if (send_userauth_info_request(ssh) == 1)
 341                         authctxt->postponed = 1;
 342                 break;
 343         default:
 344                 /* Failure! */
 345                 break;
 346         }
 347         devicename = kbdintctxt->device->name;
 348         if (!authctxt->postponed) {
 349                 if (authenticated) {
 350                         auth2_challenge_stop(ssh);
 351                 } else {
 352                         /* start next device */
 353                         /* may set authctxt->postponed */
 354                         auth2_challenge_start(ssh);
 355                 }
 356         }
 357         userauth_finish(ssh, authenticated, "keyboard-interactive",
 358             devicename);
 359         return 0;
 360 }
 361
 362 void
 363 privsep_challenge_enable(void)
 364 {
 365 #if defined(BSD_AUTH) || defined(USE_PAM)
 366         int n = 0;
 367 #endif
 368 #ifdef BSD_AUTH
 369         extern KbdintDevice mm_bsdauth_device;
 370 #endif
 371 #ifdef USE_PAM
 372         extern KbdintDevice mm_sshpam_device;
 373 #endif
 374
 375 #ifdef BSD_AUTH
 376         devices[n++] = &mm_bsdauth_device;
 377 #else
 378 #ifdef USE_PAM
 379         devices[n++] = &mm_sshpam_device;
 380 #endif
 381 #endif
 382 }