crypto/openssh/kexgexc.c

   1 /* $OpenBSD: kexgexc.c,v 1.38 2021/12/19 22:08:06 djm Exp $ */
   2 /*
   3  * Copyright (c) 2000 Niels Provos.  All rights reserved.
   4  * Copyright (c) 2001 Markus Friedl.  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 #ifdef WITH_OPENSSL
  30
  31 #include <sys/types.h>
  32
  33 #include <openssl/dh.h>
  34
  35 #include <stdarg.h>
  36 #include <stdio.h>
  37 #include <string.h>
  38 #include <signal.h>
  39
  40 #include "openbsd-compat/openssl-compat.h"
  41
  42 #include "sshkey.h"
  43 #include "cipher.h"
  44 #include "digest.h"
  45 #include "kex.h"
  46 #include "log.h"
  47 #include "packet.h"
  48 #include "dh.h"
  49 #include "ssh2.h"
  50 #include "compat.h"
  51 #include "dispatch.h"
  52 #include "ssherr.h"
  53 #include "sshbuf.h"
  54 #include "misc.h"
  55
  56 static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *);
  57 static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *);
  58
  59 int
  60 kexgex_client(struct ssh *ssh)
  61 {
  62         struct kex *kex = ssh->kex;
  63         int r;
  64         u_int nbits;
  65
  66         nbits = dh_estimate(kex->dh_need * 8);
  67
  68         kex->min = DH_GRP_MIN;
  69         kex->max = DH_GRP_MAX;
  70         kex->nbits = nbits;
  71         if (ssh->compat & SSH_BUG_DHGEX_LARGE)
  72                 kex->nbits = MINIMUM(kex->nbits, 4096);
  73         /* New GEX request */
  74         if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
  75             (r = sshpkt_put_u32(ssh, kex->min)) != 0 ||
  76             (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 ||
  77             (r = sshpkt_put_u32(ssh, kex->max)) != 0 ||
  78             (r = sshpkt_send(ssh)) != 0)
  79                 goto out;
  80         debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
  81             kex->min, kex->nbits, kex->max);
  82 #ifdef DEBUG_KEXDH
  83         fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
  84             kex->min, kex->nbits, kex->max);
  85 #endif
  86         debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
  87         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP,
  88             &input_kex_dh_gex_group);
  89         r = 0;
  90  out:
  91         return r;
  92 }
  93
  94 static int
  95 input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh)
  96 {
  97         struct kex *kex = ssh->kex;
  98         BIGNUM *p = NULL, *g = NULL;
  99         const BIGNUM *pub_key;
 100         int r, bits;
 101
 102         debug("SSH2_MSG_KEX_DH_GEX_GROUP received");
 103         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, &kex_protocol_error);
 104
 105         if ((r = sshpkt_get_bignum2(ssh, &p)) != 0 ||
 106             (r = sshpkt_get_bignum2(ssh, &g)) != 0 ||
 107             (r = sshpkt_get_end(ssh)) != 0)
 108                 goto out;
 109         if ((bits = BN_num_bits(p)) < 0 ||
 110             (u_int)bits < kex->min || (u_int)bits > kex->max) {
 111                 r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
 112                 goto out;
 113         }
 114         if ((kex->dh = dh_new_group(g, p)) == NULL) {
 115                 r = SSH_ERR_ALLOC_FAIL;
 116                 goto out;
 117         }
 118         p = g = NULL; /* belong to kex->dh now */
 119
 120         /* generate and send 'e', client DH public key */
 121         if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
 122                 goto out;
 123         DH_get0_key(kex->dh, &pub_key, NULL);
 124         if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
 125             (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||
 126             (r = sshpkt_send(ssh)) != 0)
 127                 goto out;
 128         debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
 129 #ifdef DEBUG_KEXDH
 130         DHparams_print_fp(stderr, kex->dh);
 131         fprintf(stderr, "pub= ");
 132         BN_print_fp(stderr, pub_key);
 133         fprintf(stderr, "\n");
 134 #endif
 135         debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
 136         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply);
 137         r = 0;
 138 out:
 139         BN_clear_free(p);
 140         BN_clear_free(g);
 141         return r;
 142 }
 143
 144 static int
 145 input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh)
 146 {
 147         struct kex *kex = ssh->kex;
 148         BIGNUM *dh_server_pub = NULL;
 149         const BIGNUM *pub_key, *dh_p, *dh_g;
 150         struct sshbuf *shared_secret = NULL;
 151         struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
 152         struct sshkey *server_host_key = NULL;
 153         u_char *signature = NULL;
 154         u_char hash[SSH_DIGEST_MAX_LENGTH];
 155         size_t slen, hashlen;
 156         int r;
 157
 158         debug("SSH2_MSG_KEX_DH_GEX_REPLY received");
 159         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &kex_protocol_error);
 160
 161         /* key, cert */
 162         if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
 163                 goto out;
 164         /* sshkey_fromb() consumes its buffer, so make a copy */
 165         if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
 166                 r = SSH_ERR_ALLOC_FAIL;
 167                 goto out;
 168         }
 169         if ((r = sshkey_fromb(tmp, &server_host_key)) != 0 ||
 170             (r = kex_verify_host_key(ssh, server_host_key)) != 0)
 171                 goto out;
 172         /* DH parameter f, server public DH key, signed H */
 173         if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 ||
 174             (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
 175             (r = sshpkt_get_end(ssh)) != 0)
 176                 goto out;
 177         if ((shared_secret = sshbuf_new()) == NULL) {
 178                 r = SSH_ERR_ALLOC_FAIL;
 179                 goto out;
 180         }
 181         if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0)
 182                 goto out;
 183         if (ssh->compat & SSH_OLD_DHGEX)
 184                 kex->min = kex->max = -1;
 185
 186         /* calc and verify H */
 187         DH_get0_key(kex->dh, &pub_key, NULL);
 188         DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
 189         hashlen = sizeof(hash);
 190         if ((r = kexgex_hash(
 191             kex->hash_alg,
 192             kex->client_version,
 193             kex->server_version,
 194             kex->my,
 195             kex->peer,
 196             server_host_key_blob,
 197             kex->min, kex->nbits, kex->max,
 198             dh_p, dh_g,
 199             pub_key,
 200             dh_server_pub,
 201             sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
 202             hash, &hashlen)) != 0)
 203                 goto out;
 204
 205         if ((r = sshkey_verify(server_host_key, signature, slen, hash,
 206             hashlen, kex->hostkey_alg, ssh->compat, NULL)) != 0)
 207                 goto out;
 208
 209         if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
 210             (r = kex_send_newkeys(ssh)) != 0)
 211                 goto out;
 212
 213         /* save initial signature and hostkey */
 214         if ((kex->flags & KEX_INITIAL) != 0) {
 215                 if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
 216                         r = SSH_ERR_INTERNAL_ERROR;
 217                         goto out;
 218                 }
 219                 if ((kex->initial_sig = sshbuf_new()) == NULL) {
 220                         r = SSH_ERR_ALLOC_FAIL;
 221                         goto out;
 222                 }
 223                 if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
 224                         goto out;
 225                 kex->initial_hostkey = server_host_key;
 226                 server_host_key = NULL;
 227         }
 228         /* success */
 229  out:
 230         explicit_bzero(hash, sizeof(hash));
 231         DH_free(kex->dh);
 232         kex->dh = NULL;
 233         BN_clear_free(dh_server_pub);
 234         sshbuf_free(shared_secret);
 235         sshkey_free(server_host_key);
 236         sshbuf_free(tmp);
 237         sshbuf_free(server_host_key_blob);
 238         free(signature);
 239         return r;
 240 }
 241 #endif /* WITH_OPENSSL */