crypto/openssh/kexgexs.c

   1 /* $OpenBSD: kexgexs.c,v 1.44 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
  32 #include <stdarg.h>
  33 #include <stdio.h>
  34 #include <string.h>
  35 #include <signal.h>
  36
  37 #include <openssl/dh.h>
  38
  39 #include "openbsd-compat/openssl-compat.h"
  40
  41 #include "sshkey.h"
  42 #include "cipher.h"
  43 #include "digest.h"
  44 #include "kex.h"
  45 #include "log.h"
  46 #include "packet.h"
  47 #include "dh.h"
  48 #include "ssh2.h"
  49 #include "compat.h"
  50 #ifdef GSSAPI
  51 #include "ssh-gss.h"
  52 #endif
  53 #include "monitor_wrap.h"
  54 #include "dispatch.h"
  55 #include "ssherr.h"
  56 #include "sshbuf.h"
  57 #include "misc.h"
  58
  59 static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *);
  60 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *);
  61
  62 int
  63 kexgex_server(struct ssh *ssh)
  64 {
  65         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST,
  66             &input_kex_dh_gex_request);
  67         debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST");
  68         return 0;
  69 }
  70
  71 static int
  72 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh)
  73 {
  74         struct kex *kex = ssh->kex;
  75         int r;
  76         u_int min = 0, max = 0, nbits = 0;
  77         const BIGNUM *dh_p, *dh_g;
  78
  79         debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
  80         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error);
  81
  82         if ((r = sshpkt_get_u32(ssh, &min)) != 0 ||
  83             (r = sshpkt_get_u32(ssh, &nbits)) != 0 ||
  84             (r = sshpkt_get_u32(ssh, &max)) != 0 ||
  85             (r = sshpkt_get_end(ssh)) != 0)
  86                 goto out;
  87         kex->nbits = nbits;
  88         kex->min = min;
  89         kex->max = max;
  90         min = MAXIMUM(DH_GRP_MIN, min);
  91         max = MINIMUM(DH_GRP_MAX, max);
  92         nbits = MAXIMUM(DH_GRP_MIN, nbits);
  93         nbits = MINIMUM(DH_GRP_MAX, nbits);
  94
  95         if (kex->max < kex->min || kex->nbits < kex->min ||
  96             kex->max < kex->nbits || kex->max < DH_GRP_MIN) {
  97                 r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
  98                 goto out;
  99         }
 100
 101         /* Contact privileged parent */
 102         kex->dh = PRIVSEP(choose_dh(min, nbits, max));
 103         if (kex->dh == NULL) {
 104                 sshpkt_disconnect(ssh, "no matching DH grp found");
 105                 r = SSH_ERR_ALLOC_FAIL;
 106                 goto out;
 107         }
 108         debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
 109         DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
 110         if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 ||
 111             (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 ||
 112             (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 ||
 113             (r = sshpkt_send(ssh)) != 0)
 114                 goto out;
 115
 116         /* Compute our exchange value in parallel with the client */
 117         if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
 118                 goto out;
 119
 120         debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
 121         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init);
 122         r = 0;
 123  out:
 124         return r;
 125 }
 126
 127 static int
 128 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
 129 {
 130         struct kex *kex = ssh->kex;
 131         BIGNUM *dh_client_pub = NULL;
 132         const BIGNUM *pub_key, *dh_p, *dh_g;
 133         struct sshbuf *shared_secret = NULL;
 134         struct sshbuf *server_host_key_blob = NULL;
 135         struct sshkey *server_host_public, *server_host_private;
 136         u_char *signature = NULL;
 137         u_char hash[SSH_DIGEST_MAX_LENGTH];
 138         size_t slen, hashlen;
 139         int r;
 140
 141         debug("SSH2_MSG_KEX_DH_GEX_INIT received");
 142         ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error);
 143
 144         if ((r = kex_load_hostkey(ssh, &server_host_private,
 145             &server_host_public)) != 0)
 146                 goto out;
 147
 148         /* key, cert */
 149         if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 ||
 150             (r = sshpkt_get_end(ssh)) != 0)
 151                 goto out;
 152         if ((shared_secret = sshbuf_new()) == NULL) {
 153                 r = SSH_ERR_ALLOC_FAIL;
 154                 goto out;
 155         }
 156         if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0)
 157                 goto out;
 158         if ((server_host_key_blob = sshbuf_new()) == NULL) {
 159                 r = SSH_ERR_ALLOC_FAIL;
 160                 goto out;
 161         }
 162         if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
 163                 goto out;
 164
 165         /* calc H */
 166         DH_get0_key(kex->dh, &pub_key, NULL);
 167         DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
 168         hashlen = sizeof(hash);
 169         if ((r = kexgex_hash(
 170             kex->hash_alg,
 171             kex->client_version,
 172             kex->server_version,
 173             kex->peer,
 174             kex->my,
 175             server_host_key_blob,
 176             kex->min, kex->nbits, kex->max,
 177             dh_p, dh_g,
 178             dh_client_pub,
 179             pub_key,
 180             sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
 181             hash, &hashlen)) != 0)
 182                 goto out;
 183
 184         /* sign H */
 185         if ((r = kex->sign(ssh, server_host_private, server_host_public,
 186             &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0)
 187                 goto out;
 188
 189         /* send server hostkey, DH pubkey 'f' and signed H */
 190         if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 ||
 191             (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
 192             (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||     /* f */
 193             (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
 194             (r = sshpkt_send(ssh)) != 0)
 195                 goto out;
 196
 197         if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
 198             (r = kex_send_newkeys(ssh)) != 0)
 199                 goto out;
 200
 201         /* retain copy of hostkey used at initial KEX */
 202         if (kex->initial_hostkey == NULL &&
 203             (r = sshkey_from_private(server_host_public,
 204             &kex->initial_hostkey)) != 0)
 205                 goto out;
 206         /* success */
 207  out:
 208         explicit_bzero(hash, sizeof(hash));
 209         DH_free(kex->dh);
 210         kex->dh = NULL;
 211         BN_clear_free(dh_client_pub);
 212         sshbuf_free(shared_secret);
 213         sshbuf_free(server_host_key_blob);
 214         free(signature);
 215         return r;
 216 }
 217 #endif /* WITH_OPENSSL */