1 /* $OpenBSD: kexgexs.c,v 1.31 2017/05/30 14:23:52 markus 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 "sshkey.h" 40 #include "cipher.h" 41 #include "digest.h" 42 #include "kex.h" 43 #include "log.h" 44 #include "packet.h" 45 #include "dh.h" 46 #include "ssh2.h" 47 #include "compat.h" 48 #ifdef GSSAPI 49 #include "ssh-gss.h" 50 #endif 51 #include "monitor_wrap.h" 52 #include "dispatch.h" 53 #include "ssherr.h" 54 #include "sshbuf.h" 55 #include "misc.h" 56 57 static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *); 58 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *); 59 60 int 61 kexgex_server(struct ssh *ssh) 62 { 63 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 64 &input_kex_dh_gex_request); 65 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 66 return 0; 67 } 68 69 static int 70 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh) 71 { 72 struct kex *kex = ssh->kex; 73 int r; 74 u_int min = 0, max = 0, nbits = 0; 75 76 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 77 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 78 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 79 (r = sshpkt_get_u32(ssh, &max)) != 0 || 80 (r = sshpkt_get_end(ssh)) != 0) 81 goto out; 82 kex->nbits = nbits; 83 kex->min = min; 84 kex->max = max; 85 min = MAXIMUM(DH_GRP_MIN, min); 86 max = MINIMUM(DH_GRP_MAX, max); 87 nbits = MAXIMUM(DH_GRP_MIN, nbits); 88 nbits = MINIMUM(DH_GRP_MAX, nbits); 89 90 if (kex->max < kex->min || kex->nbits < kex->min || 91 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 92 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 93 goto out; 94 } 95 96 /* Contact privileged parent */ 97 kex->dh = PRIVSEP(choose_dh(min, nbits, max)); 98 if (kex->dh == NULL) { 99 sshpkt_disconnect(ssh, "no matching DH grp found"); 100 r = SSH_ERR_ALLOC_FAIL; 101 goto out; 102 } 103 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 104 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 105 (r = sshpkt_put_bignum2(ssh, kex->dh->p)) != 0 || 106 (r = sshpkt_put_bignum2(ssh, kex->dh->g)) != 0 || 107 (r = sshpkt_send(ssh)) != 0) 108 goto out; 109 110 /* Compute our exchange value in parallel with the client */ 111 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 112 goto out; 113 114 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 115 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 116 r = 0; 117 out: 118 return r; 119 } 120 121 static int 122 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh) 123 { 124 struct kex *kex = ssh->kex; 125 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; 126 struct sshkey *server_host_public, *server_host_private; 127 u_char *kbuf = NULL, *signature = NULL, *server_host_key_blob = NULL; 128 u_char hash[SSH_DIGEST_MAX_LENGTH]; 129 size_t sbloblen, slen; 130 size_t klen = 0, hashlen; 131 int kout, r; 132 133 if (kex->load_host_public_key == NULL || 134 kex->load_host_private_key == NULL) { 135 r = SSH_ERR_INVALID_ARGUMENT; 136 goto out; 137 } 138 server_host_public = kex->load_host_public_key(kex->hostkey_type, 139 kex->hostkey_nid, ssh); 140 server_host_private = kex->load_host_private_key(kex->hostkey_type, 141 kex->hostkey_nid, ssh); 142 if (server_host_public == NULL) { 143 r = SSH_ERR_NO_HOSTKEY_LOADED; 144 goto out; 145 } 146 147 /* key, cert */ 148 if ((dh_client_pub = BN_new()) == NULL) { 149 r = SSH_ERR_ALLOC_FAIL; 150 goto out; 151 } 152 if ((r = sshpkt_get_bignum2(ssh, dh_client_pub)) != 0 || 153 (r = sshpkt_get_end(ssh)) != 0) 154 goto out; 155 156 #ifdef DEBUG_KEXDH 157 fprintf(stderr, "dh_client_pub= "); 158 BN_print_fp(stderr, dh_client_pub); 159 fprintf(stderr, "\n"); 160 debug("bits %d", BN_num_bits(dh_client_pub)); 161 #endif 162 163 #ifdef DEBUG_KEXDH 164 DHparams_print_fp(stderr, kex->dh); 165 fprintf(stderr, "pub= "); 166 BN_print_fp(stderr, kex->dh->pub_key); 167 fprintf(stderr, "\n"); 168 #endif 169 if (!dh_pub_is_valid(kex->dh, dh_client_pub)) { 170 sshpkt_disconnect(ssh, "bad client public DH value"); 171 r = SSH_ERR_MESSAGE_INCOMPLETE; 172 goto out; 173 } 174 175 klen = DH_size(kex->dh); 176 if ((kbuf = malloc(klen)) == NULL || 177 (shared_secret = BN_new()) == NULL) { 178 r = SSH_ERR_ALLOC_FAIL; 179 goto out; 180 } 181 if ((kout = DH_compute_key(kbuf, dh_client_pub, kex->dh)) < 0 || 182 BN_bin2bn(kbuf, kout, shared_secret) == NULL) { 183 r = SSH_ERR_LIBCRYPTO_ERROR; 184 goto out; 185 } 186 #ifdef DEBUG_KEXDH 187 dump_digest("shared secret", kbuf, kout); 188 #endif 189 if ((r = sshkey_to_blob(server_host_public, &server_host_key_blob, 190 &sbloblen)) != 0) 191 goto out; 192 /* calc H */ 193 hashlen = sizeof(hash); 194 if ((r = kexgex_hash( 195 kex->hash_alg, 196 kex->client_version_string, 197 kex->server_version_string, 198 sshbuf_ptr(kex->peer), sshbuf_len(kex->peer), 199 sshbuf_ptr(kex->my), sshbuf_len(kex->my), 200 server_host_key_blob, sbloblen, 201 kex->min, kex->nbits, kex->max, 202 kex->dh->p, kex->dh->g, 203 dh_client_pub, 204 kex->dh->pub_key, 205 shared_secret, 206 hash, &hashlen)) != 0) 207 goto out; 208 209 /* save session id := H */ 210 if (kex->session_id == NULL) { 211 kex->session_id_len = hashlen; 212 kex->session_id = malloc(kex->session_id_len); 213 if (kex->session_id == NULL) { 214 r = SSH_ERR_ALLOC_FAIL; 215 goto out; 216 } 217 memcpy(kex->session_id, hash, kex->session_id_len); 218 } 219 220 /* sign H */ 221 if ((r = kex->sign(server_host_private, server_host_public, &signature, 222 &slen, hash, hashlen, kex->hostkey_alg, ssh->compat)) < 0) 223 goto out; 224 225 /* destroy_sensitive_data(); */ 226 227 /* send server hostkey, DH pubkey 'f' and singed H */ 228 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 229 (r = sshpkt_put_string(ssh, server_host_key_blob, sbloblen)) != 0 || 230 (r = sshpkt_put_bignum2(ssh, kex->dh->pub_key)) != 0 || /* f */ 231 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 232 (r = sshpkt_send(ssh)) != 0) 233 goto out; 234 235 if ((r = kex_derive_keys_bn(ssh, hash, hashlen, shared_secret)) == 0) 236 r = kex_send_newkeys(ssh); 237 out: 238 DH_free(kex->dh); 239 kex->dh = NULL; 240 if (dh_client_pub) 241 BN_clear_free(dh_client_pub); 242 if (kbuf) { 243 explicit_bzero(kbuf, klen); 244 free(kbuf); 245 } 246 if (shared_secret) 247 BN_clear_free(shared_secret); 248 free(server_host_key_blob); 249 free(signature); 250 return r; 251 } 252 #endif /* WITH_OPENSSL */ 253