1 /* $OpenBSD: kexgexs.c,v 1.43 2021/01/31 22:55:29 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 28 #include <stdio.h> 29 #include <string.h> 30 #include <signal.h> 31 32 #include <openssl/dh.h> 33 34 #include "sshkey.h" 35 #include "cipher.h" 36 #include "digest.h" 37 #include "kex.h" 38 #include "log.h" 39 #include "packet.h" 40 #include "dh.h" 41 #include "ssh2.h" 42 #include "compat.h" 43 #ifdef GSSAPI 44 #include "ssh-gss.h" 45 #endif 46 #include "monitor_wrap.h" 47 #include "dispatch.h" 48 #include "ssherr.h" 49 #include "sshbuf.h" 50 #include "misc.h" 51 52 static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *); 53 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *); 54 55 int 56 kexgex_server(struct ssh *ssh) 57 { 58 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 59 &input_kex_dh_gex_request); 60 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 61 return 0; 62 } 63 64 static int 65 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh) 66 { 67 struct kex *kex = ssh->kex; 68 int r; 69 u_int min = 0, max = 0, nbits = 0; 70 const BIGNUM *dh_p, *dh_g; 71 72 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 73 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error); 74 75 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 76 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 77 (r = sshpkt_get_u32(ssh, &max)) != 0 || 78 (r = sshpkt_get_end(ssh)) != 0) 79 goto out; 80 kex->nbits = nbits; 81 kex->min = min; 82 kex->max = max; 83 min = MAXIMUM(DH_GRP_MIN, min); 84 max = MINIMUM(DH_GRP_MAX, max); 85 nbits = MAXIMUM(DH_GRP_MIN, nbits); 86 nbits = MINIMUM(DH_GRP_MAX, nbits); 87 88 if (kex->max < kex->min || kex->nbits < kex->min || 89 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 90 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 91 goto out; 92 } 93 94 /* Contact privileged parent */ 95 kex->dh = PRIVSEP(choose_dh(min, nbits, max)); 96 if (kex->dh == NULL) { 97 sshpkt_disconnect(ssh, "no matching DH grp found"); 98 r = SSH_ERR_ALLOC_FAIL; 99 goto out; 100 } 101 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 102 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 103 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 104 (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 || 105 (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 || 106 (r = sshpkt_send(ssh)) != 0) 107 goto out; 108 109 /* Compute our exchange value in parallel with the client */ 110 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 111 goto out; 112 113 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 114 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 115 r = 0; 116 out: 117 return r; 118 } 119 120 static int 121 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh) 122 { 123 struct kex *kex = ssh->kex; 124 BIGNUM *dh_client_pub = NULL; 125 const BIGNUM *pub_key, *dh_p, *dh_g; 126 struct sshbuf *shared_secret = NULL; 127 struct sshbuf *server_host_key_blob = NULL; 128 struct sshkey *server_host_public, *server_host_private; 129 u_char *signature = NULL; 130 u_char hash[SSH_DIGEST_MAX_LENGTH]; 131 size_t slen, hashlen; 132 int r; 133 134 debug("SSH2_MSG_KEX_DH_GEX_INIT received"); 135 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error); 136 137 if ((r = kex_load_hostkey(ssh, &server_host_private, 138 &server_host_public)) != 0) 139 goto out; 140 141 /* key, cert */ 142 if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 || 143 (r = sshpkt_get_end(ssh)) != 0) 144 goto out; 145 if ((shared_secret = sshbuf_new()) == NULL) { 146 r = SSH_ERR_ALLOC_FAIL; 147 goto out; 148 } 149 if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0) 150 goto out; 151 if ((server_host_key_blob = sshbuf_new()) == NULL) { 152 r = SSH_ERR_ALLOC_FAIL; 153 goto out; 154 } 155 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 156 goto out; 157 158 /* calc H */ 159 DH_get0_key(kex->dh, &pub_key, NULL); 160 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 161 hashlen = sizeof(hash); 162 if ((r = kexgex_hash( 163 kex->hash_alg, 164 kex->client_version, 165 kex->server_version, 166 kex->peer, 167 kex->my, 168 server_host_key_blob, 169 kex->min, kex->nbits, kex->max, 170 dh_p, dh_g, 171 dh_client_pub, 172 pub_key, 173 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), 174 hash, &hashlen)) != 0) 175 goto out; 176 177 /* sign H */ 178 if ((r = kex->sign(ssh, server_host_private, server_host_public, 179 &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0) 180 goto out; 181 182 /* send server hostkey, DH pubkey 'f' and signed H */ 183 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 184 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 185 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */ 186 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 187 (r = sshpkt_send(ssh)) != 0) 188 goto out; 189 190 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0) 191 r = kex_send_newkeys(ssh); 192 out: 193 explicit_bzero(hash, sizeof(hash)); 194 DH_free(kex->dh); 195 kex->dh = NULL; 196 BN_clear_free(dh_client_pub); 197 sshbuf_free(shared_secret); 198 sshbuf_free(server_host_key_blob); 199 free(signature); 200 return r; 201 } 202