1 /* $NetBSD: kexgexs.c,v 1.23 2023/10/25 20:19:57 christos Exp $ */ 2 /* $OpenBSD: kexgexs.c,v 1.46 2023/03/29 01:07:48 dtucker Exp $ */ 3 4 /* 5 * Copyright (c) 2000 Niels Provos. All rights reserved. 6 * Copyright (c) 2001 Markus Friedl. All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 */ 28 29 #include "includes.h" 30 __RCSID("$NetBSD: kexgexs.c,v 1.23 2023/10/25 20:19:57 christos Exp $"); 31 32 #include <sys/param.h> /* MIN MAX */ 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 #ifdef GSSAPI 48 #include "ssh-gss.h" 49 #endif 50 #include "monitor_wrap.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_request(int, u_int32_t, struct ssh *); 57 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *); 58 59 int 60 kexgex_server(struct ssh *ssh) 61 { 62 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 63 &input_kex_dh_gex_request); 64 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 65 return 0; 66 } 67 68 static int 69 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh) 70 { 71 struct kex *kex = ssh->kex; 72 int r; 73 u_int min = 0, max = 0, nbits = 0; 74 const BIGNUM *dh_p, *dh_g; 75 76 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 77 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error); 78 79 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 80 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 81 (r = sshpkt_get_u32(ssh, &max)) != 0 || 82 (r = sshpkt_get_end(ssh)) != 0) 83 goto out; 84 kex->nbits = nbits; 85 kex->min = min; 86 kex->max = max; 87 min = MAXIMUM(DH_GRP_MIN, min); 88 max = MINIMUM(DH_GRP_MAX, max); 89 nbits = MAXIMUM(DH_GRP_MIN, nbits); 90 nbits = MINIMUM(DH_GRP_MAX, nbits); 91 92 if (kex->max < kex->min || kex->nbits < kex->min || 93 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 94 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 95 goto out; 96 } 97 98 /* Contact privileged parent */ 99 kex->dh = PRIVSEP(choose_dh(min, nbits, max)); 100 if (kex->dh == NULL) { 101 (void)sshpkt_disconnect(ssh, "no matching DH grp found"); 102 r = SSH_ERR_ALLOC_FAIL; 103 goto out; 104 } 105 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 106 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 107 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 108 (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 || 109 (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 || 110 (r = sshpkt_send(ssh)) != 0) 111 goto out; 112 113 /* Compute our exchange value in parallel with the client */ 114 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 115 goto out; 116 117 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 118 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 119 r = 0; 120 out: 121 return r; 122 } 123 124 static int 125 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh) 126 { 127 struct kex *kex = ssh->kex; 128 BIGNUM *dh_client_pub = NULL; 129 const BIGNUM *pub_key, *dh_p, *dh_g; 130 struct sshbuf *shared_secret = NULL; 131 struct sshbuf *server_host_key_blob = NULL; 132 struct sshkey *server_host_public, *server_host_private; 133 u_char *signature = NULL; 134 u_char hash[SSH_DIGEST_MAX_LENGTH]; 135 size_t slen, hashlen; 136 int r; 137 138 debug("SSH2_MSG_KEX_DH_GEX_INIT received"); 139 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error); 140 141 if ((r = kex_load_hostkey(ssh, &server_host_private, 142 &server_host_public)) != 0) 143 goto out; 144 145 /* key, cert */ 146 if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 || 147 (r = sshpkt_get_end(ssh)) != 0) 148 goto out; 149 if ((shared_secret = sshbuf_new()) == NULL) { 150 r = SSH_ERR_ALLOC_FAIL; 151 goto out; 152 } 153 if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0) 154 goto out; 155 if ((server_host_key_blob = sshbuf_new()) == NULL) { 156 r = SSH_ERR_ALLOC_FAIL; 157 goto out; 158 } 159 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 160 goto out; 161 162 /* calc H */ 163 DH_get0_key(kex->dh, &pub_key, NULL); 164 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 165 hashlen = sizeof(hash); 166 if ((r = kexgex_hash( 167 kex->hash_alg, 168 kex->client_version, 169 kex->server_version, 170 kex->peer, 171 kex->my, 172 server_host_key_blob, 173 kex->min, kex->nbits, kex->max, 174 dh_p, dh_g, 175 dh_client_pub, 176 pub_key, 177 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), 178 hash, &hashlen)) != 0) 179 goto out; 180 181 /* sign H */ 182 if ((r = kex->sign(ssh, server_host_private, server_host_public, 183 &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0) 184 goto out; 185 186 /* send server hostkey, DH pubkey 'f' and signed H */ 187 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 188 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 189 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */ 190 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 191 (r = sshpkt_send(ssh)) != 0) 192 goto out; 193 194 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 195 (r = kex_send_newkeys(ssh)) != 0) 196 goto out; 197 198 /* retain copy of hostkey used at initial KEX */ 199 if (kex->initial_hostkey == NULL && 200 (r = sshkey_from_private(server_host_public, 201 &kex->initial_hostkey)) != 0) 202 goto out; 203 /* success */ 204 out: 205 explicit_bzero(hash, sizeof(hash)); 206 DH_free(kex->dh); 207 kex->dh = NULL; 208 BN_clear_free(dh_client_pub); 209 sshbuf_free(shared_secret); 210 sshbuf_free(server_host_key_blob); 211 free(signature); 212 return r; 213 } 214