1 /* $NetBSD: kexgexs.c,v 1.22 2023/07/26 17:58:15 christos Exp $ */ 2 /* $OpenBSD: kexgexs.c,v 1.45 2023/03/05 05:34:09 dtucker Exp $ */ 3 /* 4 * Copyright (c) 2000 Niels Provos. All rights reserved. 5 * Copyright (c) 2001 Markus Friedl. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 #include "includes.h" 29 __RCSID("$NetBSD: kexgexs.c,v 1.22 2023/07/26 17:58:15 christos Exp $"); 30 31 #include <sys/param.h> /* MIN MAX */ 32 #include <stdio.h> 33 #include <string.h> 34 #include <signal.h> 35 36 #include <openssl/dh.h> 37 38 #include "sshkey.h" 39 #include "cipher.h" 40 #include "digest.h" 41 #include "kex.h" 42 #include "log.h" 43 #include "packet.h" 44 #include "dh.h" 45 #include "ssh2.h" 46 #ifdef GSSAPI 47 #include "ssh-gss.h" 48 #endif 49 #include "monitor_wrap.h" 50 #include "dispatch.h" 51 #include "ssherr.h" 52 #include "sshbuf.h" 53 #include "misc.h" 54 55 static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *); 56 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *); 57 58 int 59 kexgex_server(struct ssh *ssh) 60 { 61 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, 62 &input_kex_dh_gex_request); 63 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST"); 64 return 0; 65 } 66 67 static int 68 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh) 69 { 70 struct kex *kex = ssh->kex; 71 int r; 72 u_int min = 0, max = 0, nbits = 0; 73 const BIGNUM *dh_p, *dh_g; 74 75 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); 76 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error); 77 78 if ((r = sshpkt_get_u32(ssh, &min)) != 0 || 79 (r = sshpkt_get_u32(ssh, &nbits)) != 0 || 80 (r = sshpkt_get_u32(ssh, &max)) != 0 || 81 (r = sshpkt_get_end(ssh)) != 0) 82 goto out; 83 kex->nbits = nbits; 84 kex->min = min; 85 kex->max = max; 86 min = MAXIMUM(DH_GRP_MIN, min); 87 max = MINIMUM(DH_GRP_MAX, max); 88 nbits = MAXIMUM(DH_GRP_MIN, nbits); 89 nbits = MINIMUM(DH_GRP_MAX, nbits); 90 91 if (kex->max < kex->min || kex->nbits < kex->min || 92 kex->max < kex->nbits || kex->max < DH_GRP_MIN) { 93 r = SSH_ERR_DH_GEX_OUT_OF_RANGE; 94 goto out; 95 } 96 97 /* Contact privileged parent */ 98 kex->dh = PRIVSEP(choose_dh(min, nbits, max)); 99 if (kex->dh == NULL) { 100 sshpkt_disconnect(ssh, "no matching DH grp found"); 101 r = SSH_ERR_ALLOC_FAIL; 102 goto out; 103 } 104 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); 105 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 106 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 || 107 (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 || 108 (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 || 109 (r = sshpkt_send(ssh)) != 0) 110 goto out; 111 112 /* Compute our exchange value in parallel with the client */ 113 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0) 114 goto out; 115 116 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); 117 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init); 118 r = 0; 119 out: 120 return r; 121 } 122 123 static int 124 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh) 125 { 126 struct kex *kex = ssh->kex; 127 BIGNUM *dh_client_pub = NULL; 128 const BIGNUM *pub_key, *dh_p, *dh_g; 129 struct sshbuf *shared_secret = NULL; 130 struct sshbuf *server_host_key_blob = NULL; 131 struct sshkey *server_host_public, *server_host_private; 132 u_char *signature = NULL; 133 u_char hash[SSH_DIGEST_MAX_LENGTH]; 134 size_t slen, hashlen; 135 int r; 136 137 debug("SSH2_MSG_KEX_DH_GEX_INIT received"); 138 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error); 139 140 if ((r = kex_load_hostkey(ssh, &server_host_private, 141 &server_host_public)) != 0) 142 goto out; 143 144 /* key, cert */ 145 if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 || 146 (r = sshpkt_get_end(ssh)) != 0) 147 goto out; 148 if ((shared_secret = sshbuf_new()) == NULL) { 149 r = SSH_ERR_ALLOC_FAIL; 150 goto out; 151 } 152 if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0) 153 goto out; 154 if ((server_host_key_blob = sshbuf_new()) == NULL) { 155 r = SSH_ERR_ALLOC_FAIL; 156 goto out; 157 } 158 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0) 159 goto out; 160 161 /* calc H */ 162 DH_get0_key(kex->dh, &pub_key, NULL); 163 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g); 164 hashlen = sizeof(hash); 165 if ((r = kexgex_hash( 166 kex->hash_alg, 167 kex->client_version, 168 kex->server_version, 169 kex->peer, 170 kex->my, 171 server_host_key_blob, 172 kex->min, kex->nbits, kex->max, 173 dh_p, dh_g, 174 dh_client_pub, 175 pub_key, 176 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret), 177 hash, &hashlen)) != 0) 178 goto out; 179 180 /* sign H */ 181 if ((r = kex->sign(ssh, server_host_private, server_host_public, 182 &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0) 183 goto out; 184 185 /* send server hostkey, DH pubkey 'f' and signed H */ 186 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 || 187 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 || 188 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */ 189 (r = sshpkt_put_string(ssh, signature, slen)) != 0 || 190 (r = sshpkt_send(ssh)) != 0) 191 goto out; 192 193 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 || 194 (r = kex_send_newkeys(ssh)) != 0) 195 goto out; 196 197 /* retain copy of hostkey used at initial KEX */ 198 if (kex->initial_hostkey == NULL && 199 (r = sshkey_from_private(server_host_public, 200 &kex->initial_hostkey)) != 0) 201 goto out; 202 /* success */ 203 out: 204 explicit_bzero(hash, sizeof(hash)); 205 DH_free(kex->dh); 206 kex->dh = NULL; 207 BN_clear_free(dh_client_pub); 208 sshbuf_free(shared_secret); 209 sshbuf_free(server_host_key_blob); 210 free(signature); 211 return r; 212 } 213