1 /* $NetBSD: kexgexs.c,v 1.24 2024/07/08 22:33:43 christos Exp $ */
2 /* $OpenBSD: kexgexs.c,v 1.47 2024/05/17 00:30:23 djm 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 1.24 2024/07/08 22:33:43 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
kexgex_server(struct ssh * ssh)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
input_kex_dh_gex_request(int type,u_int32_t seq,struct ssh * ssh)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 = mm_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
input_kex_dh_gex_init(int type,u_int32_t seq,struct ssh * ssh)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