1 /* $OpenBSD: kexgexs.c,v 1.46 2023/03/29 01:07:48 dtucker 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 #ifdef GSSAPI
43 #include "ssh-gss.h"
44 #endif
45 #include "monitor_wrap.h"
46 #include "dispatch.h"
47 #include "ssherr.h"
48 #include "sshbuf.h"
49 #include "misc.h"
50
51 static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *);
52 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *);
53
54 int
kexgex_server(struct ssh * ssh)55 kexgex_server(struct ssh *ssh)
56 {
57 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST,
58 &input_kex_dh_gex_request);
59 debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST");
60 return 0;
61 }
62
63 static int
input_kex_dh_gex_request(int type,u_int32_t seq,struct ssh * ssh)64 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh)
65 {
66 struct kex *kex = ssh->kex;
67 int r;
68 u_int min = 0, max = 0, nbits = 0;
69 const BIGNUM *dh_p, *dh_g;
70
71 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
72 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error);
73
74 if ((r = sshpkt_get_u32(ssh, &min)) != 0 ||
75 (r = sshpkt_get_u32(ssh, &nbits)) != 0 ||
76 (r = sshpkt_get_u32(ssh, &max)) != 0 ||
77 (r = sshpkt_get_end(ssh)) != 0)
78 goto out;
79 kex->nbits = nbits;
80 kex->min = min;
81 kex->max = max;
82 min = MAXIMUM(DH_GRP_MIN, min);
83 max = MINIMUM(DH_GRP_MAX, max);
84 nbits = MAXIMUM(DH_GRP_MIN, nbits);
85 nbits = MINIMUM(DH_GRP_MAX, nbits);
86
87 if (kex->max < kex->min || kex->nbits < kex->min ||
88 kex->max < kex->nbits || kex->max < DH_GRP_MIN) {
89 r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
90 goto out;
91 }
92
93 /* Contact privileged parent */
94 kex->dh = PRIVSEP(choose_dh(min, nbits, max));
95 if (kex->dh == NULL) {
96 (void)sshpkt_disconnect(ssh, "no matching DH grp found");
97 r = SSH_ERR_ALLOC_FAIL;
98 goto out;
99 }
100 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
101 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
102 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 ||
103 (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 ||
104 (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 ||
105 (r = sshpkt_send(ssh)) != 0)
106 goto out;
107
108 /* Compute our exchange value in parallel with the client */
109 if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
110 goto out;
111
112 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
113 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init);
114 r = 0;
115 out:
116 return r;
117 }
118
119 static int
input_kex_dh_gex_init(int type,u_int32_t seq,struct ssh * ssh)120 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
121 {
122 struct kex *kex = ssh->kex;
123 BIGNUM *dh_client_pub = NULL;
124 const BIGNUM *pub_key, *dh_p, *dh_g;
125 struct sshbuf *shared_secret = NULL;
126 struct sshbuf *server_host_key_blob = NULL;
127 struct sshkey *server_host_public, *server_host_private;
128 u_char *signature = NULL;
129 u_char hash[SSH_DIGEST_MAX_LENGTH];
130 size_t slen, hashlen;
131 int r;
132
133 debug("SSH2_MSG_KEX_DH_GEX_INIT received");
134 ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error);
135
136 if ((r = kex_load_hostkey(ssh, &server_host_private,
137 &server_host_public)) != 0)
138 goto out;
139
140 /* key, cert */
141 if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 ||
142 (r = sshpkt_get_end(ssh)) != 0)
143 goto out;
144 if ((shared_secret = sshbuf_new()) == NULL) {
145 r = SSH_ERR_ALLOC_FAIL;
146 goto out;
147 }
148 if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0)
149 goto out;
150 if ((server_host_key_blob = sshbuf_new()) == NULL) {
151 r = SSH_ERR_ALLOC_FAIL;
152 goto out;
153 }
154 if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
155 goto out;
156
157 /* calc H */
158 DH_get0_key(kex->dh, &pub_key, NULL);
159 DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
160 hashlen = sizeof(hash);
161 if ((r = kexgex_hash(
162 kex->hash_alg,
163 kex->client_version,
164 kex->server_version,
165 kex->peer,
166 kex->my,
167 server_host_key_blob,
168 kex->min, kex->nbits, kex->max,
169 dh_p, dh_g,
170 dh_client_pub,
171 pub_key,
172 sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
173 hash, &hashlen)) != 0)
174 goto out;
175
176 /* sign H */
177 if ((r = kex->sign(ssh, server_host_private, server_host_public,
178 &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0)
179 goto out;
180
181 /* send server hostkey, DH pubkey 'f' and signed H */
182 if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 ||
183 (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
184 (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 || /* f */
185 (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
186 (r = sshpkt_send(ssh)) != 0)
187 goto out;
188
189 if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
190 (r = kex_send_newkeys(ssh)) != 0)
191 goto out;
192
193 /* retain copy of hostkey used at initial KEX */
194 if (kex->initial_hostkey == NULL &&
195 (r = sshkey_from_private(server_host_public,
196 &kex->initial_hostkey)) != 0)
197 goto out;
198 /* success */
199 out:
200 explicit_bzero(hash, sizeof(hash));
201 DH_free(kex->dh);
202 kex->dh = NULL;
203 BN_clear_free(dh_client_pub);
204 sshbuf_free(shared_secret);
205 sshbuf_free(server_host_key_blob);
206 free(signature);
207 return r;
208 }
209