xref: /openssh-portable/kexgexs.c (revision 3dd0c64e)
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 #include "includes.h"
28 
29 #ifdef WITH_OPENSSL
30 
31 
32 #include <stdarg.h>
33 #include <stdio.h>
34 #include <string.h>
35 #include <signal.h>
36 
37 #include <openssl/dh.h>
38 
39 #include "openbsd-compat/openssl-compat.h"
40 
41 #include "sshkey.h"
42 #include "cipher.h"
43 #include "digest.h"
44 #include "kex.h"
45 #include "log.h"
46 #include "packet.h"
47 #include "dh.h"
48 #include "ssh2.h"
49 #include "compat.h"
50 #ifdef GSSAPI
51 #include "ssh-gss.h"
52 #endif
53 #include "monitor_wrap.h"
54 #include "dispatch.h"
55 #include "ssherr.h"
56 #include "sshbuf.h"
57 #include "misc.h"
58 
59 static int input_kex_dh_gex_request(int, u_int32_t, struct ssh *);
60 static int input_kex_dh_gex_init(int, u_int32_t, struct ssh *);
61 
62 int
kexgex_server(struct ssh * ssh)63 kexgex_server(struct ssh *ssh)
64 {
65 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST,
66 	    &input_kex_dh_gex_request);
67 	debug("expecting SSH2_MSG_KEX_DH_GEX_REQUEST");
68 	return 0;
69 }
70 
71 static int
input_kex_dh_gex_request(int type,u_int32_t seq,struct ssh * ssh)72 input_kex_dh_gex_request(int type, u_int32_t seq, struct ssh *ssh)
73 {
74 	struct kex *kex = ssh->kex;
75 	int r;
76 	u_int min = 0, max = 0, nbits = 0;
77 	const BIGNUM *dh_p, *dh_g;
78 
79 	debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
80 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error);
81 
82 	if ((r = sshpkt_get_u32(ssh, &min)) != 0 ||
83 	    (r = sshpkt_get_u32(ssh, &nbits)) != 0 ||
84 	    (r = sshpkt_get_u32(ssh, &max)) != 0 ||
85 	    (r = sshpkt_get_end(ssh)) != 0)
86 		goto out;
87 	kex->nbits = nbits;
88 	kex->min = min;
89 	kex->max = max;
90 	min = MAXIMUM(DH_GRP_MIN, min);
91 	max = MINIMUM(DH_GRP_MAX, max);
92 	nbits = MAXIMUM(DH_GRP_MIN, nbits);
93 	nbits = MINIMUM(DH_GRP_MAX, nbits);
94 
95 	if (kex->max < kex->min || kex->nbits < kex->min ||
96 	    kex->max < kex->nbits || kex->max < DH_GRP_MIN) {
97 		r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
98 		goto out;
99 	}
100 
101 	/* Contact privileged parent */
102 	kex->dh = PRIVSEP(choose_dh(min, nbits, max));
103 	if (kex->dh == NULL) {
104 		sshpkt_disconnect(ssh, "no matching DH grp found");
105 		r = SSH_ERR_ALLOC_FAIL;
106 		goto out;
107 	}
108 	debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
109 	DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
110 	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 ||
111 	    (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 ||
112 	    (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 ||
113 	    (r = sshpkt_send(ssh)) != 0)
114 		goto out;
115 
116 	/* Compute our exchange value in parallel with the client */
117 	if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
118 		goto out;
119 
120 	debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
121 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init);
122 	r = 0;
123  out:
124 	return r;
125 }
126 
127 static int
input_kex_dh_gex_init(int type,u_int32_t seq,struct ssh * ssh)128 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
129 {
130 	struct kex *kex = ssh->kex;
131 	BIGNUM *dh_client_pub = NULL;
132 	const BIGNUM *pub_key, *dh_p, *dh_g;
133 	struct sshbuf *shared_secret = NULL;
134 	struct sshbuf *server_host_key_blob = NULL;
135 	struct sshkey *server_host_public, *server_host_private;
136 	u_char *signature = NULL;
137 	u_char hash[SSH_DIGEST_MAX_LENGTH];
138 	size_t slen, hashlen;
139 	int r;
140 
141 	debug("SSH2_MSG_KEX_DH_GEX_INIT received");
142 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error);
143 
144 	if ((r = kex_load_hostkey(ssh, &server_host_private,
145 	    &server_host_public)) != 0)
146 		goto out;
147 
148 	/* key, cert */
149 	if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 ||
150 	    (r = sshpkt_get_end(ssh)) != 0)
151 		goto out;
152 	if ((shared_secret = sshbuf_new()) == NULL) {
153 		r = SSH_ERR_ALLOC_FAIL;
154 		goto out;
155 	}
156 	if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0)
157 		goto out;
158 	if ((server_host_key_blob = sshbuf_new()) == NULL) {
159 		r = SSH_ERR_ALLOC_FAIL;
160 		goto out;
161 	}
162 	if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
163 		goto out;
164 
165 	/* calc H */
166 	DH_get0_key(kex->dh, &pub_key, NULL);
167 	DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
168 	hashlen = sizeof(hash);
169 	if ((r = kexgex_hash(
170 	    kex->hash_alg,
171 	    kex->client_version,
172 	    kex->server_version,
173 	    kex->peer,
174 	    kex->my,
175 	    server_host_key_blob,
176 	    kex->min, kex->nbits, kex->max,
177 	    dh_p, dh_g,
178 	    dh_client_pub,
179 	    pub_key,
180 	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
181 	    hash, &hashlen)) != 0)
182 		goto out;
183 
184 	/* sign H */
185 	if ((r = kex->sign(ssh, server_host_private, server_host_public,
186 	    &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0)
187 		goto out;
188 
189 	/* send server hostkey, DH pubkey 'f' and signed H */
190 	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 ||
191 	    (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
192 	    (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||     /* f */
193 	    (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
194 	    (r = sshpkt_send(ssh)) != 0)
195 		goto out;
196 
197 	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
198 		r = kex_send_newkeys(ssh);
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 #endif /* WITH_OPENSSL */
210