xref: /openssh-portable/kexgexs.c (revision bb956eaa)
1 /* $OpenBSD: kexgexs.c,v 1.42 2019/01/23 00:30:41 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 	if ((r = sshpkt_get_u32(ssh, &min)) != 0 ||
81 	    (r = sshpkt_get_u32(ssh, &nbits)) != 0 ||
82 	    (r = sshpkt_get_u32(ssh, &max)) != 0 ||
83 	    (r = sshpkt_get_end(ssh)) != 0)
84 		goto out;
85 	kex->nbits = nbits;
86 	kex->min = min;
87 	kex->max = max;
88 	min = MAXIMUM(DH_GRP_MIN, min);
89 	max = MINIMUM(DH_GRP_MAX, max);
90 	nbits = MAXIMUM(DH_GRP_MIN, nbits);
91 	nbits = MINIMUM(DH_GRP_MAX, nbits);
92 
93 	if (kex->max < kex->min || kex->nbits < kex->min ||
94 	    kex->max < kex->nbits || kex->max < DH_GRP_MIN) {
95 		r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
96 		goto out;
97 	}
98 
99 	/* Contact privileged parent */
100 	kex->dh = PRIVSEP(choose_dh(min, nbits, max));
101 	if (kex->dh == NULL) {
102 		sshpkt_disconnect(ssh, "no matching DH grp found");
103 		r = SSH_ERR_ALLOC_FAIL;
104 		goto out;
105 	}
106 	debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
107 	DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
108 	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_GROUP)) != 0 ||
109 	    (r = sshpkt_put_bignum2(ssh, dh_p)) != 0 ||
110 	    (r = sshpkt_put_bignum2(ssh, dh_g)) != 0 ||
111 	    (r = sshpkt_send(ssh)) != 0)
112 		goto out;
113 
114 	/* Compute our exchange value in parallel with the client */
115 	if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
116 		goto out;
117 
118 	debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
119 	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_INIT, &input_kex_dh_gex_init);
120 	r = 0;
121  out:
122 	return r;
123 }
124 
125 static int
input_kex_dh_gex_init(int type,u_int32_t seq,struct ssh * ssh)126 input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
127 {
128 	struct kex *kex = ssh->kex;
129 	BIGNUM *dh_client_pub = NULL;
130 	const BIGNUM *pub_key, *dh_p, *dh_g;
131 	struct sshbuf *shared_secret = NULL;
132 	struct sshbuf *server_host_key_blob = NULL;
133 	struct sshkey *server_host_public, *server_host_private;
134 	u_char *signature = NULL;
135 	u_char hash[SSH_DIGEST_MAX_LENGTH];
136 	size_t slen, hashlen;
137 	int r;
138 
139 	if ((r = kex_load_hostkey(ssh, &server_host_private,
140 	    &server_host_public)) != 0)
141 		goto out;
142 
143 	/* key, cert */
144 	if ((r = sshpkt_get_bignum2(ssh, &dh_client_pub)) != 0 ||
145 	    (r = sshpkt_get_end(ssh)) != 0)
146 		goto out;
147 	if ((shared_secret = sshbuf_new()) == NULL) {
148 		r = SSH_ERR_ALLOC_FAIL;
149 		goto out;
150 	}
151 	if ((r = kex_dh_compute_key(kex, dh_client_pub, shared_secret)) != 0)
152 		goto out;
153 	if ((server_host_key_blob = sshbuf_new()) == NULL) {
154 		r = SSH_ERR_ALLOC_FAIL;
155 		goto out;
156 	}
157 	if ((r = sshkey_putb(server_host_public, server_host_key_blob)) != 0)
158 		goto out;
159 
160 	/* calc H */
161 	DH_get0_key(kex->dh, &pub_key, NULL);
162 	DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
163 	hashlen = sizeof(hash);
164 	if ((r = kexgex_hash(
165 	    kex->hash_alg,
166 	    kex->client_version,
167 	    kex->server_version,
168 	    kex->peer,
169 	    kex->my,
170 	    server_host_key_blob,
171 	    kex->min, kex->nbits, kex->max,
172 	    dh_p, dh_g,
173 	    dh_client_pub,
174 	    pub_key,
175 	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
176 	    hash, &hashlen)) != 0)
177 		goto out;
178 
179 	/* sign H */
180 	if ((r = kex->sign(ssh, server_host_private, server_host_public,
181 	    &signature, &slen, hash, hashlen, kex->hostkey_alg)) < 0)
182 		goto out;
183 
184 	/* send server hostkey, DH pubkey 'f' and signed H */
185 	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REPLY)) != 0 ||
186 	    (r = sshpkt_put_stringb(ssh, server_host_key_blob)) != 0 ||
187 	    (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||     /* f */
188 	    (r = sshpkt_put_string(ssh, signature, slen)) != 0 ||
189 	    (r = sshpkt_send(ssh)) != 0)
190 		goto out;
191 
192 	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
193 		r = kex_send_newkeys(ssh);
194  out:
195 	explicit_bzero(hash, sizeof(hash));
196 	DH_free(kex->dh);
197 	kex->dh = NULL;
198 	BN_clear_free(dh_client_pub);
199 	sshbuf_free(shared_secret);
200 	sshbuf_free(server_host_key_blob);
201 	free(signature);
202 	return r;
203 }
204 #endif /* WITH_OPENSSL */
205