1 files changed, 241 insertions, 0 deletions
diff --git a/kexgexc.c b/kexgexc.c
new file mode 100644
index 0000000..e99e0cf
--- /dev/null
+++ b/kexgexc.c
@@ -0,0 +1,241 @@
+/* $OpenBSD: kexgexc.c,v 1.38 2021/12/19 22:08:06 djm Exp $ */
+/*
+ * Copyright (c) 2000 Niels Provos.  All rights reserved.
+ * Copyright (c) 2001 Markus Friedl.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "includes.h"
+
+#ifdef WITH_OPENSSL
+
+#include <sys/types.h>
+
+#include <openssl/dh.h>
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <signal.h>
+
+#include "openbsd-compat/openssl-compat.h"
+
+#include "sshkey.h"
+#include "cipher.h"
+#include "digest.h"
+#include "kex.h"
+#include "log.h"
+#include "packet.h"
+#include "dh.h"
+#include "ssh2.h"
+#include "compat.h"
+#include "dispatch.h"
+#include "ssherr.h"
+#include "sshbuf.h"
+#include "misc.h"
+
+static int input_kex_dh_gex_group(int, u_int32_t, struct ssh *);
+static int input_kex_dh_gex_reply(int, u_int32_t, struct ssh *);
+
+int
+kexgex_client(struct ssh *ssh)
+{
+	struct kex *kex = ssh->kex;
+	int r;
+	u_int nbits;
+
+	nbits = dh_estimate(kex->dh_need * 8);
+
+	kex->min = DH_GRP_MIN;
+	kex->max = DH_GRP_MAX;
+	kex->nbits = nbits;
+	if (ssh->compat & SSH_BUG_DHGEX_LARGE)
+		kex->nbits = MINIMUM(kex->nbits, 4096);
+	/* New GEX request */
+	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
+	    (r = sshpkt_put_u32(ssh, kex->min)) != 0 ||
+	    (r = sshpkt_put_u32(ssh, kex->nbits)) != 0 ||
+	    (r = sshpkt_put_u32(ssh, kex->max)) != 0 ||
+	    (r = sshpkt_send(ssh)) != 0)
+		goto out;
+	debug("SSH2_MSG_KEX_DH_GEX_REQUEST(%u<%u<%u) sent",
+	    kex->min, kex->nbits, kex->max);
+#ifdef DEBUG_KEXDH
+	fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
+	    kex->min, kex->nbits, kex->max);
+#endif
+	debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
+	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP,
+	    &input_kex_dh_gex_group);
+	r = 0;
+ out:
+	return r;
+}
+
+static int
+input_kex_dh_gex_group(int type, u_int32_t seq, struct ssh *ssh)
+{
+	struct kex *kex = ssh->kex;
+	BIGNUM *p = NULL, *g = NULL;
+	const BIGNUM *pub_key;
+	int r, bits;
+
+	debug("SSH2_MSG_KEX_DH_GEX_GROUP received");
+	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_GROUP, &kex_protocol_error);
+
+	if ((r = sshpkt_get_bignum2(ssh, &p)) != 0 ||
+	    (r = sshpkt_get_bignum2(ssh, &g)) != 0 ||
+	    (r = sshpkt_get_end(ssh)) != 0)
+		goto out;
+	if ((bits = BN_num_bits(p)) < 0 ||
+	    (u_int)bits < kex->min || (u_int)bits > kex->max) {
+		r = SSH_ERR_DH_GEX_OUT_OF_RANGE;
+		goto out;
+	}
+	if ((kex->dh = dh_new_group(g, p)) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+	p = g = NULL; /* belong to kex->dh now */
+
+	/* generate and send 'e', client DH public key */
+	if ((r = dh_gen_key(kex->dh, kex->we_need * 8)) != 0)
+		goto out;
+	DH_get0_key(kex->dh, &pub_key, NULL);
+	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_INIT)) != 0 ||
+	    (r = sshpkt_put_bignum2(ssh, pub_key)) != 0 ||
+	    (r = sshpkt_send(ssh)) != 0)
+		goto out;
+	debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
+#ifdef DEBUG_KEXDH
+	DHparams_print_fp(stderr, kex->dh);
+	fprintf(stderr, "pub= ");
+	BN_print_fp(stderr, pub_key);
+	fprintf(stderr, "\n");
+#endif
+	debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
+	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &input_kex_dh_gex_reply);
+	r = 0;
+out:
+	BN_clear_free(p);
+	BN_clear_free(g);
+	return r;
+}
+
+static int
+input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh)
+{
+	struct kex *kex = ssh->kex;
+	BIGNUM *dh_server_pub = NULL;
+	const BIGNUM *pub_key, *dh_p, *dh_g;
+	struct sshbuf *shared_secret = NULL;
+	struct sshbuf *tmp = NULL, *server_host_key_blob = NULL;
+	struct sshkey *server_host_key = NULL;
+	u_char *signature = NULL;
+	u_char hash[SSH_DIGEST_MAX_LENGTH];
+	size_t slen, hashlen;
+	int r;
+
+	debug("SSH2_MSG_KEX_DH_GEX_REPLY received");
+	ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REPLY, &kex_protocol_error);
+
+	/* key, cert */
+	if ((r = sshpkt_getb_froms(ssh, &server_host_key_blob)) != 0)
+		goto out;
+	/* sshkey_fromb() consumes its buffer, so make a copy */
+	if ((tmp = sshbuf_fromb(server_host_key_blob)) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+	if ((r = sshkey_fromb(tmp, &server_host_key)) != 0 ||
+	    (r = kex_verify_host_key(ssh, server_host_key)) != 0)
+		goto out;
+	/* DH parameter f, server public DH key, signed H */
+	if ((r = sshpkt_get_bignum2(ssh, &dh_server_pub)) != 0 ||
+	    (r = sshpkt_get_string(ssh, &signature, &slen)) != 0 ||
+	    (r = sshpkt_get_end(ssh)) != 0)
+		goto out;
+	if ((shared_secret = sshbuf_new()) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+	if ((r = kex_dh_compute_key(kex, dh_server_pub, shared_secret)) != 0)
+		goto out;
+	if (ssh->compat & SSH_OLD_DHGEX)
+		kex->min = kex->max = -1;
+
+	/* calc and verify H */
+	DH_get0_key(kex->dh, &pub_key, NULL);
+	DH_get0_pqg(kex->dh, &dh_p, NULL, &dh_g);
+	hashlen = sizeof(hash);
+	if ((r = kexgex_hash(
+	    kex->hash_alg,
+	    kex->client_version,
+	    kex->server_version,
+	    kex->my,
+	    kex->peer,
+	    server_host_key_blob,
+	    kex->min, kex->nbits, kex->max,
+	    dh_p, dh_g,
+	    pub_key,
+	    dh_server_pub,
+	    sshbuf_ptr(shared_secret), sshbuf_len(shared_secret),
+	    hash, &hashlen)) != 0)
+		goto out;
+
+	if ((r = sshkey_verify(server_host_key, signature, slen, hash,
+	    hashlen, kex->hostkey_alg, ssh->compat, NULL)) != 0)
+		goto out;
+
+	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
+	    (r = kex_send_newkeys(ssh)) != 0)
+		goto out;
+
+	/* save initial signature and hostkey */
+	if ((kex->flags & KEX_INITIAL) != 0) {
+		if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
+			r = SSH_ERR_INTERNAL_ERROR;
+			goto out;
+		}
+		if ((kex->initial_sig = sshbuf_new()) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto out;
+		}
+		if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
+			goto out;
+		kex->initial_hostkey = server_host_key;
+		server_host_key = NULL;
+	}
+	/* success */
+ out:
+	explicit_bzero(hash, sizeof(hash));
+	DH_free(kex->dh);
+	kex->dh = NULL;
+	BN_clear_free(dh_server_pub);
+	sshbuf_free(shared_secret);
+	sshkey_free(server_host_key);
+	sshbuf_free(tmp);
+	sshbuf_free(server_host_key_blob);
+	free(signature);
+	return r;
+}
+#endif /* WITH_OPENSSL */