Adding upstream version 1:9.2p1.upstream/1%9.2p1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1421 insertions, 0 deletions

diff --git a/kex.c b/kex.c
new file mode 100644
index 0000000..8cdefcf
--- /dev/null
+++ b/kex.c
@@ -0,0 +1,1421 @@
+/* $OpenBSD: kex.c,v 1.173 2022/11/07 10:05:38 dtucker Exp $ */
+/*
+ * Copyright (c) 2000, 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"
+
+#include <sys/types.h>
+#include <errno.h>
+#include <signal.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#ifdef HAVE_POLL_H
+#include <poll.h>
+#endif
+
+#ifdef WITH_OPENSSL
+#include <openssl/crypto.h>
+#include <openssl/dh.h>
+#endif
+
+#include "ssh.h"
+#include "ssh2.h"
+#include "atomicio.h"
+#include "version.h"
+#include "packet.h"
+#include "compat.h"
+#include "cipher.h"
+#include "sshkey.h"
+#include "kex.h"
+#include "log.h"
+#include "mac.h"
+#include "match.h"
+#include "misc.h"
+#include "dispatch.h"
+#include "monitor.h"
+
+#include "ssherr.h"
+#include "sshbuf.h"
+#include "digest.h"
+
+/* prototype */
+static int kex_choose_conf(struct ssh *);
+static int kex_input_newkeys(int, u_int32_t, struct ssh *);
+
+static const char * const proposal_names[PROPOSAL_MAX] = {
+	"KEX algorithms",
+	"host key algorithms",
+	"ciphers ctos",
+	"ciphers stoc",
+	"MACs ctos",
+	"MACs stoc",
+	"compression ctos",
+	"compression stoc",
+	"languages ctos",
+	"languages stoc",
+};
+
+struct kexalg {
+	char *name;
+	u_int type;
+	int ec_nid;
+	int hash_alg;
+};
+static const struct kexalg kexalgs[] = {
+#ifdef WITH_OPENSSL
+	{ KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
+	{ KEX_DH14_SHA1, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 },
+	{ KEX_DH14_SHA256, KEX_DH_GRP14_SHA256, 0, SSH_DIGEST_SHA256 },
+	{ KEX_DH16_SHA512, KEX_DH_GRP16_SHA512, 0, SSH_DIGEST_SHA512 },
+	{ KEX_DH18_SHA512, KEX_DH_GRP18_SHA512, 0, SSH_DIGEST_SHA512 },
+	{ KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 },
+#ifdef HAVE_EVP_SHA256
+	{ KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 },
+#endif /* HAVE_EVP_SHA256 */
+#ifdef OPENSSL_HAS_ECC
+	{ KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2,
+	    NID_X9_62_prime256v1, SSH_DIGEST_SHA256 },
+	{ KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1,
+	    SSH_DIGEST_SHA384 },
+# ifdef OPENSSL_HAS_NISTP521
+	{ KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1,
+	    SSH_DIGEST_SHA512 },
+# endif /* OPENSSL_HAS_NISTP521 */
+#endif /* OPENSSL_HAS_ECC */
+#endif /* WITH_OPENSSL */
+#if defined(HAVE_EVP_SHA256) || !defined(WITH_OPENSSL)
+	{ KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 },
+	{ KEX_CURVE25519_SHA256_OLD, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 },
+#ifdef USE_SNTRUP761X25519
+	{ KEX_SNTRUP761X25519_SHA512, KEX_KEM_SNTRUP761X25519_SHA512, 0,
+	    SSH_DIGEST_SHA512 },
+#endif
+#endif /* HAVE_EVP_SHA256 || !WITH_OPENSSL */
+	{ NULL, 0, -1, -1},
+};
+
+char *
+kex_alg_list(char sep)
+{
+	char *ret = NULL, *tmp;
+	size_t nlen, rlen = 0;
+	const struct kexalg *k;
+
+	for (k = kexalgs; k->name != NULL; k++) {
+		if (ret != NULL)
+			ret[rlen++] = sep;
+		nlen = strlen(k->name);
+		if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
+			free(ret);
+			return NULL;
+		}
+		ret = tmp;
+		memcpy(ret + rlen, k->name, nlen + 1);
+		rlen += nlen;
+	}
+	return ret;
+}
+
+static const struct kexalg *
+kex_alg_by_name(const char *name)
+{
+	const struct kexalg *k;
+
+	for (k = kexalgs; k->name != NULL; k++) {
+		if (strcmp(k->name, name) == 0)
+			return k;
+	}
+	return NULL;
+}
+
+/* Validate KEX method name list */
+int
+kex_names_valid(const char *names)
+{
+	char *s, *cp, *p;
+
+	if (names == NULL || strcmp(names, "") == 0)
+		return 0;
+	if ((s = cp = strdup(names)) == NULL)
+		return 0;
+	for ((p = strsep(&cp, ",")); p && *p != '\0';
+	    (p = strsep(&cp, ","))) {
+		if (kex_alg_by_name(p) == NULL) {
+			error("Unsupported KEX algorithm \"%.100s\"", p);
+			free(s);
+			return 0;
+		}
+	}
+	debug3("kex names ok: [%s]", names);
+	free(s);
+	return 1;
+}
+
+/*
+ * Concatenate algorithm names, avoiding duplicates in the process.
+ * Caller must free returned string.
+ */
+char *
+kex_names_cat(const char *a, const char *b)
+{
+	char *ret = NULL, *tmp = NULL, *cp, *p, *m;
+	size_t len;
+
+	if (a == NULL || *a == '\0')
+		return strdup(b);
+	if (b == NULL || *b == '\0')
+		return strdup(a);
+	if (strlen(b) > 1024*1024)
+		return NULL;
+	len = strlen(a) + strlen(b) + 2;
+	if ((tmp = cp = strdup(b)) == NULL ||
+	    (ret = calloc(1, len)) == NULL) {
+		free(tmp);
+		return NULL;
+	}
+	strlcpy(ret, a, len);
+	for ((p = strsep(&cp, ",")); p && *p != '\0'; (p = strsep(&cp, ","))) {
+		if ((m = match_list(ret, p, NULL)) != NULL) {
+			free(m);
+			continue; /* Algorithm already present */
+		}
+		if (strlcat(ret, ",", len) >= len ||
+		    strlcat(ret, p, len) >= len) {
+			free(tmp);
+			free(ret);
+			return NULL; /* Shouldn't happen */
+		}
+	}
+	free(tmp);
+	return ret;
+}
+
+/*
+ * Assemble a list of algorithms from a default list and a string from a
+ * configuration file. The user-provided string may begin with '+' to
+ * indicate that it should be appended to the default, '-' that the
+ * specified names should be removed, or '^' that they should be placed
+ * at the head.
+ */
+int
+kex_assemble_names(char **listp, const char *def, const char *all)
+{
+	char *cp, *tmp, *patterns;
+	char *list = NULL, *ret = NULL, *matching = NULL, *opatterns = NULL;
+	int r = SSH_ERR_INTERNAL_ERROR;
+
+	if (listp == NULL || def == NULL || all == NULL)
+		return SSH_ERR_INVALID_ARGUMENT;
+
+	if (*listp == NULL || **listp == '\0') {
+		if ((*listp = strdup(def)) == NULL)
+			return SSH_ERR_ALLOC_FAIL;
+		return 0;
+	}
+
+	list = *listp;
+	*listp = NULL;
+	if (*list == '+') {
+		/* Append names to default list */
+		if ((tmp = kex_names_cat(def, list + 1)) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto fail;
+		}
+		free(list);
+		list = tmp;
+	} else if (*list == '-') {
+		/* Remove names from default list */
+		if ((*listp = match_filter_denylist(def, list + 1)) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto fail;
+		}
+		free(list);
+		/* filtering has already been done */
+		return 0;
+	} else if (*list == '^') {
+		/* Place names at head of default list */
+		if ((tmp = kex_names_cat(list + 1, def)) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto fail;
+		}
+		free(list);
+		list = tmp;
+	} else {
+		/* Explicit list, overrides default - just use "list" as is */
+	}
+
+	/*
+	 * The supplied names may be a pattern-list. For the -list case,
+	 * the patterns are applied above. For the +list and explicit list
+	 * cases we need to do it now.
+	 */
+	ret = NULL;
+	if ((patterns = opatterns = strdup(list)) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		goto fail;
+	}
+	/* Apply positive (i.e. non-negated) patterns from the list */
+	while ((cp = strsep(&patterns, ",")) != NULL) {
+		if (*cp == '!') {
+			/* negated matches are not supported here */
+			r = SSH_ERR_INVALID_ARGUMENT;
+			goto fail;
+		}
+		free(matching);
+		if ((matching = match_filter_allowlist(all, cp)) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto fail;
+		}
+		if ((tmp = kex_names_cat(ret, matching)) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto fail;
+		}
+		free(ret);
+		ret = tmp;
+	}
+	if (ret == NULL || *ret == '\0') {
+		/* An empty name-list is an error */
+		/* XXX better error code? */
+		r = SSH_ERR_INVALID_ARGUMENT;
+		goto fail;
+	}
+
+	/* success */
+	*listp = ret;
+	ret = NULL;
+	r = 0;
+
+ fail:
+	free(matching);
+	free(opatterns);
+	free(list);
+	free(ret);
+	return r;
+}
+
+/* put algorithm proposal into buffer */
+int
+kex_prop2buf(struct sshbuf *b, char *proposal[PROPOSAL_MAX])
+{
+	u_int i;
+	int r;
+
+	sshbuf_reset(b);
+
+	/*
+	 * add a dummy cookie, the cookie will be overwritten by
+	 * kex_send_kexinit(), each time a kexinit is set
+	 */
+	for (i = 0; i < KEX_COOKIE_LEN; i++) {
+		if ((r = sshbuf_put_u8(b, 0)) != 0)
+			return r;
+	}
+	for (i = 0; i < PROPOSAL_MAX; i++) {
+		if ((r = sshbuf_put_cstring(b, proposal[i])) != 0)
+			return r;
+	}
+	if ((r = sshbuf_put_u8(b, 0)) != 0 ||	/* first_kex_packet_follows */
+	    (r = sshbuf_put_u32(b, 0)) != 0)	/* uint32 reserved */
+		return r;
+	return 0;
+}
+
+/* parse buffer and return algorithm proposal */
+int
+kex_buf2prop(struct sshbuf *raw, int *first_kex_follows, char ***propp)
+{
+	struct sshbuf *b = NULL;
+	u_char v;
+	u_int i;
+	char **proposal = NULL;
+	int r;
+
+	*propp = NULL;
+	if ((proposal = calloc(PROPOSAL_MAX, sizeof(char *))) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if ((b = sshbuf_fromb(raw)) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+	if ((r = sshbuf_consume(b, KEX_COOKIE_LEN)) != 0) { /* skip cookie */
+		error_fr(r, "consume cookie");
+		goto out;
+	}
+	/* extract kex init proposal strings */
+	for (i = 0; i < PROPOSAL_MAX; i++) {
+		if ((r = sshbuf_get_cstring(b, &(proposal[i]), NULL)) != 0) {
+			error_fr(r, "parse proposal %u", i);
+			goto out;
+		}
+		debug2("%s: %s", proposal_names[i], proposal[i]);
+	}
+	/* first kex follows / reserved */
+	if ((r = sshbuf_get_u8(b, &v)) != 0 ||	/* first_kex_follows */
+	    (r = sshbuf_get_u32(b, &i)) != 0) {	/* reserved */
+		error_fr(r, "parse");
+		goto out;
+	}
+	if (first_kex_follows != NULL)
+		*first_kex_follows = v;
+	debug2("first_kex_follows %d ", v);
+	debug2("reserved %u ", i);
+	r = 0;
+	*propp = proposal;
+ out:
+	if (r != 0 && proposal != NULL)
+		kex_prop_free(proposal);
+	sshbuf_free(b);
+	return r;
+}
+
+void
+kex_prop_free(char **proposal)
+{
+	u_int i;
+
+	if (proposal == NULL)
+		return;
+	for (i = 0; i < PROPOSAL_MAX; i++)
+		free(proposal[i]);
+	free(proposal);
+}
+
+/* ARGSUSED */
+int
+kex_protocol_error(int type, u_int32_t seq, struct ssh *ssh)
+{
+	int r;
+
+	error("kex protocol error: type %d seq %u", type, seq);
+	if ((r = sshpkt_start(ssh, SSH2_MSG_UNIMPLEMENTED)) != 0 ||
+	    (r = sshpkt_put_u32(ssh, seq)) != 0 ||
+	    (r = sshpkt_send(ssh)) != 0)
+		return r;
+	return 0;
+}
+
+static void
+kex_reset_dispatch(struct ssh *ssh)
+{
+	ssh_dispatch_range(ssh, SSH2_MSG_TRANSPORT_MIN,
+	    SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
+}
+
+static int
+kex_send_ext_info(struct ssh *ssh)
+{
+	int r;
+	char *algs;
+
+	debug("Sending SSH2_MSG_EXT_INFO");
+	if ((algs = sshkey_alg_list(0, 1, 1, ',')) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	/* XXX filter algs list by allowed pubkey/hostbased types */
+	if ((r = sshpkt_start(ssh, SSH2_MSG_EXT_INFO)) != 0 ||
+	    (r = sshpkt_put_u32(ssh, 2)) != 0 ||
+	    (r = sshpkt_put_cstring(ssh, "server-sig-algs")) != 0 ||
+	    (r = sshpkt_put_cstring(ssh, algs)) != 0 ||
+	    (r = sshpkt_put_cstring(ssh,
+	    "publickey-hostbound@openssh.com")) != 0 ||
+	    (r = sshpkt_put_cstring(ssh, "0")) != 0 ||
+	    (r = sshpkt_send(ssh)) != 0) {
+		error_fr(r, "compose");
+		goto out;
+	}
+	/* success */
+	r = 0;
+ out:
+	free(algs);
+	return r;
+}
+
+int
+kex_send_newkeys(struct ssh *ssh)
+{
+	int r;
+
+	kex_reset_dispatch(ssh);
+	if ((r = sshpkt_start(ssh, SSH2_MSG_NEWKEYS)) != 0 ||
+	    (r = sshpkt_send(ssh)) != 0)
+		return r;
+	debug("SSH2_MSG_NEWKEYS sent");
+	ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_input_newkeys);
+	if (ssh->kex->ext_info_c && (ssh->kex->flags & KEX_INITIAL) != 0)
+		if ((r = kex_send_ext_info(ssh)) != 0)
+			return r;
+	debug("expecting SSH2_MSG_NEWKEYS");
+	return 0;
+}
+
+int
+kex_input_ext_info(int type, u_int32_t seq, struct ssh *ssh)
+{
+	struct kex *kex = ssh->kex;
+	u_int32_t i, ninfo;
+	char *name;
+	u_char *val;
+	size_t vlen;
+	int r;
+
+	debug("SSH2_MSG_EXT_INFO received");
+	ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &kex_protocol_error);
+	if ((r = sshpkt_get_u32(ssh, &ninfo)) != 0)
+		return r;
+	for (i = 0; i < ninfo; i++) {
+		if ((r = sshpkt_get_cstring(ssh, &name, NULL)) != 0)
+			return r;
+		if ((r = sshpkt_get_string(ssh, &val, &vlen)) != 0) {
+			free(name);
+			return r;
+		}
+		if (strcmp(name, "server-sig-algs") == 0) {
+			/* Ensure no \0 lurking in value */
+			if (memchr(val, '\0', vlen) != NULL) {
+				error_f("nul byte in %s", name);
+				return SSH_ERR_INVALID_FORMAT;
+			}
+			debug_f("%s=<%s>", name, val);
+			kex->server_sig_algs = val;
+			val = NULL;
+		} else if (strcmp(name,
+		    "publickey-hostbound@openssh.com") == 0) {
+			/* XXX refactor */
+			/* Ensure no \0 lurking in value */
+			if (memchr(val, '\0', vlen) != NULL) {
+				error_f("nul byte in %s", name);
+				return SSH_ERR_INVALID_FORMAT;
+			}
+			debug_f("%s=<%s>", name, val);
+			if (strcmp(val, "0") == 0)
+				kex->flags |= KEX_HAS_PUBKEY_HOSTBOUND;
+			else {
+				debug_f("unsupported version of %s extension",
+				    name);
+			}
+		} else
+			debug_f("%s (unrecognised)", name);
+		free(name);
+		free(val);
+	}
+	return sshpkt_get_end(ssh);
+}
+
+static int
+kex_input_newkeys(int type, u_int32_t seq, struct ssh *ssh)
+{
+	struct kex *kex = ssh->kex;
+	int r;
+
+	debug("SSH2_MSG_NEWKEYS received");
+	ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_protocol_error);
+	ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit);
+	if ((r = sshpkt_get_end(ssh)) != 0)
+		return r;
+	if ((r = ssh_set_newkeys(ssh, MODE_IN)) != 0)
+		return r;
+	kex->done = 1;
+	kex->flags &= ~KEX_INITIAL;
+	sshbuf_reset(kex->peer);
+	/* sshbuf_reset(kex->my); */
+	kex->flags &= ~KEX_INIT_SENT;
+	free(kex->name);
+	kex->name = NULL;
+	return 0;
+}
+
+int
+kex_send_kexinit(struct ssh *ssh)
+{
+	u_char *cookie;
+	struct kex *kex = ssh->kex;
+	int r;
+
+	if (kex == NULL) {
+		error_f("no kex");
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	if (kex->flags & KEX_INIT_SENT)
+		return 0;
+	kex->done = 0;
+
+	/* generate a random cookie */
+	if (sshbuf_len(kex->my) < KEX_COOKIE_LEN) {
+		error_f("bad kex length: %zu < %d",
+		    sshbuf_len(kex->my), KEX_COOKIE_LEN);
+		return SSH_ERR_INVALID_FORMAT;
+	}
+	if ((cookie = sshbuf_mutable_ptr(kex->my)) == NULL) {
+		error_f("buffer error");
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	arc4random_buf(cookie, KEX_COOKIE_LEN);
+
+	if ((r = sshpkt_start(ssh, SSH2_MSG_KEXINIT)) != 0 ||
+	    (r = sshpkt_putb(ssh, kex->my)) != 0 ||
+	    (r = sshpkt_send(ssh)) != 0) {
+		error_fr(r, "compose reply");
+		return r;
+	}
+	debug("SSH2_MSG_KEXINIT sent");
+	kex->flags |= KEX_INIT_SENT;
+	return 0;
+}
+
+/* ARGSUSED */
+int
+kex_input_kexinit(int type, u_int32_t seq, struct ssh *ssh)
+{
+	struct kex *kex = ssh->kex;
+	const u_char *ptr;
+	u_int i;
+	size_t dlen;
+	int r;
+
+	debug("SSH2_MSG_KEXINIT received");
+	if (kex == NULL) {
+		error_f("no kex");
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, NULL);
+	ptr = sshpkt_ptr(ssh, &dlen);
+	if ((r = sshbuf_put(kex->peer, ptr, dlen)) != 0)
+		return r;
+
+	/* discard packet */
+	for (i = 0; i < KEX_COOKIE_LEN; i++) {
+		if ((r = sshpkt_get_u8(ssh, NULL)) != 0) {
+			error_fr(r, "discard cookie");
+			return r;
+		}
+	}
+	for (i = 0; i < PROPOSAL_MAX; i++) {
+		if ((r = sshpkt_get_string(ssh, NULL, NULL)) != 0) {
+			error_fr(r, "discard proposal");
+			return r;
+		}
+	}
+	/*
+	 * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
+	 * KEX method has the server move first, but a server might be using
+	 * a custom method or one that we otherwise don't support. We should
+	 * be prepared to remember first_kex_follows here so we can eat a
+	 * packet later.
+	 * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
+	 * for cases where the server *doesn't* go first. I guess we should
+	 * ignore it when it is set for these cases, which is what we do now.
+	 */
+	if ((r = sshpkt_get_u8(ssh, NULL)) != 0 ||	/* first_kex_follows */
+	    (r = sshpkt_get_u32(ssh, NULL)) != 0 ||	/* reserved */
+	    (r = sshpkt_get_end(ssh)) != 0)
+			return r;
+
+	if (!(kex->flags & KEX_INIT_SENT))
+		if ((r = kex_send_kexinit(ssh)) != 0)
+			return r;
+	if ((r = kex_choose_conf(ssh)) != 0)
+		return r;
+
+	if (kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL)
+		return (kex->kex[kex->kex_type])(ssh);
+
+	error_f("unknown kex type %u", kex->kex_type);
+	return SSH_ERR_INTERNAL_ERROR;
+}
+
+struct kex *
+kex_new(void)
+{
+	struct kex *kex;
+
+	if ((kex = calloc(1, sizeof(*kex))) == NULL ||
+	    (kex->peer = sshbuf_new()) == NULL ||
+	    (kex->my = sshbuf_new()) == NULL ||
+	    (kex->client_version = sshbuf_new()) == NULL ||
+	    (kex->server_version = sshbuf_new()) == NULL ||
+	    (kex->session_id = sshbuf_new()) == NULL) {
+		kex_free(kex);
+		return NULL;
+	}
+	return kex;
+}
+
+void
+kex_free_newkeys(struct newkeys *newkeys)
+{
+	if (newkeys == NULL)
+		return;
+	if (newkeys->enc.key) {
+		explicit_bzero(newkeys->enc.key, newkeys->enc.key_len);
+		free(newkeys->enc.key);
+		newkeys->enc.key = NULL;
+	}
+	if (newkeys->enc.iv) {
+		explicit_bzero(newkeys->enc.iv, newkeys->enc.iv_len);
+		free(newkeys->enc.iv);
+		newkeys->enc.iv = NULL;
+	}
+	free(newkeys->enc.name);
+	explicit_bzero(&newkeys->enc, sizeof(newkeys->enc));
+	free(newkeys->comp.name);
+	explicit_bzero(&newkeys->comp, sizeof(newkeys->comp));
+	mac_clear(&newkeys->mac);
+	if (newkeys->mac.key) {
+		explicit_bzero(newkeys->mac.key, newkeys->mac.key_len);
+		free(newkeys->mac.key);
+		newkeys->mac.key = NULL;
+	}
+	free(newkeys->mac.name);
+	explicit_bzero(&newkeys->mac, sizeof(newkeys->mac));
+	freezero(newkeys, sizeof(*newkeys));
+}
+
+void
+kex_free(struct kex *kex)
+{
+	u_int mode;
+
+	if (kex == NULL)
+		return;
+
+#ifdef WITH_OPENSSL
+	DH_free(kex->dh);
+#ifdef OPENSSL_HAS_ECC
+	EC_KEY_free(kex->ec_client_key);
+#endif /* OPENSSL_HAS_ECC */
+#endif /* WITH_OPENSSL */
+	for (mode = 0; mode < MODE_MAX; mode++) {
+		kex_free_newkeys(kex->newkeys[mode]);
+		kex->newkeys[mode] = NULL;
+	}
+	sshbuf_free(kex->peer);
+	sshbuf_free(kex->my);
+	sshbuf_free(kex->client_version);
+	sshbuf_free(kex->server_version);
+	sshbuf_free(kex->client_pub);
+	sshbuf_free(kex->session_id);
+	sshbuf_free(kex->initial_sig);
+	sshkey_free(kex->initial_hostkey);
+	free(kex->failed_choice);
+	free(kex->hostkey_alg);
+	free(kex->name);
+	free(kex);
+}
+
+int
+kex_ready(struct ssh *ssh, char *proposal[PROPOSAL_MAX])
+{
+	int r;
+
+	if ((r = kex_prop2buf(ssh->kex->my, proposal)) != 0)
+		return r;
+	ssh->kex->flags = KEX_INITIAL;
+	kex_reset_dispatch(ssh);
+	ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit);
+	return 0;
+}
+
+int
+kex_setup(struct ssh *ssh, char *proposal[PROPOSAL_MAX])
+{
+	int r;
+
+	if ((r = kex_ready(ssh, proposal)) != 0)
+		return r;
+	if ((r = kex_send_kexinit(ssh)) != 0) {		/* we start */
+		kex_free(ssh->kex);
+		ssh->kex = NULL;
+		return r;
+	}
+	return 0;
+}
+
+/*
+ * Request key re-exchange, returns 0 on success or a ssherr.h error
+ * code otherwise. Must not be called if KEX is incomplete or in-progress.
+ */
+int
+kex_start_rekex(struct ssh *ssh)
+{
+	if (ssh->kex == NULL) {
+		error_f("no kex");
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	if (ssh->kex->done == 0) {
+		error_f("requested twice");
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	ssh->kex->done = 0;
+	return kex_send_kexinit(ssh);
+}
+
+static int
+choose_enc(struct sshenc *enc, char *client, char *server)
+{
+	char *name = match_list(client, server, NULL);
+
+	if (name == NULL)
+		return SSH_ERR_NO_CIPHER_ALG_MATCH;
+	if ((enc->cipher = cipher_by_name(name)) == NULL) {
+		error_f("unsupported cipher %s", name);
+		free(name);
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	enc->name = name;
+	enc->enabled = 0;
+	enc->iv = NULL;
+	enc->iv_len = cipher_ivlen(enc->cipher);
+	enc->key = NULL;
+	enc->key_len = cipher_keylen(enc->cipher);
+	enc->block_size = cipher_blocksize(enc->cipher);
+	return 0;
+}
+
+static int
+choose_mac(struct ssh *ssh, struct sshmac *mac, char *client, char *server)
+{
+	char *name = match_list(client, server, NULL);
+
+	if (name == NULL)
+		return SSH_ERR_NO_MAC_ALG_MATCH;
+	if (mac_setup(mac, name) < 0) {
+		error_f("unsupported MAC %s", name);
+		free(name);
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	mac->name = name;
+	mac->key = NULL;
+	mac->enabled = 0;
+	return 0;
+}
+
+static int
+choose_comp(struct sshcomp *comp, char *client, char *server)
+{
+	char *name = match_list(client, server, NULL);
+
+	if (name == NULL)
+		return SSH_ERR_NO_COMPRESS_ALG_MATCH;
+#ifdef WITH_ZLIB
+	if (strcmp(name, "zlib@openssh.com") == 0) {
+		comp->type = COMP_DELAYED;
+	} else if (strcmp(name, "zlib") == 0) {
+		comp->type = COMP_ZLIB;
+	} else
+#endif	/* WITH_ZLIB */
+	if (strcmp(name, "none") == 0) {
+		comp->type = COMP_NONE;
+	} else {
+		error_f("unsupported compression scheme %s", name);
+		free(name);
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	comp->name = name;
+	return 0;
+}
+
+static int
+choose_kex(struct kex *k, char *client, char *server)
+{
+	const struct kexalg *kexalg;
+
+	k->name = match_list(client, server, NULL);
+
+	debug("kex: algorithm: %s", k->name ? k->name : "(no match)");
+	if (k->name == NULL)
+		return SSH_ERR_NO_KEX_ALG_MATCH;
+	if ((kexalg = kex_alg_by_name(k->name)) == NULL) {
+		error_f("unsupported KEX method %s", k->name);
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	k->kex_type = kexalg->type;
+	k->hash_alg = kexalg->hash_alg;
+	k->ec_nid = kexalg->ec_nid;
+	return 0;
+}
+
+static int
+choose_hostkeyalg(struct kex *k, char *client, char *server)
+{
+	free(k->hostkey_alg);
+	k->hostkey_alg = match_list(client, server, NULL);
+
+	debug("kex: host key algorithm: %s",
+	    k->hostkey_alg ? k->hostkey_alg : "(no match)");
+	if (k->hostkey_alg == NULL)
+		return SSH_ERR_NO_HOSTKEY_ALG_MATCH;
+	k->hostkey_type = sshkey_type_from_name(k->hostkey_alg);
+	if (k->hostkey_type == KEY_UNSPEC) {
+		error_f("unsupported hostkey algorithm %s", k->hostkey_alg);
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	k->hostkey_nid = sshkey_ecdsa_nid_from_name(k->hostkey_alg);
+	return 0;
+}
+
+static int
+proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
+{
+	static int check[] = {
+		PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
+	};
+	int *idx;
+	char *p;
+
+	for (idx = &check[0]; *idx != -1; idx++) {
+		if ((p = strchr(my[*idx], ',')) != NULL)
+			*p = '\0';
+		if ((p = strchr(peer[*idx], ',')) != NULL)
+			*p = '\0';
+		if (strcmp(my[*idx], peer[*idx]) != 0) {
+			debug2("proposal mismatch: my %s peer %s",
+			    my[*idx], peer[*idx]);
+			return (0);
+		}
+	}
+	debug2("proposals match");
+	return (1);
+}
+
+/* returns non-zero if proposal contains any algorithm from algs */
+static int
+has_any_alg(const char *proposal, const char *algs)
+{
+	char *cp;
+
+	if ((cp = match_list(proposal, algs, NULL)) == NULL)
+		return 0;
+	free(cp);
+	return 1;
+}
+
+static int
+kex_choose_conf(struct ssh *ssh)
+{
+	struct kex *kex = ssh->kex;
+	struct newkeys *newkeys;
+	char **my = NULL, **peer = NULL;
+	char **cprop, **sprop;
+	int nenc, nmac, ncomp;
+	u_int mode, ctos, need, dh_need, authlen;
+	int r, first_kex_follows;
+
+	debug2("local %s KEXINIT proposal", kex->server ? "server" : "client");
+	if ((r = kex_buf2prop(kex->my, NULL, &my)) != 0)
+		goto out;
+	debug2("peer %s KEXINIT proposal", kex->server ? "client" : "server");
+	if ((r = kex_buf2prop(kex->peer, &first_kex_follows, &peer)) != 0)
+		goto out;
+
+	if (kex->server) {
+		cprop=peer;
+		sprop=my;
+	} else {
+		cprop=my;
+		sprop=peer;
+	}
+
+	/* Check whether client supports ext_info_c */
+	if (kex->server && (kex->flags & KEX_INITIAL)) {
+		char *ext;
+
+		ext = match_list("ext-info-c", peer[PROPOSAL_KEX_ALGS], NULL);
+		kex->ext_info_c = (ext != NULL);
+		free(ext);
+	}
+
+	/* Check whether client supports rsa-sha2 algorithms */
+	if (kex->server && (kex->flags & KEX_INITIAL)) {
+		if (has_any_alg(peer[PROPOSAL_SERVER_HOST_KEY_ALGS],
+		    "rsa-sha2-256,rsa-sha2-256-cert-v01@openssh.com"))
+			kex->flags |= KEX_RSA_SHA2_256_SUPPORTED;
+		if (has_any_alg(peer[PROPOSAL_SERVER_HOST_KEY_ALGS],
+		    "rsa-sha2-512,rsa-sha2-512-cert-v01@openssh.com"))
+			kex->flags |= KEX_RSA_SHA2_512_SUPPORTED;
+	}
+
+	/* Algorithm Negotiation */
+	if ((r = choose_kex(kex, cprop[PROPOSAL_KEX_ALGS],
+	    sprop[PROPOSAL_KEX_ALGS])) != 0) {
+		kex->failed_choice = peer[PROPOSAL_KEX_ALGS];
+		peer[PROPOSAL_KEX_ALGS] = NULL;
+		goto out;
+	}
+	if ((r = choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
+	    sprop[PROPOSAL_SERVER_HOST_KEY_ALGS])) != 0) {
+		kex->failed_choice = peer[PROPOSAL_SERVER_HOST_KEY_ALGS];
+		peer[PROPOSAL_SERVER_HOST_KEY_ALGS] = NULL;
+		goto out;
+	}
+	for (mode = 0; mode < MODE_MAX; mode++) {
+		if ((newkeys = calloc(1, sizeof(*newkeys))) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto out;
+		}
+		kex->newkeys[mode] = newkeys;
+		ctos = (!kex->server && mode == MODE_OUT) ||
+		    (kex->server && mode == MODE_IN);
+		nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
+		nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
+		ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
+		if ((r = choose_enc(&newkeys->enc, cprop[nenc],
+		    sprop[nenc])) != 0) {
+			kex->failed_choice = peer[nenc];
+			peer[nenc] = NULL;
+			goto out;
+		}
+		authlen = cipher_authlen(newkeys->enc.cipher);
+		/* ignore mac for authenticated encryption */
+		if (authlen == 0 &&
+		    (r = choose_mac(ssh, &newkeys->mac, cprop[nmac],
+		    sprop[nmac])) != 0) {
+			kex->failed_choice = peer[nmac];
+			peer[nmac] = NULL;
+			goto out;
+		}
+		if ((r = choose_comp(&newkeys->comp, cprop[ncomp],
+		    sprop[ncomp])) != 0) {
+			kex->failed_choice = peer[ncomp];
+			peer[ncomp] = NULL;
+			goto out;
+		}
+		debug("kex: %s cipher: %s MAC: %s compression: %s",
+		    ctos ? "client->server" : "server->client",
+		    newkeys->enc.name,
+		    authlen == 0 ? newkeys->mac.name : "<implicit>",
+		    newkeys->comp.name);
+	}
+	need = dh_need = 0;
+	for (mode = 0; mode < MODE_MAX; mode++) {
+		newkeys = kex->newkeys[mode];
+		need = MAXIMUM(need, newkeys->enc.key_len);
+		need = MAXIMUM(need, newkeys->enc.block_size);
+		need = MAXIMUM(need, newkeys->enc.iv_len);
+		need = MAXIMUM(need, newkeys->mac.key_len);
+		dh_need = MAXIMUM(dh_need, cipher_seclen(newkeys->enc.cipher));
+		dh_need = MAXIMUM(dh_need, newkeys->enc.block_size);
+		dh_need = MAXIMUM(dh_need, newkeys->enc.iv_len);
+		dh_need = MAXIMUM(dh_need, newkeys->mac.key_len);
+	}
+	/* XXX need runden? */
+	kex->we_need = need;
+	kex->dh_need = dh_need;
+
+	/* ignore the next message if the proposals do not match */
+	if (first_kex_follows && !proposals_match(my, peer))
+		ssh->dispatch_skip_packets = 1;
+	r = 0;
+ out:
+	kex_prop_free(my);
+	kex_prop_free(peer);
+	return r;
+}
+
+static int
+derive_key(struct ssh *ssh, int id, u_int need, u_char *hash, u_int hashlen,
+    const struct sshbuf *shared_secret, u_char **keyp)
+{
+	struct kex *kex = ssh->kex;
+	struct ssh_digest_ctx *hashctx = NULL;
+	char c = id;
+	u_int have;
+	size_t mdsz;
+	u_char *digest;
+	int r;
+
+	if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0)
+		return SSH_ERR_INVALID_ARGUMENT;
+	if ((digest = calloc(1, ROUNDUP(need, mdsz))) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+
+	/* K1 = HASH(K || H || "A" || session_id) */
+	if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL ||
+	    ssh_digest_update_buffer(hashctx, shared_secret) != 0 ||
+	    ssh_digest_update(hashctx, hash, hashlen) != 0 ||
+	    ssh_digest_update(hashctx, &c, 1) != 0 ||
+	    ssh_digest_update_buffer(hashctx, kex->session_id) != 0 ||
+	    ssh_digest_final(hashctx, digest, mdsz) != 0) {
+		r = SSH_ERR_LIBCRYPTO_ERROR;
+		error_f("KEX hash failed");
+		goto out;
+	}
+	ssh_digest_free(hashctx);
+	hashctx = NULL;
+
+	/*
+	 * expand key:
+	 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
+	 * Key = K1 || K2 || ... || Kn
+	 */
+	for (have = mdsz; need > have; have += mdsz) {
+		if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL ||
+		    ssh_digest_update_buffer(hashctx, shared_secret) != 0 ||
+		    ssh_digest_update(hashctx, hash, hashlen) != 0 ||
+		    ssh_digest_update(hashctx, digest, have) != 0 ||
+		    ssh_digest_final(hashctx, digest + have, mdsz) != 0) {
+			error_f("KDF failed");
+			r = SSH_ERR_LIBCRYPTO_ERROR;
+			goto out;
+		}
+		ssh_digest_free(hashctx);
+		hashctx = NULL;
+	}
+#ifdef DEBUG_KEX
+	fprintf(stderr, "key '%c'== ", c);
+	dump_digest("key", digest, need);
+#endif
+	*keyp = digest;
+	digest = NULL;
+	r = 0;
+ out:
+	free(digest);
+	ssh_digest_free(hashctx);
+	return r;
+}
+
+#define NKEYS	6
+int
+kex_derive_keys(struct ssh *ssh, u_char *hash, u_int hashlen,
+    const struct sshbuf *shared_secret)
+{
+	struct kex *kex = ssh->kex;
+	u_char *keys[NKEYS];
+	u_int i, j, mode, ctos;
+	int r;
+
+	/* save initial hash as session id */
+	if ((kex->flags & KEX_INITIAL) != 0) {
+		if (sshbuf_len(kex->session_id) != 0) {
+			error_f("already have session ID at kex");
+			return SSH_ERR_INTERNAL_ERROR;
+		}
+		if ((r = sshbuf_put(kex->session_id, hash, hashlen)) != 0)
+			return r;
+	} else if (sshbuf_len(kex->session_id) == 0) {
+		error_f("no session ID in rekex");
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	for (i = 0; i < NKEYS; i++) {
+		if ((r = derive_key(ssh, 'A'+i, kex->we_need, hash, hashlen,
+		    shared_secret, &keys[i])) != 0) {
+			for (j = 0; j < i; j++)
+				free(keys[j]);
+			return r;
+		}
+	}
+	for (mode = 0; mode < MODE_MAX; mode++) {
+		ctos = (!kex->server && mode == MODE_OUT) ||
+		    (kex->server && mode == MODE_IN);
+		kex->newkeys[mode]->enc.iv  = keys[ctos ? 0 : 1];
+		kex->newkeys[mode]->enc.key = keys[ctos ? 2 : 3];
+		kex->newkeys[mode]->mac.key = keys[ctos ? 4 : 5];
+	}
+	return 0;
+}
+
+int
+kex_load_hostkey(struct ssh *ssh, struct sshkey **prvp, struct sshkey **pubp)
+{
+	struct kex *kex = ssh->kex;
+
+	*pubp = NULL;
+	*prvp = NULL;
+	if (kex->load_host_public_key == NULL ||
+	    kex->load_host_private_key == NULL) {
+		error_f("missing hostkey loader");
+		return SSH_ERR_INVALID_ARGUMENT;
+	}
+	*pubp = kex->load_host_public_key(kex->hostkey_type,
+	    kex->hostkey_nid, ssh);
+	*prvp = kex->load_host_private_key(kex->hostkey_type,
+	    kex->hostkey_nid, ssh);
+	if (*pubp == NULL)
+		return SSH_ERR_NO_HOSTKEY_LOADED;
+	return 0;
+}
+
+int
+kex_verify_host_key(struct ssh *ssh, struct sshkey *server_host_key)
+{
+	struct kex *kex = ssh->kex;
+
+	if (kex->verify_host_key == NULL) {
+		error_f("missing hostkey verifier");
+		return SSH_ERR_INVALID_ARGUMENT;
+	}
+	if (server_host_key->type != kex->hostkey_type ||
+	    (kex->hostkey_type == KEY_ECDSA &&
+	    server_host_key->ecdsa_nid != kex->hostkey_nid))
+		return SSH_ERR_KEY_TYPE_MISMATCH;
+	if (kex->verify_host_key(server_host_key, ssh) == -1)
+		return  SSH_ERR_SIGNATURE_INVALID;
+	return 0;
+}
+
+#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
+void
+dump_digest(const char *msg, const u_char *digest, int len)
+{
+	fprintf(stderr, "%s\n", msg);
+	sshbuf_dump_data(digest, len, stderr);
+}
+#endif
+
+/*
+ * Send a plaintext error message to the peer, suffixed by \r\n.
+ * Only used during banner exchange, and there only for the server.
+ */
+static void
+send_error(struct ssh *ssh, char *msg)
+{
+	char *crnl = "\r\n";
+
+	if (!ssh->kex->server)
+		return;
+
+	if (atomicio(vwrite, ssh_packet_get_connection_out(ssh),
+	    msg, strlen(msg)) != strlen(msg) ||
+	    atomicio(vwrite, ssh_packet_get_connection_out(ssh),
+	    crnl, strlen(crnl)) != strlen(crnl))
+		error_f("write: %.100s", strerror(errno));
+}
+
+/*
+ * Sends our identification string and waits for the peer's. Will block for
+ * up to timeout_ms (or indefinitely if timeout_ms <= 0).
+ * Returns on 0 success or a ssherr.h code on failure.
+ */
+int
+kex_exchange_identification(struct ssh *ssh, int timeout_ms,
+    const char *version_addendum)
+{
+	int remote_major, remote_minor, mismatch, oerrno = 0;
+	size_t len, n;
+	int r, expect_nl;
+	u_char c;
+	struct sshbuf *our_version = ssh->kex->server ?
+	    ssh->kex->server_version : ssh->kex->client_version;
+	struct sshbuf *peer_version = ssh->kex->server ?
+	    ssh->kex->client_version : ssh->kex->server_version;
+	char *our_version_string = NULL, *peer_version_string = NULL;
+	char *cp, *remote_version = NULL;
+
+	/* Prepare and send our banner */
+	sshbuf_reset(our_version);
+	if (version_addendum != NULL && *version_addendum == '\0')
+		version_addendum = NULL;
+	if ((r = sshbuf_putf(our_version, "SSH-%d.%d-%.100s%s%s\r\n",
+	    PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_VERSION,
+	    version_addendum == NULL ? "" : " ",
+	    version_addendum == NULL ? "" : version_addendum)) != 0) {
+		oerrno = errno;
+		error_fr(r, "sshbuf_putf");
+		goto out;
+	}
+
+	if (atomicio(vwrite, ssh_packet_get_connection_out(ssh),
+	    sshbuf_mutable_ptr(our_version),
+	    sshbuf_len(our_version)) != sshbuf_len(our_version)) {
+		oerrno = errno;
+		debug_f("write: %.100s", strerror(errno));
+		r = SSH_ERR_SYSTEM_ERROR;
+		goto out;
+	}
+	if ((r = sshbuf_consume_end(our_version, 2)) != 0) { /* trim \r\n */
+		oerrno = errno;
+		error_fr(r, "sshbuf_consume_end");
+		goto out;
+	}
+	our_version_string = sshbuf_dup_string(our_version);
+	if (our_version_string == NULL) {
+		error_f("sshbuf_dup_string failed");
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+	debug("Local version string %.100s", our_version_string);
+
+	/* Read other side's version identification. */
+	for (n = 0; ; n++) {
+		if (n >= SSH_MAX_PRE_BANNER_LINES) {
+			send_error(ssh, "No SSH identification string "
+			    "received.");
+			error_f("No SSH version received in first %u lines "
+			    "from server", SSH_MAX_PRE_BANNER_LINES);
+			r = SSH_ERR_INVALID_FORMAT;
+			goto out;
+		}
+		sshbuf_reset(peer_version);
+		expect_nl = 0;
+		for (;;) {
+			if (timeout_ms > 0) {
+				r = waitrfd(ssh_packet_get_connection_in(ssh),
+				    &timeout_ms);
+				if (r == -1 && errno == ETIMEDOUT) {
+					send_error(ssh, "Timed out waiting "
+					    "for SSH identification string.");
+					error("Connection timed out during "
+					    "banner exchange");
+					r = SSH_ERR_CONN_TIMEOUT;
+					goto out;
+				} else if (r == -1) {
+					oerrno = errno;
+					error_f("%s", strerror(errno));
+					r = SSH_ERR_SYSTEM_ERROR;
+					goto out;
+				}
+			}
+
+			len = atomicio(read, ssh_packet_get_connection_in(ssh),
+			    &c, 1);
+			if (len != 1 && errno == EPIPE) {
+				error_f("Connection closed by remote host");
+				r = SSH_ERR_CONN_CLOSED;
+				goto out;
+			} else if (len != 1) {
+				oerrno = errno;
+				error_f("read: %.100s", strerror(errno));
+				r = SSH_ERR_SYSTEM_ERROR;
+				goto out;
+			}
+			if (c == '\r') {
+				expect_nl = 1;
+				continue;
+			}
+			if (c == '\n')
+				break;
+			if (c == '\0' || expect_nl) {
+				error_f("banner line contains invalid "
+				    "characters");
+				goto invalid;
+			}
+			if ((r = sshbuf_put_u8(peer_version, c)) != 0) {
+				oerrno = errno;
+				error_fr(r, "sshbuf_put");
+				goto out;
+			}
+			if (sshbuf_len(peer_version) > SSH_MAX_BANNER_LEN) {
+				error_f("banner line too long");
+				goto invalid;
+			}
+		}
+		/* Is this an actual protocol banner? */
+		if (sshbuf_len(peer_version) > 4 &&
+		    memcmp(sshbuf_ptr(peer_version), "SSH-", 4) == 0)
+			break;
+		/* If not, then just log the line and continue */
+		if ((cp = sshbuf_dup_string(peer_version)) == NULL) {
+			error_f("sshbuf_dup_string failed");
+			r = SSH_ERR_ALLOC_FAIL;
+			goto out;
+		}
+		/* Do not accept lines before the SSH ident from a client */
+		if (ssh->kex->server) {
+			error_f("client sent invalid protocol identifier "
+			    "\"%.256s\"", cp);
+			free(cp);
+			goto invalid;
+		}
+		debug_f("banner line %zu: %s", n, cp);
+		free(cp);
+	}
+	peer_version_string = sshbuf_dup_string(peer_version);
+	if (peer_version_string == NULL)
+		error_f("sshbuf_dup_string failed");
+	/* XXX must be same size for sscanf */
+	if ((remote_version = calloc(1, sshbuf_len(peer_version))) == NULL) {
+		error_f("calloc failed");
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+
+	/*
+	 * Check that the versions match.  In future this might accept
+	 * several versions and set appropriate flags to handle them.
+	 */
+	if (sscanf(peer_version_string, "SSH-%d.%d-%[^\n]\n",
+	    &remote_major, &remote_minor, remote_version) != 3) {
+		error("Bad remote protocol version identification: '%.100s'",
+		    peer_version_string);
+ invalid:
+		send_error(ssh, "Invalid SSH identification string.");
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	debug("Remote protocol version %d.%d, remote software version %.100s",
+	    remote_major, remote_minor, remote_version);
+	compat_banner(ssh, remote_version);
+
+	mismatch = 0;
+	switch (remote_major) {
+	case 2:
+		break;
+	case 1:
+		if (remote_minor != 99)
+			mismatch = 1;
+		break;
+	default:
+		mismatch = 1;
+		break;
+	}
+	if (mismatch) {
+		error("Protocol major versions differ: %d vs. %d",
+		    PROTOCOL_MAJOR_2, remote_major);
+		send_error(ssh, "Protocol major versions differ.");
+		r = SSH_ERR_NO_PROTOCOL_VERSION;
+		goto out;
+	}
+
+	if (ssh->kex->server && (ssh->compat & SSH_BUG_PROBE) != 0) {
+		logit("probed from %s port %d with %s.  Don't panic.",
+		    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
+		    peer_version_string);
+		r = SSH_ERR_CONN_CLOSED; /* XXX */
+		goto out;
+	}
+	if (ssh->kex->server && (ssh->compat & SSH_BUG_SCANNER) != 0) {
+		logit("scanned from %s port %d with %s.  Don't panic.",
+		    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
+		    peer_version_string);
+		r = SSH_ERR_CONN_CLOSED; /* XXX */
+		goto out;
+	}
+	if ((ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
+		logit("Remote version \"%.100s\" uses unsafe RSA signature "
+		    "scheme; disabling use of RSA keys", remote_version);
+	}
+	/* success */
+	r = 0;
+ out:
+	free(our_version_string);
+	free(peer_version_string);
+	free(remote_version);
+	if (r == SSH_ERR_SYSTEM_ERROR)
+		errno = oerrno;
+	return r;
+}
+