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openssh-portable
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openssh-portable/kex.c

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/* $OpenBSD: kex.c,v 1.186 2024/05/17 00:30:23 djm 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 "myproposal.h"
#include "ssherr.h"
#include "sshbuf.h"
#include "digest.h"
#include "xmalloc.h"
/* prototype */
static int kex_choose_conf(struct ssh *, uint32_t seq);
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",
};
/*
* Fill out a proposal array with dynamically allocated values, which may
* be modified as required for compatibility reasons.
* Any of the options may be NULL, in which case the default is used.
* Array contents must be freed by calling kex_proposal_free_entries.
*/
void
kex_proposal_populate_entries(struct ssh *ssh, char *prop[PROPOSAL_MAX],
const char *kexalgos, const char *ciphers, const char *macs,
const char *comp, const char *hkalgs)
{
const char *defpropserver[PROPOSAL_MAX] = { KEX_SERVER };
const char *defpropclient[PROPOSAL_MAX] = { KEX_CLIENT };
const char **defprop = ssh->kex->server ? defpropserver : defpropclient;
u_int i;
char *cp;
if (prop == NULL)
fatal_f("proposal missing");
/* Append EXT_INFO signalling to KexAlgorithms */
if (kexalgos == NULL)
kexalgos = defprop[PROPOSAL_KEX_ALGS];
if ((cp = kex_names_cat(kexalgos, ssh->kex->server ?
"ext-info-s,kex-strict-s-v00@openssh.com" :
"ext-info-c,kex-strict-c-v00@openssh.com")) == NULL)
fatal_f("kex_names_cat");
for (i = 0; i < PROPOSAL_MAX; i++) {
switch(i) {
case PROPOSAL_KEX_ALGS:
prop[i] = compat_kex_proposal(ssh, cp);
break;
case PROPOSAL_ENC_ALGS_CTOS:
case PROPOSAL_ENC_ALGS_STOC:
prop[i] = xstrdup(ciphers ? ciphers : defprop[i]);
break;
case PROPOSAL_MAC_ALGS_CTOS:
case PROPOSAL_MAC_ALGS_STOC:
prop[i] = xstrdup(macs ? macs : defprop[i]);
break;
case PROPOSAL_COMP_ALGS_CTOS:
case PROPOSAL_COMP_ALGS_STOC:
prop[i] = xstrdup(comp ? comp : defprop[i]);
break;
case PROPOSAL_SERVER_HOST_KEY_ALGS:
prop[i] = xstrdup(hkalgs ? hkalgs : defprop[i]);
break;
default:
prop[i] = xstrdup(defprop[i]);
}
}
free(cp);
}
void
kex_proposal_free_entries(char *prop[PROPOSAL_MAX])
{
u_int i;
for (i = 0; i < PROPOSAL_MAX; i++)
free(prop[i]);
}
/* 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);
}
int
kex_protocol_error(int type, u_int32_t seq, struct ssh *ssh)
{
int r;
/* If in strict mode, any unexpected message is an error */
if ((ssh->kex->flags & KEX_INITIAL) && ssh->kex->kex_strict) {
ssh_packet_disconnect(ssh, "strict KEX violation: "
"unexpected packet type %u (seqnr %u)", type, seq);
}
error_f("type %u 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);
}
void
kex_set_server_sig_algs(struct ssh *ssh, const char *allowed_algs)
{
char *alg, *oalgs, *algs, *sigalgs;
const char *sigalg;
/*
* NB. allowed algorithms may contain certificate algorithms that
* map to a specific plain signature type, e.g.
* rsa-sha2-512-cert-v01@openssh.com => rsa-sha2-512
* We need to be careful here to match these, retain the mapping
* and only add each signature algorithm once.
*/
if ((sigalgs = sshkey_alg_list(0, 1, 1, ',')) == NULL)
fatal_f("sshkey_alg_list failed");
oalgs = algs = xstrdup(allowed_algs);
free(ssh->kex->server_sig_algs);
ssh->kex->server_sig_algs = NULL;
for ((alg = strsep(&algs, ",")); alg != NULL && *alg != '\0';
(alg = strsep(&algs, ","))) {
if ((sigalg = sshkey_sigalg_by_name(alg)) == NULL)
continue;
if (!kex_has_any_alg(sigalg, sigalgs))
continue;
/* Don't add an algorithm twice. */
if (ssh->kex->server_sig_algs != NULL &&
kex_has_any_alg(sigalg, ssh->kex->server_sig_algs))
continue;
xextendf(&ssh->kex->server_sig_algs, ",", "%s", sigalg);
}
free(oalgs);
free(sigalgs);
if (ssh->kex->server_sig_algs == NULL)
ssh->kex->server_sig_algs = xstrdup("");
}
static int
kex_compose_ext_info_server(struct ssh *ssh, struct sshbuf *m)
{
int r;
if (ssh->kex->server_sig_algs == NULL &&
(ssh->kex->server_sig_algs = sshkey_alg_list(0, 1, 1, ',')) == NULL)
return SSH_ERR_ALLOC_FAIL;
if ((r = sshbuf_put_u32(m, 3)) != 0 ||
(r = sshbuf_put_cstring(m, "server-sig-algs")) != 0 ||
(r = sshbuf_put_cstring(m, ssh->kex->server_sig_algs)) != 0 ||
(r = sshbuf_put_cstring(m,
"publickey-hostbound@openssh.com")) != 0 ||
(r = sshbuf_put_cstring(m, "0")) != 0 ||
(r = sshbuf_put_cstring(m, "ping@openssh.com")) != 0 ||
(r = sshbuf_put_cstring(m, "0")) != 0) {
error_fr(r, "compose");
return r;
}
return 0;
}
static int
kex_compose_ext_info_client(struct ssh *ssh, struct sshbuf *m)
{
int r;
if ((r = sshbuf_put_u32(m, 1)) != 0 ||
(r = sshbuf_put_cstring(m, "ext-info-in-auth@openssh.com")) != 0 ||
(r = sshbuf_put_cstring(m, "0")) != 0) {
error_fr(r, "compose");
goto out;
}
/* success */
r = 0;
out:
return r;
}
static int
kex_maybe_send_ext_info(struct ssh *ssh)
{
int r;
struct sshbuf *m = NULL;
if ((ssh->kex->flags & KEX_INITIAL) == 0)
return 0;
if (!ssh->kex->ext_info_c && !ssh->kex->ext_info_s)
return 0;
/* Compose EXT_INFO packet. */
if ((m = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
if (ssh->kex->ext_info_c &&
(r = kex_compose_ext_info_server(ssh, m)) != 0)
goto fail;
if (ssh->kex->ext_info_s &&
(r = kex_compose_ext_info_client(ssh, m)) != 0)
goto fail;
/* Send the actual KEX_INFO packet */
debug("Sending SSH2_MSG_EXT_INFO");
if ((r = sshpkt_start(ssh, SSH2_MSG_EXT_INFO)) != 0 ||
(r = sshpkt_putb(ssh, m)) != 0 ||
(r = sshpkt_send(ssh)) != 0) {
error_f("send EXT_INFO");
goto fail;
}
r = 0;
fail:
sshbuf_free(m);
return r;
}
int
kex_server_update_ext_info(struct ssh *ssh)
{
int r;
if ((ssh->kex->flags & KEX_HAS_EXT_INFO_IN_AUTH) == 0)
return 0;
debug_f("Sending SSH2_MSG_EXT_INFO");
if ((r = sshpkt_start(ssh, SSH2_MSG_EXT_INFO)) != 0 ||
(r = sshpkt_put_u32(ssh, 1)) != 0 ||
(r = sshpkt_put_cstring(ssh, "server-sig-algs")) != 0 ||
(r = sshpkt_put_cstring(ssh, ssh->kex->server_sig_algs)) != 0 ||
(r = sshpkt_send(ssh)) != 0) {
error_f("send EXT_INFO");
return r;
}
return 0;
}
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 ((r = kex_maybe_send_ext_info(ssh)) != 0)
return r;
debug("expecting SSH2_MSG_NEWKEYS");
return 0;
}
/* Check whether an ext_info value contains the expected version string */
static int
kex_ext_info_check_ver(struct kex *kex, const char *name,
const u_char *val, size_t len, const char *want_ver, u_int flag)
{
if (memchr(val, '\0', len) != NULL) {
error("SSH2_MSG_EXT_INFO: %s value contains nul byte", name);
return SSH_ERR_INVALID_FORMAT;
}
debug_f("%s=<%s>", name, val);
if (strcmp(val, want_ver) == 0)
kex->flags |= flag;
else
debug_f("unsupported version of %s extension", name);
return 0;
}
static int
kex_ext_info_client_parse(struct ssh *ssh, const char *name,
const u_char *value, size_t vlen)
{
int r;
/* NB. some messages are only accepted in the initial EXT_INFO */
if (strcmp(name, "server-sig-algs") == 0) {
/* Ensure no \0 lurking in value */
if (memchr(value, '\0', vlen) != NULL) {
error_f("nul byte in %s", name);
return SSH_ERR_INVALID_FORMAT;
}
debug_f("%s=<%s>", name, value);
free(ssh->kex->server_sig_algs);
ssh->kex->server_sig_algs = xstrdup((const char *)value);
} else if (ssh->kex->ext_info_received == 1 &&
strcmp(name, "publickey-hostbound@openssh.com") == 0) {
if ((r = kex_ext_info_check_ver(ssh->kex, name, value, vlen,
"0", KEX_HAS_PUBKEY_HOSTBOUND)) != 0) {
return r;
}
} else if (ssh->kex->ext_info_received == 1 &&
strcmp(name, "ping@openssh.com") == 0) {
if ((r = kex_ext_info_check_ver(ssh->kex, name, value, vlen,
"0", KEX_HAS_PING)) != 0) {
return r;
}
} else
debug_f("%s (unrecognised)", name);
return 0;
}
static int
kex_ext_info_server_parse(struct ssh *ssh, const char *name,
const u_char *value, size_t vlen)
{
int r;
if (strcmp(name, "ext-info-in-auth@openssh.com") == 0) {
if ((r = kex_ext_info_check_ver(ssh->kex, name, value, vlen,
"0", KEX_HAS_EXT_INFO_IN_AUTH)) != 0) {
return r;
}
} else
debug_f("%s (unrecognised)", name);
return 0;
}
int
kex_input_ext_info(int type, u_int32_t seq, struct ssh *ssh)
{
struct kex *kex = ssh->kex;
const int max_ext_info = kex->server ? 1 : 2;
u_int32_t i, ninfo;
char *name;
u_char *val;
size_t vlen;
int r;
debug("SSH2_MSG_EXT_INFO received");
if (++kex->ext_info_received > max_ext_info) {
error("too many SSH2_MSG_EXT_INFO messages sent by peer");
return dispatch_protocol_error(type, seq, ssh);
}
ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &kex_protocol_error);
if ((r = sshpkt_get_u32(ssh, &ninfo)) != 0)
return r;
if (ninfo >= 1024) {
error("SSH2_MSG_EXT_INFO with too many entries, expected "
"<=1024, received %u", ninfo);
return dispatch_protocol_error(type, seq, ssh);
}
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;
}
debug3_f("extension %s", name);
if (kex->server) {
if ((r = kex_ext_info_server_parse(ssh, name,
val, vlen)) != 0)
return r;
} else {
if ((r = kex_ext_info_client_parse(ssh, name,
val, vlen)) != 0)
return r;
}
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, initial = (kex->flags & KEX_INITIAL) != 0;
char *cp, **prop;
debug("SSH2_MSG_NEWKEYS received");
if (kex->ext_info_c && initial)
ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &kex_input_ext_info);
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;
if (initial) {
/* Remove initial KEX signalling from proposal for rekeying */
if ((r = kex_buf2prop(kex->my, NULL, &prop)) != 0)
return r;
if ((cp = match_filter_denylist(prop[PROPOSAL_KEX_ALGS],
kex->server ?
"ext-info-s,kex-strict-s-v00@openssh.com" :
"ext-info-c,kex-strict-c-v00@openssh.com")) == NULL) {
error_f("match_filter_denylist failed");
goto fail;
}
free(prop[PROPOSAL_KEX_ALGS]);
prop[PROPOSAL_KEX_ALGS] = cp;
if ((r = kex_prop2buf(ssh->kex->my, prop)) != 0) {
error_f("kex_prop2buf failed");
fail:
kex_proposal_free_entries(prop);
free(prop);
return SSH_ERR_INTERNAL_ERROR;
}
kex_proposal_free_entries(prop);
free(prop);
}
kex->done = 1;
kex->flags &= ~KEX_INITIAL;
sshbuf_reset(kex->peer);
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;
}
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, &kex_protocol_error);
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, seq)) != 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)
{
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 (!kex_name_valid(k->name)) {
error_f("unsupported KEX method %s", k->name);
return SSH_ERR_INTERNAL_ERROR;
}
k->kex_type = kex_type_from_name(k->name);
k->hash_alg = kex_hash_from_name(k->name);
k->ec_nid = kex_nid_from_name(k->name);
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);
}
static int
kexalgs_contains(char **peer, const char *ext)
{
return kex_has_any_alg(peer[PROPOSAL_KEX_ALGS], ext);
}
static int
kex_choose_conf(struct ssh *ssh, uint32_t seq)
{
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 peer supports ext_info/kex_strict */
if ((kex->flags & KEX_INITIAL) != 0) {
if (kex->server) {
kex->ext_info_c = kexalgs_contains(peer, "ext-info-c");
kex->kex_strict = kexalgs_contains(peer,
"kex-strict-c-v00@openssh.com");
} else {
kex->ext_info_s = kexalgs_contains(peer, "ext-info-s");
kex->kex_strict = kexalgs_contains(peer,
"kex-strict-s-v00@openssh.com");
}
if (kex->kex_strict) {
debug3_f("will use strict KEX ordering");
if (seq != 0)
ssh_packet_disconnect(ssh,
"strict KEX violation: "
"KEXINIT was not the first packet");
}
}
/* Check whether client supports rsa-sha2 algorithms */
if (kex->server && (kex->flags & KEX_INITIAL)) {
if (kex_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 (kex_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-%s%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, NULL);
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) {
verbose_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) {
verbose_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) {
verbose_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) {
verbose_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)
fatal_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;
}
/* 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;
}
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