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/* $OpenBSD: ssh-keysign.c,v 1.39 2013/12/06 13:39:49 markus Exp $ */
/*
* Copyright (c) 2002 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 <sys/types.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/rsa.h>
#include <fcntl.h>
#include <paths.h>
#include <pwd.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "xmalloc.h"
#include "log.h"
#include "key.h"
#include "ssh.h"
#include "ssh2.h"
#include "misc.h"
#include "buffer.h"
#include "authfile.h"
#include "msg.h"
#include "canohost.h"
#include "pathnames.h"
#include "readconf.h"
#include "uidswap.h"
/* XXX readconf.c needs these */
uid_t original_real_uid;
static int
valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
u_int datalen)
{
Buffer b;
Key *key = NULL;
u_char *pkblob;
u_int blen, len;
char *pkalg, *p;
int pktype, fail;
fail = 0;
buffer_init(&b);
buffer_append(&b, data, datalen);
/* session id, currently limited to SHA1 (20 bytes) or SHA256 (32) */
p = buffer_get_string(&b, &len);
if (len != 20 && len != 32)
fail++;
free(p);
if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
fail++;
/* server user */
buffer_skip_string(&b);
/* service */
p = buffer_get_string(&b, NULL);
if (strcmp("ssh-connection", p) != 0)
fail++;
free(p);
/* method */
p = buffer_get_string(&b, NULL);
if (strcmp("hostbased", p) != 0)
fail++;
free(p);
/* pubkey */
pkalg = buffer_get_string(&b, NULL);
pkblob = buffer_get_string(&b, &blen);
pktype = key_type_from_name(pkalg);
if (pktype == KEY_UNSPEC)
fail++;
else if ((key = key_from_blob(pkblob, blen)) == NULL)
fail++;
else if (key->type != pktype)
fail++;
free(pkalg);
free(pkblob);
/* client host name, handle trailing dot */
p = buffer_get_string(&b, &len);
debug2("valid_request: check expect chost %s got %s", host, p);
if (strlen(host) != len - 1)
fail++;
else if (p[len - 1] != '.')
fail++;
else if (strncasecmp(host, p, len - 1) != 0)
fail++;
free(p);
/* local user */
p = buffer_get_string(&b, NULL);
if (strcmp(pw->pw_name, p) != 0)
fail++;
free(p);
/* end of message */
if (buffer_len(&b) != 0)
fail++;
buffer_free(&b);
debug3("valid_request: fail %d", fail);
if (fail && key != NULL)
key_free(key);
else
*ret = key;
return (fail ? -1 : 0);
}
int
main(int argc, char **argv)
{
Buffer b;
Options options;
#define NUM_KEYTYPES 4
Key *keys[NUM_KEYTYPES], *key = NULL;
struct passwd *pw;
int key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
u_char *signature, *data;
char *host;
u_int slen, dlen;
u_int32_t rnd[256];
/* Ensure that stdin and stdout are connected */
if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2)
exit(1);
/* Leave /dev/null fd iff it is attached to stderr */
if (fd > 2)
close(fd);
i = 0;
key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY);
key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY);
key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
original_real_uid = getuid(); /* XXX readconf.c needs this */
if ((pw = getpwuid(original_real_uid)) == NULL)
fatal("getpwuid failed");
pw = pwcopy(pw);
permanently_set_uid(pw);
#ifdef DEBUG_SSH_KEYSIGN
log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
#endif
/* verify that ssh-keysign is enabled by the admin */
initialize_options(&options);
(void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", &options, 0);
fill_default_options(&options);
if (options.enable_ssh_keysign != 1)
fatal("ssh-keysign not enabled in %s",
_PATH_HOST_CONFIG_FILE);
for (i = found = 0; i < NUM_KEYTYPES; i++) {
if (key_fd[i] != -1)
found = 1;
}
if (found == 0)
fatal("could not open any host key");
OpenSSL_add_all_algorithms();
for (i = 0; i < 256; i++)
rnd[i] = arc4random();
RAND_seed(rnd, sizeof(rnd));
found = 0;
for (i = 0; i < NUM_KEYTYPES; i++) {
keys[i] = NULL;
if (key_fd[i] == -1)
continue;
keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC,
NULL, NULL);
close(key_fd[i]);
if (keys[i] != NULL)
found = 1;
}
if (!found)
fatal("no hostkey found");
buffer_init(&b);
if (ssh_msg_recv(STDIN_FILENO, &b) < 0)
fatal("ssh_msg_recv failed");
if (buffer_get_char(&b) != version)
fatal("bad version");
fd = buffer_get_int(&b);
if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO))
fatal("bad fd");
if ((host = get_local_name(fd)) == NULL)
fatal("cannot get local name for fd");
data = buffer_get_string(&b, &dlen);
if (valid_request(pw, host, &key, data, dlen) < 0)
fatal("not a valid request");
free(host);
found = 0;
for (i = 0; i < NUM_KEYTYPES; i++) {
if (keys[i] != NULL &&
key_equal_public(key, keys[i])) {
found = 1;
break;
}
}
if (!found)
fatal("no matching hostkey found");
if (key_sign(keys[i], &signature, &slen, data, dlen) != 0)
fatal("key_sign failed");
free(data);
/* send reply */
buffer_clear(&b);
buffer_put_string(&b, signature, slen);
if (ssh_msg_send(STDOUT_FILENO, version, &b) == -1)
fatal("ssh_msg_send failed");
return (0);
}
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