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openssh/ssh-keysign.c

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/* $OpenBSD: ssh-keysign.c,v 1.71 2022/08/01 11:09:26 djm 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 "includes.h"
#include <fcntl.h>
#ifdef HAVE_PATHS_H
#include <paths.h>
#endif
#include <pwd.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#ifdef WITH_OPENSSL
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/rsa.h>
#include "openbsd-compat/openssl-compat.h"
#endif
#include "xmalloc.h"
#include "log.h"
#include "sshkey.h"
#include "ssh.h"
#include "ssh2.h"
#include "misc.h"
#include "sshbuf.h"
#include "authfile.h"
#include "msg.h"
#include "canohost.h"
#include "pathnames.h"
#include "readconf.h"
#include "uidswap.h"
#include "ssherr.h"
extern char *__progname;
static int
valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp,
u_char *data, size_t datalen)
{
struct sshbuf *b;
struct sshkey *key = NULL;
u_char type, *pkblob;
char *p;
size_t blen, len;
char *pkalg, *luser;
int r, pktype, fail;
if (ret != NULL)
*ret = NULL;
if (pkalgp != NULL)
*pkalgp = NULL;
fail = 0;
if ((b = sshbuf_from(data, datalen)) == NULL)
fatal_f("sshbuf_from failed");
/* session id */
if ((r = sshbuf_get_string(b, NULL, &len)) != 0)
fatal_fr(r, "parse session ID");
if (len != 20 && /* SHA1 */
len != 32 && /* SHA256 */
len != 48 && /* SHA384 */
len != 64) /* SHA512 */
fail++;
if ((r = sshbuf_get_u8(b, &type)) != 0)
fatal_fr(r, "parse type");
if (type != SSH2_MSG_USERAUTH_REQUEST)
fail++;
/* server user */
if ((r = sshbuf_skip_string(b)) != 0)
fatal_fr(r, "parse user");
/* service */
if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
fatal_fr(r, "parse service");
if (strcmp("ssh-connection", p) != 0)
fail++;
free(p);
/* method */
if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0)
fatal_fr(r, "parse method");
if (strcmp("hostbased", p) != 0)
fail++;
free(p);
/* pubkey */
if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 ||
(r = sshbuf_get_string(b, &pkblob, &blen)) != 0)
fatal_fr(r, "parse pk");
pktype = sshkey_type_from_name(pkalg);
if (pktype == KEY_UNSPEC)
fail++;
else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
error_fr(r, "decode key");
fail++;
} else if (key->type != pktype)
fail++;
/* client host name, handle trailing dot */
if ((r = sshbuf_get_cstring(b, &p, &len)) != 0)
fatal_fr(r, "parse hostname");
debug2_f("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 */
if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0)
fatal_fr(r, "parse luser");
if (strcmp(pw->pw_name, luser) != 0)
fail++;
free(luser);
/* end of message */
if (sshbuf_len(b) != 0)
fail++;
sshbuf_free(b);
debug3_f("fail %d", fail);
if (!fail) {
if (ret != NULL) {
*ret = key;
key = NULL;
}
if (pkalgp != NULL) {
*pkalgp = pkalg;
pkalg = NULL;
}
}
sshkey_free(key);
free(pkalg);
free(pkblob);
return (fail ? -1 : 0);
}
int
main(int argc, char **argv)
{
struct sshbuf *b;
Options options;
#define NUM_KEYTYPES 5
struct sshkey *keys[NUM_KEYTYPES], *key = NULL;
struct passwd *pw;
int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd;
u_char *signature, *data, rver;
char *host, *fp, *pkalg;
size_t slen, dlen;
if (pledge("stdio rpath getpw dns id", NULL) != 0)
fatal("%s: pledge: %s", __progname, strerror(errno));
/* 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;
/* XXX This really needs to read sshd_config for the paths */
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_XMSS_KEY_FILE, O_RDONLY);
key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
if ((pw = getpwuid(getuid())) == NULL)
fatal("getpwuid failed");
pw = pwcopy(pw);
permanently_set_uid(pw);
seed_rng();
#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, NULL);
(void)fill_default_options(&options);
if (options.enable_ssh_keysign != 1)
fatal("ssh-keysign not enabled in %s",
_PATH_HOST_CONFIG_FILE);
if (pledge("stdio dns", NULL) != 0)
fatal("%s: pledge: %s", __progname, strerror(errno));
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");
found = 0;
for (i = 0; i < NUM_KEYTYPES; i++) {
keys[i] = NULL;
if (key_fd[i] == -1)
continue;
r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC,
NULL, &key, NULL);
close(key_fd[i]);
if (r != 0)
debug_r(r, "parse key %d", i);
else if (key != NULL) {
keys[i] = key;
found = 1;
}
}
if (!found)
fatal("no hostkey found");
if ((b = sshbuf_new()) == NULL)
fatal("%s: sshbuf_new failed", __progname);
if (ssh_msg_recv(STDIN_FILENO, b) < 0)
fatal("%s: ssh_msg_recv failed", __progname);
if ((r = sshbuf_get_u8(b, &rver)) != 0)
fatal_r(r, "%s: buffer error", __progname);
if (rver != version)
fatal("%s: bad version: received %d, expected %d",
__progname, rver, version);
if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0)
fatal_r(r, "%s: buffer error", __progname);
if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO)
fatal("%s: bad fd = %d", __progname, fd);
if ((host = get_local_name(fd)) == NULL)
fatal("%s: cannot get local name for fd", __progname);
if ((r = sshbuf_get_string(b, &data, &dlen)) != 0)
fatal_r(r, "%s: buffer error", __progname);
if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0)
fatal("%s: not a valid request", __progname);
free(host);
found = 0;
for (i = 0; i < NUM_KEYTYPES; i++) {
if (keys[i] != NULL &&
sshkey_equal_public(key, keys[i])) {
found = 1;
break;
}
}
if (!found) {
if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
SSH_FP_DEFAULT)) == NULL)
fatal("%s: sshkey_fingerprint failed", __progname);
fatal("%s: no matching hostkey found for key %s %s", __progname,
sshkey_type(key), fp ? fp : "");
}
if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen,
pkalg, NULL, NULL, 0)) != 0)
fatal_r(r, "%s: sshkey_sign failed", __progname);
free(data);
/* send reply */
sshbuf_reset(b);
if ((r = sshbuf_put_string(b, signature, slen)) != 0)
fatal_r(r, "%s: buffer error", __progname);
if (ssh_msg_send(STDOUT_FILENO, version, b) == -1)
fatal("%s: ssh_msg_send failed", __progname);
return (0);
}
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