1 files changed, 306 insertions, 0 deletions
diff --git a/ssh-keysign.c b/ssh-keysign.c
new file mode 100644
index 0000000..b989f5e
--- /dev/null
+++ b/ssh-keysign.c
@@ -0,0 +1,306 @@
+/* $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);
+}