Add a ssh_config HostbasedKeyType option to control which

host public key types are tried during hostbased authentication.

This may be used to prevent too many keys being sent to the server,
and blowing past its MaxAuthTries limit.

bz#2211 based on patch by Iain Morgan; ok markus@

1 files changed, 198 insertions, 108 deletions

diff --git a/usr.bin/ssh/sshconnect2.c b/usr.bin/ssh/sshconnect2.c
index 12515fdf986..9af29559d9a 100644
--- a/usr.bin/ssh/sshconnect2.c
+++ b/usr.bin/ssh/sshconnect2.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect2.c,v 1.222 2015/01/28 22:36:00 djm Exp $ */
+/* $OpenBSD: sshconnect2.c,v 1.223 2015/01/30 11:43:14 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Damien Miller.  All rights reserved.
@@ -267,6 +267,8 @@ struct cauthctxt {
 	int agent_fd;
 	/* hostbased */
 	Sensitive *sensitive;
+	char *oktypes, *ktypes;
+	const char *active_ktype;
 	/* kbd-interactive */
 	int info_req_seen;
 	/* generic */
@@ -395,6 +397,7 @@ ssh_userauth2(const char *local_user, const char *server_user, char *host,
 	authctxt.authlist = NULL;
 	authctxt.methoddata = NULL;
 	authctxt.sensitive = sensitive;
+	authctxt.active_ktype = authctxt.oktypes = authctxt.ktypes = NULL;
 	authctxt.info_req_seen = 0;
 	authctxt.agent_fd = -1;
 	if (authctxt.method == NULL)
@@ -1446,78 +1449,116 @@ input_userauth_info_req(int type, u_int32_t seq, void *ctxt)
 }
 
 static int
-ssh_keysign(Key *key, u_char **sigp, u_int *lenp,
-    u_char *data, u_int datalen)
+ssh_keysign(struct sshkey *key, u_char **sigp, size_t *lenp,
+    const u_char *data, size_t datalen)
 {
-	Buffer b;
+	struct sshbuf *b;
 	struct stat st;
 	pid_t pid;
-	int to[2], from[2], status, version = 2;
+	int i, r, to[2], from[2], status, sock = packet_get_connection_in();
+	u_char rversion = 0, version = 2;
+	void (*osigchld)(int);
 
-	debug2("ssh_keysign called");
+	*sigp = NULL;
+	*lenp = 0;
 
 	if (stat(_PATH_SSH_KEY_SIGN, &st) < 0) {
-		error("ssh_keysign: not installed: %s", strerror(errno));
+		error("%s: not installed: %s", __func__, strerror(errno));
+		return -1;
+	}
+	if (fflush(stdout) != 0) {
+		error("%s: fflush: %s", __func__, strerror(errno));
 		return -1;
 	}
-	if (fflush(stdout) != 0)
-		error("ssh_keysign: fflush: %s", strerror(errno));
 	if (pipe(to) < 0) {
-		error("ssh_keysign: pipe: %s", strerror(errno));
+		error("%s: pipe: %s", __func__, strerror(errno));
 		return -1;
 	}
 	if (pipe(from) < 0) {
-		error("ssh_keysign: pipe: %s", strerror(errno));
+		error("%s: pipe: %s", __func__, strerror(errno));
 		return -1;
 	}
 	if ((pid = fork()) < 0) {
-		error("ssh_keysign: fork: %s", strerror(errno));
+		error("%s: fork: %s", __func__, strerror(errno));
 		return -1;
 	}
+	osigchld = signal(SIGCHLD, SIG_DFL);
 	if (pid == 0) {
 		/* keep the socket on exec */
-		fcntl(packet_get_connection_in(), F_SETFD, 0);
+		fcntl(sock, F_SETFD, 0);
 		permanently_drop_suid(getuid());
 		close(from[0]);
 		if (dup2(from[1], STDOUT_FILENO) < 0)
-			fatal("ssh_keysign: dup2: %s", strerror(errno));
+			fatal("%s: dup2: %s", __func__, strerror(errno));
 		close(to[1]);
 		if (dup2(to[0], STDIN_FILENO) < 0)
-			fatal("ssh_keysign: dup2: %s", strerror(errno));
+			fatal("%s: dup2: %s", __func__, strerror(errno));
 		close(from[1]);
 		close(to[0]);
+		/* Close everything but stdio and the socket */
+		for (i = STDERR_FILENO + 1; i < sock; i++)
+			close(i);
+		closefrom(sock + 1);
+		debug3("%s: [child] pid=%ld, exec %s",
+		    __func__, (long)getpid(), _PATH_SSH_KEY_SIGN);
 		execl(_PATH_SSH_KEY_SIGN, _PATH_SSH_KEY_SIGN, (char *) 0);
-		fatal("ssh_keysign: exec(%s): %s", _PATH_SSH_KEY_SIGN,
+		fatal("%s: exec(%s): %s", __func__, _PATH_SSH_KEY_SIGN,
 		    strerror(errno));
 	}
 	close(from[1]);
 	close(to[0]);
 
-	buffer_init(&b);
-	buffer_put_int(&b, packet_get_connection_in()); /* send # of socket */
-	buffer_put_string(&b, data, datalen);
-	if (ssh_msg_send(to[1], version, &b) == -1)
-		fatal("ssh_keysign: couldn't send request");
-
-	if (ssh_msg_recv(from[0], &b) < 0) {
-		error("ssh_keysign: no reply");
-		buffer_free(&b);
-		return -1;
-	}
+	if ((b = sshbuf_new()) == NULL)
+		fatal("%s: sshbuf_new failed", __func__);
+	/* send # of sock, data to be signed */
+	if ((r = sshbuf_put_u32(b, sock) != 0) ||
+	    (r = sshbuf_put_string(b, data, datalen)) != 0)
+		fatal("%s: buffer error: %s", __func__, ssh_err(r));
+	if (ssh_msg_send(to[1], version, b) == -1)
+		fatal("%s: couldn't send request", __func__);
+	sshbuf_reset(b);
+	r = ssh_msg_recv(from[0], b);
 	close(from[0]);
 	close(to[1]);
+	if (r < 0) {
+		error("%s: no reply", __func__);
+		goto fail;
+	}
 
-	while (waitpid(pid, &status, 0) < 0)
-		if (errno != EINTR)
-			break;
-
-	if (buffer_get_char(&b) != version) {
-		error("ssh_keysign: bad version");
-		buffer_free(&b);
+	errno = 0;
+	while (waitpid(pid, &status, 0) < 0) {
+		if (errno != EINTR) {
+			error("%s: waitpid %ld: %s",
+			    __func__, (long)pid, strerror(errno));
+			goto fail;
+		}
+	}
+	if (!WIFEXITED(status)) {
+		error("%s: exited abnormally", __func__);
+		goto fail;
+	}
+	if (WEXITSTATUS(status) != 0) {
+		error("%s: exited with status %d",
+		    __func__, WEXITSTATUS(status));
+		goto fail;
+	}
+	if ((r = sshbuf_get_u8(b, &rversion)) != 0) {
+		error("%s: buffer error: %s", __func__, ssh_err(r));
+		goto fail;
+	}
+	if (rversion != version) {
+		error("%s: bad version", __func__);
+		goto fail;
+	}
+	if ((r = sshbuf_get_string(b, sigp, lenp)) != 0) {
+		error("%s: buffer error: %s", __func__, ssh_err(r));
+ fail:
+		signal(SIGCHLD, osigchld);
+		sshbuf_free(b);
 		return -1;
 	}
-	*sigp = buffer_get_string(&b, lenp);
-	buffer_free(&b);
+	signal(SIGCHLD, osigchld);
+	sshbuf_free(b);
 
 	return 0;
 }
@@ -1525,100 +1566,149 @@ ssh_keysign(Key *key, u_char **sigp, u_int *lenp,
 int
 userauth_hostbased(Authctxt *authctxt)
 {
-	Key *private = NULL;
-	Sensitive *sensitive = authctxt->sensitive;
-	Buffer b;
-	u_char *signature, *blob;
-	char *chost, *pkalg, *p;
+	struct ssh *ssh = active_state;
+	struct sshkey *private = NULL;
+	struct sshbuf *b = NULL;
 	const char *service;
-	u_int blen, slen;
-	int ok, i, found = 0;
-
-	/* XXX provide some way to allow user to specify key types attempted */
+	u_char *sig = NULL, *keyblob = NULL;
+	char *fp = NULL, *chost = NULL, *lname = NULL;
+	size_t siglen = 0, keylen = 0;
+	int i, r, success = 0;
+
+	if (authctxt->ktypes == NULL) {
+		authctxt->oktypes = xstrdup(options.hostbased_key_types);
+		authctxt->ktypes = authctxt->oktypes;
+	}
 
-	/* check for a useful key */
-	for (i = 0; i < sensitive->nkeys; i++) {
-		private = sensitive->keys[i];
-		if (private && private->type != KEY_RSA1) {
-			found = 1;
+	/*
+	 * Work through each listed type pattern in HostbasedKeyTypes,
+	 * trying each hostkey that matches the type in turn.
+	 */
+	for (;;) {
+		if (authctxt->active_ktype == NULL)
+			authctxt->active_ktype = strsep(&authctxt->ktypes, ",");
+		if (authctxt->active_ktype == NULL ||
+		    *authctxt->active_ktype == '\0')
+			break;
+		debug3("%s: trying key type %s", __func__,
+		    authctxt->active_ktype);
+
+		/* check for a useful key */
+		private = NULL;
+		for (i = 0; i < authctxt->sensitive->nkeys; i++) {
+			if (authctxt->sensitive->keys[i] == NULL ||
+			    authctxt->sensitive->keys[i]->type == KEY_RSA1 ||
+			    authctxt->sensitive->keys[i]->type == KEY_UNSPEC)
+				continue;
+			if (match_pattern_list(
+			    sshkey_ssh_name(authctxt->sensitive->keys[i]),
+			    authctxt->active_ktype,
+			    strlen(authctxt->active_ktype), 0) != 1)
+				continue;
 			/* we take and free the key */
-			sensitive->keys[i] = NULL;
+			private = authctxt->sensitive->keys[i];
+			authctxt->sensitive->keys[i] = NULL;
 			break;
 		}
+		/* Found one */
+		if (private != NULL)
+			break;
+		/* No more keys of this type; advance */
+		authctxt->active_ktype = NULL;
 	}
-	if (!found) {
+	if (private == NULL) {
+		free(authctxt->oktypes);
+		authctxt->oktypes = authctxt->ktypes = NULL;
+		authctxt->active_ktype = NULL;
 		debug("No more client hostkeys for hostbased authentication.");
-		return 0;
+		goto out;
 	}
 
-	debug("%s: trying hostkey type %s", __func__, key_type(private));
-
-	if (key_to_blob(private, &blob, &blen) == 0) {
-		key_free(private);
-		return 0;
+	if ((fp = sshkey_fingerprint(private, options.fingerprint_hash,
+	    SSH_FP_DEFAULT)) == NULL) {
+		error("%s: sshkey_fingerprint failed", __func__);
+		goto out;
 	}
+	debug("%s: trying hostkey %s %s",
+	    __func__, sshkey_ssh_name(private), fp);
 
 	/* figure out a name for the client host */
-	p = get_local_name(packet_get_connection_in());
-	if (p == NULL) {
-		error("userauth_hostbased: cannot get local ipaddr/name");
-		key_free(private);
-		free(blob);
-		return 0;
+	if ((lname = get_local_name(packet_get_connection_in())) == NULL) {
+		error("%s: cannot get local ipaddr/name", __func__);
+		goto out;
 	}
-	xasprintf(&chost, "%s.", p);
-	debug2("userauth_hostbased: chost %s", chost);
-	free(p);
+
+	/* XXX sshbuf_put_stringf? */
+	xasprintf(&chost, "%s.", lname);
+	debug2("%s: chost %s", __func__, chost);
 
 	service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
 	    authctxt->service;
-	pkalg = xstrdup(key_ssh_name(private));
-	buffer_init(&b);
+
 	/* construct data */
-	buffer_put_string(&b, session_id2, session_id2_len);
-	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
-	buffer_put_cstring(&b, authctxt->server_user);
-	buffer_put_cstring(&b, service);
-	buffer_put_cstring(&b, authctxt->method->name);
-	buffer_put_cstring(&b, pkalg);
-	buffer_put_string(&b, blob, blen);
-	buffer_put_cstring(&b, chost);
-	buffer_put_cstring(&b, authctxt->local_user);
+	if ((b = sshbuf_new()) == NULL) {
+		error("%s: sshbuf_new failed", __func__);
+		goto out;
+	}
+	if ((r = sshkey_to_blob(private, &keyblob, &keylen)) != 0) {
+		error("%s: sshkey_to_blob: %s", __func__, ssh_err(r));
+		goto out;
+	}
+	if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 0 ||
+	    (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
+	    (r = sshbuf_put_cstring(b, authctxt->server_user)) != 0 ||
+	    (r = sshbuf_put_cstring(b, service)) != 0 ||
+	    (r = sshbuf_put_cstring(b, authctxt->method->name)) != 0 ||
+	    (r = sshbuf_put_cstring(b, key_ssh_name(private))) != 0 ||
+	    (r = sshbuf_put_string(b, keyblob, keylen)) != 0 ||
+	    (r = sshbuf_put_cstring(b, chost)) != 0 ||
+	    (r = sshbuf_put_cstring(b, authctxt->local_user)) != 0) {
+		error("%s: buffer error: %s", __func__, ssh_err(r));
+		goto out;
+	}
+
 #ifdef DEBUG_PK
-	buffer_dump(&b);
+	sshbuf_dump(b, stderr);
 #endif
-	if (sensitive->external_keysign)
-		ok = ssh_keysign(private, &signature, &slen,
-		    buffer_ptr(&b), buffer_len(&b));
-	else
-		ok = key_sign(private, &signature, &slen,
-		    buffer_ptr(&b), buffer_len(&b));
-	key_free(private);
-	buffer_free(&b);
-	if (ok != 0) {
-		error("key_sign failed");
-		free(chost);
-		free(pkalg);
-		free(blob);
-		return 0;
+	if (authctxt->sensitive->external_keysign)
+		r = ssh_keysign(private, &sig, &siglen,
+		    sshbuf_ptr(b), sshbuf_len(b));
+	else if ((r = sshkey_sign(private, &sig, &siglen,
+	    sshbuf_ptr(b), sshbuf_len(b), datafellows)) != 0)
+		debug("%s: sshkey_sign: %s", __func__, ssh_err(r));
+	if (r != 0) {
+		error("sign using hostkey %s %s failed",
+		    sshkey_ssh_name(private), fp);
+		goto out;
 	}
-	packet_start(SSH2_MSG_USERAUTH_REQUEST);
-	packet_put_cstring(authctxt->server_user);
-	packet_put_cstring(authctxt->service);
-	packet_put_cstring(authctxt->method->name);
-	packet_put_cstring(pkalg);
-	packet_put_string(blob, blen);
-	packet_put_cstring(chost);
-	packet_put_cstring(authctxt->local_user);
-	packet_put_string(signature, slen);
-	explicit_bzero(signature, slen);
-	free(signature);
+	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
+	    (r = sshpkt_put_cstring(ssh, authctxt->server_user)) != 0 ||
+	    (r = sshpkt_put_cstring(ssh, authctxt->service)) != 0 ||
+	    (r = sshpkt_put_cstring(ssh, authctxt->method->name)) != 0 ||
+	    (r = sshpkt_put_cstring(ssh, key_ssh_name(private))) != 0 ||
+	    (r = sshpkt_put_string(ssh, keyblob, keylen)) != 0 ||
+	    (r = sshpkt_put_cstring(ssh, chost)) != 0 ||
+	    (r = sshpkt_put_cstring(ssh, authctxt->local_user)) != 0 ||
+	    (r = sshpkt_put_string(ssh, sig, siglen)) != 0 ||
+	    (r = sshpkt_send(ssh)) != 0) {
+		error("%s: packet error: %s", __func__, ssh_err(r));
+		goto out;
+	}
+	success = 1;
+
+ out:
+	if (sig != NULL) {
+		explicit_bzero(sig, siglen);
+		free(sig);
+	}
+	free(keyblob);
+	free(lname);
+	free(fp);
 	free(chost);
-	free(pkalg);
-	free(blob);
+	sshkey_free(private);
+	sshbuf_free(b);
 
-	packet_send();
-	return 1;
+	return success;
 }
 
 /* find auth method */