knownhosts: detect variations of ecdsa

include/libssh/knownhosts.h

@@ -0,0 +1,27 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 20014 by Aris Adamantiadis <aris@badcode.be>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+
+#ifndef KNOWNHOSTS_H_
+#define KNOWNHOSTS_H_
+
+char **ssh_knownhosts_algorithms(ssh_session session);
+
+#endif /* KNOWNHOSTS_H_ */

include/libssh/libssh.h

@@ -517,7 +517,6 @@ LIBSSH_API int ssh_key_cmp(const ssh_key k1,
                            const ssh_key k2,
                            enum ssh_keycmp_e what);
 
-LIBSSH_API int ssh_knownhosts_algorithms(ssh_session session);
 LIBSSH_API int ssh_pki_generate(enum ssh_keytypes_e type, int parameter,
         ssh_key *pkey);
 LIBSSH_API int ssh_pki_import_privkey_base64(const char *b64_key,

src/kex.c

@@ -35,6 +35,7 @@
 #include "libssh/ssh2.h"
 #include "libssh/string.h"
 #include "libssh/curve25519.h"
+#include "libssh/knownhosts.h"
 
 #ifdef HAVE_LIBGCRYPT
 # define BLOWFISH "blowfish-cbc,"
@@ -373,6 +374,51 @@ void ssh_list_kex(struct ssh_kex_struct *kex) {
   }
 }
 
+/**
+ * @internal
+ * @brief selects the hostkey mechanisms to be chosen for the key exchange,
+ * as some hostkey mechanisms may be present in known_hosts file and preferred
+ * @returns a cstring containing a comma-separated list of hostkey methods.
+ *          NULL if no method matches
+ */
+static char *ssh_client_select_hostkeys(ssh_session session){
+    char methods_buffer[128]={0};
+    static const char *preferred_hostkeys[]={"ecdsa-sha2-nistp521","ecdsa-sha2-nistp384",
+    		"ecdsa-sha2-nistp256", "ssh-rsa", "ssh-dss", "ssh-rsa1", NULL};
+    char **methods;
+    int i,j;
+    int needcoma=0;
+
+    methods = ssh_knownhosts_algorithms(session);
+	if (methods == NULL || methods[0] == NULL)
+		return NULL;
+
+	for (i=0;preferred_hostkeys[i] != NULL; ++i){
+		for (j=0; methods[j] != NULL; ++j){
+			if(strcmp(preferred_hostkeys[i], methods[j]) == 0){
+				if (verify_existing_algo(SSH_HOSTKEYS, methods[j])){
+					if(needcoma)
+						strncat(methods_buffer,",",sizeof(methods_buffer)-strlen(methods_buffer)-1);
+					strncat(methods_buffer, methods[j], sizeof(methods_buffer)-strlen(methods_buffer)-1);
+					needcoma = 1;
+				}
+			}
+		}
+	}
+	for(i=0;methods[i]!= NULL; ++i){
+		SAFE_FREE(methods[i]);
+	}
+	SAFE_FREE(methods);
+
+	if(strlen(methods_buffer) > 0){
+		SSH_LOG(SSH_LOG_DEBUG, "Changing host key method to \"%s\"", methods_buffer);
+		return strdup(methods_buffer);
+	} else {
+		SSH_LOG(SSH_LOG_DEBUG, "No supported kex method for existing key in known_hosts file");
+		return NULL;
+	}
+
+}
 /**
  * @brief sets the key exchange parameters to be sent to the server,
  *        in function of the options and available methods.
@@ -380,10 +426,7 @@ void ssh_list_kex(struct ssh_kex_struct *kex) {
 int set_client_kex(ssh_session session){
     struct ssh_kex_struct *client= &session->next_crypto->client_kex;
     const char *wanted;
-    char methods_buffer[128]={0};
+    int i;
-    int prefered_hostkeys[]={SSH_KEYTYPE_ECDSA, SSH_KEYTYPE_RSA,
-    		SSH_KEYTYPE_DSS, SSH_KEYTYPE_RSA1, SSH_KEYTYPE_UNKNOWN};
-    int i, methods, needcoma=0;
 
     ssh_get_random(client->cookie, 16, 0);
 
@@ -391,25 +434,8 @@ int set_client_kex(ssh_session session){
     /* first check if we have specific host key methods */
     if(session->opts.wanted_methods[SSH_HOSTKEYS] == NULL){
     	/* Only if no override */
-    	methods = ssh_knownhosts_algorithms(session);
+    	session->opts.wanted_methods[SSH_HOSTKEYS] =
-    	if (methods != SSH_ERROR && methods != 0){
+    			ssh_client_select_hostkeys(session);
-    		for(i=0; prefered_hostkeys[i] != SSH_KEYTYPE_UNKNOWN;++i){
-    			if (methods & (1 << prefered_hostkeys[i])){
-    				if (verify_existing_algo(SSH_HOSTKEYS, ssh_key_type_to_char(prefered_hostkeys[i]))){
-    					if(needcoma)
-    						strncat(methods_buffer,",",sizeof(methods_buffer)-strlen(methods_buffer)-1);
-    					strncat(methods_buffer, ssh_key_type_to_char(prefered_hostkeys[i]), sizeof(methods_buffer)-strlen(methods_buffer)-1);
-    					needcoma = 1;
-    				}
-    			}
-    		}
-    		if(strlen(methods_buffer) > 0){
-    			SSH_LOG(SSH_LOG_DEBUG, "Changing host key method to \"%s\"", methods_buffer);
-    			session->opts.wanted_methods[SSH_HOSTKEYS] = strdup(methods_buffer);
-    		} else {
-    			SSH_LOG(SSH_LOG_DEBUG, "No supported kex method for existing key in known_hosts file");
-    		}
-    	}
     }
 
     for (i = 0; i < KEX_METHODS_SIZE; i++) {

src/known_hosts.c

@@ -34,7 +34,7 @@
 #include "libssh/misc.h"
 #include "libssh/pki.h"
 #include "libssh/options.h"
-
+#include "libssh/knownhosts.h"
 /*todo: remove this include */
 #include "libssh/string.h"
 
@@ -647,29 +647,33 @@ int ssh_write_knownhost(ssh_session session) {
     return 0;
 }
 
+#define KNOWNHOSTS_MAXTYPES 10
+
 /**
+ * @internal
  * @brief Check which kind of host keys should be preferred for connection
  *        by reading the known_hosts file.
  *
  * @param[in]  session  The SSH session to use.
  *
- * @returns Bitfield of supported SSH hostkey algorithms
+ * @returns array of supported key types
- *					SSH_ERROR on error
+ *			NULL on error
  */
-int ssh_knownhosts_algorithms(ssh_session session) {
+char **ssh_knownhosts_algorithms(ssh_session session) {
   FILE *file = NULL;
   char **tokens;
   char *host;
   char *hostport;
   const char *type;
   int match;
-  int ret = 0;
+  char **array;
+  int i=0, j;
 
   if (session->opts.knownhosts == NULL) {
     if (ssh_options_apply(session) < 0) {
       ssh_set_error(session, SSH_REQUEST_DENIED,
           "Can't find a known_hosts file");
-      return SSH_ERROR;
+      return NULL;
     }
   }
 
@@ -683,8 +687,13 @@ int ssh_knownhosts_algorithms(ssh_session session) {
     ssh_set_error_oom(session);
     SAFE_FREE(host);
     SAFE_FREE(hostport);
+    return NULL;
+  }
 
-    return SSH_ERROR;
+  array = malloc(sizeof(char *) * KNOWNHOSTS_MAXTYPES);
+  if (array==NULL){
+	  ssh_set_error_oom(session);
+	  return NULL;
   }
 
   do {
@@ -709,11 +718,24 @@ int ssh_knownhosts_algorithms(ssh_session session) {
       /* We got a match. Now check the key type */
     	SSH_LOG(SSH_LOG_DEBUG, "server %s:%d has %s in known_hosts",
     							host, session->opts.port, type);
-    	ret |= 1 << ssh_key_type_from_name(type);
+    	/* don't copy more than once */
+    	for(j=0;j<i && match;++j){
+    		if(strcmp(array[j], type)==0)
+    			match=0;
+    	}
+    	if (match){
+    		array[i] = strdup(type);
+    		i++;
+    		if(i>= KNOWNHOSTS_MAXTYPES-1){
+    			tokens_free(tokens);
+    			break;
+    		}
+    	}
     }
     tokens_free(tokens);
   } while (1);
 
+  array[i]=NULL;
   SAFE_FREE(host);
   SAFE_FREE(hostport);
   if (file != NULL) {
@@ -721,7 +743,7 @@ int ssh_knownhosts_algorithms(ssh_session session) {
   }
 
   /* Return the current state at end of file */
-  return ret;
+  return array;
 }
 
 /** @} */

tests/client/torture_knownhosts.c

@@ -23,6 +23,7 @@
 
 #include "torture.h"
 #include "session.c"
+#include "known_hosts.c"
 
 #define KNOWNHOSTFILES "libssh_torture_knownhosts"
 #define BADRSA "AAAAB3NzaC1yc2EAAAADAQABAAABAQChm5" \
@@ -255,8 +256,7 @@ static void torture_knownhosts_precheck(void **state) {
     ssh_session session = *state;
     FILE *file;
     int rc;
-    int dsa;
+    char **kex;
-    int rsa;
 
     rc = ssh_options_set(session, SSH_OPTIONS_HOST, "localhost");
     assert_true(rc == SSH_OK);
@@ -270,14 +270,14 @@ static void torture_knownhosts_precheck(void **state) {
     fprintf(file, "localhost ssh-dss %s\n", BADDSA);
     fclose(file);
 
-    rc = ssh_knownhosts_algorithms(session);
+    kex = ssh_knownhosts_algorithms(session);
-    assert_true(rc != SSH_ERROR);
+    assert_true(kex != NULL);
-    dsa = 1 << SSH_KEYTYPE_DSS;
+    assert_string_equal(kex[0],"ssh-rsa");
-    rsa = 1 << SSH_KEYTYPE_RSA;
+    assert_string_equal(kex[1],"ssh-dss");
-    assert_true(rc & dsa);
+    assert_true(kex[2]==NULL);
-    assert_true(rc & rsa);
+    free(kex[1]);
-    /* nothing else than dsa and rsa */
+    free(kex[0]);
-    assert_true((rc & (dsa | rsa)) == rc);
+    free(kex);
 }
 
 int torture_run_tests(void) {