tests: Add interoperability tests against TinySSH

This adds a new test suite 'torture_tinyssh' that verifies interoperability with the TinySSH server using various key exchange methods.

Fixes #271

Signed-off-by: Bulitha Kawushika De Zoysa <bulithakaushika99@gmail.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

tests/CMakeLists.txt

@@ -259,6 +259,20 @@ else()
     set(PUTTYGEN_EXECUTABLE "/bin/puttygen-not-found")
 endif()
 
+find_program(TINYSSHD_EXECUTABLE
+             NAMES 
+                tinysshd
+             PATHS
+                /sbin 
+                /usr/sbin 
+                /usr/local/sbin)
+
+if (TINYSSHD_EXECUTABLE)
+    message(STATUS "Found TinySSH server: ${TINYSSHD_EXECUTABLE}")
+else()
+    message(STATUS "Could NOT find TinySSH server")
+endif()
+
 find_program(SSHD_EXECUTABLE
              NAME
                 sshd
@@ -391,6 +405,14 @@ if (CLIENT_TESTING OR SERVER_TESTING)
     file(COPY keys/id_ed25519_sk DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/home/bob/.ssh/ FILE_PERMISSIONS OWNER_READ OWNER_WRITE)
     file(COPY keys/id_ed25519_sk.pub DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/home/bob/.ssh/ FILE_PERMISSIONS OWNER_READ OWNER_WRITE)
 
+    # TINYSSH Key Setup
+    set(TINYSSH_KEY_DIR "${CMAKE_CURRENT_BINARY_DIR}/etc/tinyssh")
+    file(MAKE_DIRECTORY ${TINYSSH_KEY_DIR})
+
+    # Copy the TINYSSH hostkeys
+    file(COPY keys/ed25519.pk DESTINATION ${TINYSSH_KEY_DIR})
+    file(COPY keys/.ed25519.sk DESTINATION ${TINYSSH_KEY_DIR})
+
     # Allow to auth with bob's public keys on alice and doe account
     configure_file(keys/id_rsa.pub ${CMAKE_CURRENT_BINARY_DIR}/home/alice/.ssh/authorized_keys @ONLY)
     configure_file(keys/id_rsa.pub ${CMAKE_CURRENT_BINARY_DIR}/home/doe/.ssh/authorized_keys @ONLY)

tests/client/CMakeLists.txt

@@ -36,6 +36,10 @@ if (WITH_PKCS11_URI)
         torture_auth_pkcs11)
 endif()
 
+if (TINYSSHD_EXECUTABLE AND NCAT_EXECUTABLE)
+    set(LIBSSH_CLIENT_TESTS ${LIBSSH_CLIENT_TESTS} torture_tinyssh)
+endif()
+
 if (HAVE_PTHREAD)
     set(LIBSSH_CLIENT_TESTS
         ${LIBSSH_CLIENT_TESTS}
@@ -92,6 +96,12 @@ foreach(_CLI_TEST ${LIBSSH_CLIENT_TESTS})
                     LINK_LIBRARIES ${TORTURE_LIBRARY} util
     )
 
+    if (_CLI_TEST STREQUAL "torture_tinyssh")
+        target_compile_definitions(${_CLI_TEST} PRIVATE 
+            TINYSSH_KEYS_DIR="${TINYSSH_KEY_DIR}"
+        )
+    endif()
+
     if (OSX)
         set_property(
             TEST

tests/client/torture_tinyssh.c

@@ -0,0 +1,328 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2026 by Your Bulitha Kawushika De Zoysa
+ *
+ * The SSH 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, or (at your
+ * option) any later version.
+ *
+ * The SSH 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 the SSH Library; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+#include "config.h"
+#include "tests_config.h"
+
+#define LIBSSH_STATIC
+
+#include "libssh/libssh.h"
+#include "libssh/priv.h"
+#include "libssh/session.h"
+#include "torture.h"
+
+#include <errno.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define TINYSSH_PIDFILE "tinyssh.pid"
+#define TINYSSH_PORT    22
+
+/* TINYSSH Server Setup and Teardown */
+
+static int tinyssh_setup(void **state)
+{
+    struct torture_state *s = NULL;
+    char cmd[4096];
+    char pid_path[1024];
+    int rc;
+
+    torture_setup_socket_dir(state);
+    s = *state;
+
+    snprintf(pid_path,
+             sizeof(pid_path),
+             "%s/%s",
+             s->socket_dir,
+             TINYSSH_PIDFILE);
+    free(s->srv_pidfile);
+    s->srv_pidfile = strdup(pid_path);
+    if (s->srv_pidfile == NULL) {
+        return -1;
+    }
+
+    snprintf(cmd,
+             sizeof(cmd),
+             "%s -l %s %d -k -c \"%s %s -v %s\" "
+             "> %s/tinyssh.log 2>&1 & echo $! > %s",
+             NCAT_EXECUTABLE,
+             TORTURE_SSH_SERVER,
+             TINYSSH_PORT,
+             TINYSSHD_EXECUTABLE,
+             "",
+             TINYSSH_KEYS_DIR,
+             s->socket_dir,
+             s->srv_pidfile);
+
+    SSH_LOG(SSH_LOG_DEBUG, "Executing: %s\n", cmd);
+
+    rc = system(cmd);
+    if (rc != 0) {
+        return -1;
+    }
+
+    rc = torture_wait_for_daemon(15);
+    if (rc != 0) {
+        return -1;
+    }
+
+    return 0;
+}
+
+static int tinyssh_teardown(void **state)
+{
+    struct torture_state *s = *state;
+    torture_terminate_process(s->srv_pidfile);
+    torture_teardown_socket_dir(state);
+    return 0;
+}
+
+/* LIBSSH Client Setup and Teardown */
+
+static int session_setup(void **state)
+{
+    struct torture_state *s = *state;
+    int verbosity = torture_libssh_verbosity();
+    bool process_config = false;
+    int port = TINYSSH_PORT;
+    struct passwd *pwd = NULL;
+    int rc;
+
+    pwd = getpwnam("bob");
+    assert_non_null(pwd);
+
+    rc = setuid(pwd->pw_uid);
+    assert_return_code(rc, errno);
+
+    s->ssh.session = ssh_new();
+    assert_non_null(s->ssh.session);
+
+    ssh_options_set(s->ssh.session, SSH_OPTIONS_LOG_VERBOSITY, &verbosity);
+    ssh_options_set(s->ssh.session, SSH_OPTIONS_HOST, TORTURE_SSH_SERVER);
+    ssh_options_set(s->ssh.session, SSH_OPTIONS_PORT, &port);
+    ssh_options_set(s->ssh.session, SSH_OPTIONS_USER, "bob");
+    ssh_options_set(s->ssh.session,
+                    SSH_OPTIONS_PROCESS_CONFIG,
+                    &process_config);
+
+    return 0;
+}
+
+static int session_teardown(void **state)
+{
+    struct torture_state *s = *state;
+    if (s->ssh.session) {
+        ssh_disconnect(s->ssh.session);
+        ssh_free(s->ssh.session);
+    }
+    return 0;
+}
+
+/* Algorithms Helper */
+
+static void test_specific_algorithm(ssh_session session,
+                                    const char *kex,
+                                    const char *cipher,
+                                    const char *hostkey,
+                                    int expected_rc)
+{
+    int rc;
+    char data[256];
+    size_t len_to_test[] = {1,  2,  3,  4,  5,  6,  7,  8,  10,  12,  15,
+                            16, 20, 31, 32, 33, 63, 64, 65, 100, 127, 128};
+    unsigned int i;
+
+    /* Set Key Exchange */
+    if (kex != NULL) {
+        rc = ssh_options_set(session, SSH_OPTIONS_KEY_EXCHANGE, kex);
+        assert_ssh_return_code(session, rc);
+    }
+
+    /* Set Ciphers */
+    if (cipher != NULL) {
+        rc = ssh_options_set(session, SSH_OPTIONS_CIPHERS_C_S, cipher);
+        assert_ssh_return_code(session, rc);
+        rc = ssh_options_set(session, SSH_OPTIONS_CIPHERS_S_C, cipher);
+        assert_ssh_return_code(session, rc);
+    }
+
+    /* Set Hostkey */
+    if (hostkey != NULL) {
+        rc = ssh_options_set(session, SSH_OPTIONS_HOSTKEYS, hostkey);
+        assert_ssh_return_code(session, rc);
+    }
+
+    rc = ssh_connect(session);
+
+    if (expected_rc == SSH_OK) {
+        assert_ssh_return_code(session, rc);
+
+        if (cipher != NULL) {
+            const char *used_cipher = ssh_get_cipher_out(session);
+            assert_non_null(used_cipher);
+            assert_string_equal(used_cipher, cipher);
+        }
+
+        if (hostkey != NULL) {
+            ssh_key pubkey = NULL;
+            const char *type_str = NULL;
+
+            rc = ssh_get_server_publickey(session, &pubkey);
+            assert_int_equal(rc, SSH_OK);
+            assert_non_null(pubkey);
+
+            type_str = ssh_key_type_to_char(ssh_key_type(pubkey));
+            assert_non_null(type_str);
+            assert_string_equal(type_str, hostkey);
+            ssh_key_free(pubkey);
+        }
+
+        memset(data, 0, sizeof(data));
+        for (i = 0; i < (sizeof(len_to_test) / sizeof(size_t)); i++) {
+            memset(data, 'A', len_to_test[i]);
+            ssh_send_ignore(session, data);
+            ssh_handle_packets(session, 50);
+        }
+
+        rc = ssh_userauth_none(session, NULL);
+        if (rc != SSH_OK) {
+            rc = ssh_get_error_code(session);
+            assert_int_equal(rc, SSH_REQUEST_DENIED);
+        }
+
+    } else {
+        assert_int_not_equal(rc, SSH_OK);
+    }
+}
+
+/* Test Cases */
+
+static void torture_tinyssh_curve25519(void **state)
+{
+    struct torture_state *s = *state;
+    test_specific_algorithm(s->ssh.session,
+                            "curve25519-sha256",
+                            NULL,
+                            NULL,
+                            SSH_OK);
+}
+
+static void torture_tinyssh_curve25519_libssh(void **state)
+{
+    struct torture_state *s = *state;
+    test_specific_algorithm(s->ssh.session,
+                            "curve25519-sha256@libssh.org",
+                            NULL,
+                            NULL,
+                            SSH_OK);
+}
+
+static void torture_tinyssh_sntrup761(void **state)
+{
+    struct torture_state *s = *state;
+    test_specific_algorithm(s->ssh.session,
+                            "sntrup761x25519-sha512@openssh.com",
+                            NULL,
+                            NULL,
+                            SSH_OK);
+}
+
+static void torture_tinyssh_chacha20(void **state)
+{
+    struct torture_state *s = *state;
+    test_specific_algorithm(s->ssh.session,
+                            NULL,
+                            "chacha20-poly1305@openssh.com",
+                            NULL,
+                            SSH_OK);
+}
+
+static void torture_tinyssh_neg_cipher(void **state)
+{
+    struct torture_state *s = *state;
+
+    /* TinySSH does not support older ciphers like aes128-cbc.*/
+
+    test_specific_algorithm(s->ssh.session,
+                            NULL,
+                            "aes128-cbc",
+                            NULL,
+                            SSH_ERROR);
+}
+
+static void torture_tinyssh_hostkey_ed25519(void **state)
+{
+    struct torture_state *s = *state;
+    test_specific_algorithm(s->ssh.session, NULL, NULL, "ssh-ed25519", SSH_OK);
+}
+
+static void torture_tinyssh_neg_kex(void **state)
+{
+    struct torture_state *s = *state;
+
+    /* TinySSH does not support legacy Diffie-Hellman groups or NIST curves.*/
+
+    test_specific_algorithm(s->ssh.session,
+                            "diffie-hellman-group1-sha1",
+                            NULL,
+                            NULL,
+                            SSH_ERROR);
+}
+
+int torture_run_tests(void)
+{
+    int rc;
+
+    struct CMUnitTest tests[] = {
+        cmocka_unit_test_setup_teardown(torture_tinyssh_curve25519,
+                                        session_setup,
+                                        session_teardown),
+        cmocka_unit_test_setup_teardown(torture_tinyssh_curve25519_libssh,
+                                        session_setup,
+                                        session_teardown),
+        cmocka_unit_test_setup_teardown(torture_tinyssh_sntrup761,
+                                        session_setup,
+                                        session_teardown),
+        cmocka_unit_test_setup_teardown(torture_tinyssh_hostkey_ed25519,
+                                        session_setup,
+                                        session_teardown),
+        cmocka_unit_test_setup_teardown(torture_tinyssh_chacha20,
+                                        session_setup,
+                                        session_teardown),
+        cmocka_unit_test_setup_teardown(torture_tinyssh_neg_cipher,
+                                        session_setup,
+                                        session_teardown),
+        cmocka_unit_test_setup_teardown(torture_tinyssh_neg_kex,
+                                        session_setup,
+                                        session_teardown),
+    };
+
+    ssh_init();
+
+    torture_filter_tests(tests);
+    rc = cmocka_run_group_tests(tests, tinyssh_setup, tinyssh_teardown);
+
+    ssh_finalize();
+    return rc;
+}

tests/keys/ed25519.pk

@@ -0,0 +1 @@
+<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>C<EFBFBD><EFBFBD>K<EFBFBD>ݛ<EFBFBD>1<1C><>'j&<26>e<EFBFBD><65><EFBFBD><EF8A8D>

tests/tests_config.h.cmake

@@ -86,3 +86,7 @@
 #cmakedefine PKCS11SPY "${PKCS11SPY}"
 #cmakedefine HAVE_SK_DUMMY 1
 #cmakedefine SK_DUMMY_LIBRARY_PATH "${SK_DUMMY_LIBRARY_PATH}"
+
+/* TinySSH Executable */
+
+#cmakedefine TINYSSHD_EXECUTABLE "${TINYSSHD_EXECUTABLE}"