client configuration fuzzing and fixes

Signed-off-by: Stanislav Zidek <szidek@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

tests/fuzz/CMakeLists.txt

@@ -21,3 +21,4 @@ endmacro()
 
 fuzzer(ssh_client_fuzzer)
 fuzzer(ssh_server_fuzzer)
+fuzzer(ssh_client_config_fuzzer)

tests/fuzz/ssh_client_config_fuzzer.cpp

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2021 Stanislav Zidek <szidek@redhat.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+extern "C" {
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define LIBSSH_STATIC 1
+#include "libssh/libssh.h"
+#include "libssh/options.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+    ssh_session session = NULL;
+    char *input = NULL;
+
+    input = (char *)malloc(size+1);
+    if (!input) {
+        return 1;
+    }
+    strncpy(input, (const char *)data, size);
+    input[size] = '\0';
+
+    ssh_init();
+
+    session = ssh_new();
+    assert(session != NULL);
+
+    ssh_config_parse_string(session, input);
+
+    ssh_free(session);
+    ssh_finalize();
+
+    free(input);
+
+    return 0;
+}
+
+}