From ce26b56e13d813800ad1fe97cec26d2830f6ed7a Mon Sep 17 00:00:00 2001
From: Stanislav Zidek <szidek@redhat.com>
Date: Mon, 25 Oct 2021 20:28:41 +0200
Subject: [PATCH] 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>
---
 src/misc.c                              | 30 ++++++++++++--
 tests/fuzz/CMakeLists.txt               |  1 +
 tests/fuzz/ssh_client_config_fuzzer.cpp | 55 +++++++++++++++++++++++++
 3 files changed, 83 insertions(+), 3 deletions(-)
 create mode 100644 tests/fuzz/ssh_client_config_fuzzer.cpp

diff --git a/src/misc.c b/src/misc.c
index 6472d583..97c3a0ef 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -1156,7 +1156,15 @@ char *ssh_path_expand_escape(ssh_session session, const char *s) {
             case '%':
                 goto escape;
             case 'd':
-                x = strdup(session->opts.sshdir);
+                if (session->opts.sshdir) {
+                    x = strdup(session->opts.sshdir);
+                } else {
+                    ssh_set_error(session, SSH_FATAL,
+                            "Cannot expand sshdir");
+                    free(buf);
+                    free(r);
+                    return NULL;
+                }
                 break;
             case 'u':
                 x = ssh_get_local_username();
@@ -1167,10 +1175,26 @@ char *ssh_path_expand_escape(ssh_session session, const char *s) {
                 }
                 break;
             case 'h':
-                x = strdup(session->opts.host);
+                if (session->opts.host) {
+                    x = strdup(session->opts.host);
+                } else {
+                    ssh_set_error(session, SSH_FATAL,
+                            "Cannot expand host");
+                    free(buf);
+                    free(r);
+                    return NULL;
+                }
                 break;
             case 'r':
-                x = strdup(session->opts.username);
+                if (session->opts.username) {
+                    x = strdup(session->opts.username);
+                } else {
+                    ssh_set_error(session, SSH_FATAL,
+                            "Cannot expand username");
+                    free(buf);
+                    free(r);
+                    return NULL;
+                }
                 break;
             case 'p':
                 if (session->opts.port < 65536) {
diff --git a/tests/fuzz/CMakeLists.txt b/tests/fuzz/CMakeLists.txt
index 5982e81c..dcdfd808 100644
--- a/tests/fuzz/CMakeLists.txt
+++ b/tests/fuzz/CMakeLists.txt
@@ -21,3 +21,4 @@ endmacro()
 
 fuzzer(ssh_client_fuzzer)
 fuzzer(ssh_server_fuzzer)
+fuzzer(ssh_client_config_fuzzer)
diff --git a/tests/fuzz/ssh_client_config_fuzzer.cpp b/tests/fuzz/ssh_client_config_fuzzer.cpp
new file mode 100644
index 00000000..47fd4222
--- /dev/null
+++ b/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;
+}
+
+}