Kernel/VFS: Don't overwrite files when renaming a directory

Kernel/FileSystem/VirtualFileSystem.cpp

@@ -636,6 +636,9 @@ ErrorOr<void> VirtualFileSystem::rename(VFSRootContext const& vfs_root_context,
     if (!new_custody_or_error.is_error()) {
         auto& new_inode = new_custody_or_error.value()->inode();
 
+        if (old_inode.is_directory() && !new_inode.is_directory())
+            return ENOTDIR;
+
         if (old_inode.index() != new_inode.index() && old_inode.is_directory() && new_inode.is_directory()) {
             size_t child_count = 0;
             TRY(new_inode.traverse_as_directory([&child_count](auto&) -> ErrorOr<void> {

Tests/Kernel/POSIX/CMakeLists.txt

@@ -4,6 +4,7 @@ set(TEST_SOURCES
     TestFIFO.cpp
     TestPathLength.cpp
     TestPthreadCond.cpp
+    TestRename.cpp
 )
 
 foreach(libtest_source IN LISTS TEST_SOURCES)

Tests/Kernel/POSIX/TestRename.cpp

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2026, Lucas Chollet <[email protected]>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/System.h>
+#include <LibFileSystem/TempFile.h>
+#include <LibTest/TestCase.h>
+
+TEST_CASE(rename_directory_over_file_fails)
+{
+    auto directory = TRY_OR_FAIL(FileSystem::TempFile::create_temp_directory());
+    auto file = TRY_OR_FAIL(FileSystem::TempFile::create_temp_file());
+
+    auto error = Core::System::rename(directory->path(), file->path());
+    EXPECT(error.is_error());
+    EXPECT_EQ(error.error().code(), ENOTDIR);
+}