ntdll: Check for DLL files when creating new processes.

dlls/ntdll/unix/env.c

@@ -1917,7 +1917,11 @@ static RTL_USER_PROCESS_PARAMETERS *build_initial_params(void)
     env[env_pos++] = 0;
 
     status = load_main_exe( NULL, main_argv[1], curdir, &image, &module, &image_info );
-    if (!status && image_info.Machine != current_machine) status = STATUS_INVALID_IMAGE_FORMAT;
+    if (!status)
+    {
+        if (image_info.ImageCharacteristics & IMAGE_FILE_DLL) status = STATUS_INVALID_IMAGE_FORMAT;
+        if (image_info.Machine != current_machine) status = STATUS_INVALID_IMAGE_FORMAT;
+    }
 
     if (status)  /* try launching it through start.exe */
     {

dlls/ntdll/unix/process.c

@@ -365,6 +365,7 @@ static NTSTATUS get_pe_file_info( UNICODE_STRING *path, HANDLE *handle, pe_image
         }
         SERVER_END_REQ;
         NtClose( mapping );
+        if (info->image_charact & IMAGE_FILE_DLL) return STATUS_INVALID_IMAGE_FORMAT;
     }
     else if (status == STATUS_INVALID_IMAGE_NOT_MZ)
     {