The config_line_t linked list could be refactored to use the TOR_SLIST macros in tor_queue.h
I would suggest using the TOR_SIMPLEQ macros instead. There are places where it would be helpful to have an O(1) append. (config_get_lines_aux() explicitly works around this by temporarily creating a list_last pointer and mentions O(n^2^) performance as an issue.)