ASan allocates a global data initialization array at the tail end of each compunit's .data section. This vector is not poisoned. Because of this the first symbol of the following section has no left red zone. As a result, ASan cannot detect underflow for such symbols.
Poison ASan allocated metadata, it should not be accessible to user code.
This fix does not eliminate the problem with missing left red zones but it reduces the set of vulnerable symbols from first symbols in each input data section to first symbols in the output section of the binary.