CVE-2023-53484

In the Linux kernel, the following vulnerability has been resolved:

lib: cpu_rmap: Avoid use after free on rmap->obj array entries

When calling irqsetaffinitynotifier() with NULL at the notify argument, it will cause freeing of the glue pointer in the corresponding array entry but will leave the pointer in the array. A subsequent call to freeirqcpurmap() will try to free this entry again leading to possible use after free.

Fix that by setting NULL to the array entry and checking that we have non-zero at the array entry when iterating over the array in freeirqcpu_rmap().

The current code does not suffer from this since there are no cases where irqsetaffinitynotifier(irq, NULL) (note the NULL passed for the notify arg) is called, followed by a call to freeirqcpurmap() so we don't hit and issue. Subsequent patches in this series excersize this flow, hence the required fix.