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 irq_set_affinity_notifier() 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 free_irq_cpu_rmap() 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 free_irq_cpu_rmap().

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

The bug stems from calling irq_set_affinity_notifier(irq, NULL) which frees the notifier “glue” but leaves a stale pointer in rmap->obj[index]. A later free_irq_cpu_rmap() iteration may free it again, causing a use-after-free. For the CVSS the PR:H is because this is a kernel-internal API used by drivers.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.