net: stmmac: Fix accessing freed irq affinity_hint

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

net: stmmac: Fix accessing freed irq affinity_hint

In stmmac_request_irq_multi_msi(), a pointer to the stack variable

cpu_mask is passed to irq_set_affinity_hint(). This value is stored in

irq_desc->affinity_hint, but once stmmac_request_irq_multi_msi()

returns, the pointer becomes dangling.

The affinity_hint is exposed via procfs with S_IRUGO permissions,

allowing any unprivileged process to read it. Accessing this stale

pointer can lead to:

- a kernel oops or panic if the referenced memory has been released and

unmapped, or

- leakage of kernel data into userspace if the memory is re-used for

other purposes.

All platforms that use stmmac with PCI MSI (Intel, Loongson, etc) are

affected.