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.