Affected: Linux

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

virt: vmgenid: set driver_data before registering notification handlers

Both probe paths register their notification handler before assigning driver_data, which the handler dereferences.

In the devicetree path, the notification IRQ can fire as soon as devm_request_irq() registers the handler: the interrupt may already be pending at probe time, for example when a VMM injects the generation-changed notification while restoring a guest from a snapshot that was taken before the driver had probed (Firecracker does exactly this on snapshot restore). The IRQ is also requested with IRQF_SHARED, so another device sharing the line can trigger the handler just as early. The handler then calls vmgenid_notify(), which dereferences the still-NULL driver_data and panics:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010 CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.18.38+ #1 PREEMPT(none) Hardware name: linux,dummy-virt (DT) pc : vmgenid_notify.isra.0+0x24/0x8c lr : vmgenid_of_irq_handler+0x14/0x34 Call trace: vmgenid_notify.isra.0+0x24/0x8c (P) vmgenid_of_irq_handler+0x14/0x34 __handle_irq_event_percpu+0x44/0x1bc handle_irq_event+0x4c/0xb4 handle_fasteoi_irq+0xf8/0x1f8

The ACPI path has the same ordering problem: the handler is installed with acpi_install_notify_handler() before driver_data is assigned. ACPI notifications are dispatched asynchronously…