CVE-2026-98841

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 from a workqueue, so the window is narrow, but a notification arriving between the two calls hits the same NULL dereference.

Assign driver data before registering the handlers. The state is fully initialized at that point, so the handlers are safe to run. Should registration fail, the probe error path leaves no dangling pointer behind: the driver core clears driver data in device unbind cleanup().