UBUNTU-CVE-2026-93251: Use After Free

In the Linux kernel, the following vulnerability has been resolved: ACPI: bus: Introduce acpibusgetprimarydevice() The function used for obtaining the first "physical" device for which the given ACPI one is the ACPI companion, acpigetfirstphysicalnode(), may return a stale device pointer (mostly in theory) because acpiunbindone() may run as a whole after dropping the ACPI device's physicalnodelock in acpigetfirstphysicalnode() and before it returns. The last reference to the "physical" device may be dropped then before the pointer to it is returned to the caller. If that happens and the acpigetfirstphysicalnode() caller invokes getdevice() on the pointer obtained from it, which is done by the majority of its callers, a use-after-free will occur. To prepare for addressing this problem, introduce a new function for getting the first "physical" device associated with the given ACPI one (the "primary physical device") that will also reference count the device in question before returning a pointer to it. Make that new function and acpigetfirstphysicalnode() share the physical node list lookup code. No intentional functional impact.