CVE-2024-26812

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

vfio/pci: Create persistent INTx handler

A vulnerability exists where the eventfd for INTx signaling can be

deconfigured, which unregisters the IRQ handler but still allows

eventfds to be signaled with a NULL context through the SET_IRQS ioctl

or through unmask irqfd if the device interrupt is pending.

Ideally this could be solved with some additional locking; the igate

mutex serializes the ioctl and config space accesses, and the interrupt

handler is unregistered relative to the trigger, but the irqfd path

runs asynchronous to those. The igate mutex cannot be acquired from the

atomic context of the eventfd wake function. Disabling the irqfd

relative to the eventfd registration is potentially incompatible with

existing userspace.

As a result, the solution implemented here moves configuration of the

INTx interrupt handler to track the lifetime of the INTx context object

and irq_type configuration, rather than registration of a particular

trigger eventfd. Synchronization is added between the ioctl path and

eventfd_signal() wrapper such that the eventfd trigger can be

dynamically updated relative to in-flight interrupts or irqfd callbacks.