Linux kernel (drivers/vfio/pci): Whoever holds the VFIO device fd for a passed-through PCI function can make the host

Impact

Whoever holds the VFIO device fd for a passed-through PCI function can make the host kernel allocate and never free a saved-PCI-state buffer, once per iteration of a tight loop. The upstream fix explicitly describes this as a malicious sequence that drives the host into OOM, which kills or stalls every other tenant sharing the node, not just the one doing it.

Who can reach it

A tenant VM's VMM (or any container given /dev/vfio/*) that owns a passthrough device: put the device into D3hot, then issue VFIO_DEVICE_RESET or VFIO_DEVICE_PCI_HOT_RESET, repeat. The reset path silently returns the device to D0 so the driver skips the free, and the previously saved state buffer leaks. Only affects devices whose PMCSR lacks the No_Soft_Reset bit, so the driver takes the software power-state-save path. Requires vfio-pci bound to a device and the device node exposed to the tenant.

What to do

No fixed release is listed in this record; pick up the fix from the linked stable commits and run a current stable/LTS kernel on every node that does PCI passthrough. Interim: do not hand raw VFIO_DEVICE_RESET / VFIO_DEVICE_PCI_HOT_RESET rights to untrusted tenants, cap the VMM process with a memory cgroup so the leak hits the tenant's own limit rather than the node, and alert on unexplained host slab growth on passthrough nodes.

References