In the Linux kernel, the following vulnerability has been resolved:
PCI/sysfs: Add lockdown checks to legacy I/O and memory handlers
Currently, the legacy I/O and memory sysfs handlers do not check
security_locked_down(LOCKDOWN_PCI_ACCESS), leaving the legacy_io and
legacy_mem files unprotected when the kernel is locked down.
Commit eb627e17727e ("PCI: Lock down BAR access when the kernel is locked
down") added the check to pci_write_config(), pci_mmap_resource(), and
pci_write_resource_io() to prevent userspace from programming DMA-capable
hardware that could be used to modify kernel code, but did not cover the
legacy handlers.
As a result, root can still write arbitrary I/O ports and map the legacy
I/O and memory spaces while the kernel is locked down, which is the same
capability the lockdown is meant to remove.
Add the same check to pci_write_legacy_io(), pci_mmap_legacy_mem(), and
pci_mmap_legacy_io().
These generic handlers cover both architectures that define HAVE_PCI_LEGACY
(such as Alpha and PowerPC).
[bhelgaas: add Link]