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

PCI/MSI: Handle the NOMASK flag correctly for all PCI/MSI backends

The conversion of the XEN specific global variable pci_msi_ignore_mask to a
MSI domain flag, missed the facts that:

    1) Legacy architectures do not provide a interrupt domain
    2) Parent MSI domains do not necessarily have a domain info attached
   
Both cases result in an unconditional NULL pointer dereference. This was
unfortunatly missed in review and testing revealed it late.

Cure this by using the existing pci_msi_domain_supports() helper, which
handles all possible cases correctly.