iommu/s390: Fix memory corruption when using identity domain

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: iommu/s390: Fix memory corruption when using identity domain zpci_get_iommu_ctrs() returns counter information to be reported as part of device statistics; these counters are stored as part of the s390_domain. The problem, however, is that the identity domain is not backed by an s390_domain and so the conversion via to_s390_domain() yields a bad address that is zero'd initially and read on-demand later via a sysfs read. These counters aren't necessary for the identity domain; just return NULL in this case. This issue was discovered via KASAN with reports that look like: BUG: KASAN: global-out-of-bounds in zpci_fmb_enable_device when using the identity domain for a device on s390.

References

• https://git.kernel.org/stable/c/17a58caf3863163c4a84a218a9649be2c8061443
• https://git.kernel.org/stable/c/b3506e9bcc777ed6af2ab631c86a9990ed97b474