CVE-2025-39939: iommu/s390: Fix memory corruption when using identity domain

Vulnerability summary

CVE-2025-39939 is a high (CVSS 7.8) Out-of-bounds Write vulnerability in linux. EPSS estimates a 0.15% chance of exploitation in the next 30 days, higher than 3.9% of scored vulnerabilities.

Timeline

1. 04-10-2025
   PublishedVulnerability first disclosed.
2. 15-10-2026
   Last modifiedVulnerability information updated.

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.

• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.