CVE-2025-68250

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

hung_task: fix warnings caused by unaligned lock pointers

The blocker tracking mechanism assumes that lock pointers are at least 4-byte aligned to use their lower bits for type encoding.

However, as reported by Eero Tamminen, some architectures like m68k only guarantee 2-byte alignment of 32-bit values. This breaks the assumption and causes two related WARN_ON_ONCE checks to trigger.

To fix this, the runtime checks are adjusted to silently ignore any lock that is not 4-byte aligned, effectively disabling the feature in such cases and avoiding the related warnings.

Thanks to Geert Uytterhoeven for bisecting!

A low impact flaw was found in the Linux kernel's hung task detector (hung_task) blocker tracking mechanism, which encodes a blocking type in the lower bits of a lock pointer and therefore assumes that lock pointers are at least 4-byte aligned. On architectures that guarantee only 2-byte alignment of 32-bit values, such as m68k, valid lock pointers can have non-zero low bits that collide with this type encoding, causing two WARN_ON_ONCE checks in the blocker set and clear paths to trigger. The direct consequence is spurious kernel warnings and unreliable hung task diagnostics; on systems configured to treat kernel warnings as fatal, for example with panic_on_warn enabled, these warnings could escalate into a local denial of service. Red Hat assesses this flaw as low impact because it is local in nature, has no confidentiality or integrity impact, and manifests only on architectures with weaker pointer alignment guarantees.

The vulnerable blocker tracking code was introduced in the upstream Linux 6.16 kernel and is not present in the Red Hat Enterprise Linux kernels shipped in supported Red Hat products. All in-support Red Hat products, including Red Hat Enterprise Linux 7 through 10 (kernel and kernel-rt) and Red Hat In-Vehicle OS, are recorded as not affected for this flaw because the vulnerable code is not present; the Red Hat Enterprise Linux 6 Extended Lifecycle Support stream is out of support scope. The upstream CVE record assigns a higher severity (CVSS 3.1 score 8.2, Important, based on a network attack vector with confidentiality and availability impact). Red Hat's assessment differs because the verified behavior is a local, warning-only defect that cannot be triggered by a remote or unauthenticated network attacker; Red Hat rates it low impact with CVSS 3.1 score 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.