CVE-2026-97946 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
x86/amd_node: Fix PCI device reference counting in amd_smn_init()
The local "root" pointer is a temporary variable used during the device search. Therefore, refcount related to the search iterators should be cleaned up after the search is complete.
Use the __free() cleanup macro to ensure the refcount is decremented when the temporary pointer goes out of scope.
Additionally, increment the refcount when caching a root pointer. This ensures the in-use refcount is separate from the temporary search refcounting.
Finally, drop the redundant "root = NULL" before the second search loop. The pci_get_class() iterator always decrements the refcount of its "from" argument, so the first loop can only fall through with "root" already NULL.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability addressed in this Linux kernel update pertains to improper reference counting within the x86 AMD System Management Node driver initialization routine, specifically amd_smn_init(). In complex systems involving hardware enumeration and device management, maintaining accurate reference counts for kernel objects is critical to prevent resource leaks or premature deallocation. The core issue stems from a temporary local pointer used during PCI device searches that was not properly managed regarding its lifecycle and refcount status. When iterating through devices using functions like pci_get_class(), the iterator increments the reference count of each found device. If this incremented count is not explicitly decremented when the iteration concludes or if it interferes with persistent pointers, it leads to a memory leak where kernel objects remain allocated indefinitely even after they are no longer needed. This type of flaw falls under CWE-401, which describes missing release of memory after effective lifetime, and can also be associated with CWE-755 due to improper handling of exception conditions or cleanup paths if the refcount imbalance causes subsequent operations on stale pointers.
The technical resolution involves restructuring how reference counts are handled for both temporary search iterators and persistent cached pointers. The fix introduces the use of the __free() cleanup macro, a kernel mechanism that ensures automatic resource deallocation when a variable goes out of scope. By applying this to the local root pointer used during the initial device search, the code guarantees that any refcount increments performed by the iterator are correctly decremented once the loop finishes or an error occurs. This prevents the accumulation of unreleased references for devices that were merely inspected but not retained for active use. Furthermore, when a valid root device is identified and cached for later access, its reference count must be explicitly incremented to distinguish it from the temporary search context. Without this separation, caching the pointer without adjusting its refcount could lead to double-free errors or use-after-free conditions if the iterator's cleanup logic incorrectly attempts to release an object that is still in active use by the driver.
The operational impact of such reference counting errors can vary significantly depending on system load and duration of uptime. In many cases, a simple memory leak may not cause immediate catastrophic failure but will gradually degrade system performance as kernel memory becomes fragmented or exhausted over time. However, if the refcount logic is flawed in a way that allows access to freed memory structures, it could potentially lead to undefined behavior, including crashes, data corruption, or exploitable conditions where an attacker might manipulate object lifecycles. While this specific instance appears primarily focused on preventing leaks and ensuring correct lifecycle management rather than addressing a direct privilege escalation vector, improper kernel state is often a precursor to more severe vulnerabilities. The ATT&CK framework does not have a direct entry for simple memory leaks in the same way it maps to exploitation techniques like Use After Free (T1204) or Memory Corruption, but the underlying flaw type aligns with CWE-755 and CWE-401, which are foundational weaknesses that security analysts monitor during code audits.
Mitigation strategies primarily involve applying the provided kernel patch to ensure proper refcount handling in amd_smn_init(). For system administrators, this means updating to a patched version of the Linux kernel where these reference counting rules are enforced via modern cleanup macros and explicit increment logic for cached pointers. Developers contributing to similar subsystems should adopt the __free() macro pattern consistently to automate resource management and reduce human error in manual refcount manipulation. Additionally, rigorous code review processes that specifically check iterator usage patterns against their corresponding decrement operations can help identify such issues before they reach production environments. Ensuring that temporary search iterators do not interfere with persistent object references is a best practice for maintaining kernel stability and security integrity across all hardware abstraction layers.