CVE-2026-80821 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
nvmet: pci-epf: put CQ ref on create_cq mapping failure
nvmet_pci_epf_create_cq() calls nvmet_cq_create(), which takes a reference on the controller and installs the completion queue. If the subsequent PCI address-space mapping fails or returns a too-small partial mapping, the function jumps to err_internal / err_unmap_queue without calling nvmet_cq_put(). The matching put in nvmet_pci_epf_delete_cq() is gated on NVMET_PCI_EPF_Q_LIVE, which is only set after the mapping succeeds, so teardown never releases these references. A remote PCI host that drives Create IO CQ commands with a failing PRP1/pci_addr therefore leaks the CQ and a controller reference on each attempt.
Drop the CQ reference on the mapping-failure paths. The err_internal and err_unmap_queue labels are only reachable after nvmet_cq_create() has succeeded, so this pairs the create/put correctly.
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Analysis
by VulDB Data Team • 09/04/2026
The Linux kernel subsystem for NVMe over Fabrics target implementation contains a resource management flaw within its PCI endpoint function driver that results in reference count leaks during specific error conditions. This vulnerability is located in the nvmet_pci_epf_create_cq() function, which is responsible for initializing completion queues for incoming IO commands from remote hosts. The core issue arises when the system attempts to map physical memory regions associated with these queues into the kernel address space using PCI mapping functions. If this mapping operation fails or returns a partial result that does not meet size requirements, the control flow diverts to error handling labels such as err_internal and err_unmap_queue. However, in these specific failure paths, the code neglects to invoke nvmet_cq_put(), which is the counterpart function required to decrement the reference count on the controller object acquired during the initial creation phase via nvmet_cq_create().
This oversight creates a classic resource leak scenario where every failed attempt by a remote PCI host to create an IO completion queue results in the kernel retaining a stale reference to both the completion queue structure and the underlying NVMe controller. Because the cleanup logic within nvmet_pci_epf_delete_cq() is gated behind a flag named NVMET_PCI_EPF_Q_LIVE, which is only set after successful memory mapping, the teardown routine never executes for these partially initialized structures. Consequently, the references are never released back to the kernel's resource management subsystem. Over time, particularly under conditions where an attacker or misconfigured host repeatedly issues Create IO CQ commands with invalid physical region descriptors such as failing PRP1 entries, this leak accumulates rapidly.
The operational impact of this vulnerability is primarily centered on resource exhaustion and potential denial of service against the target system. As the kernel retains these unreleased references, it prevents the garbage collection or deallocation of associated memory structures and controller objects. This gradual accumulation can lead to increased memory consumption and eventually exhaust available resources within the NVMe subsystem. In severe cases, this may cause the nvmet_pci_epf driver to become unresponsive or crash due to resource limits being reached, effectively disrupting service for legitimate users connected to the storage array. The vulnerability is exploitable remotely by any entity capable of sending NVMe commands over a PCI-based fabric connection that supports endpoint functionality, making it relevant in cloud and data center environments where such hardware acceleration is common.
From a classification perspective, this flaw aligns with CWE-401, which describes missing release of memory after effective usage, specifically manifesting as a reference count leak rather than simple heap corruption. It also relates to CWE-755, concerning improper handling of unusual or unexpected input, as the failure stems from invalid PCI address mappings provided by external actors. In terms of adversarial tactics, this vulnerability supports ATT&CK technique T1496, Resource Hijacking, where an attacker consumes system resources to degrade performance or cause denial of service without necessarily gaining unauthorized access to data. The exploitation does not require privilege escalation but relies on the ability to interact with the NVMe target interface and trigger mapping failures repeatedly.
To mitigate this vulnerability, immediate patching is required by updating the Linux kernel to a version that includes the fix for nvmet_pci_epf_create_cq(). The corrective action involves modifying the error handling paths in the source code to ensure that nvmet_cq_put() is called whenever nvmet_cq_create() has successfully acquired references, regardless of whether subsequent PCI mapping operations succeed or fail. Administrators should verify their kernel versions and apply updates provided by their distribution vendors if they are running affected releases. Additionally, implementing strict input validation on incoming NVMe commands at the fabric layer can help reduce the frequency of such error conditions reaching this specific code path, although the primary defense remains the software patch that correctly pairs resource acquisition with release operations in all execution paths.