CVE-2026-72022 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
llc: fix SAP refcount leak in llc_ui_autobind()
llc_ui_autobind() opens a SAP after choosing a dynamic LSAP. llc_sap_open() returns a reference owned by the caller, and llc_sap_add_socket() takes a second reference for the socket's membership in the SAP hash tables.
llc_ui_bind() drops the caller's reference after adding the socket, but llc_ui_autobind() keeps it. When the socket is closed, llc_sap_remove_socket() releases only the socket reference, leaving the SAP on llc_sap_list with sk_count == 0.
This is user-visible because repeated autobind and close cycles can consume all dynamic SAP values and make later autobinds fail with -EUSERS.
Drop the caller's reference after a successful autobind, matching llc_ui_bind()'s ownership model.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability described represents a memory management flaw in the Linux kernel's Logical Link Control (LLC) subsystem that results in a reference count leak within the llc_ui_autobind() function. This issue specifically affects the handling of Service Access Point (SAP) references during automatic binding operations, creating a resource exhaustion condition that impacts system stability and network functionality. The problem manifests as a progressive consumption of dynamic SAP values due to improper reference counting practices.
The technical implementation flaw occurs when llc_ui_autobind() performs SAP allocation and socket binding operations without properly managing reference ownership semantics. During the autobind process, llc_sap_open() correctly returns a reference to the caller that must be managed, while llc_sap_add_socket() internally takes an additional reference to maintain the socket's membership in SAP hash tables. This dual reference mechanism is consistent with proper kernel resource management patterns but fails in the autobind code path where the caller's reference is not properly released.
The operational impact of this vulnerability creates a persistent resource leak that becomes increasingly problematic over time. When sockets undergo repeated autobind and close cycles, the leaked SAP references accumulate on the llc_sap_list without proper cleanup. Each cycle leaves behind one reference count that never gets decremented to zero, causing the system to consume available dynamic SAP values until exhaustion occurs. This results in subsequent autobind operations failing with -EUSERS error codes, effectively preventing network communication from establishing new LLC connections through automatic binding mechanisms.
The root cause aligns with CWE-404, which addresses improper resource management and memory leaks in kernel space implementations. The vulnerability demonstrates poor adherence to reference counting principles that should maintain consistent ownership models across similar functions within the same subsystem. While llc_ui_bind() correctly implements reference dropping after socket addition, llc_ui_autobind() fails to follow the same pattern, creating an inconsistency that leads to resource accumulation.
This issue has significant implications for network service availability and system reliability in environments where dynamic LLC binding occurs frequently. The reference leak directly impacts the LLC subsystem's ability to manage service access points efficiently, potentially causing cascading failures in network communication protocols that depend on proper SAP management. The problem is particularly concerning in high-traffic network environments where repeated socket creation and destruction cycles occur regularly.
The recommended mitigation involves implementing consistent reference counting behavior between llc_ui_bind() and llc_ui_autobind() functions by ensuring that the caller's reference is properly dropped after successful autobind operations. This aligns with established kernel development practices and ATT&CK technique T1070.004, which addresses the use of system resources for persistence or denial-of-service conditions. The fix requires modifying the llc_ui_autobind() function to match the ownership model used in llc_ui_bind(), ensuring that reference counting remains consistent across all code paths and preventing the accumulation of unreleased SAP references.
The vulnerability demonstrates a classic example of how subtle inconsistencies in kernel resource management can lead to significant operational problems, particularly in network subsystems where proper reference counting is essential for maintaining system stability and preventing resource exhaustion attacks. This type of issue highlights the importance of rigorous code review processes that focus on resource management consistency across similar functions within kernel subsystems.