CVE-2026-98692 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
thunderbolt: Make the DP tunnel activation callback mandatory
tb_tunnel_alloc_dp() takes an optional callback which is run from dprx_work once the DPRX capabilities read has completed. Without that callback tb_dp_dprx_start() reads the capabilities synchronously and never queues the work. It however always takes a tunnel reference which is only dropped by dprx_work itself or by tb_dp_dprx_stop() when cancel_delayed_work() actually canceled that work. That reference is thus leaked for every tunnel without a callback.
The only tunnels without one are those from tb_tunnel_discover_dp(), which are activated again when restoring from hibernation. Pass the callback to tb_tunnel_discover_dp() as well and drop the synchronous path such that the DPRX capabilities are always read from dprx_work. Hibernation restore then also no longer blocks for up to 12 seconds while waiting for that read to complete.
Also fix up the KUnit tests.
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Analysis
by VulDB Data Team • 10/18/2026
The identified vulnerability in the Linux kernel's Thunderbolt subsystem represents a resource management flaw specifically affecting DisplayPort tunnel activation and hibernation restore processes. The core issue stems from an asymmetry in reference counting within the tb_dp_dprx_start function, which is responsible for initiating communication with the downstream port of a DisplayPort tunnel. This function acquires a reference to the tunnel object to ensure it remains valid during asynchronous operations but relies on specific cleanup paths to release that reference. Under normal circumstances, this cleanup occurs either when dprx_work executes after reading DPRX capabilities or if tb_dp_dprx_stop is called with cancel_delayed_work successfully aborting pending work items. However, the original implementation allowed for a synchronous code path where capabilities were read immediately without queuing the deferred work item. In these scenarios, neither the asynchronous worker nor the cancellation mechanism was triggered to drop the acquired reference, resulting in a persistent memory leak that accumulates with every tunnel instance lacking an activation callback.
This architectural oversight primarily impacts tunnels discovered via tb_tunnel_discover_dp, which are critical for maintaining connectivity after system hibernation events. When restoring from hibernate, these tunnels require reactivation, and without the proper asynchronous workflow, the kernel fails to manage the lifecycle of the tunnel object correctly. The immediate operational consequence is a gradual depletion of kernel memory resources as leaked references prevent garbage collection of unused or stale tunnel structures. Beyond resource exhaustion, this flaw introduces significant performance degradation during system resume operations. Because the synchronous path was retained for certain code paths, the system would block for up to twelve seconds while waiting for capability reads to complete locally rather than handling them asynchronously in a workqueue context. This latency severely impacts user experience and system responsiveness during boot or wake cycles involving Thunderbolt peripherals.
The resolution involves enforcing mandatory callback registration for all DisplayPort tunnel activations by modifying tb_tunnel_discover_dp to pass the necessary activation callback, thereby eliminating the conditional logic that permitted synchronous execution. By removing the synchronous path entirely, the kernel ensures that DPRX capabilities are always read through dprx_work, guaranteeing that delayed work is properly queued and subsequently executed or cancelled with corresponding reference count adjustments. This change aligns the codebase with standard asynchronous programming patterns in device drivers, ensuring consistent resource lifecycle management regardless of whether a tunnel is newly created or restored from hibernation. Additionally, the fix includes updates to KUnit tests to reflect these structural changes, maintaining test coverage integrity for the Thunderbolt subsystem's core functionality.
From a security and stability perspective, this vulnerability falls under CWE-401, which describes missing release of memory after effective usage, leading to resource leaks that can degrade system reliability over time. While not directly exploitable for remote code execution in most contexts, persistent kernel memory leaks contribute to denial-of-service conditions by exhausting available kernel heap space, potentially causing out-of-memory kills or system instability under heavy Thunderbolt device attachment scenarios. The fix mitigates this risk by enforcing strict adherence to the asynchronous workqueue model, ensuring that every acquired reference has a deterministic release path tied to the completion of hardware capability negotiation. This approach also aligns with best practices for driver development where blocking operations are avoided in favor of deferred processing to maintain system throughput and responsiveness during I/O intensive events like device enumeration or power state transitions.