CVE-2026-98587 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
firewire: cdev: fix back-transition for iso_resource_auto client resource
The todo member of iso_resource_auto structure represents the state of the client resource and normally transitions in the following order:
ISO_RES_AUTO_ALLOC -> ISO_RES_AUTO_REALLOC -> ISO_RES_AUTO_DEALLOC
However, concurrent access from the work item and the file descriptor release function can cause the state to transition backwards from ISO_RES_AUTO_DEALLOC to ISO_RES_AUTO_REALLOC.
Prevent the back-transition by checking the current state before updating it in the work item.
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Analysis
by VulDB Data Team • 10/19/2026
The Linux kernel's FireWire character device interface, specifically within the iso_resource_auto subsystem, contained a concurrency-related race condition that could lead to incorrect resource management and potential system instability. This vulnerability stems from improper synchronization between asynchronous work items and file descriptor release operations when managing isochronous resources used for high-bandwidth data transfers such as audio or video streams. The core issue lies in the state machine governing iso_resource_auto structures, which tracks the lifecycle of these resources through distinct phases: allocation, reallocation, and deallocation. Under normal sequential execution, a resource transitions from ISO_RES_AUTO_ALLOC to ISO_RES_AUTO_REALLOC upon request for additional bandwidth or buffer adjustments, and finally to ISO_RES_AUTO_DEALLOC when the client releases its hold on the resource. However, this linear progression assumes exclusive access during state updates, an assumption violated by concurrent threads of control in multi-core environments.
The technical flaw arises from a lack of atomicity or proper locking mechanisms protecting the todo member of the iso_resource_auto structure during critical transitions. Specifically, when a file descriptor is closed via release functions, it triggers deallocation logic that sets the state to ISO_RES_AUTO_DEALLOC. Simultaneously, background work items scheduled by the kernel may attempt to reallocate resources based on prior states or pending requests, unaware that the resource has already been marked for deallocation. This race condition allows a concurrent operation to overwrite the DEALLOC state with REALLOC, effectively reversing the intended cleanup process. Such back-transitioning violates the expected lifecycle of the resource and can result in use-after-free scenarios where memory is accessed after being freed, or double-free conditions if subsequent operations attempt to release already-deallocated buffers.
From an operational impact perspective, this vulnerability poses significant risks including kernel panics, data corruption, and denial-of-service conditions for applications relying on FireWire devices. Since iso_resource_auto handles real-time streaming data, any disruption in resource management can lead to dropped packets, audio glitches, or video artifacts. More critically, the memory safety violations inherent in race conditions like this often serve as entry points for privilege escalation attacks if an attacker can trigger the specific timing window required to exploit the state reversal. The absence of proper synchronization primitives means that under high load or concurrent access patterns typical in multimedia applications, the likelihood of hitting this code path increases substantially, making it a persistent threat rather than an edge-case anomaly.
This vulnerability aligns with CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition'), as multiple execution paths modify shared state without adequate mutual exclusion. It also relates to CWE-416: Use After Free, given the potential for accessing memory that has been deallocated due to incorrect state transitions. In terms of MITRE ATT&CK mapping, this falls under Tactic TA0005: Defense Evasion and Technique T1203: Exploitation for Defense Evasion if leveraged in an attack chain, though primarily it represents a reliability issue categorized under software faults rather than explicit malicious exploitation vectors. The root cause is identified as insufficient locking around the state variable update operations within both the work item handler and the file descriptor release path.
To mitigate this vulnerability, developers must implement atomic operations or spinlocks to protect updates to the todo member of iso_resource_auto structures. Specifically, using compare-and-swap (CAS) instructions ensures that state transitions occur only if the current value matches the expected previous state, thereby preventing back-transitions from DEALLOC to REALLOC. Alternatively, introducing a mutex around critical sections involving both work item processing and file descriptor release can serialize access to shared resource states. Additionally, adding explicit checks before proceeding with reallocation logic to verify that the resource has not already been marked for deallocation provides an extra layer of defense against race conditions. Kernel maintainers should review similar state machines across other subsystems to identify analogous vulnerabilities where asynchronous operations interact with synchronous release paths without adequate synchronization barriers.