CVE-2026-93082 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
firmware: arm_scmi: Unwind P2A receiver mailbox setup failure
mailbox_chan_setup() can request an additional P2A receiver channel after successfully acquiring the primary P2A channel. If that later request fails, the function returns immediately and leaves the primary channel allocated.
Unwind the primary mailbox channel before returning the error so probe deferral or other setup failures do not leave the channel busy for later probe attempts.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel firmware subsystem contains a resource management flaw within the System Control and Management Interface (SCMI) driver, specifically in the arm_scmi implementation. This vulnerability arises from an improper error handling sequence during the initialization of mailbox communication channels between the processor and system controllers. The SCMI protocol relies on bidirectional messaging to facilitate power management, performance scaling, and other hardware control operations. To establish this communication, the kernel must allocate specific mailbox channels for sending commands (Processor-to-Admin or P2A) and receiving responses. During the probe phase of driver initialization, the function mailbox_chan_setup is responsible for acquiring these resources. The code logic attempts to secure a primary P2A channel first. If successful, it proceeds to request an additional receiver channel to handle incoming messages from the admin entity.
The core technical flaw lies in the failure path when the secondary receiver channel allocation fails. In this scenario, the function returns an error code immediately without releasing or cleaning up the previously acquired primary P2A channel. This results in a resource leak where the mailbox hardware remains locked and marked as busy by the kernel subsystem. Because the driver initialization aborts due to the missing receiver channel, the system cannot proceed with SCMI operations. However, since the transmitter channel was never released, subsequent attempts to probe or initialize other devices that depend on similar resources may fail because the underlying hardware interface is already claimed but not fully functional. This creates a state where valid drivers are blocked from loading due to phantom resource occupancy.
From an operational perspective, this vulnerability leads to denial of service for SCMI-dependent features within affected systems. Devices relying on ARM System Control and Management Interface protocols will fail to initialize correctly if the secondary channel request fails for any reason, such as hardware configuration errors or driver conflicts. Furthermore, because the primary channel remains allocated, it prevents other kernel components from reusing that specific mailbox interface during retry attempts or in parallel initialization processes. This can cause system instability, boot failures on embedded platforms with strict resource constraints, and unnecessary delays as the kernel repeatedly fails to bind drivers due to exhausted communication endpoints. The issue is particularly critical in environments where probe deferral is common, as each failed attempt leaves behind a lingering lock that accumulates over time or across multiple device trees.
This vulnerability aligns with CWE-401, which describes missing release of memory after successful allocation, and more specifically relates to improper resource cleanup during error handling paths. In the context of the MITRE ATT&CK framework for Linux systems, this behavior can be categorized under Tactic TA0005 (Defense Evasion) or TA0003 Persistence if exploited in a manner that exhausts system resources to prevent legitimate services from running, though it is primarily an unintentional reliability flaw rather than a malicious exploit vector. The lack of proper unwinding violates the principle of atomic resource acquisition and release, leading to state corruption within the kernel's device management layer.
To mitigate this vulnerability, developers must ensure that all acquired resources are released in reverse order if any subsequent allocation step fails. In the specific case of arm_scmi, the fix involves calling the appropriate cleanup function for the primary P2A channel before returning an error code from mailbox_chan_setup when the receiver channel request is unsuccessful. This ensures that no hardware locks remain held after a failed initialization attempt. System administrators and developers should apply kernel patches that include this unwinding logic to restore proper resource lifecycle management. Regular auditing of driver probe functions for balanced acquire-release patterns can prevent similar issues in other subsystems, ensuring robust operation across diverse ARM-based embedded platforms and servers utilizing SCMI protocols.