CVE-2026-93142 in Linux
Summary
by MITRE • 09/18/2026
In the Linux kernel, the following vulnerability has been resolved:
thermal/drivers/rcar: Fix error checking in probe()
This code accidentally calls thermal_zone_device_enable() before checking whether thermal_zone_device_register_with_trips() failed. Move the call until later to avoid an error pointer dereference of "priv->zone".
The driver works differently depending on if we are using OF thermal or not. We use thermal_add_hwmon_sysfs() if we are using OF thermal and call thermal_zone_device_enable() if not. We can share same error check for if either of these fail.
Moving the thermal_zone_device_enable() call is a bit cleaner as well. The original code used a three step process to cleanup: 1. Call thermal_zone_device_unregister() to cleanup. 2. Set priv->zone to an error pointer to preserve the error code. 3. Set priv->zone to NULL to avoid a second call to thermal_zone_device_unregister() in the rcar_thermal_remove() function.
Now we can just do a direct goto error_unregister and rcar_thermal_remove() handles the cleanup properly.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel driver for Renesas R-Car thermal management contains a critical logic flaw within its initialization sequence, specifically in the probe function responsible for setting up hardware resources. This vulnerability arises from an incorrect ordering of operations where the system attempts to enable a thermal zone device before verifying that the registration process completed successfully. The root cause lies in the failure to check the return value or pointer status of the thermal_zone_device_register_with_trips() call prior to invoking thermal_zone_device_enable(). In kernel programming, functions that allocate and initialize complex structures often return error pointers on failure rather than null pointers or standard error codes. By proceeding to enable the device without this validation, the driver risks dereferencing an invalid memory address if the registration step fails due to resource exhaustion, hardware incompatibility, or configuration errors. This constitutes a classic instance of improper input handling and unchecked return value checking, which are frequently categorized under CWE-252 for unchecked return values and CWE-787 for out-of-bounds write access resulting from invalid pointer dereferences.
The operational impact of this vulnerability is primarily stability-related rather than security-exploitable in a traditional sense, although it can lead to system crashes or kernel panics that result in denial of service conditions. When thermal_zone_device_enable() is called on an uninitialized or failed zone structure, the kernel attempts to access memory fields within the priv->zone object that do not contain valid data structures. This invalid pointer dereference triggers a fault exception, causing the operating system to halt execution to prevent further corruption. While this does not directly allow for privilege escalation or remote code execution in most scenarios, it compromises the reliability of the thermal management subsystem. If the kernel panics during boot due to this error, the entire system may fail to start, rendering the hardware unusable until the driver is patched or disabled via configuration changes.
The technical complexity of this issue was exacerbated by the divergent code paths used for different thermal control methods. The driver behaves differently depending on whether it is utilizing Open Firmware (OF) thermal management or a non-OF approach. In OF scenarios, the system calls thermal_add_hwmon_sysfs(), whereas in other cases, it relies directly on thermal_zone_device_enable(). Both of these functions require that the underlying zone device be properly registered and valid. The original implementation failed to unify the error handling for these two distinct paths, leading to a situation where one path might succeed while the other fails, yet both could potentially trigger the premature enable call if not carefully guarded. This lack of unified validation logic increases the attack surface by creating multiple entry points for potential failure states that are not consistently handled across different hardware configurations or kernel versions.
The resolution involves restructuring the probe function to ensure strict sequential integrity in resource allocation and initialization. The thermal_zone_device_enable() call is moved to occur only after a successful verification of the registration step, ensuring that priv->zone holds a valid pointer before any operations dependent on its state are executed. This change simplifies the error handling logic significantly. Previously, cleanup required a three-step process involving unregistering the device, setting the zone pointer to an error code marker, and then nullifying it to prevent double-unregistration in the remove function. The updated approach utilizes a direct goto statement to jump to a unified error handler that calls thermal_zone_device_unregister(). This not only prevents the invalid dereference but also leverages existing cleanup routines more effectively, reducing code duplication and potential for future logic errors.
From a mitigation perspective, this issue is addressed through upstream kernel patches that correct the control flow within the driver source code. System administrators should ensure their Linux kernels are updated to versions containing this fix, particularly those running on Renesas R-Car hardware platforms. For environments where immediate patching is not feasible, disabling the specific thermal driver or configuring the system to use alternative thermal management methods may prevent the trigger condition, though this could impact temperature monitoring capabilities. The incident highlights the importance of rigorous static analysis and code review practices that enforce checking return values from allocation functions before proceeding with dependent operations. Adhering to these standards aligns with best practices outlined in industry frameworks such as CWE-252 for proper error handling and contributes to overall system resilience against stability-related vulnerabilities.