CVE-2026-97501 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
pinctrl: mediatek: paris: bypass pinctrl GPIO layer in set GPIO direction
pinctrl_gpio_direction_input() / pinctrl_gpio_direction_output() take the pinctrl mutex. This causes a gpiochip operations to need to sleep. Worse yet, the .can_sleep field in the gpiochip is not set. This causes the shared GPIO proxy to trip over, as it uses gpiod_cansleep() to check whether it can use a spinlock or needs a mutex. In this case, it ends up taking a spinlock, then calls pinctrl_gpio_direction_output(), which takes a mutex. This causes a huge warning.
While this class of Mediatek hardware does not have separate clear/set registers, the pinctrl context has a spinlock that is taken whenever a register read-modify-write is done. Also, once the GPIO function is selected / muxed in, further GPIO operations do not involve pinctrl operations or state. The GPIO direction and level values do not require toggling the pinmux or any other pin config options.
Switch to directly calling mtk_pinmux_gpio_set_direction() in the GPIO set direction callbacks to avoid taking the pinctrl mutex. Drop the .gpio_set_direction field in mtk_pmxops to signal we are no longer using the pinctrl GPIO layer for setting the direction.
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Analysis
by VulDB Data Team • 09/24/2026
The vulnerability described involves a concurrency and locking hierarchy violation within the Linux kernel's pin control subsystem, specifically affecting the Mediatek Paris driver implementation of General Purpose Input/Output (GPIO) operations. The core technical flaw arises from an incorrect assumption regarding sleepability in hardware abstraction layers. When functions such as pinctrl_gpio_direction_input or pinctrl_gpio_direction_output are invoked to change a GPIO pin's direction, they internally acquire the pinctrl mutex. This acquisition implies that these operations may block and require sleeping context. However, the associated gpiochip structure for this Mediatek hardware does not set the .can_sleep flag to true. This discrepancy creates a critical mismatch between the driver's behavior and its declared capabilities within the kernel GPIO subsystem framework.
This misconfiguration triggers a severe operational failure in the shared GPIO proxy layer of the Linux kernel. The proxy mechanism relies on the gpiod_cansleep function to determine whether it can safely utilize spinlocks for atomic operations or must employ mutexes which allow sleeping. Because .can_sleep is unset, the proxy assumes that all subsequent calls are safe within a non-sleeping context and proceeds to acquire a spinlock. It then invokes pinctrl_gpio_direction_output, which attempts to take the pinctrl mutex while holding that spinlock. This sequence results in an invalid locking hierarchy where a sleeping function is called from an atomic context protected by a spinlock. The kernel detects this violation and generates a significant warning or stack trace, potentially leading to system instability, deadlocks, or unpredictable behavior during GPIO configuration tasks.
From the perspective of industry standards, this issue aligns with CWE-674, which covers Uncontrolled Recursion, although more accurately it represents a Locking Hierarchy Violation often associated with improper synchronization primitives usage. In terms of the MITRE ATT&CK framework for enterprise security and system reliability, while not an exploitable attack vector in the traditional sense, this flaw impacts Availability by causing kernel warnings that can clutter logs or lead to hangs if the deadlock conditions are exacerbated under high load. The root cause is a design oversight where the driver author did account for the specific hardware constraints of Mediatek chips which do not require pinmux toggling during direction changes once initialized.
The resolution involves bypassing the generic pinctrl GPIO layer entirely for setting directions, thereby avoiding the acquisition of the problematic mutex. Instead, the fix switches to directly calling mtk_pinmux_gpio_set_direction within the GPIO set direction callbacks. This direct hardware access is safe because it operates without requiring sleep and does not interact with the pinctrl state machine that manages pin multiplexing configurations. Furthermore, the .gpio_set_direction field in the mtk_pmxops structure is removed to explicitly signal to the kernel subsystems that this driver no longer utilizes the standard pinctrl GPIO layer for direction control. This architectural change ensures that GPIO operations remain atomic and compatible with contexts where sleeping is prohibited, thus eliminating the locking conflict entirely.
To mitigate similar issues in other drivers or during maintenance of existing codebase components, developers must ensure strict adherence to kernel API contracts regarding sleepability flags. The .can_sleep field in gpiochip structures must accurately reflect whether any operation within that chip can block and require a sleeping context. If a driver performs operations that might sleep, such as acquiring mutexes or calling functions known to potentially block on hardware interrupts or I/O waits, the flag must be set. Conversely, if all operations are atomic, no sleeping primitives should be used in callbacks exposed through GPIO interfaces. Regular static analysis and code reviews focusing on locking hierarchies can help prevent these types of concurrency bugs before they reach production environments.