CVE-2026-74733 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
gpio: pca953x: fix pca953x_irq_bus_sync_unlock regmap lock
Locking is disabled in the regmap config as this driver uses its own lock. This means that all calls to regmap functions (read or write) must hold the i2c_lock. The function pca953x_irq_bus_sync_unlock() did not do this, and it was therefore possible that multiple threads could cause an incorrect register to be read/written.
A previous patch partly fixed this, but only protected the write to the interrupt mask register, and not the read from the direction register.
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Analysis
by VulDB Data Team • 08/22/2026
The vulnerability identified in the Linux kernel's pca953x GPIO driver represents a critical concurrency flaw rooted in improper synchronization of hardware access operations. The underlying issue stems from the specific configuration of the regmap subsystem used by this driver, where locking is explicitly disabled within the regmap config structure because the driver implements its own custom locking mechanism via an i2c_lock. This architectural decision places the entire burden of thread safety on the developer to ensure that every interaction with the hardware registers through regmap functions is protected by acquiring and releasing this specific lock. The pca953x_irq_bus_sync_unlock function, which handles interrupt synchronization during bus unlock operations, failed to adhere to this requirement. By omitting the acquisition of the i2c_lock before performing register access, the code created a race condition where multiple execution threads could simultaneously attempt to read or write to shared hardware registers without mutual exclusion.
The technical consequence of this missing lock is a classic time-of-check-to-time-of-use scenario that leads to data corruption and undefined behavior within the GPIO subsystem. Specifically, while a previous patch attempted to mitigate part of this issue by protecting the write operation to the interrupt mask register, it neglected to protect the read operation from the direction register. This partial fix left a significant gap in the synchronization logic. When multiple threads execute concurrently, one thread might be reading the current state of the direction register to determine pin configurations while another thread is simultaneously modifying those same registers or related control states. Without the i2c_lock ensuring serial access, these operations can interleave unpredictably, causing the driver to read stale data, overwrite critical configuration bits incorrectly, or trigger hardware faults due to inconsistent internal states.
From an operational impact perspective, this vulnerability compromises the reliability and stability of systems relying on pca953x GPIO expanders for input/output control. In embedded environments where these chips are commonly used for managing peripherals such as switches, LEDs, or sensors, incorrect register access can lead to devices behaving erratically, failing to respond to commands, or causing system hangs if the kernel attempts to operate on invalid hardware states. For security-conscious deployments, while this is primarily a stability issue rather than an exploit vector for privilege escalation, it undermines the integrity of the device management layer. An attacker with local access could potentially trigger these race conditions through concurrent I/O operations to destabilize the system or cause denial-of-service by forcing the kernel into error states that require a reboot to recover.
This flaw is best categorized under CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization, as it involves multiple threads accessing shared resources without proper coordination. In terms of attack surface mapping via MITRE ATT&CK, this relates to techniques involving resource manipulation and potential denial-of-service through instability rather than direct exploitation for data theft. The remediation requires a comprehensive review of all regmap interactions within the pca953x driver to ensure that every read and write operation is enclosed within the appropriate lock acquisition and release blocks. Developers must verify that both the interrupt mask register writes and the direction register reads are protected by the i2c_lock in pca953x_irq_bus_sync_unlock, thereby restoring mutual exclusion guarantees for all hardware access paths associated with this driver.