CVE-2024-26806 is a vulnerability identified in the Linux kernel specifically affecting the cadence-qspi SPI controller driver. The issue arises from improper handling of runtime power management (PM) callbacks within the driver. The cadence-qspi driver incorrectly invokes system-wide suspend helper functions spi_controller_suspend() and spi_controller_resume() inside its runtime_suspend() and runtime_resume() callbacks. These helper functions manage the stopping and starting of the SPI queue and toggle the SPI_CONTROLLER_SUSPENDED flag, operations that require acquiring the ctlr->bus_lock_mutex mutex. However, cadence-qspi is a non-queued SPI controller, making the queue stop/start logic irrelevant. More critically, the invocation of spi_controller_resume() during runtime_resume() leads to a deadlock because the bus_lock_mutex is already held in the context of the exec_op() callback, which increments the usage count and calls pm_runtime_resume_and_get(). This mutex deadlock prevents the SPI controller from resuming properly after auto-suspend, effectively blocking all SPI operations on the device once it enters auto-suspend mode. The deadlock occurs because spi_controller_resume() attempts to acquire a mutex that is already locked higher up in the call stack, causing the kernel thread to hang indefinitely. This flaw can cause system instability or denial of service (DoS) conditions on affected systems using the cadence-qspi driver. The vulnerability has been addressed by removing the inappropriate calls to spi_controller_suspend() and spi_controller_resume() from the cadence-qspi driver's runtime PM hooks, thereby preventing the deadlock scenario. No known exploits are currently reported in the wild, and the vulnerability affects specific Linux kernel versions containing the faulty cadence-qspi driver implementation.

For European organizations, the impact of CVE-2024-26806 primarily involves potential system instability or denial of service on devices running affected Linux kernel versions with the cadence-qspi SPI controller driver. This is particularly relevant for embedded systems, industrial control systems, or IoT devices that rely on this specific SPI controller for communication with peripherals. A deadlock in the SPI controller driver can halt critical device operations, leading to service interruptions or failures in operational technology environments. Organizations using Linux-based infrastructure in sectors such as manufacturing, telecommunications, or transportation may experience disruptions if their hardware platforms incorporate the cadence-qspi controller. Although this vulnerability does not appear to allow privilege escalation or remote code execution, the resulting DoS could impact availability of critical systems. Since no exploits are known in the wild, the immediate risk is moderate, but unpatched systems remain vulnerable to potential future exploitation or accidental triggering of the deadlock. The impact is more pronounced in environments where uptime and reliability are critical and where devices cannot be easily rebooted or maintained frequently.

To mitigate CVE-2024-26806, organizations should: 1) Apply the latest Linux kernel patches that remove the improper calls to spi_controller_suspend() and spi_controller_resume() in the cadence-qspi driver. This is the definitive fix to prevent the deadlock condition. 2) Identify and inventory devices and systems using the cadence-qspi SPI controller, focusing on embedded and IoT devices running affected Linux kernel versions. 3) For devices where immediate patching is not feasible, consider implementing monitoring to detect symptoms of the deadlock, such as hung kernel threads or unresponsive SPI peripherals, and plan for controlled reboots or failover to maintain availability. 4) Coordinate with hardware vendors and Linux distribution maintainers to ensure timely updates are available and deployed. 5) Review runtime power management configurations and consider disabling auto-suspend on affected devices as a temporary workaround, understanding this may impact power efficiency. 6) Incorporate this vulnerability into vulnerability management and incident response processes to ensure rapid detection and remediation.