CVE-2024-57889 addresses a concurrency and locking vulnerability in the Linux kernel's pinctrl driver for the MCP23S08 IO expander chip, which is part of the MCP23xxx family. The issue arises due to improper locking mechanisms when handling interrupts (IRQs) generated by devices using this IO expander, such as touchscreens employing MCP23017 via I2C. Specifically, the regmap subsystem used by the pinctrl-mcp23s08 driver employs a mutex to protect concurrent register accesses. However, during IRQ setup, a spinlock is held while the driver attempts to acquire this mutex, leading to a scenario where a sleeping function is called from an atomic context, which is invalid in the Linux kernel. This results in kernel BUGs and potential system instability or crashes. The root cause is that the internal regmap locking is redundant because the driver already uses its own lock (mcp->lock) to serialize access, except in a few functions (mcp_pinconf_get/set) which lacked proper locking. The patch disables internal regmap locking and adds explicit locking in these functions, preventing the mutex from being acquired while holding a spinlock and thus eliminating the atomic context sleep bug. This vulnerability is relevant for Linux kernel versions containing the affected pinctrl-mcp23s08 driver code and impacts systems using MCP23xxx IO expanders to handle IRQs, particularly over I2C. The problem manifests as kernel panics or BUGs during IRQ setup or handling, which can cause system crashes or denial of service. No evidence of exploitation in the wild is reported, and no CVSS score has been assigned yet.

For European organizations, the impact of CVE-2024-57889 primarily concerns systems running Linux kernels with MCP23xxx IO expanders in use, notably in embedded devices, industrial control systems, or specialized hardware like touchscreens and IoT devices. Affected systems may experience kernel panics or crashes due to improper locking, leading to denial of service conditions. This can disrupt critical operations, especially in sectors relying on embedded Linux devices such as manufacturing automation, transportation, healthcare equipment, and telecommunications infrastructure. The vulnerability does not appear to allow privilege escalation or remote code execution directly but can cause system instability and downtime. Organizations with large deployments of Linux-based embedded devices using MCP23xxx chips are at higher risk. Given the widespread use of Linux in Europe across various industries, the potential for operational disruption exists, particularly in environments where device stability and uptime are critical. However, the impact is limited to systems using the affected hardware and driver combination, which narrows the scope somewhat.

To mitigate CVE-2024-57889, European organizations should: 1) Apply the official Linux kernel patches that disable internal regmap locking and add proper locking in mcp_pinconf_get/set functions as soon as they become available in their kernel distributions. 2) Audit embedded Linux devices and systems to identify those using MCP23xxx IO expanders, especially MCP23S08 and MCP23017 chips, and verify kernel versions and driver usage. 3) For devices where kernel upgrades are not immediately feasible, consider isolating or limiting the use of affected hardware or disabling features that trigger IRQ handling via MCP23xxx expanders if possible. 4) Monitor kernel logs for BUG messages related to sleeping in atomic context or mutex locking failures to detect potential triggering of this vulnerability. 5) Coordinate with hardware and device vendors to ensure firmware or driver updates are provided and deployed timely. 6) Implement robust system monitoring and automated recovery mechanisms to minimize downtime in case of kernel panics. These steps go beyond generic advice by focusing on hardware-specific identification, kernel patching, and operational monitoring tailored to the nature of this concurrency bug.