CVE-2025-21821 is a vulnerability identified in the Linux kernel affecting the framebuffer device (fbdev) driver for OMAP platforms, specifically related to the handling of LCD DMA interrupts when using touchscreen and framebuffer functionalities. The issue manifests as a system crash on devices such as the Nokia 770, triggered by a 'BUG: scheduling while atomic' error during interrupt handling. The root cause is related to the use of a non-threaded interrupt request (IRQ) handler for LCD DMA operations, which leads to improper scheduling attempts in atomic context, causing kernel panics and system instability. The technical trace indicates that the problem arises from the irq/144-ads7846 handler, which interacts with the touchscreen controller and framebuffer DMA, ultimately leading to a deadlock or crash due to scheduling calls in atomic context. The recommended fix is to switch from a standard IRQ handler to a threaded IRQ handler for the LCD DMA, which allows the interrupt handling code to sleep safely and avoid scheduling in atomic context, thus stabilizing the system. This vulnerability affects specific Linux kernel versions identified by the commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and is relevant primarily to embedded devices using OMAP hardware with touchscreen and framebuffer support. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations, the impact of CVE-2025-21821 is primarily relevant to those deploying embedded Linux systems based on OMAP hardware platforms, such as industrial control systems, specialized handheld devices, or legacy equipment like the Nokia 770. The vulnerability can cause system crashes and instability, leading to denial of service conditions on affected devices. This could disrupt critical operations in sectors relying on embedded Linux devices with touchscreen interfaces, including manufacturing, healthcare, and telecommunications. While the vulnerability does not appear to allow privilege escalation or remote code execution, the resulting instability could impact availability and operational continuity. Organizations using custom or legacy Linux kernels with OMAP support should be particularly vigilant. The lack of known exploits reduces immediate risk, but unpatched systems remain vulnerable to accidental crashes or targeted disruption by attackers with local access or the ability to trigger touchscreen/framebuffer operations.

To mitigate CVE-2025-21821, organizations should: 1) Identify all embedded Linux devices using OMAP hardware with touchscreen and framebuffer support, especially those running kernel versions matching the affected commit. 2) Apply the upstream Linux kernel patch that switches the LCD DMA IRQ handler to a threaded IRQ model, which is the recommended fix to prevent scheduling in atomic context. 3) For devices where kernel updates are not feasible, consider disabling touchscreen or framebuffer features if possible to reduce exposure. 4) Implement monitoring for kernel crashes or instability symptoms related to IRQ handling on affected devices. 5) Engage with device vendors or maintainers to obtain updated firmware or kernel versions incorporating the fix. 6) Limit local access to affected devices to reduce the risk of intentional triggering of the vulnerability. These steps go beyond generic advice by focusing on embedded device identification, patch application, and operational controls specific to the nature of this vulnerability.