CVE-2025-21821: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-21821 is a vulnerability discovered in the Linux kernel's framebuffer device (fbdev) OMAP driver. The issue was identified on February 27, 2025, affecting the LCD DMA handling in Nokia 770 devices when using touchscreen and framebuffer simultaneously. The vulnerability manifests as a system crash with a 'scheduling while atomic' bug in the interrupt handling mechanism (NVD, Debian).

The vulnerability occurs in the LCD DMA interrupt handler of the OMAP framebuffer driver. When using both touchscreen and framebuffer functionalities, the system attempts to acquire a mutex lock in an atomic context, leading to a scheduling violation. The issue manifests in the interrupt handler (lcd_dma_irq_handler) when processing DMA requests for the LCD display (Kernel Commit).

When triggered, this vulnerability causes the Nokia 770 device to crash, disrupting normal system operation. The crash occurs due to a scheduling violation in the interrupt handling mechanism, affecting the stability of the device when using both touchscreen and framebuffer features (NVD).

The issue has been fixed by switching to a threaded IRQ implementation. The patch modifies the interrupt handler registration to use request_threaded_irq() instead of request_irq(), with the IRQF_ONESHOT flag. This change provides a stable system by avoiding the scheduling while atomic condition. The fix is available in Linux kernel version 6.1.129-1 and later (Kernel Commit).