CVE-2025-39713

In the Linux kernel, the following vulnerability has been resolved:

media: rainshadow-cec: fix TOCTOU race condition in rain_interrupt()

In the interrupt handler rain_interrupt(), the buffer full check on rain->buf_len is performed before acquiring rain->buf_lock. This creates a Time-of-Check to Time-of-Use (TOCTOU) race condition, as rain->buf_len is concurrently accessed and modified in the work handler rain_irq_work_handler() under the same lock.

Multiple interrupt invocations can race, with each reading buf_len before it becomes full and then proceeding. This can lead to both interrupts attempting to write to the buffer, incrementing buf_len beyond its capacity (DATA_SIZE) and causing a buffer overflow.

Fix this bug by moving the spin_lock() to before the buffer full check. This ensures that the check and the subsequent buffer modification are performed atomically, preventing the race condition. An corresponding spin_unlock() is added to the overflow path to correctly release the lock.

This possible bug was found by an experimental static analysis tool developed by our team.

A TOCTOU race in the RainShadow USB CEC driver (rain_interrupt()) checked buf_len before taking buf_lock, allowing concurrent interrupts to overrun the driver’s ring-buffer accounting and corrupt skb state, leading to a kernel crash. The fix moves the spinlock to cover the fullness check and the subsequent write, and adds an unlock on the overflow path. Impact is limited to Availability (DoS). Exploitation requires an attached/malicious CEC USB device.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.