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.