CVE-2025-38687
HighCVSS 7.3Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
A race condition was found in the comedi driver of the Linux kernel between poll and device detaching. During detach, the async area was removed even though poll requests were still active on the wait_queue_head, leading to use-after-free.
Risk Assessment
This could lead to memory corruption, potentially enabling privilege escalation or denial of service.
Recommendation
Update the Linux kernel to a version containing the fix that prevents device detach when tasks are queued on subdevice wait queues.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: comedi: fix race between polling and detaching syzbot reports a use-after-free in comedi in the below link, which is due to comedi gladly removing the allocated async area even though poll requests are still active on the wait_queue_head inside of it. This can cause a use-after-free when the poll entries are later triggered or removed, as the memory for the wait_queue_head has been freed. We need to check there are no tasks queued on any of the subdevices' wait queues before allowing the device to be detached by the `COMEDI_DEVCONFIG` ioctl. Tasks will read-lock `dev->attach_lock` before adding themselves to the subdevice wait queue, so fix the problem in the `COMEDI_DEVCONFIG` ioctl handler by write-locking `dev->attach_lock` before checking that all of the subdevices are safe to be deleted. This includes testing for any sleepers on the subdevices' wait queues. It remains locked until the device has been detached. This requires the `comedi_device_detach()` function to be refactored slightly, moving the bulk of it into new function `comedi_device_detach_locked()`. Note that the refactor of `comedi_device_detach()` results in `comedi_device_cancel_all()` now being called while `dev->attach_lock` is write-locked, which wasn't the case previously, but that does not matter. Thanks to Jens Axboe for diagnosing the problem and co-developing this patch.