🛡️ AZL-66860 — kernel (CVE-2025-38687)

CVE-2025-38687 affecting package kernel for versions less than 6.6.104.2-1

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.