Re: [PATCH v2 2/3] virtio_input: stop callbacks before unregistering input device

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

Pre-existing issues:
- [High] Missing `virtio_reset_device()` in the error path of `virtinput_probe()` before deleting virtqueues, potentially leading to use-after-free or memory corruption by the active hardware/hypervisor.
- [High] The driver leaks DMA mappings for unconsumed buffers in the event virtqueue (`vi->evt`) upon device removal or suspend/freeze.
--

commit 71bbbcca0b03e3c67fa905a8357e9d3ad23e7fe4
Author: Karl Mehltretter <kmehltretter@gmail.com>

virtio_input: stop callbacks before unregistering input device

virtinput_remove() unregisters the input device before resetting the
virtio device. virtinput_recv_events() drops vi->lock around input_event(),
so clearing vi->ready does not stop a callback that passed the entry check.
It can still use vi->idev, requeue buffers and kick the queue.

> diff --git a/drivers/virtio/virtio_input.c b/drivers/virtio/virtio_input.c
> index deec24e8e6828..7b654af0a42cb 100644
> --- a/drivers/virtio/virtio_input.c
> +++ b/drivers/virtio/virtio_input.c
[ ... ]
> @@ -350,8 +353,9 @@ static void virtinput_remove(struct virtio_device *vdev)
>  	vi->ready = false;
>  	spin_unlock_irqrestore(&vi->lock, flags);
>  
> -	input_unregister_device(vi->idev);
> +	/* Callbacks use vi->idev. */
>  	virtio_reset_device(vdev);
> +	input_unregister_device(vi->idev);
>  	while ((buf = virtqueue_detach_unused_buf(vi->sts)) != NULL)
>  		kfree(buf);
>  	vdev->config->del_vqs(vdev);

[Severity: High]
This is a pre-existing issue, but does this cleanup leak DMA mappings for
the event virtqueue (vi->evt)?

The cleanup loop correctly detaches and unmaps vi->sts using
virtqueue_detach_unused_buf(), but it ignores vi->evt. Since
virtinput_fill_evt() populates vi->evt with buffers using
virtqueue_add_inbuf_cache_clean(), which establishes DMA mappings under
the hood, omitting the detachment step leaves these mappings active.

Does this result in a persistent DMA mapping leak every time the device is
unbound? Furthermore, since the memory for these buffers (vi->evts) is freed,
does this leave active DMA mappings pointing to freed memory, posing a memory
corruption risk if delayed DMA occurs?

Does this exact same DMA mapping leak also occur during the power management
suspend cycle in virtinput_freeze() which performs the same cleanup?

[Severity: High]
This is also a pre-existing issue, but is there a missing
virtio_reset_device() in the error path of virtinput_probe()?

Looking at virtinput_probe(), the device is marked as ready:

drivers/virtio/virtio_input.c:virtinput_probe() {
    ...
	virtio_device_ready(vdev);
	vi->ready = true;
	err = input_register_device(vi->idev);
	if (err)
		goto err_input_register;
    ...
}

If input_register_device() fails, the error path deletes the virtqueues:

drivers/virtio/virtio_input.c:virtinput_probe() {
    ...
err_input_alloc:
	vdev->config->del_vqs(vdev);
    ...
}

Since virtio_device_ready() sets the device status to DRIVER_OK and enables
the host/hardware to start processing virtqueues, does deleting the active
virtqueue structures without first calling virtio_reset_device() to halt
the device risk a use-after-free or memory corruption by the host backend
if it continues to access the freed vring memory?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260905152059.89560-1-kmehltretter@gmail.com?part=2