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media: rtl2832_sdr: use vb2_video_unregister_device() on remove to fix DMA leak

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rtl2832_sdr_remove() runs on USB disconnect and clears dev->udev to
NULL before any pending streaming teardown has run. When user space
later closes its file descriptor, vb2 calls rtl2832_sdr_stop_streaming()
which in turn calls rtl2832_sdr_free_stream_bufs(). That helper releases
each coherent buffer with:

    usb_free_coherent(dev->udev, dev->buf_size,
                      dev->buf_list[dev->buf_num],
                      dev->dma_addr[dev->buf_num]);

usb_free_coherent() returns immediately when its dev argument is NULL,
so every DMA stream buffer that was live at disconnect is silently
leaked. The URBs allocated in rtl2832_sdr_alloc_urbs() outlive the
device for the same reason.

The rtl2832_sdr driver uses vb2_fop_release() in its file_operations,
so replace video_unregister_device(&dev->vdev) with
vb2_video_unregister_device(&dev->vdev) and move it before clearing
dev->udev. vb2_video_unregister_device() releases the vb2 queue, which
synchronously runs rtl2832_sdr_stop_streaming() if streaming is active,
so URBs and coherent DMA stream buffers are freed while dev->udev is
still valid.

vb2_video_unregister_device() locks vdev->queue->lock (vb_queue_lock)
internally, and stop_streaming() locks v4l2_lock, so the previous outer
mutex_lock(&dev->vb_queue_lock) / mutex_lock(&dev->v4l2_lock) pair
around the unregister sequence would self-deadlock and has been removed.
A short v4l2_lock critical section around dev->udev = NULL remains so
any ioctl path that still holds the file descriptor sees coherent state.

Issue identified by automated review of the INV-003 series at
https://sashiko.dev/

Fixes: 771138920e ("[media] rtl2832_sdr: Realtek RTL2832 SDR driver module")
Cc: stable@vger.kernel.org
Suggested-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Valery Borovsky <vebohr@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
This commit is contained in:
Valery Borovsky
2026-05-23 19:53:37 +03:00
committed by Hans Verkuil
parent ab8c3ed895
commit dabb047c62
1 changed files with 14 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
drivers/media/dvb-frontends/rtl2832_sdr.c
View File

@@ -1477,14 +1477,22 @@ static void rtl2832_sdr_remove(struct platform_device *pdev)
dev_dbg(&pdev->dev, "\n");
mutex_lock(&dev->vb_queue_lock);
mutex_lock(&dev->v4l2_lock);
/* No need to keep the urbs around after disconnection */
dev->udev = NULL;
/*
* vb2_video_unregister_device() releases the vb2 queue, which
* triggers rtl2832_sdr_stop_streaming() if streaming is active.
* stop_streaming() uses dev->udev to free URBs and coherent DMA
* stream buffers via usb_free_coherent(), so it must run before
* dev->udev is cleared. vb2_video_unregister_device() locks
* vb_queue_lock internally and stop_streaming() locks v4l2_lock,
* so neither may be held by the caller.
*/
v4l2_device_disconnect(&dev->v4l2_dev);
video_unregister_device(&dev->vdev);
vb2_video_unregister_device(&dev->vdev);
mutex_lock(&dev->v4l2_lock);
dev->udev = NULL;
mutex_unlock(&dev->v4l2_lock);
mutex_unlock(&dev->vb_queue_lock);
v4l2_device_put(&dev->v4l2_dev);
module_put(pdev->dev.parent->driver->owner);
}