[PATCH] media: rtl2832_sdr: release URBs and stream buffers on start_streaming() failure

[Valery Borovsky <vebohr@gmail.com>]

rtl2832_sdr_start_streaming() calls rtl2832_sdr_alloc_stream_bufs(),
rtl2832_sdr_alloc_urbs() and rtl2832_sdr_submit_urbs() in sequence and
shares a single err: label that only unlocks the mutex and returns.
When alloc_urbs() succeeds but submit_urbs() fails, or when alloc_urbs()
itself returns -ENOMEM after alloc_stream_bufs() has already succeeded,
the URBs and/or the coherent DMA stream buffers stay allocated while
streaming reports failure to vb2. Two latent defects follow on the next
VIDIOC_STREAMON:

1) rtl2832_sdr_alloc_stream_bufs() unconditionally resets dev->buf_num
   to 0 and overwrites dev->buf_list[]/dev->dma_addr[], permanently
   leaking the coherent DMA memory allocated by the previous attempt.

2) rtl2832_sdr_alloc_urbs() never resets dev->urbs_initialized and only
   increments it. After a second successful pass urbs_initialized can
   exceed MAX_BULK_BUFS, so the subsequent rtl2832_sdr_free_urbs() walks
   from urbs_initialized - 1 down to 0 and reads past the end of
   dev->urb_list[], passing garbage pointers to usb_free_urb().

Mirror the teardown that stop_streaming() already performs: on the error
path call rtl2832_sdr_free_urbs() and rtl2832_sdr_free_stream_bufs()
before unlocking. Both helpers are idempotent (free_urbs kills and zeros
urbs_initialized; free_stream_bufs is gated on URB_BUF and clears the
buf_num counter), so partial-failure paths and the no-allocation paths
remain safe.

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

Fixes: 771138920eaf ("[media] rtl2832_sdr: Realtek RTL2832 SDR driver module")
Cc: stable@vger.kernel.org
Signed-off-by: Valery Borovsky <vebohr@gmail.com>
---
 drivers/media/dvb-frontends/rtl2832_sdr.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/media/dvb-frontends/rtl2832_sdr.c b/drivers/media/dvb-frontends/rtl2832_sdr.c
index 422d1a7b5456..efcef1317cf9 100644
--- a/drivers/media/dvb-frontends/rtl2832_sdr.c
+++ b/drivers/media/dvb-frontends/rtl2832_sdr.c
@@ -900,7 +900,13 @@ static int rtl2832_sdr_start_streaming(struct vb2_queue *vq, unsigned int count)
 	if (ret)
 		goto err;
 
+	mutex_unlock(&dev->v4l2_lock);
+
+	return 0;
+
 err:
+	rtl2832_sdr_free_urbs(dev);
+	rtl2832_sdr_free_stream_bufs(dev);
 	mutex_unlock(&dev->v4l2_lock);
 
 	return ret;
-- 
2.51.0