[PATCH] media: usbtv: keep device alive while ALSA card exists

[Shuangpeng Bai <shuangpeng.kernel@gmail.com>]

The ALSA PCM callbacks store the driver state in pcm->private_data. An
open PCM file can outlive USB disconnect because usbtv_audio_free() uses
snd_card_free_when_closed(). The disconnect path can then drop the V4L2
device reference and free struct usbtv before ALSA releases the substream,
so a later close dereferences freed memory in snd_usbtv_pcm_close().

Take a V4L2 device reference for the ALSA card and drop it from the card
private_free callback. This keeps struct usbtv valid until ALSA has closed
the remaining files and freed the card.

Closes: https://lore.kernel.org/r/178144969601.60470.4852887710381872458@gmail.com
Fixes: 63ddf68de52e ("[media] usbtv: add audio support")
Signed-off-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>
---
 drivers/media/usb/usbtv/usbtv-audio.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/media/usb/usbtv/usbtv-audio.c b/drivers/media/usb/usbtv/usbtv-audio.c
index 333bd305a4f9..ae0a14e5ed2a 100644
--- a/drivers/media/usb/usbtv/usbtv-audio.c
+++ b/drivers/media/usb/usbtv/usbtv-audio.c
@@ -317,6 +317,13 @@ static const struct snd_pcm_ops snd_usbtv_pcm_ops = {
 	.pointer = snd_usbtv_pointer,
 };
 
+static void usbtv_audio_card_free(struct snd_card *card)
+{
+	struct usbtv *usbtv = card->private_data;
+
+	v4l2_device_put(&usbtv->v4l2_dev);
+}
+
 int usbtv_audio_init(struct usbtv *usbtv)
 {
 	int rv;
@@ -331,6 +338,10 @@ int usbtv_audio_init(struct usbtv *usbtv)
 	if (rv < 0)
 		return rv;
 
+	v4l2_device_get(&usbtv->v4l2_dev);
+	card->private_data = usbtv;
+	card->private_free = usbtv_audio_card_free;
+
 	strscpy(card->driver, usbtv->dev->driver->name, sizeof(card->driver));
 	strscpy(card->shortname, "usbtv", sizeof(card->shortname));
 	snprintf(card->longname, sizeof(card->longname),
-- 
2.43.0