[PATCH] media: usbtv: Lock resolution while streaming

[PATCH] media: usbtv: Lock resolution while streaming

[Ludwig Disterhof]

When an program is streaming (ffplay) and another program (qv4l2)
changes the TV standard from NTSC to PAL, the kernel crashes due to trying
to copy to unmapped memory.

Changing from NTSC to PAL increases the resolution in the usbtv struct,
but the video plane buffer isn't adjusted, so it overflows.

Fixes: 0e0fe3958fdd13d ("[media] usbtv: Add support for PAL video source")

Signed-off-by: Ludwig Disterhof <ludwig@disterhof.eu>
---
 drivers/media/usb/usbtv/usbtv-video.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/media/usb/usbtv/usbtv-video.c b/drivers/media/usb/usbtv/usbtv-video.c
index be22a9697197..965a8ae82afe 100644
--- a/drivers/media/usb/usbtv/usbtv-video.c
+++ b/drivers/media/usb/usbtv/usbtv-video.c
@@ -73,6 +73,10 @@ static int usbtv_configure_for_norm(struct usbtv *usbtv, v4l2_std_id norm)
 	}
 
 	if (params) {
+		if (vb2_is_streaming(&usbtv->vb2q) &&
+		    (usbtv->width != params->cap_width ||
+		     usbtv->height != params->cap_height))
+			return -EBUSY;
 		usbtv->width = params->cap_width;
 		usbtv->height = params->cap_height;
 		usbtv->n_chunks = usbtv->width * usbtv->height
-- 
2.43.0

Re: [PATCH] media: usbtv: Lock resolution while streaming

[Hans Verkuil]

Hi Ludwig,

I'm taking this patch, but with one change:

On 28/04/2025 20:16, Ludwig Disterhof wrote:
> When an program is streaming (ffplay) and another program (qv4l2)
> changes the TV standard from NTSC to PAL, the kernel crashes due to trying
> to copy to unmapped memory.
> 
> Changing from NTSC to PAL increases the resolution in the usbtv struct,
> but the video plane buffer isn't adjusted, so it overflows.
> 
> Fixes: 0e0fe3958fdd13d ("[media] usbtv: Add support for PAL video source")
> 
> Signed-off-by: Ludwig Disterhof <ludwig@disterhof.eu>
> ---
>  drivers/media/usb/usbtv/usbtv-video.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/media/usb/usbtv/usbtv-video.c b/drivers/media/usb/usbtv/usbtv-video.c
> index be22a9697197..965a8ae82afe 100644
> --- a/drivers/media/usb/usbtv/usbtv-video.c
> +++ b/drivers/media/usb/usbtv/usbtv-video.c
> @@ -73,6 +73,10 @@ static int usbtv_configure_for_norm(struct usbtv *usbtv, v4l2_std_id norm)
>  	}
>  
>  	if (params) {
> +		if (vb2_is_streaming(&usbtv->vb2q) &&

This should be vb2_is_busy(), not vb2_is_streaming().

is_busy() checks if buffers have been allocated since in that case you can't
make changes to the resolution until all buffers are released.

No need to do anything, I've made this change myself.

Regards,

	Hans

> +		    (usbtv->width != params->cap_width ||
> +		     usbtv->height != params->cap_height))
> +			return -EBUSY;
>  		usbtv->width = params->cap_width;
>  		usbtv->height = params->cap_height;
>  		usbtv->n_chunks = usbtv->width * usbtv->height