Re: [PATCH fixes v3] media: vivid: check for NULL dev in vivid_probe() control setup

[Hans Verkuil <hverkuil+cisco@kernel.org>]

On 27/09/2026 05:33, Rohinthan P wrote:
> In vivid_probe(), after creating instances, the driver iterates
> through vivid_devs[0..n_devs-1] to populate HDMI and S-Video
> 'Connected To' controls. However, it dereferences dev->has_vid_out
> without verifying that dev is non-NULL.
> 
> If an instance fails during creation, vivid_devs[i] remains NULL,
> causing a general protection fault:
> 
>     Oops: general protection fault
>     KASAN: probably user-memory-access in range
>     [0x0000000000005f38-0x0000000000005f3f]
>     RIP: 0010:vivid_probe+0x579/0x10d0
> 
> Add NULL pointer checks in both loops in vivid_probe() before accessing
> vivid_devs[i].
> 
> Fixes: d7c969f37515 ("media: vivid: Add 'Is Connected To' menu controls")
> Cc: stable@vger.kernel.org
> Reported-by: syzbot+caaca441bae2799984d3@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=caaca441bae2799984d3
> Signed-off-by: Rohinthan P <rokinthanp03@gmail.com>
> ---
> Changes in v3:
> - Add "fixes" branch prefix to subject and base-commit info targeting
>   media-committers.git fixes branch to satisfy media-ci test-valid-ancestor check.

Don't add a fixes prefix, it serves no purpose.

> - Add Cc: stable@vger.kernel.org for media-patchstyle check.
> 
> Changes in v2:
> - Remove .suppress_bind_attrs = true so driver bind/unbind via sysfs
>   remains supported as required by the test-media test suite.
> - Update author name to "Rohinthan P".
> 
>  drivers/media/test-drivers/vivid/vivid-core.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/test-drivers/vivid/vivid-core.c b/drivers/media/test-drivers/vivid/vivid-core.c
> index 62cfb5f..1860ad6 100644
> --- a/drivers/media/test-drivers/vivid/vivid-core.c
> +++ b/drivers/media/test-drivers/vivid/vivid-core.c
> @@ -2116,17 +2116,19 @@ static int vivid_probe(struct platform_device *pdev)
>  	for (int i = 0; i < n_devs; i++) {
>  		struct vivid_dev *dev = vivid_devs[i];
>  
> +		if (!dev)
> +			continue;

As I mentioned in my earlier reply: AFAICT this can never happen.

Looking at the code, vivid_devs is non-NULL for all indices 0...n_devs-1. See the for loop
at the start of vivid_probe where the instances are created.

So if vivid_devs[i] is ever NULL, then that's the bug that needs to be addressed:
why is it NULL at all?

Do you have proof that it is actually NULL?

The syzkaller report shows this at the start of the crash log:

cec: vivid-003-vid-cap0: kthread_run() failed

So why does it fail, and why does it cause a crash later on.

Anyway, I'm rejecting this patch since it doesn't address the real cause.

Regards,

	Hans

>  		if (!dev->has_vid_out)
>  			continue;
>  		for (int j = 0; j < dev->num_outputs && hdmi_count < MAX_MENU_ITEMS; ++j) {
>  			if (dev->output_type[j] == HDMI) {
> -				vivid_ctrl_hdmi_to_output_instance[hdmi_count] = vivid_devs[i];
> +				vivid_ctrl_hdmi_to_output_instance[hdmi_count] = dev;
>  				vivid_ctrl_hdmi_to_output_index[hdmi_count++] = j;
>  			}
>  		}
>  		for (int j = 0; j < dev->num_outputs && svid_count < MAX_MENU_ITEMS; ++j) {
>  			if (dev->output_type[j] == SVID) {
> -				vivid_ctrl_svid_to_output_instance[svid_count] = vivid_devs[i];
> +				vivid_ctrl_svid_to_output_instance[svid_count] = dev;
>  				vivid_ctrl_svid_to_output_index[svid_count++] = j;
>  			}
>  		}
> @@ -2134,13 +2136,17 @@ static int vivid_probe(struct platform_device *pdev)
>  	hdmi_count = min(hdmi_count, MAX_MENU_ITEMS);
>  	svid_count = min(svid_count, MAX_MENU_ITEMS);
>  	for (int i = 0; i < n_devs; i++) {
> -		for (int j = 0; j < vivid_devs[i]->num_hdmi_inputs; j++) {
> -			struct v4l2_ctrl *c = vivid_devs[i]->ctrl_hdmi_to_output[j];
> +		struct vivid_dev *dev = vivid_devs[i];
> +
> +		if (!dev)
> +			continue;
> +		for (int j = 0; j < dev->num_hdmi_inputs; j++) {
> +			struct v4l2_ctrl *c = dev->ctrl_hdmi_to_output[j];
>  
>  			v4l2_ctrl_modify_range(c, c->minimum, hdmi_count - 1, 0, c->default_value);
>  		}
> -		for (int j = 0; j < vivid_devs[i]->num_svid_inputs; j++) {
> -			struct v4l2_ctrl *c = vivid_devs[i]->ctrl_svid_to_output[j];
> +		for (int j = 0; j < dev->num_svid_inputs; j++) {
> +			struct v4l2_ctrl *c = dev->ctrl_svid_to_output[j];
>  
>  			v4l2_ctrl_modify_range(c, c->minimum, svid_count - 1, 0, c->default_value);
>  		}