Subject: Re: [PATCH] drm: zynqmp_dp: Fix uninitialized variable in debugfs()

From: Sean Anderson <[email-masked]>
Date: Wed, 27 May 2026 20:31:59 -0400

On 5/25/26 03:16, Dan Carpenter wrote:
> If the *ppos is non-zero then simple_write_to_buffer() will not
> initialize the start of the buf[] buffer.  It doesn't really make sense
> to allow non-zero values for *ppos, so check for that at the start and
> return -EINVAL.

non-zero ppos seems to be handled properly by simple_write_to_buffer.

--Sean

> Fixes: 28edaacb821c ("drm: zynqmp_dp: Add debugfs interface for compliance testing")
> Signed-off-by: Dan Carpenter <[email-masked]>
> ---
>   drivers/gpu/drm/xlnx/zynqmp_dp.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> index 7fb11b0a44f0..847179476041 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> @@ -1888,6 +1888,9 @@ static ssize_t zynqmp_dp_pattern_write(struct file *file,
>   	ssize_t ret;
>   	int pattern;
>   
> +	if (*ppos != 0)
> +		return -EINVAL;
> +
>   	ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, user_buf,
>   				     count);
>   	if (ret < 0)
> @@ -2028,6 +2031,9 @@ static ssize_t zynqmp_dp_custom_write(struct file *file,
>   	ssize_t ret;
>   	char buf[sizeof(dp->test.custom)];
>   
> +	if (*ppos != 0)
> +		return -EINVAL;
> +
>   	ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
>   	if (ret < 0)
>   		return ret;