Re: [PATCH v2] media: uvc: don't do DMA on stack

Laurent Pinchart
2021-06-21T13:28:50Z

Hi Mauro,

Thank you for the patch.

On Mon, Jun 21, 2021 at 03:23:35PM +0200, Mauro Carvalho Chehab wrote:
> As warned by smatch:
> drivers/media/usb/uvc/uvc_v4l2.c:911 uvc_ioctl_g_input() error: doing dma on the stack (&i)
> drivers/media/usb/uvc/uvc_v4l2.c:943 uvc_ioctl_s_input() error: doing dma on the stack (&i)
>
> those two functions call uvc_query_ctrl passing a pointer to
> a data at the DMA stack. those are used to send URBs via
> usb_control_msg(). Using DMA stack is not supported and should
> not work anymore on modern Linux versions.
>
> So, use a temporary buffer, allocated together with
> struct uvc_video_chain.

The second part of the sentence isn't correct anymore.

> Cc: stable@vger.kernel.org # Kernel 4.9 and upper
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> ---
> drivers/media/usb/uvc/uvc_v4l2.c | 26 ++++++++++++++++++--------
> 1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 252136cc885c..d680ae8a5f87 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -899,8 +899,8 @@ static int uvc_ioctl_g_input(struct file *file, void *fh, unsigned int *input)
> {
> struct uvc_fh *handle = fh;
> struct uvc_video_chain *chain = handle->chain;
> + char *buf;

I'd make this

u8 *buf;

as the selector value is unsigned.

> int ret;
> - u8 i;
>
> if (chain->selector == NULL ||
> (chain->dev->quirks & UVC_QUIRK_IGNORE_SELECTOR_UNIT)) {
> @@ -908,13 +908,18 @@ static int uvc_ioctl_g_input(struct file *file, void *fh, unsigned int *input)
> return 0;
> }
>
> + buf = kmalloc(1, GFP_KERNEL);

MIssing error check.

> +
> ret = uvc_query_ctrl(chain->dev, UVC_GET_CUR, chain->selector->id,
> chain->dev->intfnum, UVC_SU_INPUT_SELECT_CONTROL,
> - &i, 1);
> + buf, 1);
> if (ret < 0)
> return ret;
>
> - *input = i - 1;
> + *input = *buf;
> +
> + kfree(buf);
> +
> return 0;
> }
>
> @@ -922,8 +927,8 @@ static int uvc_ioctl_s_input(struct file *file, void *fh, unsigned int input)
> {
> struct uvc_fh *handle = fh;
> struct uvc_video_chain *chain = handle->chain;
> + char *buf;

u8 * here too.

> int ret;
> - u32 i;
>
> ret = uvc_acquire_privileges(handle);
> if (ret < 0)
> @@ -939,10 +944,15 @@ static int uvc_ioctl_s_input(struct file *file, void *fh, unsigned int input)
> if (input >= chain->selector->bNrInPins)
> return -EINVAL;
>
> - i = input + 1;
> - return uvc_query_ctrl(chain->dev, UVC_SET_CUR, chain->selector->id,
> - chain->dev->intfnum, UVC_SU_INPUT_SELECT_CONTROL,
> - &i, 1);
> + buf = kmalloc(1, GFP_KERNEL);

And missing error check.

> +
> + *buf = input + 1;
> + ret = uvc_query_ctrl(chain->dev, UVC_SET_CUR, chain->selector->id,
> + chain->dev->intfnum, UVC_SU_INPUT_SELECT_CONTROL,
> + buf, 1);
> + kfree(buf);
> +
> + return ret;
> }
>
> static int uvc_ioctl_queryctrl(struct file *file, void *fh,

--
Regards,

Laurent Pinchart