Re: [PATCH] media: i2c: imx471: Fix uninitialized error value in imx471_set_ctrl()

[David CARLIER]

Hi,

On Mon, 27 Jul 2026 at 08:01, Kate Hsuan <hpa@xxxxxxxxxx> wrote:
>
> Hi David,
>
> Thank you for the fix.
>
> On Fri, Jul 24, 2026 at 12:14 PM David Carlier <devnexen@xxxxxxxxx> wrote:
> >
> > The exposure control write passes the address of the local ret variable
> > to cci_write() as its error pointer while ret is still uninitialized.
> > cci_write() returns early without touching the hardware when the error
> > value it is handed is already non-zero, so a non-zero garbage value on
> > the stack silently skips programming the exposure register and makes the
> > control write return a bogus, possibly positive, status.
> >
> > This path runs on every stream start and on every exposure update from
> > userspace. Initialize ret to zero so the exposure register is always
> > written and a correct status is returned.
> >
> > Fixes: be1589e567ae ("media: i2c: imx471: Add Sony IMX471 image sensor driver")
> > Signed-off-by: David Carlier <devnexen@xxxxxxxxx>
> > ---
> >  drivers/media/i2c/imx471.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/i2c/imx471.c b/drivers/media/i2c/imx471.c
> > index 6d358b11e96d..5aca5f2355d6 100644
> > --- a/drivers/media/i2c/imx471.c
> > +++ b/drivers/media/i2c/imx471.c
> > @@ -306,7 +306,7 @@ static int imx471_set_ctrl(struct v4l2_ctrl *ctrl)
> >                         v4l2_subdev_get_locked_active_state(&sensor->sd);
> >         const struct v4l2_mbus_framefmt *format =
> >                         v4l2_subdev_state_get_format(state, 0);
> > -       int ret;
> > +       int ret = 0;
>
> Setting ret to 0 can resolve the issue, but the root cause is at lines
> 337 and 342. Since we don't need the previous error state when calling
> cci_write() in imx471_set_ctrl(), the fourth parameter of cci_write()
> should be NULL.
> So the fix for the V4L2_CID_EXPOSURE and V4L2_CID_VBLANK is
>
> case V4L2_CID_EXPOSURE:
>     ret = cci_write(sensor->regmap, IMX471_REG_EXPOSURE, ctrl->val, NULL);
>     break;
> case V4L2_CID_VBLANK:
>     /* Update FLL that meets expected vertical blanking */
>     ret = cci_write(sensor->regmap, IMX471_REG_FLL, format->height +
> ctrl->val, NULL);
>     break;
>
> This ensures the cci_write() writes the data to the register without
> being influenced by an uninitialized ret value and the ret can be set
> properly.
>
> >
> >         if (ctrl->id == V4L2_CID_VBLANK) {
> >                 s64 exposure_max = format->height + ctrl->val -
> > --
> > 2.53.0
> >
>
>
> --
> BR,
> Kate
>

Good suggestion, will send v2 tomorrow.

Cheers.