media: stm32-csi: Fix dereference before NULL check

commit 80eaf32672871bd2623ce6ba13ffc1f018756580 upstream.

In 'stm32_csi_start', 'csidev->s_subdev' is dereferenced directly while
assigning a value to the 'src_pad'. However the same value is being
checked against NULL at a later point of time indicating that there
are chances that the value can be NULL.

Move the dereference after the NULL check.

Fixes: e7bad98 ("media: v4l: Convert the users of v4l2_get_link_freq to call it on a pad")
Cc: [email protected]
Signed-off-by: Chandra Mohan Sundar <[email protected]>
Signed-off-by: Sakari Ailus <[email protected]>
Signed-off-by: Hans Verkuil <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Chandra Mohan Sundar

drivers/media/platform/st/stm32/stm32-csi.c

@@ -443,8 +443,7 @@ static void stm32_csi_phy_reg_write(struct stm32_csi_dev *csidev,
 static int stm32_csi_start(struct stm32_csi_dev *csidev,
 			   struct v4l2_subdev_state *state)
 {
-	struct media_pad *src_pad =
-		&csidev->s_subdev->entity.pads[csidev->s_subdev_pad_nb];
+	struct media_pad *src_pad;
 	const struct stm32_csi_mbps_phy_reg *phy_regs = NULL;
 	struct v4l2_mbus_framefmt *sink_fmt;
 	const struct stm32_csi_fmts *fmt;
@@ -466,6 +465,7 @@ static int stm32_csi_start(struct stm32_csi_dev *csidev,
 	if (!csidev->s_subdev)
 		return -EIO;
 
+	src_pad = &csidev->s_subdev->entity.pads[csidev->s_subdev_pad_nb];
 	link_freq = v4l2_get_link_freq(src_pad,
 				       fmt->bpp, 2 * csidev->num_lanes);
 	if (link_freq < 0)