[PATCH v2 1/5] drm/gud: Fix probe failure on non-DMA devices by moving descriptor check

[Hui Peng <benquike@gmail.com>]

In gud_probe(), evaluating drm->mode_config.min_width before
drmm_mode_config_init() and before assigning fields from the display
descriptor causes the check to evaluate against 0, returning -EINVAL
and unconditionally failing driver probe on non-DMA USB display devices.

Move the display descriptor min/max width and height validation to after
drmm_mode_config_init() and field assignments.

Tested in QEMU against Linux 7.3.0-rc3 with a non-DMA USB GUD display
device: on the unfixed kernel gud_probe() evaluates zero-initialized
drm->mode_config fields before drmm_mode_config_init() and returns -EINVAL
(failing device initialization); whereas with this fix applied, gud_probe()
validates descriptor min/max bounds after initialization, allowing the
driver to probe cleanly.

Fixes: 40e1a70b4aed ("drm: Add GUD USB Display driver")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
 drivers/gpu/drm/gud/gud_drv.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/gud/gud_drv.c b/drivers/gpu/drm/gud/gud_drv.c
index 3a1b9e2a2eaa..f7826e3d849f 100644
--- a/drivers/gpu/drm/gud/gud_drv.c
+++ b/drivers/gpu/drm/gud/gud_drv.c
@@ -506,6 +506,12 @@ static int gud_probe(struct usb_interface *intf, const struct usb_device_id *id
 	drm->mode_config.max_width = le32_to_cpu(desc.max_width);
 	drm->mode_config.min_height = le32_to_cpu(desc.min_height);
 	drm->mode_config.max_height = le32_to_cpu(desc.max_height);
+
+	if (!drm->mode_config.min_width || !drm->mode_config.min_height ||
+	    drm->mode_config.max_width < drm->mode_config.min_width ||
+	    drm->mode_config.max_height < drm->mode_config.min_height)
+		return -EINVAL;
+
 	drm->mode_config.funcs = &gud_mode_config_funcs;
 	drm->mode_config.helper_private = &gud_mode_config_helpers;