[PATCH v2 1/2] drm/connector: hdmi: Handle NULL display mode in state check helper

[Cristian Ciocaltea <cristian.ciocaltea@collabora.com>]

drm_atomic_helper_connector_hdmi_check() helper makes use of
connector_state_get_mode() to obtain a drm_display_mode pointer, but it
doesn't validate it, which may lead to a NULL pointer dereference in
some cases, i.e. unloading a DRM module:

[ 1002.910414] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[...]
[ 1002.923833] Hardware name: Radxa ROCK 5B (DT)
[ 1002.924819] pc : drm_match_cea_mode+0x30/0x280 [drm]
[ 1002.925318] lr : hdmi_try_format_bpc+0x7c/0x580 [drm_display_helper]
[...]
[ 1002.932411] Call trace:
[ 1002.932626]  drm_match_cea_mode+0x30/0x280 [drm] (P)
[ 1002.933120]  hdmi_try_format_bpc+0x7c/0x580 [drm_display_helper]
[ 1002.933662]  drm_atomic_helper_connector_hdmi_check+0x10c/0x478 [drm_display_helper]
[ 1002.934355]  drm_bridge_connector_atomic_check+0x20/0x40 [drm_display_helper]
[ 1002.934993]  drm_atomic_helper_check_modeset+0x698/0xd28 [drm_kms_helper]
[ 1002.935607]  drm_atomic_helper_check+0x28/0xb8 [drm_kms_helper]
[ 1002.936143]  drm_atomic_check_only+0x794/0x988 [drm]
[ 1002.936635]  drm_atomic_commit+0x60/0xe0 [drm]
[ 1002.937082]  drm_atomic_helper_disable_all+0x184/0x218 [drm_kms_helper]
[ 1002.937678]  drm_atomic_helper_shutdown+0x90/0x150 [drm_kms_helper]
[ 1002.938243]  rockchip_drm_unbind+0x38/0x80 [rockchipdrm]
[ 1002.938720]  component_master_del+0xac/0xf8
[ 1002.939089]  rockchip_drm_platform_remove+0x34/0x78 [rockchipdrm]
[...]

Add the missing NULL check before passing the mode pointer further.

Fixes: f035f4097f1e ("drm/connector: hdmi: Calculate TMDS character rate")
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
---
 drivers/gpu/drm/display/drm_hdmi_state_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
index cfc2aaee1da08a103cbf933c891d5cc31b0886a8..e4d4fce6ab59d37067327d3e6da235c9a5a45b42 100644
--- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
+++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
@@ -503,6 +503,9 @@ int drm_atomic_helper_connector_hdmi_check(struct drm_connector *connector,
 		connector_state_get_mode(new_conn_state);
 	int ret;
 
+	if (!mode)
+		return 0;
+
 	new_conn_state->hdmi.is_limited_range = hdmi_is_limited_range(connector, new_conn_state);
 
 	ret = hdmi_compute_config(connector, new_conn_state, mode);

-- 
2.47.1