[PATCH 5.18 838/879] stm: ltdc: fix two incorrect NULL checks on list iterator

Greg Kroah-Hartman
2022-06-08T00:23:11Z

From: Xiaomeng Tong <xiam0nd.tong@gmail.com>

commit 2e6c86be0e57079d1fb6c7c7e5423db096d0548a upstream.

The two bugs are here:
if (encoder) {
if (bridge && bridge->timings)

The list iterator value 'encoder/bridge' will *always* be set and
non-NULL by drm_for_each_encoder()/list_for_each_entry(), so it is
incorrect to assume that the iterator value will be NULL if the
list is empty or no element is found.

To fix the bug, use a new variable '*_iter' as the list iterator,
while use the old variable 'encoder/bridge' as a dedicated pointer
to point to the found element.

Cc: stable@vger.kernel.org
Fixes: 99e360442f223 ("drm/stm: Fix bus_flags handling")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Acked-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Signed-off-by: Philippe Cornu <philippe.cornu@foss.st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220327055355.3808-1-xiam0nd.tong@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/stm/ltdc.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)

--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c
@@ -869,8 +869,8 @@ static void ltdc_crtc_mode_set_nofb(stru
struct drm_device *ddev = crtc->dev;
struct drm_connector_list_iter iter;
struct drm_connector *connector = NULL;
- struct drm_encoder *encoder = NULL;
- struct drm_bridge *bridge = NULL;
+ struct drm_encoder *encoder = NULL, *en_iter;
+ struct drm_bridge *bridge = NULL, *br_iter;
struct drm_display_mode *mode = &crtc->state->adjusted_mode;
u32 hsync, vsync, accum_hbp, accum_vbp, accum_act_w, accum_act_h;
u32 total_width, total_height;
@@ -880,15 +880,19 @@ static void ltdc_crtc_mode_set_nofb(stru
int ret;

/* get encoder from crtc */
- drm_for_each_encoder(encoder, ddev)
- if (encoder->crtc == crtc)
+ drm_for_each_encoder(en_iter, ddev)
+ if (en_iter->crtc == crtc) {
+ encoder = en_iter;
break;
+ }

if (encoder) {
/* get bridge from encoder */
- list_for_each_entry(bridge, &encoder->bridge_chain, chain_node)
- if (bridge->encoder == encoder)
+ list_for_each_entry(br_iter, &encoder->bridge_chain, chain_node)
+ if (br_iter->encoder == encoder) {
+ bridge = br_iter;
break;
+ }

/* Get the connector from encoder */
drm_connector_list_iter_begin(ddev, &iter);