[PATCH 4.19 37/62] tilcdc: tilcdc_external: fix an incorrect NULL check on list iterator

Greg Kroah-Hartman
2022-07-27T16:33:48Z

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

[ Upstream commit 8b917cbe38e9b0d002492477a9fc2bfee2412ce4 ]

The bug is here:
if (!encoder) {

The list iterator value 'encoder' will *always* be set and non-NULL
by 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 original variable 'encoder' as a dedicated pointer
to point to the found element.

Cc: stable@vger.kernel.org
Fixes: ec9eab097a500 ("drm/tilcdc: Add drm bridge support for attaching drm bridge drivers")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Reviewed-by: Jyri Sarha <jyri.sarha@iki.fi>
Tested-by: Jyri Sarha <jyri.sarha@iki.fi>
Signed-off-by: Jyri Sarha <jyri.sarha@iki.fi>
Link: https://patchwork.freedesktop.org/patch/msgid/20220327061516.5076-1-xiam0nd.tong@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/tilcdc/tilcdc_external.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_external.c b/drivers/gpu/drm/tilcdc/tilcdc_external.c
index a2f623550ce3..9c1be0635b53 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_external.c
+++ b/drivers/gpu/drm/tilcdc/tilcdc_external.c
@@ -60,11 +60,13 @@ struct drm_connector *tilcdc_encoder_find_connector(struct drm_device *ddev,
int tilcdc_add_component_encoder(struct drm_device *ddev)
{
struct tilcdc_drm_private *priv = ddev->dev_private;
- struct drm_encoder *encoder;
+ struct drm_encoder *encoder = NULL, *iter;

- list_for_each_entry(encoder, &ddev->mode_config.encoder_list, head)
- if (encoder->possible_crtcs & (1 << priv->crtc->index))
+ list_for_each_entry(iter, &ddev->mode_config.encoder_list, head)
+ if (iter->possible_crtcs & (1 << priv->crtc->index)) {
+ encoder = iter;
break;
+ }

if (!encoder) {
dev_err(ddev->dev, "%s: No suitable encoder found\n", __func__);
--
2.35.1