linux-kernel - [PATCH v2] drm/mediatek: Initialize pointer to avoid undefined behavior

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Message-Id: <20250112-uninitializedpointer1601557-v2-1-61ac4c80b76d@gmail.com>
Date: Sun, 12 Jan 2025 09:05:30 +0000
From: Karan Sanghavi <karansanghvi98@...il.com>
To: Chun-Kuang Hu <chunkuang.hu@...nel.org>, 
 Philipp Zabel <p.zabel@...gutronix.de>, David Airlie <airlied@...il.com>, 
 Simona Vetter <simona@...ll.ch>, Matthias Brugger <matthias.bgg@...il.com>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
 Alexandre Mergnat <amergnat@...libre.com>, 
 Sui Jingfeng <sui.jingfeng@...ux.dev>, CK Hu <ck.hu@...iatek.com>
Cc: dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 Shuah Khan <skhan@...uxfoundation.org>, 
 Karan Sanghavi <karansanghvi98@...il.com>
Subject: [PATCH v2] drm/mediatek: Initialize pointer to avoid undefined
 behavior

Initialize the `next` pointer with NULL as the function
`mtk_drm_of_get_ddp_ep_cid` might return early without assigning a
value to `next`.

Dereferencing an uninitialized pointer can lead to undefined behavior,
as it might point to an invalid memory location.

Coverity CID: 1601557

Fixes: 4c932840db1d ("drm/mediatek: Implement OF graphs support for display paths")
Signed-off-by: Karan Sanghavi <karansanghvi98@...il.com>
---
Coverity Message:
CID 1601557: (#1 of 1): Uninitialized pointer read (UNINIT)
3. uninit_use: Using uninitialized value next.

Coverity Link:
https://scan7.scan.coverity.com/#/project-view/10043/11354?selectedIssue=1601557
---
Changes in v2:
- Updated the patch subject and summary log
- Link to v1: https://lore.kernel.org/r/20241111-uninitializedpointer1601557-v1-1-7d03668e8141@gmail.com
---
 drivers/gpu/drm/mediatek/mtk_drm_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index 9a8ef8558da9..bc06c664e80f 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -900,7 +900,7 @@ static int mtk_drm_of_ddp_path_build_one(struct device *dev, enum mtk_crtc_path
 					 const unsigned int **out_path,
 					 unsigned int *out_path_len)
 {
-	struct device_node *next, *prev, *vdo = dev->parent->of_node;
+	struct device_node *next = NULL, *prev, *vdo = dev->parent->of_node;
 	unsigned int temp_path[DDP_COMPONENT_DRM_ID_MAX] = { 0 };
 	unsigned int *final_ddp_path;
 	unsigned short int idx = 0;

---
base-commit: 6d59cab07b8d74d0f0422b750038123334f6ecc2
change-id: 20241111-uninitializedpointer1601557-9803b725b6bd

Best regards,
-- 
Karan Sanghavi <karansanghvi98@...il.com>