linux-kernel - [PATCH AUTOSEL 6.1 11/41] drm/stm: ltdc: fix late dereference check

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Date:   Sun, 23 Jul 2023 21:20:44 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>,
        kernel test robot <lkp@...el.com>,
        Dan Carpenter <error27@...il.com>,
        Philippe Cornu <philippe.cornu@...s.st.com>,
        Sasha Levin <sashal@...nel.org>, yannick.fertre@...s.st.com,
        airlied@...il.com, daniel@...ll.ch, mcoquelin.stm32@...il.com,
        alexandre.torgue@...s.st.com, dri-devel@...ts.freedesktop.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH AUTOSEL 6.1 11/41] drm/stm: ltdc: fix late dereference check

From: Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>

[ Upstream commit 898a9e3f56db9860ab091d4bf41b6caa99aafc3d ]

In ltdc_crtc_set_crc_source(), struct drm_crtc was dereferenced in a
container_of() before the pointer check. This could cause a kernel panic.

Fix this smatch warning:
drivers/gpu/drm/stm/ltdc.c:1124 ltdc_crtc_set_crc_source() warn: variable dereferenced before check 'crtc' (see line 1119)

Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/lkml/202212241802.zeLFZCXB-lkp@intel.com/
Reported-by: Dan Carpenter <error27@...il.com>
Closes: https://lore.kernel.org/lkml/202212241802.zeLFZCXB-lkp@intel.com/
Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>
Acked-by: Philippe Cornu <philippe.cornu@...s.st.com>
Signed-off-by: Philippe Cornu <philippe.cornu@...s.st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230515123818.93971-1-raphael.gallais-pou@foss.st.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/stm/ltdc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
index 03c6becda795c..b8be4c1db4235 100644
--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c
@@ -1145,7 +1145,7 @@ static void ltdc_crtc_disable_vblank(struct drm_crtc *crtc)
 
 static int ltdc_crtc_set_crc_source(struct drm_crtc *crtc, const char *source)
 {
-	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
+	struct ltdc_device *ldev;
 	int ret;
 
 	DRM_DEBUG_DRIVER("\n");
@@ -1153,6 +1153,8 @@ static int ltdc_crtc_set_crc_source(struct drm_crtc *crtc, const char *source)
 	if (!crtc)
 		return -ENODEV;
 
+	ldev = crtc_to_ltdc(crtc);
+
 	if (source && strcmp(source, "auto") == 0) {
 		ldev->crc_active = true;
 		ret = regmap_set_bits(ldev->regmap, LTDC_GCR, GCR_CRCEN);
-- 
2.39.2