linux-kernel - [PATCH 5.17 738/772] tilcdc: tilcdc_external: fix an incorrect NULL check on list iterator

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Message-Id: <20220607165010.783351592@linuxfoundation.org>
Date:   Tue,  7 Jun 2022 19:05:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xiaomeng Tong <xiam0nd.tong@...il.com>,
        Jyri Sarha <jyri.sarha@....fi>
Subject: [PATCH 5.17 738/772] tilcdc: tilcdc_external: fix an incorrect NULL check on list iterator

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

commit 8b917cbe38e9b0d002492477a9fc2bfee2412ce4 upstream.

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

--- 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_fin
 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__);