linux-kernel - [PATCH] omapdrm: fix missing check on list iterator

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Date:   Sun, 27 Mar 2022 13:33:44 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     tomba@...nel.org
Cc:     airlied@...ux.ie, daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Xiaomeng Tong <xiam0nd.tong@...il.com>, stable@...r.kernel.org
Subject: [PATCH] omapdrm: fix missing check on list iterator

The bug is here:
	bus_flags = connector->display_info.bus_flags;

The list iterator 'connector-' will point to a bogus position containing
HEAD if the list is empty or no element is found. This case must
be checked before any use of the iterator, otherwise it will lead
to a invalid memory access.

To fix this bug, add an check. Use a new value 'iter' as the list
iterator, while use the old value 'connector' as a dedicated variable
to point to the found element.

Cc: stable@...r.kernel.org
Fixes: ("drm/omap: Add support for drm_panel")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
---
 drivers/gpu/drm/omapdrm/omap_encoder.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/omapdrm/omap_encoder.c b/drivers/gpu/drm/omapdrm/omap_encoder.c
index 4dd05bc732da..d648ab4223b1 100644
--- a/drivers/gpu/drm/omapdrm/omap_encoder.c
+++ b/drivers/gpu/drm/omapdrm/omap_encoder.c
@@ -76,14 +76,16 @@ static void omap_encoder_mode_set(struct drm_encoder *encoder,
 	struct omap_encoder *omap_encoder = to_omap_encoder(encoder);
 	struct omap_dss_device *output = omap_encoder->output;
 	struct drm_device *dev = encoder->dev;
-	struct drm_connector *connector;
+	struct drm_connector *connector = NULL, *iter;
 	struct drm_bridge *bridge;
 	struct videomode vm = { 0 };
 	u32 bus_flags;
 
-	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
-		if (connector->encoder == encoder)
+	list_for_each_entry(iter, &dev->mode_config.connector_list, head) {
+		if (iter->encoder == encoder) {
+			connector = iter;
 			break;
+		}
 	}
 
 	drm_display_mode_to_videomode(adjusted_mode, &vm);
@@ -106,8 +108,10 @@ static void omap_encoder_mode_set(struct drm_encoder *encoder,
 		omap_encoder_update_videomode_flags(&vm, bus_flags);
 	}
 
-	bus_flags = connector->display_info.bus_flags;
-	omap_encoder_update_videomode_flags(&vm, bus_flags);
+	if (connector) {
+		bus_flags = connector->display_info.bus_flags;
+		omap_encoder_update_videomode_flags(&vm, bus_flags);
+	}
 
 	/* Set timings for all devices in the display pipeline. */
 	dss_mgr_set_timings(output, &vm);
-- 
2.17.1