linux-kernel - [PATCH] drm/edid: Fix crash with zero/invalid EDID

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Message-Id: <20211004092100.1.Ic90a5ebd44c75db963112be167a03cc96f9fb249@changeid>
Date:   Mon,  4 Oct 2021 09:21:27 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     dri-devel@...ts.freedesktop.org
Cc:     geert@...ux-m68k.org, oliver.sang@...el.com,
        Douglas Anderson <dianders@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...el.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] drm/edid: Fix crash with zero/invalid EDID

In the commit bac9c2948224 ("drm/edid: Break out reading block 0 of
the EDID") I broke out reading the base block of the EDID to its own
function. Unfortunately, when I did that I messed up the handling when
drm_edid_is_zero() indicated that we had an EDID that was all 0x00 or
when we went through 4 loops and didn't get a valid EDID. Specifically
I needed to pass the broken EDID to connector_bad_edid() but now I was
passing an error-pointer.

Let's re-jigger things so we can pass the bad EDID in properly.

Fixes: bac9c2948224 ("drm/edid: Break out reading block 0 of the EDID")
Reported-by: kernel test robot <oliver.sang@...el.com>
Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

 drivers/gpu/drm/drm_edid.c | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 9b19eee0e1b4..9c9463ec5465 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1911,13 +1911,15 @@ int drm_add_override_edid_modes(struct drm_connector *connector)
 }
 EXPORT_SYMBOL(drm_add_override_edid_modes);
 
-static struct edid *drm_do_get_edid_base_block(
+static struct edid *drm_do_get_edid_base_block(struct drm_connector *connector,
 	int (*get_edid_block)(void *data, u8 *buf, unsigned int block,
 			      size_t len),
-	void *data, bool *edid_corrupt, int *null_edid_counter)
+	void *data)
 {
-	int i;
+	int *null_edid_counter = connector ? &connector->null_edid_counter : NULL;
+	bool *edid_corrupt = connector ? &connector->edid_corrupt : NULL;
 	void *edid;
+	int i;
 
 	edid = kmalloc(EDID_LENGTH, GFP_KERNEL);
 	if (edid == NULL)
@@ -1941,9 +1943,8 @@ static struct edid *drm_do_get_edid_base_block(
 	return edid;
 
 carp:
-	kfree(edid);
-	return ERR_PTR(-EINVAL);
-
+	if (connector)
+		connector_bad_edid(connector, edid, 1);
 out:
 	kfree(edid);
 	return NULL;
@@ -1982,14 +1983,9 @@ struct edid *drm_do_get_edid(struct drm_connector *connector,
 	if (override)
 		return override;
 
-	edid = (u8 *)drm_do_get_edid_base_block(get_edid_block, data,
-						&connector->edid_corrupt,
-						&connector->null_edid_counter);
-	if (IS_ERR_OR_NULL(edid)) {
-		if (IS_ERR(edid))
-			connector_bad_edid(connector, edid, 1);
+	edid = (u8 *)drm_do_get_edid_base_block(connector, get_edid_block, data);
+	if (!edid)
 		return NULL;
-	}
 
 	/* if there's no extensions or no connector, we're done */
 	valid_extensions = edid[0x7e];
@@ -2142,14 +2138,13 @@ u32 drm_edid_get_panel_id(struct i2c_adapter *adapter)
 	struct edid *edid;
 	u32 panel_id;
 
-	edid = drm_do_get_edid_base_block(drm_do_probe_ddc_edid, adapter,
-					  NULL, NULL);
+	edid = drm_do_get_edid_base_block(NULL, drm_do_probe_ddc_edid, adapter);
 
 	/*
 	 * There are no manufacturer IDs of 0, so if there is a problem reading
 	 * the EDID then we'll just return 0.
 	 */
-	if (IS_ERR_OR_NULL(edid))
+	if (!edid)
 		return 0;
 
 	panel_id = edid_extract_panel_id(edid);
-- 
2.33.0.800.g4c38ced690-goog