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From:   Zheyu Ma <zheyuma97@gmail.com>
To:     peter.senna@gmail.com, martin.donnelly@ge.com,
        martyn.welch@collabora.co.uk, andrzej.hajda@intel.com,
        narmstrong@baylibre.com, robert.foss@linaro.org,
        Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se,
        jernej.skrabec@gmail.com, airlied@linux.ie, daniel@ffwll.ch
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Zheyu Ma <zheyuma97@gmail.com>
Subject: [PATCH v2] drm/bridge: megachips: Fix a null pointer dereference bug
Date:   Tue, 30 Aug 2022 15:34:50 +0800
Message-Id: <20220830073450.1897020-1-zheyuma97@gmail.com>
MIME-Version: 1.0
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When removing the module we will get the following warning:

[   31.911505] i2c-core: driver [stdp2690-ge-b850v3-fw] unregistered
[   31.912484] general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN PTI
[   31.913338] KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
[   31.915280] RIP: 0010:drm_bridge_remove+0x97/0x130
[   31.921825] Call Trace:
[   31.922533]  stdp4028_ge_b850v3_fw_remove+0x34/0x60 [megachips_stdpxxxx_ge_b850v3_fw]
[   31.923139]  i2c_device_remove+0x181/0x1f0

The two bridges (stdp2690, stdp4028) do not probe at the same time, so
the driver does not call ge_b850v3_resgiter() when probing, causing the
driver to try to remove the object that has not been initialized.

Fix this by checking whether both the bridges are probed.

Fixes: 11632d4aa2b3 ("drm/bridge: megachips: Ensure both bridges are probed before registration")
Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
Changes in v2:
    - Alignment format
---
 drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
index cce98bf2a4e7..72248a565579 100644
--- a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
+++ b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
@@ -296,7 +296,9 @@ static void ge_b850v3_lvds_remove(void)
 	 * This check is to avoid both the drivers
 	 * removing the bridge in their remove() function
 	 */
-	if (!ge_b850v3_lvds_ptr)
+	if (!ge_b850v3_lvds_ptr ||
+	    !ge_b850v3_lvds_ptr->stdp2690_i2c ||
+		!ge_b850v3_lvds_ptr->stdp4028_i2c)
 		goto out;
 
 	drm_bridge_remove(&ge_b850v3_lvds_ptr->bridge);
-- 
2.25.1