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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Zheyu Ma <zheyuma97@gmail.com>,
        Robert Foss <robert.foss@linaro.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 095/255] drm/bridge: megachips: Fix a null pointer dereference bug
Date:   Mon, 24 Oct 2022 13:30:05 +0200
Message-Id: <20221024113005.647585310@linuxfoundation.org>
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From: Zheyu Ma <zheyuma97@gmail.com>

[ Upstream commit 1ff673333d46d2c1b053ebd0c1c7c7c79e36943e ]

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>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220830073450.1897020-1-zheyuma97@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 5302dd90a7a5..b72f6f541d4e 100644
--- a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
+++ b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
@@ -279,7 +279,9 @@ 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);
-- 
2.35.1