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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, Yizhuo Zhai <yzhai003@ucr.edu>,
        Alex Deucher <alexander.deucher@amd.com>
Subject: [PATCH 5.15 692/846] drm/amd/display: Fix the uninitialized variable in enable_stream_features()
Date:   Mon, 24 Jan 2022 19:43:29 +0100
Message-Id: <20220124184124.916573388@linuxfoundation.org>
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From: Yizhuo Zhai <yzhai003@ucr.edu>

commit 0726ed3065eeb910f9cea0c933bc021a848e00b3 upstream.

In function enable_stream_features(), the variable "old_downspread.raw"
could be uninitialized if core_link_read_dpcd() fails, however, it is
used in the later if statement, and further, core_link_write_dpcd()
may write random value, which is potentially unsafe.

Fixes: 6016cd9dba0f ("drm/amd/display: add helper for enabling mst stream features")
Cc: stable@vger.kernel.org
Signed-off-by: Yizhuo Zhai <yzhai003@ucr.edu>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -1696,6 +1696,8 @@ static void enable_stream_features(struc
 		union down_spread_ctrl old_downspread;
 		union down_spread_ctrl new_downspread;
 
+		memset(&old_downspread, 0, sizeof(old_downspread));
+
 		core_link_read_dpcd(link, DP_DOWNSPREAD_CTRL,
 				&old_downspread.raw, sizeof(old_downspread));