linux-kernel - [PATCH][drm-next] drm/amd/display: fix a potential null pointer dereference

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Message-Id: <20190816221011.10750-1-colin.king@canonical.com>
Date:   Fri, 16 Aug 2019 23:10:11 +0100
From:   Colin King <colin.king@...onical.com>
To:     Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Zhou <David1.Zhou@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][drm-next] drm/amd/display: fix a potential null pointer dereference

From: Colin Ian King <colin.king@...onical.com>

Currently the pointer init_data is dereferenced on the assignment
of fw_info before init_data is sanity checked to see if it is null.
Fix te potential null pointer dereference on init_data by only
performing dereference after it is null checked.

Addresses-Coverity: ("Dereference before null check")
Fixes: 9adc8050bf3c ("drm/amd/display: make firmware info only load once during dc_bios create")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
index bee81bf288be..926954c804a6 100644
--- a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
+++ b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
@@ -1235,7 +1235,7 @@ static bool calc_pll_max_vco_construct(
 			struct calc_pll_clock_source_init_data *init_data)
 {
 	uint32_t i;
-	struct dc_firmware_info *fw_info = &init_data->bp->fw_info;
+	struct dc_firmware_info *fw_info;
 	if (calc_pll_cs == NULL ||
 			init_data == NULL ||
 			init_data->bp == NULL)
@@ -1244,6 +1244,7 @@ static bool calc_pll_max_vco_construct(
 	if (init_data->bp->fw_info_valid)
 		return false;
 
+	fw_info = &init_data->bp->fw_info;
 	calc_pll_cs->ctx = init_data->ctx;
 	calc_pll_cs->ref_freq_khz = fw_info->pll_info.crystal_frequency;
 	calc_pll_cs->min_vco_khz =
-- 
2.20.1