linux-kernel - [PATCH][next] drm/amd/display: fix dereference of pointer aconnector when it is null

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Date:   Fri,  8 Nov 2019 14:38:14 +0000
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>, Lyude Paul <lyude@...hat.com>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        Mikita Lipski <mikita.lipski@....com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][next] drm/amd/display: fix dereference of pointer aconnector when it is null

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

Currently pointer aconnector is being dereferenced by the call to
to_dm_connector_state before it is being null checked, this could
lead to a null pointer dereference.  Fix this by checking that
aconnector is null before dereferencing it.

Addresses-Coverity: ("Dereference before null check")
Fixes: 5133c6241d9c ("drm/amd/display: Add MST atomic routines")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
index e3cda6984d28..72e677796a48 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
@@ -193,12 +193,11 @@ bool dm_helpers_dp_mst_write_payload_allocation_table(
 	 * that blocks before commit guaranteeing that the state
 	 * is not gonna be swapped while still in use in commit tail */
 
-	dm_conn_state = to_dm_connector_state(aconnector->base.state);
-
-
 	if (!aconnector || !aconnector->mst_port)
 		return false;
 
+	dm_conn_state = to_dm_connector_state(aconnector->base.state);
+
 	mst_mgr = &aconnector->mst_port->mst_mgr;
 
 	if (!mst_mgr->mst_state)
-- 
2.20.1