From: Shirish S <shirish.s@amd.com>
Date: Tue, 13 Mar 2018 11:55:11 +0530
Subject: drm/amd/display: Check msg->size before starting aux transfer
Git-commit: 2a7b58293dd0f188d27491a8d07b145a9487e172
Patch-mainline: v4.17-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

This patch adds an essential check related to the size of the
payload to be transferred via aux channel.

Without this check dal_ddc_service_read_dpcd_data() is fed with
inappropriate payload size leading to deadlocks.

Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -85,6 +85,9 @@ static ssize_t dm_dp_aux_transfer(struct
 	enum ddc_result res;
 	ssize_t read_bytes;
 
+	if (WARN_ON(msg->size > 16))
+		return -E2BIG;
+
 	switch (msg->request & ~DP_AUX_I2C_MOT) {
 	case DP_AUX_NATIVE_READ:
 		read_bytes = dal_ddc_service_read_dpcd_data(