[PATCH AUTOSEL 5.4 04/22] drm/amd/display: Check num_valid_sets before accessing reader_wm_sets[]

[Sasha Levin]

From: Alex Hung <alex.h...@amd.com>

[ Upstream commit b38a4815f79b87efb196cd5121579fc51e29a7fb ]

[WHY & HOW]
num_valid_sets needs to be checked to avoid a negative index when
accessing reader_wm_sets[num_valid_sets - 1].

This fixes an OVERRUN issue reported by Coverity.

Reviewed-by: Harry Wentland <harry.wentl...@amd.com>
Acked-by: Tom Chung <chiahsuan.ch...@amd.com>
Signed-off-by: Alex Hung <alex.h...@amd.com>
Tested-by: Daniel Wheeler <daniel.whee...@amd.com>
Signed-off-by: Alex Deucher <alexander.deuc...@amd.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c 
b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c
index 9f301f8575a54..fec3ca955b264 100644
--- a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c
+++ b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn21/rn_clk_mgr.c
@@ -453,7 +453,8 @@ void build_watermark_ranges(struct clk_bw_params 
*bw_params, struct pp_smu_wm_ra
                        ranges->reader_wm_sets[num_valid_sets].max_fill_clk_mhz 
= PP_SMU_WM_SET_RANGE_CLK_UNCONSTRAINED_MAX;
 
                        /* Modify previous watermark range to cover up to max */
-                       ranges->reader_wm_sets[num_valid_sets - 
1].max_fill_clk_mhz = PP_SMU_WM_SET_RANGE_CLK_UNCONSTRAINED_MAX;
+                       if (num_valid_sets > 0)
+                               ranges->reader_wm_sets[num_valid_sets - 
1].max_fill_clk_mhz = PP_SMU_WM_SET_RANGE_CLK_UNCONSTRAINED_MAX;
                }
                num_valid_sets++;
        }
-- 
2.43.0