[PATCH 4.14 060/229] drm/radeon: fix potential buffer overflow in ni_set_mc_special_registers()

[Greg Kroah-Hartman]

From: Alexey Kodanev <aleksei.kodanev@xxxxxxxxxxx>

[ Upstream commit 136f614931a2bb73616b292cf542da3a18daefd5 ]

The last case label can write two buffers 'mc_reg_address[j]' and
'mc_data[j]' with 'j' offset equal to SMC_NISLANDS_MC_REGISTER_ARRAY_SIZE
since there are no checks for this value in both case labels after the
last 'j++'.

Instead of changing '>' to '>=' there, add the bounds check at the start
of the second 'case' (the first one already has it).

Also, remove redundant last checks for 'j' index bigger than array size.
The expression is always false. Moreover, before or after the patch
'table->last' can be equal to SMC_NISLANDS_MC_REGISTER_ARRAY_SIZE and it
seems it can be a valid value.

Detected using the static analysis tool - Svace.
Fixes: 69e0b57a91ad ("drm/radeon/kms: add dpm support for cayman (v5)")
Signed-off-by: Alexey Kodanev <aleksei.kodanev@xxxxxxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/gpu/drm/radeon/ni_dpm.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/radeon/ni_dpm.c b/drivers/gpu/drm/radeon/ni_dpm.c
index d491b3aa124f..fa88c1809946 100644
--- a/drivers/gpu/drm/radeon/ni_dpm.c
+++ b/drivers/gpu/drm/radeon/ni_dpm.c
@@ -2738,10 +2738,10 @@ static int ni_set_mc_special_registers(struct radeon_device *rdev,
 					table->mc_reg_table_entry[k].mc_data[j] |= 0x100;
 			}
 			j++;
-			if (j > SMC_NISLANDS_MC_REGISTER_ARRAY_SIZE)
-				return -EINVAL;
 			break;
 		case MC_SEQ_RESERVE_M >> 2:
+			if (j >= SMC_NISLANDS_MC_REGISTER_ARRAY_SIZE)
+				return -EINVAL;
 			temp_reg = RREG32(MC_PMG_CMD_MRS1);
 			table->mc_reg_address[j].s1 = MC_PMG_CMD_MRS1 >> 2;
 			table->mc_reg_address[j].s0 = MC_SEQ_PMG_CMD_MRS1_LP >> 2;
@@ -2750,8 +2750,6 @@ static int ni_set_mc_special_registers(struct radeon_device *rdev,
 					(temp_reg & 0xffff0000) |
 					(table->mc_reg_table_entry[k].mc_data[i] & 0x0000ffff);
 			j++;
-			if (j > SMC_NISLANDS_MC_REGISTER_ARRAY_SIZE)
-				return -EINVAL;
 			break;
 		default:
 			break;
-- 
2.35.1