linux-kernel - [PATCH] drm/amdgpu: Avoid possible buffer overflow

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Date:   Mon, 21 Aug 2023 14:19:45 +0800
From:   Su Hui <suhui@...china.com>
To:     alexander.deucher@....com, christian.koenig@....com,
        Xinhui.Pan@....com, airlied@...il.com, daniel@...ll.ch
Cc:     Hawking.Zhang@....com, le.ma@....com, lijo.lazar@....com,
        yifan1.zhang@....com, candice.li@....com, Yuliang.Shi@....com,
        guchun.chen@....com, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org, Su Hui <suhui@...china.com>
Subject: [PATCH] drm/amdgpu: Avoid possible buffer overflow

smatch error:
drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1257 amdgpu_discovery_reg_base_init() error:
testing array offset 'adev->vcn.num_vcn_inst' after use.

change the assignment order to avoid buffer overflow.

Fixes: c40bdfb2ffa4 ("drm/amdgpu: fix incorrect VCN revision in SRIOV")
Signed-off-by: Su Hui <suhui@...china.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
index 8e1cfc87122d..ba95526c3d45 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
@@ -1250,11 +1250,12 @@ static int amdgpu_discovery_reg_base_init(struct amdgpu_device *adev)
 				 *     0b10 : encode is disabled
 				 *     0b01 : decode is disabled
 				 */
-				adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
-					ip->revision & 0xc0;
+
 				ip->revision &= ~0xc0;
 				if (adev->vcn.num_vcn_inst <
 				    AMDGPU_MAX_VCN_INSTANCES) {
+					adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
+						ip->revision & 0xc0;
 					adev->vcn.num_vcn_inst++;
 					adev->vcn.inst_mask |=
 						(1U << ip->instance_number);
-- 
2.30.2