Re: [PATCH] drm/amdgpu: Avoid possible buffer overflow

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On 2023/8/21 14:47, Christophe JAILLET wrote:
Le 21/08/2023 à 08:19, Su Hui a écrit :
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@xxxxxxxxxxxx>
---
  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;

Hi,
I don't think that the patch is correct.

Because of the "ip->revision &= ~0xc0" which is now above it, "ip->revision & 0xc0" should now always be 0.

Maybe both lines should be moved within the "if"?

CJ

Hi,

Oh, really sorry for this, I just missed this line.
you are right, I will send v2 soon.
Thanks for your reminder!

Su Hui






adev->vcn.num_vcn_inst++;
                      adev->vcn.inst_mask |=
                          (1U << ip->instance_number);




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