[PATCH] drm/amdgpu: Avoid possible buffer overflow

[Su Hui]

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 at nfschina.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;
>
> 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

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