[PATCH] drm/ast: Avoid possible NULL dereference

[Su Hui]

On 2023/8/21 15:04, Christophe JAILLET wrote:
> Le 21/08/2023 à 08:22, Su Hui a écrit :
>> smatch error:
>> drivers/gpu/drm/ast/ast_dp501.c:227 ast_launch_m68k() error:
>> we previously assumed 'ast->dp501_fw' could be null (see line 223)
>>
>> when "!ast->dp501_fw" and "ast_load_dp501_microcode(dev) >= 0" is true,
>> there will be a NULL dereference of 'ast->dp501_fw'.
>>
>> Fixes: 12f8030e05c6 ("drm/ast: Actually load DP501 firmware when 
>> required")
>> Signed-off-by: Su Hui <suhui at nfschina.com>
>> ---
>>   drivers/gpu/drm/ast/ast_dp501.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ast/ast_dp501.c 
>> b/drivers/gpu/drm/ast/ast_dp501.c
>> index 1bc35a992369..d9f3a0786a6f 100644
>> --- a/drivers/gpu/drm/ast/ast_dp501.c
>> +++ b/drivers/gpu/drm/ast/ast_dp501.c
>> @@ -224,8 +224,10 @@ static bool ast_launch_m68k(struct drm_device *dev)
>>                   ast_load_dp501_microcode(dev) < 0)
>>                   return false;
>>   -            fw_addr = (u8 *)ast->dp501_fw->data;
>> -            len = ast->dp501_fw->size;
>> +            if (ast->dp501_fw) {
>> +                fw_addr = (u8 *)ast->dp501_fw->data;
>> +                len = ast->dp501_fw->size;
>> +            }
>>           }
>>           /* Get BootAddress */
>>           ast_moutdwm(ast, 0x1e6e2000, 0x1688a8a8);
>
> Hi,
>
> this looks like a false positive.
>
> If "!ast->dp501_fw", and ast_load_dp501_microcode()>=0, then 
> ast_load_dp501_microcode() will set a valid value in ast->dp501_fw.

Hi,

Sorry for the noise, you are right, this is a false positive.
I will take more careful next time.

Su Hui

>
> CJ