Re: [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@xxxxxxxxxxxx>
> > ---
> >   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