Re: [PATCH] drm/mm: prevent a potential null-pointer dereference

[Jing Xiangfeng]

On 2020/9/10 16:58, Christian König wrote:
> Am 10.09.20 um 04:38 schrieb Jing Xiangfeng:
> > The macro 'DECLARE_NEXT_HOLE_ADDR' may hit a potential null-pointer
> > dereference. So use 'entry' after checking it.
>
> I don't see a potential null-pointer dereference here.
>
> Where should that be?

In current code，the "entry" pointer is checked after entry->rb_hole_addr.
	Thanks
> Christian.
>
> > Fixes: 5fad79fd66ff ("drm/mm: cleanup and improve next_hole_*_addr()")
> > Signed-off-by: Jing Xiangfeng <jingxiangfeng@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/drm_mm.c | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
> > index a4a04d246135..6fcf70f71962 100644
> > --- a/drivers/gpu/drm/drm_mm.c
> > +++ b/drivers/gpu/drm/drm_mm.c
> > @@ -392,11 +392,14 @@ first_hole(struct drm_mm *mm,
> >   #define DECLARE_NEXT_HOLE_ADDR(name, first, last)            \
> >   static struct drm_mm_node *name(struct drm_mm_node *entry, u64
> > size)    \
> >   {                                    \
> > -    struct rb_node *parent, *node = &entry->rb_hole_addr;        \
> > +    struct rb_node *parent, *node;                    \
> >                                       \
> > -    if (!entry || RB_EMPTY_NODE(node))                \
> > +    if (!entry)                            \
> >           return NULL;                        \
> >                                       \
> > +    node = &entry->rb_hole_addr;                    \
> > +    if (RB_EMPTY_NODE(node))                    \
> > +        return NULL;                        \
> >       if (usable_hole_addr(node->first, size)) {            \
> >           node = node->first;                    \
> >           while (usable_hole_addr(node->last, size))        \
>
> .