Re: [PATCH] mm/slub: return 0 when object pointer is NULL

[Ben Luo]

Hello Hyeonggon,

Thanks for replying :)

在 2022/9/12 15:18, Hyeonggon Yoo 写道:
> On Mon, Sep 12, 2022 at 01:59:39PM +0800, Ben Luo wrote:
> > NULL is definitly not a valid address
> >
> > Signed-off-by: Ben Luo <luoben@xxxxxxxxxxxxxxxxx>
> > ---
> >   mm/slub.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 862dbd9..50fad18 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -674,7 +674,7 @@ static inline int check_valid_pointer(struct kmem_cache *s,
> >   	void *base;
> >   
> >   	if (!object)
> > -		return 1;
> > +		return 0;
> >   
> >   	base = slab_address(slab);
> >   	object = kasan_reset_tag(object);
> > --
> > 1.8.3.1
> Hello Ben.
>
> The return value is used to check if the @object has valid pointer
> in @slab. (used for debugging) the return value is 0 if valid, 1 if invalid.
>
> It does not return a pointer. So changing it to 0 because 1 is invalid
> address does not make sense.

I know the meaning of this return value, but I think this function was 
expected by returning 0 if invalid ,1 if valid

Check this original code:

        if (object < base || object >= base + slab->objects * s->size ||
                (object - base) % s->size) {
                return 0;
        }

Object not in range of [base, base+length) is an invalid slab address, 
and it will return 0


--

Thanks,

Ben

>