Re: [PATCH 3/4] blk-cgroup: Add NULL check of pd_alloc_fn in blkcg_activate_policy

[Yu Kuai]

Hi, Tejun

在 2022/10/11 4:29, Tejun Heo 写道:
> On Mon, Oct 10, 2022 at 10:38:58AM +0800, Kemeng Shi wrote:
> > Function only make sure pd_alloc_fn and pd_free_fn in
> > pairs, so pd_alloc_fn could be NULL in registered blkcg_policy. Check NULL
> > before use for pd_alloc_fn in blkcg_activate_policy to avoid protential
> > NULL dereference.
> >
> > Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxx>
> > ---
> >   block/blk-cgroup.c | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> > index 463c568d3e86..fc083c35dc42 100644
> > --- a/block/blk-cgroup.c
> > +++ b/block/blk-cgroup.c
> > @@ -1404,6 +1404,9 @@ int blkcg_activate_policy(struct request_queue *q,
> >   	if (blkcg_policy_enabled(q, pol))
> >   		return 0;
> >   
> > +	if (pol->pd_alloc_fn == NULL)
> > +		return -EINVAL;
>
> This isn't the only place this function is called, so the above won't
> achieve much. Given that this is rather trivially noticeable and all the
> current users do implement pd_alloc_fn, I'm not sure we need to update this
> now.

It's right all the current users implement pd_alloc_fn, can we check
pd_alloc/free_fn NULL instead in blkcg_policy_register()?

Thanks,
Kuai
> Thanks.