Re: [PATCH] block, bfq: fix uaf for bfqq in bic_set_bfqq()

[Holger Hoffstätte]

On 2023-02-21 08:04, Yu Kuai wrote:
> Hi, Jens
>
> 在 2023/01/13 17:44, Yu Kuai 写道:
> > After commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'"),
> > bic->bfqq will be accessed in bic_set_bfqq(), however, in some context
> > bic->bfqq will be freed first, and bic_set_bfqq() is called with the freed
> > bic->bfqq.
> >
> > Fix the problem by always freeing bfqq after bic_set_bfqq().
> >
> > Fixes: 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
> > Reported-and-tested-by: Shinichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > ---
> >   block/bfq-cgroup.c  | 2 +-
> >   block/bfq-iosched.c | 4 +++-
> >   2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> > index a6e8da5f5cfd..feb13ac25557 100644
> > --- a/block/bfq-cgroup.c
> > +++ b/block/bfq-cgroup.c
> > @@ -749,8 +749,8 @@ static void bfq_sync_bfqq_move(struct bfq_data *bfqd,
> >            * old cgroup.
> >            */
> >           bfq_put_cooperator(sync_bfqq);
> > -        bfq_release_process_ref(bfqd, sync_bfqq);
> >           bic_set_bfqq(bic, NULL, true, act_idx);
> > +        bfq_release_process_ref(bfqd, sync_bfqq);
> >       }
> >   }
>
> It seems this change is missed in GIT PULL for-6.3. I'll send a seperate
> patch to fix this...

It was already applied in time for 6.2 as b600de2d7d3a16f9007fad1bdae82a3951a26af2
and also already merged to 6.1-stable.

cheers
Holger