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

[Yu Kuai]

Hi,

在 2023/02/21 18:19, Holger Hoffstätte 写道:
> 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.

Yes, 6.2 and 6.1 doesn't have such problem because bfq_sync_bfqq_move()
doesn't exist. The problem only exist in master branch currently.

Thanks,
Kuai
> cheers
> Holger
>
> .