Re: [PATCH] block, bfq: free 'sync_bfqq' after bic_set_bfqq() in bfq_sync_bfqq_move()

[Yu Kuai]

Hi,

在 2023/02/21 17:14, Damien Le Moal 写道:
> On 2/21/23 17:29, Yu Kuai wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > As explained in commit b600de2d7d3a ("block, bfq: fix uaf for bfqq in
> > bic_set_bfqq()"), bfqq should not be freed before bic_set_bfqq().
> > However, this is broken while merging commit 9778369a2d6c ("block, bfq:
> > split sync bfq_queues on a per-actuator basis") from branch
> > for-6.3/block.
>
> The patch looks OK to me, but the commit message is not super clear. What is
> broken exactly ?

1) bfq_sync_bfqq_move() is introduced in commit 9778369a2d6c ("block,
bfq: split sync bfq_queues on a per-actuator basis"), which is merged to
block/for-6.3 branch.

2) commit 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'")
is merged to mainline.

3) later, the fix for 2) b600de2d7d3a ("block, bfq: fix uaf for bfqq in
bic_set_bfqq()") is merged to mainline as well, however,
bfq_sync_bfqq_move() in block/for-6.3 branch is not changed.

4) At last, 1) is merged to mainline and bfq_sync_bfqq_move() is
still problematic.

Thanks,
Kuai
> > Fixes: 9778369a2d6c ("block, bfq: split sync bfq_queues on a per-actuator basis")
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > ---
> >   block/bfq-cgroup.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> > index ea3638e06e04..89ffb3aa992c 100644
> > --- a/block/bfq-cgroup.c
> > +++ b/block/bfq-cgroup.c
> > @@ -746,8 +746,8 @@ 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);
> >   	}
> >   }
> >