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

[Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

On Jan 13, 2023 / 17:44, Yu Kuai wrote:
> 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@wdc.com>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  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);
>  	}
>  }
>  

Yu, thanks for posting this fix, but it can not be applied to v6.2-rc5. The
hunk above looks different from the patch I tested. Could you take a look?

-- 
Shin'ichiro Kawasaki