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

[Yu Kuai]

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...

Thanks,
Kuai