Subject: Re: [PATCH] block, bfq: fix uaf for bfqq in bic_set_bfqq()
To:     jack@suse.cz, tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk,
        paolo.valente@linaro.org, shinichiro.kawasaki@wdc.com
Cc:     cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, yukuai1@huaweicloud.com,
        yi.zhang@huawei.com, yangerkun@huawei.com
References: <20230113094410.2907223-1-yukuai3@huawei.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <ca9fefd4-7109-042c-3b25-9eb795141145@huaweicloud.com>
Date:   Tue, 21 Feb 2023 15:04:08 +0800
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Precedence: bulk

Hi, Jens

?? 2023/01/13 17:44, Yu Kuai д??:
> 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);
>   	}
>   }
>  

It seems this change is missed in GIT PULL for-6.3. I'll send a seperate
patch to fix this...

Thanks,
Kuai