linux-kernel - Re: [PATCH 3/4] blk-cgroup: Add NULL check of pd_alloc_fn in blkcg_activate

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Date:   Tue, 11 Oct 2022 15:53:28 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Tejun Heo <tj@...nel.org>, Kemeng Shi <shikemeng@...wei.com>
Cc:     axboe@...nel.dk, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH 3/4] blk-cgroup: Add NULL check of pd_alloc_fn in
 blkcg_activate_policy

Hi, Tejun

在 2022/10/11 4:29, Tejun Heo 写道:
> On Mon, Oct 10, 2022 at 10:38:58AM +0800, Kemeng Shi wrote:
>> Function only make sure pd_alloc_fn and pd_free_fn in
>> pairs, so pd_alloc_fn could be NULL in registered blkcg_policy. Check NULL
>> before use for pd_alloc_fn in blkcg_activate_policy to avoid protential
>> NULL dereference.
>>
>> Signed-off-by: Kemeng Shi <shikemeng@...wei.com>
>> ---
>>   block/blk-cgroup.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
>> index 463c568d3e86..fc083c35dc42 100644
>> --- a/block/blk-cgroup.c
>> +++ b/block/blk-cgroup.c
>> @@ -1404,6 +1404,9 @@ int blkcg_activate_policy(struct request_queue *q,
>>   	if (blkcg_policy_enabled(q, pol))
>>   		return 0;
>>   
>> +	if (pol->pd_alloc_fn == NULL)
>> +		return -EINVAL;
> 
> This isn't the only place this function is called, so the above won't
> achieve much. Given that this is rather trivially noticeable and all the
> current users do implement pd_alloc_fn, I'm not sure we need to update this
> now.

It's right all the current users implement pd_alloc_fn, can we check
pd_alloc/free_fn NULL instead in blkcg_policy_register()?

Thanks,
Kuai
> 
> Thanks.
>