From: Yufen Yu <yuyufen@huawei.com>
To: Tejun Heo <tj@kernel.org>
Cc: <axboe@kernel.dk>, <linux-block@vger.kernel.org>, <jack@suse.cz>,
<bvanassche@acm.org>
Subject: Re: [PATCH] bdi: fix use-after-free for bdi device
Date: Fri, 14 Feb 2020 10:50:01 +0800 [thread overview]
Message-ID: <f369a99d-e794-0c1b-85cf-83b577fb0f46@huawei.com> (raw)
In-Reply-To: <20200213135809.GH88887@mtj.thefacebook.com>
On 2020/2/13 21:58, Tejun Heo wrote:
> Hello,
>
> On Thu, Feb 13, 2020 at 03:51:40PM +0800, Yufen Yu wrote:
>> If we destroy the device asynchronously by call_rcu(), we may need to
>> add a new member 'rcu_head' into struct backing_dev_info. Right?
>
> Yes.
>
>> The code may be like:
>>
>> bdi_unregister()
>> {
>> ...
>> if (bdi->dev) {
>> ...
>> device_get(bdi->dev);
>> device_unregister(bdi->dev);
>> bdi->dev = NULL; //XXX
>> bdi_get(bdi); //avoiding bdi to be freed before calling bdi_release_device
>> call_rcu(&bdi->rcu_head, bdi_release_device);
>> }
>> ...
>> }
>>
>> bdi_release_device()
>> {
>> ...
>> put_device(bdi->dev);//XXX
>> bdi_put(bdi);
>> }
>>
>> But, the problem is how do we get 'bdi->dev' in bdi_release_device().
>> If we do not set bdi->dev as 'NULL', re-registration bdi may cannot work well.
>
> So, unregistering can leave ->dev along and re-registering can test
> whether it's NULL and if not put the existing one and put a new one
> there. Wouldn't that work?
Do you mean set bdi->dev as 'NULL' in call_rcu() callback function
(i.e. bdi_release_device()) and test 'bdi->dev' in bdi_register_va()?
I think that may do not work.
We cannot make sure the order of rcu callback function and re-registering.
Then bdi_release_device() may put the new allocated device by re-registering.
Thanks,
Yufen
next prev parent reply other threads:[~2020-02-14 2:50 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 14:00 [PATCH] bdi: fix use-after-free for bdi device Yufen Yu
2020-02-11 13:57 ` Yufen Yu
2020-02-12 21:33 ` Tejun Heo
2020-02-13 2:46 ` Yufen Yu
2020-02-13 3:48 ` Tejun Heo
2020-02-13 7:51 ` Yufen Yu
2020-02-13 13:58 ` Tejun Heo
2020-02-14 2:50 ` Yufen Yu [this message]
2020-02-14 14:05 ` Tejun Heo
2020-02-15 13:54 ` Yufen Yu
2020-02-19 12:55 ` Jan Kara
2020-02-19 15:12 ` Tejun Heo
2020-02-20 11:07 ` Yufen Yu
2020-02-20 12:07 ` Jan Kara
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