Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Subject: Re: [PATCH -next v7 5/5] md: protect md_thread with rcu
To:     Song Liu <song@kernel.org>, Yu Kuai <yukuai1@huaweicloud.com>
Cc:     logang@deltatee.com, axboe@kernel.dk, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org,
        yi.zhang@huawei.com, yangerkun@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20230425115256.3663932-1-yukuai1@huaweicloud.com>
 <20230425115256.3663932-6-yukuai1@huaweicloud.com>
 <CAPhsuW4_tDcmPZbo8Qs32LRxLAQfE6SNNTDys8bOoeHwx-1N=A@mail.gmail.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <059a8c6a-628f-ed18-0d5e-7ad3cad93813@huaweicloud.com>
Date:   Wed, 26 Apr 2023 11:57:32 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <CAPhsuW4_tDcmPZbo8Qs32LRxLAQfE6SNNTDys8bOoeHwx-1N=A@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

Hi,

在 2023/04/26 11:20, Song Liu 写道:
> On Tue, Apr 25, 2023 at 4:54 AM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> Our test reports a uaf for 'mddev->sync_thread':
>>
>> T1                      T2
>> md_start_sync
>>   md_register_thread
>>   // mddev->sync_thread is set
>>                          raid1d
>>                           md_check_recovery
>>                            md_reap_sync_thread
>>                             md_unregister_thread
>>                              kfree
>>
>>   md_wakeup_thread
>>    wake_up
>>    ->sync_thread was freed
>>
>> Root cause is that there is a small windown between register thread and
>> wake up thread, where the thread can be freed concurrently.
>>
>> Currently, a global spinlock 'pers_lock' is borrowed to protect
>> 'mddev->thread', this problem can be fixed likewise, however, there are
>> similar problems elsewhere, and use a global lock for all the cases is
>> not good.
>>
>> This patch protect all md_thread with rcu.
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   block/blk-cgroup.c        |  3 ++
>>   drivers/md/md-bitmap.c    | 10 ++++--
>>   drivers/md/md-cluster.c   | 17 ++++++----
>>   drivers/md/md-multipath.c |  4 +--
>>   drivers/md/md.c           | 69 ++++++++++++++++++---------------------
>>   drivers/md/md.h           |  8 ++---
>>   drivers/md/raid1.c        |  7 ++--
>>   drivers/md/raid1.h        |  2 +-
>>   drivers/md/raid10.c       | 20 +++++++-----
>>   drivers/md/raid10.h       |  2 +-
>>   drivers/md/raid5-cache.c  | 22 ++++++++-----
>>   drivers/md/raid5.c        | 15 +++++----
>>   drivers/md/raid5.h        |  2 +-
>>   13 files changed, 100 insertions(+), 81 deletions(-)
>>
>> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
>> index 1c1ebeb51003..0ecb4cce8af2 100644
>> --- a/block/blk-cgroup.c
>> +++ b/block/blk-cgroup.c
>> @@ -527,6 +527,9 @@ static void blkg_destroy_all(struct gendisk *disk)
>>          list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
>>                  struct blkcg *blkcg = blkg->blkcg;
>>
>> +               if (hlist_unhashed(&blkg->blkcg_node))
>> +                       continue;
>> +
> 
> This change is not related, right?

Yes, it's not related. Sorry that I missed another fix patch into
this...

> 
> I don't think we can rush this change in the 6.4 merge window. Let's
> test it more thoroughly and ship it in the next merge window.

Of course.

Thanks,
Kuai