linux-kernel - Re: [BUG] possible race between md_free_disk and md_notify

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <6748f138-ad52-b7c5-ac53-1c7fa6fab9b7@huaweicloud.com>
Date: Thu, 20 Feb 2025 19:55:13 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Yu Kuai <yukuai1@...weicloud.com>, Guillaume Morin <guillaume@...infr.org>
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
 song@...nel.org, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [BUG] possible race between md_free_disk and md_notify_reboot

Hi,

在 2025/02/20 12:06, Yu Kuai 写道:
> Hi,
> 
> 在 2025/02/20 11:45, Guillaume Morin 写道:
>> On 20 Feb 11:19, Yu Kuai wrote:
>>>
>>> Hi,
>>>
>>> 在 2025/02/20 11:05, Guillaume Morin 写道:
>>>> how it was guaranteed that mddev_get() would fail as mddev_free() 
>>>> does not check or synchronize with the active atomic
>>>
>>> Please check how mddev is freed, start from mddev_put(). There might be
>>> something wrong, but it's not what you said.
>>
>> I will take a look. Though if you're confident that this logic protects
>> any uaf, that makes sense to me.
>>
>> However as I mentioned this is not what the crash was about (I mentioned
>> the UAF in passing). The GPF seems to be about deleting the _next_
>> pointer while iterating over all mddevs. The mddev_get on the
>> current item is not going to help with this.
>>
> 
> You don't need to emphasize this, it is still speculate without solid
> theoretical analysis. The point about mddev_get() is that it's done
> inside the lock, it shoud gurantee continue iterating should be fine.
> 
> I just take a quick look, the problem looks obviously to me, see how
> md_seq_show() handle the iteration.
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 465ca2af1e6e..7c7a58f618c1 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -9911,8 +9911,11 @@ static int md_notify_reboot(struct notifier_block 
> *this,
>                          mddev_unlock(mddev);
>                  }
>                  need_delay = 1;
> -               mddev_put(mddev);
> -               spin_lock(&all_mddevs_lock);
> +
> +               spin_lock(&all_mddevs_lock)
> +               if (atomic_dec_and_test(&mddev->active))
> +                       __mddev_put(mddev);
> +
>          }
>          spin_unlock(&all_mddevs_lock);

While cooking the patch, this is not enough, list_for_each_entry_safe()
should be replaced with list_for_each_entry() as well.

Will send the patch soon, with:

Reported-by: Guillaume Morin <guillaume@...infr.org>

Thanks,
Kuai
> 
> 
> Thanks,
> Kuai
> 
> .
>