linux-kernel - Re: [PATCH] nbd: pass nbd_sock to nbd_read

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Date:   Thu, 28 Sep 2023 17:06:40 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Ming Lei <ming.lei@...hat.com>, Yu Kuai <yukuai1@...weicloud.com>
Cc:     linan666@...weicloud.com, josef@...icpanda.com, axboe@...nel.dk,
        linux-block@...r.kernel.org, nbd@...er.debian.org,
        linux-kernel@...r.kernel.org, linan122@...wei.com,
        yi.zhang@...wei.com, houtao1@...wei.com, yangerkun@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] nbd: pass nbd_sock to nbd_read_reply() instead of index

Hi,

在 2023/09/28 16:57, Ming Lei 写道:
> On Thu, Sep 28, 2023 at 04:55:03PM +0800, Yu Kuai wrote:
>> Hi,
>>
>> 在 2023/09/28 15:40, Ming Lei 写道:
>>> On Thu, Sep 28, 2023 at 02:03:28PM +0800, Yu Kuai wrote:
>>>> Hi,
>>>>
>>>> 在 2023/09/28 12:05, Ming Lei 写道:
>>>>> On Mon, Sep 11, 2023 at 10:33:08AM +0800, linan666@...weicloud.com wrote:
>>>>>> From: Li Nan <linan122@...wei.com>
>>>>>>
>>>>>> If a socket is processing ioctl 'NBD_SET_SOCK', config->socks might be
>>>>>> krealloc in nbd_add_socket(), and a garbage request is received now, a UAF
>>>>>> may occurs.
>>>>>>
>>>>>>      T1
>>>>>>      nbd_ioctl
>>>>>>       __nbd_ioctl
>>>>>>        nbd_add_socket
>>>>>>         blk_mq_freeze_queue
>>>>>> 				T2
>>>>>>      				recv_work
>>>>>>      				 nbd_read_reply
>>>>>>      				  sock_xmit
>>>>>>         krealloc config->socks
>>>>>> 				   def config->socks
>>>>>>
>>>>>> Pass nbd_sock to nbd_read_reply(). And introduce a new function
>>>>>> sock_xmit_recv(), which differs from sock_xmit only in the way it get
>>>>>> socket.
>>>>>>
>>>>>
>>>>> I am wondering why not grab queue usage counter before calling nbd_read_reply()
>>>>> for avoiding such issue, something like the following change:
>>>>>
>>>>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
>>>>> index df1cd0f718b8..09215b605b12 100644
>>>>> --- a/drivers/block/nbd.c
>>>>> +++ b/drivers/block/nbd.c
>>>>> @@ -837,9 +837,6 @@ static void recv_work(struct work_struct *work)
>>>>>     	while (1) {
>>>>>     		struct nbd_reply reply;
>>>>> -		if (nbd_read_reply(nbd, args->index, &reply))
>>>>> -			break;
>>>>> -
>>>>>     		/*
>>>>>     		 * Grab .q_usage_counter so request pool won't go away, then no
>>>>>     		 * request use-after-free is possible during nbd_handle_reply().
>>>>> @@ -852,6 +849,9 @@ static void recv_work(struct work_struct *work)
>>>>>     			break;
>>>>>     		}
>>>>
>>>> This break how nbd works, if there is no reply yet, recv_work() will
>>>> wait for reply in:
>>>>
>>>> nbd_read_reply
>>>>    sock_xmit
>>>>     sock_recvmsg
>>>>
>>>> After this change, recv_work() will just return if there is no io.
>>>
>>> OK, got it, thanks for the input.
>>>
>>> But I feel it isn't necessary & fragile to store one extra reference of nsock in
>>> `recv_thread_args`.
>>>
>>> Just run a quick look, the only potential UAF on config->socks should be recv_work(),
>>> so you can retrieve the `nsock` reference at the entry of recv_work(),
>>
>> I don't understand what you mean retrieve the 'nsock', is following what
>> you expected?
>>
>> blk_queue_enter() -> prevent concurrent with nbd_add_socket
>> nsock = config->socks[args->index]
>> blk_queue_exit()
> 
> Yeah, turns out you do understand, :-)

Ok, I was not sure about this blk_queue_enter(). By the way, this
remind me of what you did to fix uaf of access queue->mq_hctx[] by
convert the array to xarray.


Maybe it's better to covert config->socks[] to xarray to fix this uaf as
well?

Thanks,
Kuai