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

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Message-ID: <41161d21-299c-3657-6020-0a3a9cf109ec@huaweicloud.com>
Date:   Thu, 28 Sep 2023 16:55:03 +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 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()

while (1) {
	...
	// pass nsock to nbd_read_reply() and nbd_handle_reply()
}

> and just pass it(local variable) to nbd_read_reply() and nbd_handle_reply()
> since `nsock` won't be freed.
> 
> 
> Thanks,
> Ming
> 
> .
>