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SubjectRe: [PATCH] nbd: pass nbd_sock to nbd_read_reply() instead of index
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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@huaweicloud.com wrote:
>>>> From: Li Nan <linan122@huawei.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
>
> .
>

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