Messages in this thread | | | Subject | Re: [PATCH] nbd: pass nbd_sock to nbd_read_reply() instead of index | From | Yu Kuai <> | Date | Mon, 30 Oct 2023 10:07:13 +0800 |
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Hi,
在 2023/09/28 17:40, Yu Kuai 写道: > Hi, > > 在 2023/09/28 17:24, Ming Lei 写道: >> On Thu, Sep 28, 2023 at 05:06:40PM +0800, Yu Kuai wrote: >>> 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@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() >>>> >>>> Yeah, turns out you do understand, :-) >>> >>> Ok, I was not sure about this blk_queue_enter(). By the way, this >> >> blk_queue_enter() isn't exported, but you can grab ->config_lock >> for getting the `nsock`. >> >>> 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? >> >> ->socks[idx] is needed in nbd fast path, so xarray may not be one good >> idea >> since xarray_load() introduces extra load, especially ->socks[] uaf >> should exist in recv_work() very likely. For other cases, the active >> block request holds queue usage counter. > > Thanks for the explanation, grab 'config_lock' to get 'nsock' in the > begining sounds good to me.
After reviewing some code, I found that it's wrong to grab config_lock, because other context will grab such lock and flush_workqueue(), and there is no gurantee that recv_work() will grab the lock first.
Will it be acceptable to export blk_queue_enter()? I can't think of other way to retrieve the`nsock` reference at the entry of recv_work().
Thanks, Kuai
> > Kuai > >> >> >> Thanks, >> Ming >> >> . >> > > . >
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