Re: [PATCH] nbd: pass nbd_sock to nbd_read_reply() instead of index

[Yu Kuai <yukuai1@huaweicloud.com>]

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
>
> .