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

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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@xxxxxxxxxxxxxxx wrote:
From: Li Nan <linan122@xxxxxxxxxx>

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.

Kuai



Thanks,
Ming

.





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