[v2,net] hv_sock: Fix hang when a connection is closed

There is a race condition for an established connection that is being closed
by the guest: the refcnt is 4 at the end of hvs_release() (Note: here the
'remove_sock' is false):

1 for the initial value;
1 for the sk being in the bound list;
1 for the sk being in the connected list;
1 for the delayed close_work.

After hvs_release() finishes, __vsock_release() -> sock_put(sk) *may*
decrease the refcnt to 3.

Concurrently, hvs_close_connection() runs in another thread:
  calls vsock_remove_sock() to decrease the refcnt by 2;
  call sock_put() to decrease the refcnt to 0, and free the sk;
  next, the "release_sock(sk)" may hang due to use-after-free.

In the above, after hvs_release() finishes, if hvs_close_connection() runs
faster than "__vsock_release() -> sock_put(sk)", then there is not any issue,
because at the beginning of hvs_close_connection(), the refcnt is still 4.

The issue can be resolved if an extra reference is taken when the
connection is established.

Fixes: a9eeb998c28d ("hv_sock: Add support for delayed close")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: stable@vger.kernel.org

---

Changes in v2: 
  Changed the location of the sock_hold() call. 
  Updated the changelog accordingly.
  
  Thanks Sunil for the suggestion!


With the proper kernel debugging options enabled, first a warning can
appear:

kworker/1:0/4467 is freeing memory ..., with a lock still held there!
stack backtrace:
Workqueue: events vmbus_onmessage_work [hv_vmbus]
Call Trace:
 dump_stack+0x67/0x90
 debug_check_no_locks_freed.cold.52+0x78/0x7d
 slab_free_freelist_hook+0x85/0x140
 kmem_cache_free+0xa5/0x380
 __sk_destruct+0x150/0x260
 hvs_close_connection+0x24/0x30 [hv_sock]
 vmbus_onmessage_work+0x1d/0x30 [hv_vmbus]
 process_one_work+0x241/0x600
 worker_thread+0x3c/0x390
 kthread+0x11b/0x140
 ret_from_fork+0x24/0x30

and then the following release_sock(sk) can hang:

watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [kworker/1:0:4467]
...
irq event stamp: 62890
CPU: 1 PID: 4467 Comm: kworker/1:0 Tainted: G        W         5.2.0+ #39
Workqueue: events vmbus_onmessage_work [hv_vmbus]
RIP: 0010:queued_spin_lock_slowpath+0x2b/0x1e0
...
Call Trace:
 do_raw_spin_lock+0xab/0xb0
 release_sock+0x19/0xb0
 vmbus_onmessage_work+0x1d/0x30 [hv_vmbus]
 process_one_work+0x241/0x600
 worker_thread+0x3c/0x390
 kthread+0x11b/0x140
 ret_from_fork+0x24/0x30

 net/vmw_vsock/hyperv_transport.c | 8 ++++++++
 1 file changed, 8 insertions(+)

> -----Original Message-----
> From: Dexuan Cui <decui@microsoft.com>
> Sent: Tuesday, July 30, 2019 6:26 PM
> To: Sunil Muthuswamy <sunilmut@microsoft.com>; David Miller <davem@davemloft.net>; netdev@vger.kernel.org
> Cc: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>; Stephen Hemminger
> <sthemmin@microsoft.com>; sashal@kernel.org; Michael Kelley <mikelley@microsoft.com>; linux-hyperv@vger.kernel.org; linux-
> kernel@vger.kernel.org; olaf@aepfle.de; apw@canonical.com; jasowang@redhat.com; vkuznets <vkuznets@redhat.com>;
> marcelo.cerri@canonical.com
> Subject: [PATCH v2 net] hv_sock: Fix hang when a connection is closed
> 
> 
> There is a race condition for an established connection that is being closed
> by the guest: the refcnt is 4 at the end of hvs_release() (Note: here the
> 'remove_sock' is false):
> 
> 1 for the initial value;
> 1 for the sk being in the bound list;
> 1 for the sk being in the connected list;
> 1 for the delayed close_work.
> 
> After hvs_release() finishes, __vsock_release() -> sock_put(sk) *may*
> decrease the refcnt to 3.
> 
> Concurrently, hvs_close_connection() runs in another thread:
>   calls vsock_remove_sock() to decrease the refcnt by 2;
>   call sock_put() to decrease the refcnt to 0, and free the sk;
>   next, the "release_sock(sk)" may hang due to use-after-free.
> 
> In the above, after hvs_release() finishes, if hvs_close_connection() runs
> faster than "__vsock_release() -> sock_put(sk)", then there is not any issue,
> because at the beginning of hvs_close_connection(), the refcnt is still 4.
> 
> The issue can be resolved if an extra reference is taken when the
> connection is established.
> 
> Fixes: a9eeb998c28d ("hv_sock: Add support for delayed close")
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> Cc: stable@vger.kernel.org
> 
> ---
> 
> Changes in v2:
>   Changed the location of the sock_hold() call.
>   Updated the changelog accordingly.
> 
>   Thanks Sunil for the suggestion!
> 
> 
> With the proper kernel debugging options enabled, first a warning can
> appear:
> 
> kworker/1:0/4467 is freeing memory ..., with a lock still held there!
> stack backtrace:
> Workqueue: events vmbus_onmessage_work [hv_vmbus]
> Call Trace:
>  dump_stack+0x67/0x90
>  debug_check_no_locks_freed.cold.52+0x78/0x7d
>  slab_free_freelist_hook+0x85/0x140
>  kmem_cache_free+0xa5/0x380
>  __sk_destruct+0x150/0x260
>  hvs_close_connection+0x24/0x30 [hv_sock]
>  vmbus_onmessage_work+0x1d/0x30 [hv_vmbus]
>  process_one_work+0x241/0x600
>  worker_thread+0x3c/0x390
>  kthread+0x11b/0x140
>  ret_from_fork+0x24/0x30
> 
> and then the following release_sock(sk) can hang:
> 
> watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [kworker/1:0:4467]
> ...
> irq event stamp: 62890
> CPU: 1 PID: 4467 Comm: kworker/1:0 Tainted: G        W         5.2.0+ #39
> Workqueue: events vmbus_onmessage_work [hv_vmbus]
> RIP: 0010:queued_spin_lock_slowpath+0x2b/0x1e0
> ...
> Call Trace:
>  do_raw_spin_lock+0xab/0xb0
>  release_sock+0x19/0xb0
>  vmbus_onmessage_work+0x1d/0x30 [hv_vmbus]
>  process_one_work+0x241/0x600
>  worker_thread+0x3c/0x390
>  kthread+0x11b/0x140
>  ret_from_fork+0x24/0x30
> 
>  net/vmw_vsock/hyperv_transport.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> index f2084e3f7aa4..9d864ebeb7b3 100644
> --- a/net/vmw_vsock/hyperv_transport.c
> +++ b/net/vmw_vsock/hyperv_transport.c
> @@ -312,6 +312,11 @@ static void hvs_close_connection(struct vmbus_channel *chan)
>  	lock_sock(sk);
>  	hvs_do_close_lock_held(vsock_sk(sk), true);
>  	release_sock(sk);
> +
> +	/* Release the refcnt for the channel that's opened in
> +	 * hvs_open_connection().
> +	 */
> +	sock_put(sk);
>  }
> 
>  static void hvs_open_connection(struct vmbus_channel *chan)
> @@ -407,6 +412,9 @@ static void hvs_open_connection(struct vmbus_channel *chan)
>  	}
> 
>  	set_per_channel_state(chan, conn_from_host ? new : sk);
> +
> +	/* This reference will be dropped by hvs_close_connection(). */
> +	sock_hold(conn_from_host ? new : sk);
>  	vmbus_set_chn_rescind_callback(chan, hvs_close_connection);
> 
>  	/* Set the pending send size to max packet size to always get
> --
> 2.19.1

Reviewed-by: Sunil Muthuswamy <sunilmut@microsoft.com>

From: Dexuan Cui <decui@microsoft.com>
Date: Wed, 31 Jul 2019 01:25:45 +0000

> 
> There is a race condition for an established connection that is being closed
> by the guest: the refcnt is 4 at the end of hvs_release() (Note: here the
> 'remove_sock' is false):
> 
> 1 for the initial value;
> 1 for the sk being in the bound list;
> 1 for the sk being in the connected list;
> 1 for the delayed close_work.
> 
> After hvs_release() finishes, __vsock_release() -> sock_put(sk) *may*
> decrease the refcnt to 3.
> 
> Concurrently, hvs_close_connection() runs in another thread:
>   calls vsock_remove_sock() to decrease the refcnt by 2;
>   call sock_put() to decrease the refcnt to 0, and free the sk;
>   next, the "release_sock(sk)" may hang due to use-after-free.
> 
> In the above, after hvs_release() finishes, if hvs_close_connection() runs
> faster than "__vsock_release() -> sock_put(sk)", then there is not any issue,
> because at the beginning of hvs_close_connection(), the refcnt is still 4.
> 
> The issue can be resolved if an extra reference is taken when the
> connection is established.
> 
> Fixes: a9eeb998c28d ("hv_sock: Add support for delayed close")
> Signed-off-by: Dexuan Cui <decui@microsoft.com>

Applied and queued up for -stable.

Do not ever CC: stable for networking patches, we submit to -stable manually.

Thank you.

> From: linux-hyperv-owner@vger.kernel.org
> Sent: Friday, August 2, 2019 5:27 PM
> ...
> Applied and queued up for -stable.
> 
> Do not ever CC: stable for networking patches, we submit to -stable manually.
 
Thanks, David!
I'll remember to not add the stable tag for network patches.

Thanks,
-- Dexuan