RE: [PATCH v2] Drivers: hv: vmbus: Initialize unload_event statically

[Michael Kelley]

From: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Sent: Monday, April 19, 2021 6:44 PM
> 
> If a malicious or compromised Hyper-V sends a spurious message of type
> CHANNELMSG_UNLOAD_RESPONSE, the function vmbus_unload_response() will
> call complete() on an uninitialized event, and cause an oops.
> 
> Reported-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> ---
> Changes since v1[1]:
>   - add inline comment in vmbus_unload_response()
> 
> [1] https://lore.kernel.org/linux-hyperv/20210416143932.16512-1-parri.andrea@xxxxxxxxx/
> 
>  drivers/hv/channel_mgmt.c | 7 ++++++-
>  drivers/hv/connection.c   | 2 ++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 

Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>

> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 4c9e45d1f462c..335a10ee03a5e 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -826,6 +826,11 @@ static void vmbus_unload_response(struct
> vmbus_channel_message_header *hdr)
>  	/*
>  	 * This is a global event; just wakeup the waiting thread.
>  	 * Once we successfully unload, we can cleanup the monitor state.
> +	 *
> +	 * NB.  A malicious or compromised Hyper-V could send a spurious
> +	 * message of type CHANNELMSG_UNLOAD_RESPONSE, and trigger a call
> +	 * of the complete() below.  Make sure that unload_event has been
> +	 * initialized by the time this complete() is executed.
>  	 */
>  	complete(&vmbus_connection.unload_event);
>  }
> @@ -841,7 +846,7 @@ void vmbus_initiate_unload(bool crash)
>  	if (vmbus_proto_version < VERSION_WIN8_1)
>  		return;
> 
> -	init_completion(&vmbus_connection.unload_event);
> +	reinit_completion(&vmbus_connection.unload_event);
>  	memset(&hdr, 0, sizeof(struct vmbus_channel_message_header));
>  	hdr.msgtype = CHANNELMSG_UNLOAD;
>  	vmbus_post_msg(&hdr, sizeof(struct vmbus_channel_message_header),
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index dc19d5ae4373c..311cd005b3be6 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -26,6 +26,8 @@
> 
>  struct vmbus_connection vmbus_connection = {
>  	.conn_state		= DISCONNECTED,
> +	.unload_event		= COMPLETION_INITIALIZER(
> +				  vmbus_connection.unload_event),
>  	.next_gpadl_handle	= ATOMIC_INIT(0xE1E10),
> 
>  	.ready_for_suspend_event = COMPLETION_INITIALIZER(
> --
> 2.25.1