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

[Andrea Parri (Microsoft)]

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://lkml.kernel.org/r/20210416143932.16512-1-parri.andrea@xxxxxxxxx

 drivers/hv/channel_mgmt.c | 7 ++++++-
 drivers/hv/connection.c   | 2 ++
 2 files changed, 8 insertions(+), 1 deletion(-)

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