relid2channel() assumes vmbus channel array to be allocated when called.
However, if the guest receives a vmbus interrupt during driver initialization
before vmbus_connect() is called or if vmbus_connect() fails, the vmbus
interrupt service routine is called which in turn calls relid2channel()
and can cause a null pointer dereference.

So Make relid2channel() check if vmbus channels is allocated first and return
NULL to the caller if not allocated.

Fixes: 8b6a877c060e ("Drivers: hv: vmbus: Replace the per-CPU channel lists with a global array of channels")

Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
---
 drivers/hv/connection.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 9dc27e5d367a..5c603c4f75a2 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -409,6 +409,8 @@ void vmbus_disconnect(void)
  */
 struct vmbus_channel *relid2channel(u32 relid)
 {
+	if (WARN_ON(vmbus_connection.channels == NULL))
+		return NULL;
 	if (WARN_ON(relid >= MAX_CHANNEL_RELIDS))
 		return NULL;
 	return READ_ONCE(vmbus_connection.channels[relid]);
-- 
2.38.1

> From: Mohammed Gamal <mgamal@redhat.com>
> Sent: Wednesday, February 8, 2023 3:34 AM
> 
> relid2channel() assumes vmbus channel array to be allocated when called.
> However, if the guest receives a vmbus interrupt during driver initialization
> before vmbus_connect() is called or if vmbus_connect() fails, the vmbus
> interrupt service routine is called which in turn calls relid2channel()
> and can cause a null pointer dereference.

Before vmbus_connect() is called or if vmbus_connect() fails, there should
be no VMBus channel related interrupts at all, so relid2channel() can't be
called. 

Can you please share the log or at least the crash call-stack?
I'm curious how the crash can happen.