vmbus: don't return values for uninitalized channels

For unsupported device types, the vmbus channel ringbuffer is never
initialized, and therefore reading the sysfs files will return garbage
or cause a kernel OOPS.

Fixes: c2e5df6 ("vmbus: add per-channel sysfs info")

Signed-off-by: Stephen Hemminger <[email protected]>
Signed-off-by: K. Y. Srinivasan <[email protected]>
Cc: <[email protected]> # 4.15
Signed-off-by: Greg Kroah-Hartman <[email protected]>
(cherry picked from commit 6712cc9)

Orabug: 28671425

Signed-off-by: Liam Merwick <[email protected]>
Reviewed-by: Darren Kenny <[email protected]>
Reviewed-by: Alejandro Jimenez <[email protected]>
Tested-by: Vijay Balakrishna <[email protected]>

Author: shemminger

drivers/hv/vmbus_drv.c

@@ -1291,6 +1291,9 @@ static ssize_t vmbus_chan_attr_show(struct kobject *kobj,
 	if (!attribute->show)
 		return -EIO;
 
+	if (chan->state != CHANNEL_OPENED_STATE)
+		return -EINVAL;
+
 	return attribute->show(chan, buf);
 }