ipmi/powernv: Fix potential invalid pointer dereference

If the OPAL call to receive the ipmi message fails, then we free up the
smi message and return. But, the driver still holds the reference to
old smi message in the 'cur_msg' which can potentially be accessed later
and freed again leading to kernel oops. To fix it up,

The kernel driver should reset the 'cur_msg' and send reply to the user
in addition to freeing the message.
Signed-off-by: Neelesh Gupta <neelegup@linux.vnet.ibm.com>

Fixed a checkpatch warning dealing with an else after a return.
Signed-off-by: Corey Minyard <cminyard@mvista.com>

drivers/char/ipmi/ipmi_powernv.c

@@ -143,8 +143,15 @@ static int ipmi_powernv_recv(struct ipmi_smi_powernv *smi)
 	pr_devel("%s:   -> %d (size %lld)\n", __func__,
 			rc, rc == 0 ? size : 0);
 	if (rc) {
+		/* If came via the poll, and response was not yet ready */
+		if (rc == OPAL_EMPTY) {
 			spin_unlock_irqrestore(&smi->msg_lock, flags);
-		ipmi_free_smi_msg(msg);
+			return 0;
+		}
+
+		smi->cur_msg = NULL;
+		spin_unlock_irqrestore(&smi->msg_lock, flags);
+		send_error_reply(smi, msg, IPMI_ERR_UNSPECIFIED);
 		return 0;
 	}