cxl: fix potential NULL dereference in free_adapter()

commit 8fbaa51d upstream.

If kzalloc() fails when allocating adapter->guest in
cxl_guest_init_adapter(), we call free_adapter() before erroring out.
free_adapter() in turn attempts to dereference adapter->guest, which in
this case is NULL.

In free_adapter(), skip the adapter->guest cleanup if adapter->guest is
NULL.

Fixes: 14baf4d9 ("cxl: Add guest-specific code")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/cxl/guest.c

@@ -1052,6 +1052,7 @@ static void free_adapter(struct cxl *adapter)
 	struct irq_avail *cur;
 	int i;
 
+	if (adapter->guest) {
 		if (adapter->guest->irq_avail) {
 			for (i = 0; i < adapter->guest->irq_nranges; i++) {
 				cur = &adapter->guest->irq_avail[i];
@@ -1060,8 +1061,9 @@ static void free_adapter(struct cxl *adapter)
 			kfree(adapter->guest->irq_avail);
 		}
 		kfree(adapter->guest->status);
-	cxl_remove_adapter_nr(adapter);
 		kfree(adapter->guest);
+	}
+	cxl_remove_adapter_nr(adapter);
 	kfree(adapter);
 }