s390x/s390-virtio-ccw: fix loadparm property getter

The function machine_get_loadparm() is supposed to produce a C-string,
that is a NUL-terminated one, but it does not. ElectricFence can detect
this problem if the loadparm machine property is used.

Let us make the returned string a NUL-terminated one.

Fixes: 7104bae ("hw/s390x: provide loadparm property for the machine")
Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20200723162717.88485-1-pasic@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

hw/s390x/s390-virtio-ccw.c

@@ -701,8 +701,12 @@ bool hpage_1m_allowed(void)
 static char *machine_get_loadparm(Object *obj, Error **errp)
 {
     S390CcwMachineState *ms = S390_CCW_MACHINE(obj);
+    char *loadparm_str;
 
-    return g_memdup(ms->loadparm, sizeof(ms->loadparm));
+    /* make a NUL-terminated string */
+    loadparm_str = g_memdup(ms->loadparm, sizeof(ms->loadparm) + 1);
+    loadparm_str[sizeof(ms->loadparm)] = 0;
+    return loadparm_str;
 }
 
 static void machine_set_loadparm(Object *obj, const char *val, Error **errp)