net: dsa: bcm_sf2: potential array overflow in bcm_sf2_sw_suspend()

The value of ->num_ports comes from bcm_sf2_sw_probe() and it is less
than or equal to DSA_MAX_PORTS.  The ds->ports[] array is used inside
the dsa_is_user_port() and dsa_is_cpu_port() functions.  The ds->ports[]
array is allocated in dsa_switch_alloc() and it has ds->num_ports
elements so this leads to a static checker warning about a potential out
of bounds read.

Fixes: 8cfa9498 ("net: dsa: bcm_sf2: add suspend/resume callbacks")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/bcm_sf2.c

@@ -690,7 +690,7 @@ static int bcm_sf2_sw_suspend(struct dsa_switch *ds)
 	 * port, the other ones have already been disabled during
 	 * bcm_sf2_sw_setup
 	 */
-	for (port = 0; port < DSA_MAX_PORTS; port++) {
+	for (port = 0; port < ds->num_ports; port++) {
 		if (dsa_is_user_port(ds, port) || dsa_is_cpu_port(ds, port))
 			bcm_sf2_port_disable(ds, port, NULL);
 	}