sfc: don't try and read ef10 data on non-ef10 NIC

The MAC stats command takes a port ID, which doesn't exist on
pre-ef10 NICs (5000- and 6000- series). This is extracted from the
NIC specific data; we misinterpret this as the ef10 data structure,
causing us to read potentially unallocated data. With a KASAN kernel
this can cause errors with:
   BUG: KASAN: slab-out-of-bounds in efx_mcdi_mac_stats

Fixes: 0a2ab4d9 ("sfc: set the port-id when calling MC_CMD_MAC_STATS")
Reported-by: Stefano Brivio <sbrivio@redhat.com>
Tested-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Bert Kenward <bkenward@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/mcdi_port.c

@@ -938,7 +938,6 @@ enum efx_stats_action {
 static int efx_mcdi_mac_stats(struct efx_nic *efx,
 			      enum efx_stats_action action, int clear)
 {
-	struct efx_ef10_nic_data *nic_data = efx->nic_data;
 	MCDI_DECLARE_BUF(inbuf, MC_CMD_MAC_STATS_IN_LEN);
 	int rc;
 	int change = action == EFX_STATS_PULL ? 0 : 1;
@@ -960,7 +959,12 @@ static int efx_mcdi_mac_stats(struct efx_nic *efx,
 			      MAC_STATS_IN_PERIODIC_NOEVENT, 1,
 			      MAC_STATS_IN_PERIOD_MS, period);
 	MCDI_SET_DWORD(inbuf, MAC_STATS_IN_DMA_LEN, dma_len);
+
+	if (efx_nic_rev(efx) >= EFX_REV_HUNT_A0) {
+		struct efx_ef10_nic_data *nic_data = efx->nic_data;
+
 		MCDI_SET_DWORD(inbuf, MAC_STATS_IN_PORT_ID, nic_data->vport_id);
+	}
 
 	rc = efx_mcdi_rpc_quiet(efx, MC_CMD_MAC_STATS, inbuf, sizeof(inbuf),
 				NULL, 0, NULL);