i40evf: ethtool RSS fixes

Add an extra check to make sure that the indirection table pointer is
valid before dereferencing it.

Change-ID: I698adbf3daff03081d01f489dc95a9f1ad8b12f1
Reported-by: NBen Hutchings <ben@decadent.org.uk>
Signed-off-by: NMitch Williams <mitch.a.williams@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40evf/i40evf_ethtool.c

@@ -642,12 +642,14 @@ static int i40evf_get_rxfh(struct net_device *netdev, u32 *indir, u8 *key,
 	if (!indir)
 		return 0;
 
-	for (i = 0, j = 0; i <= I40E_VFQF_HLUT_MAX_INDEX; i++) {
-		hlut_val = rd32(hw, I40E_VFQF_HLUT(i));
-		indir[j++] = hlut_val & 0xff;
-		indir[j++] = (hlut_val >> 8) & 0xff;
-		indir[j++] = (hlut_val >> 16) & 0xff;
-		indir[j++] = (hlut_val >> 24) & 0xff;
+	if (indir) {
+		for (i = 0, j = 0; i <= I40E_VFQF_HLUT_MAX_INDEX; i++) {
+			hlut_val = rd32(hw, I40E_VFQF_HLUT(i));
+			indir[j++] = hlut_val & 0xff;
+			indir[j++] = (hlut_val >> 8) & 0xff;
+			indir[j++] = (hlut_val >> 16) & 0xff;
+			indir[j++] = (hlut_val >> 24) & 0xff;
+		}
 	}
 	return 0;
 }