net: ena: fix potential crash when rxfh key is NULL

When ethtool -X is called without an hkey, ena_com_fill_hash_function()
is called with key=NULL, which is passed to memcpy causing a crash.

This commit fixes this issue by checking key is not NULL.

Fixes: 1738cd3e ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/amazon/ena/ena_com.c

@@ -2297,15 +2297,16 @@ int ena_com_fill_hash_function(struct ena_com_dev *ena_dev,
 
 	switch (func) {
 	case ENA_ADMIN_TOEPLITZ:
-		if (key_len > sizeof(hash_key->key)) {
-			pr_err("key len (%hu) is bigger than the max supported (%zu)\n",
+		if (key) {
+			if (key_len != sizeof(hash_key->key)) {
+				pr_err("key len (%hu) doesn't equal the supported size (%zu)\n",
 				       key_len, sizeof(hash_key->key));
 				return -EINVAL;
 			}
-
 			memcpy(hash_key->key, key, key_len);
 			rss->hash_init_val = init_val;
 			hash_key->keys_num = key_len >> 2;
+		}
 		break;
 	case ENA_ADMIN_CRC32:
 		rss->hash_init_val = init_val;