net: ethernet: mtk_eth_soc: fix potential memory leak in mtk_rx_alloc()

When fail to dma_map_single() in mtk_rx_alloc(), it returns directly.
But the memory allocated for local variable data is not freed, and
local variabel data has not been attached to ring->data[i] yet, so the
memory allocated for local variable data will not be freed outside
mtk_rx_alloc() too. Thus memory leak would occur in this scenario.

Add skb_free_frag(data) when dma_map_single() failed.

Fixes: 23233e57 ("net: ethernet: mtk_eth_soc: rely on page_pool for single page buffers")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Acked-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Link: https://lore.kernel.org/r/20221120035405.1464341-1-william.xuanziyang@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -2378,8 +2378,10 @@ static int mtk_rx_alloc(struct mtk_eth *eth, int ring_no, int rx_flag)
 				data + NET_SKB_PAD + eth->ip_align,
 				ring->buf_size, DMA_FROM_DEVICE);
 			if (unlikely(dma_mapping_error(eth->dma_dev,
-						       dma_addr)))
+						       dma_addr))) {
+				skb_free_frag(data);
 				return -ENOMEM;
+			}
 		}
 		rxd->rxd1 = (unsigned int)dma_addr;
 		ring->data[i] = data;