Code: int hns_nic_net_xmit_hw(struct net_device *ndev,
			struct sk_buff *skb,
			struct hns_nic_ring_data *ring_data)
 {
 	struct hns_nic_priv *priv = netdev_priv(ndev);
 	struct hnae_ring *ring = ring_data->ring;
	struct device *dev = ring_to_dev(ring);
	struct netdev_queue *dev_queue;
	struct skb_frag_struct *frag;
	int buf_num;
	int seg_num;
	dma_addr_t dma;
	int size, next_to_use;
	int i;

	switch (priv->ops.maybe_stop_tx(&skb, &buf_num, ring)) {
	case -EBUSY:
		ring->stats.tx_busy++;
		goto out_net_tx_busy;
	case -ENOMEM:
		ring->stats.sw_err_cnt++;
		netdev_err(ndev, "no memory to xmit!\n");
		goto out_err_tx_ok;
	default:
		break;
	}

	/* no. of segments (plus a header) */
	seg_num = skb_shinfo(skb)->nr_frags + 1;
	next_to_use = ring->next_to_use;

	/* fill the first part */
	size = skb_headlen(skb);
	dma = dma_map_single(dev, skb->data, size, DMA_TO_DEVICE);
	if (dma_mapping_error(dev, dma)) {
		netdev_err(ndev, "TX head DMA map failed\n");
		ring->stats.sw_err_cnt++;
		goto out_err_tx_ok;
	}
	priv->ops.fill_desc(ring, skb, size, dma, seg_num == 1 ? 1 : 0,
			    buf_num, DESC_TYPE_SKB, ndev->mtu);

	/* fill the fragments */
	for (i = 1; i < seg_num; i++) {
		frag = &skb_shinfo(skb)->frags[i - 1];
		size = skb_frag_size(frag);
		dma = skb_frag_dma_map(dev, frag, 0, size, DMA_TO_DEVICE);
		if (dma_mapping_error(dev, dma)) {
			netdev_err(ndev, "TX frag(%d) DMA map failed\n", i);
			ring->stats.sw_err_cnt++;
			goto out_map_frag_fail;
		}
		priv->ops.fill_desc(ring, skb_frag_page(frag), size, dma,
				    seg_num - 1 == i ? 1 : 0, buf_num,
				    DESC_TYPE_PAGE, ndev->mtu);
	}

	/*complete translate all packets*/
 	dev_queue = netdev_get_tx_queue(ndev, skb->queue_mapping);
 	netdev_tx_sent_queue(dev_queue, skb->len);
 
 	wmb(); /* commit all data before submit */
 	assert(skb->queue_mapping < priv->ae_handle->q_num);
 	hnae_queue_xmit(priv->ae_handle->qs[skb->queue_mapping], buf_num);
	ring->stats.tx_pkts++;
	ring->stats.tx_bytes += skb->len;

	return NETDEV_TX_OK;

out_map_frag_fail:

	while (ring->next_to_use != next_to_use) {
		unfill_desc(ring);
		if (ring->next_to_use != next_to_use)
			dma_unmap_page(dev,
				       ring->desc_cb[ring->next_to_use].dma,
				       ring->desc_cb[ring->next_to_use].length,
				       DMA_TO_DEVICE);
		else
			dma_unmap_single(dev,
					 ring->desc_cb[next_to_use].dma,
					 ring->desc_cb[next_to_use].length,
					 DMA_TO_DEVICE);
	}

out_err_tx_ok:

	dev_kfree_skb_any(skb);
	return NETDEV_TX_OK;

out_net_tx_busy:

	netif_stop_subqueue(ndev, skb->queue_mapping);

	/* Herbert's original patch had:
	 *  smp_mb__after_netif_stop_queue();
	 * but since that doesn't exist yet, just open code it.
	 */
	smp_mb();
	return NETDEV_TX_BUSY;
}

Vulnerability Type: DoS 
CWE ID: CWE-416
Summary: In drivers/net/ethernet/hisilicon/hns/hns_enet.c in the Linux kernel before 4.13, local users can cause a denial of service (use-after-free and BUG) or possibly have unspecified other impact by leveraging differences in skb handling between hns_nic_net_xmit_hw and hns_nic_net_xmit.
Commit Message: net: hns: Fix a skb used after free bug

skb maybe freed in hns_nic_net_xmit_hw() and return NETDEV_TX_OK,
which cause hns_nic_net_xmit to use a freed skb.

BUG: KASAN: use-after-free in hns_nic_net_xmit_hw+0x62c/0x940...
	[17659.112635]      alloc_debug_processing+0x18c/0x1a0
	[17659.117208]      __slab_alloc+0x52c/0x560
	[17659.120909]      kmem_cache_alloc_node+0xac/0x2c0
	[17659.125309]      __alloc_skb+0x6c/0x260
	[17659.128837]      tcp_send_ack+0x8c/0x280
	[17659.132449]      __tcp_ack_snd_check+0x9c/0xf0
	[17659.136587]      tcp_rcv_established+0x5a4/0xa70
	[17659.140899]      tcp_v4_do_rcv+0x27c/0x620
	[17659.144687]      tcp_prequeue_process+0x108/0x170
	[17659.149085]      tcp_recvmsg+0x940/0x1020
	[17659.152787]      inet_recvmsg+0x124/0x180
	[17659.156488]      sock_recvmsg+0x64/0x80
	[17659.160012]      SyS_recvfrom+0xd8/0x180
	[17659.163626]      __sys_trace_return+0x0/0x4
	[17659.167506] INFO: Freed in kfree_skbmem+0xa0/0xb0 age=23 cpu=1 pid=13
	[17659.174000]      free_debug_processing+0x1d4/0x2c0
	[17659.178486]      __slab_free+0x240/0x390
	[17659.182100]      kmem_cache_free+0x24c/0x270
	[17659.186062]      kfree_skbmem+0xa0/0xb0
	[17659.189587]      __kfree_skb+0x28/0x40
	[17659.193025]      napi_gro_receive+0x168/0x1c0
	[17659.197074]      hns_nic_rx_up_pro+0x58/0x90
	[17659.201038]      hns_nic_rx_poll_one+0x518/0xbc0
	[17659.205352]      hns_nic_common_poll+0x94/0x140
	[17659.209576]      net_rx_action+0x458/0x5e0
	[17659.213363]      __do_softirq+0x1b8/0x480
	[17659.217062]      run_ksoftirqd+0x64/0x80
	[17659.220679]      smpboot_thread_fn+0x224/0x310
	[17659.224821]      kthread+0x150/0x170
	[17659.228084]      ret_from_fork+0x10/0x40

	BUG: KASAN: use-after-free in hns_nic_net_xmit+0x8c/0xc0...
	[17751.080490]      __slab_alloc+0x52c/0x560
	[17751.084188]      kmem_cache_alloc+0x244/0x280
	[17751.088238]      __build_skb+0x40/0x150
	[17751.091764]      build_skb+0x28/0x100
	[17751.095115]      __alloc_rx_skb+0x94/0x150
	[17751.098900]      __napi_alloc_skb+0x34/0x90
	[17751.102776]      hns_nic_rx_poll_one+0x180/0xbc0
	[17751.107097]      hns_nic_common_poll+0x94/0x140
	[17751.111333]      net_rx_action+0x458/0x5e0
	[17751.115123]      __do_softirq+0x1b8/0x480
	[17751.118823]      run_ksoftirqd+0x64/0x80
	[17751.122437]      smpboot_thread_fn+0x224/0x310
	[17751.126575]      kthread+0x150/0x170
	[17751.129838]      ret_from_fork+0x10/0x40
	[17751.133454] INFO: Freed in kfree_skbmem+0xa0/0xb0 age=19 cpu=7 pid=43
	[17751.139951]      free_debug_processing+0x1d4/0x2c0
	[17751.144436]      __slab_free+0x240/0x390
	[17751.148051]      kmem_cache_free+0x24c/0x270
	[17751.152014]      kfree_skbmem+0xa0/0xb0
	[17751.155543]      __kfree_skb+0x28/0x40
	[17751.159022]      napi_gro_receive+0x168/0x1c0
	[17751.163074]      hns_nic_rx_up_pro+0x58/0x90
	[17751.167041]      hns_nic_rx_poll_one+0x518/0xbc0
	[17751.171358]      hns_nic_common_poll+0x94/0x140
	[17751.175585]      net_rx_action+0x458/0x5e0
	[17751.179373]      __do_softirq+0x1b8/0x480
	[17751.183076]      run_ksoftirqd+0x64/0x80
	[17751.186691]      smpboot_thread_fn+0x224/0x310
	[17751.190826]      kthread+0x150/0x170
	[17751.194093]      ret_from_fork+0x10/0x40

Fixes: 13ac695e7ea1 ("net:hns: Add support of Hip06 SoC to the Hislicon Network Subsystem")
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: lipeng <lipeng321@huawei.com>
Reported-by: Jun He <hjat2005@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>