netdev - [BUG] ethernet:enic: A use after free bug in enic_hard_start

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Message-ID: <65becad9.62766.17911406ff0.Coremail.lyl2019@mail.ustc.edu.cn>
Date:   Tue, 27 Apr 2021 10:55:06 +0800 (GMT+08:00)
From:   lyl2019@...l.ustc.edu.cn
To:     benve@...co.com, _govind@....com, davem@...emloft.net,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [BUG] ethernet:enic: A use after free bug in enic_hard_start_xmit

Hi, maintainers.
    Our code analyzer reported a uaf bug, but it is a little
difficult for me to fix it directly.

File: drivers/net/ethernet/cisco/enic/enic_main.c
In enic_hard_start_xmit, it calls enic_queue_wq_skb(). Inside
enic_queue_wq_skb, if some error happens, the skb will be freed
by dev_kfree_skb(skb). But the freed skb is still used in 
skb_tx_timestamp(skb).

```
	enic_queue_wq_skb(enic, wq, skb);// skb could freed here

	if (vnic_wq_desc_avail(wq) < MAX_SKB_FRAGS + ENIC_DESC_MAX_SPLITS)
		netif_tx_stop_queue(txq);
	skb_tx_timestamp(skb); // freed skb is used here.
```
Bug introduced by fb7516d42478e ("enic: add sw timestamp support").

Thanks for your time, looking forwarding to your reply.
Lv Yunlong <lyl2019@...l.ustc.edu.cn>