linux-kernel - Re: [BUG] ethernet:enic: A use after free bug in enic_hard_start

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Date:   Fri, 30 Apr 2021 17:10:02 -0700
From:   Govindarajulu Varadarajan <govind.varadar@...il.com>
To:     lyl2019@...l.ustc.edu.cn, benve@...co.com, davem@...emloft.net,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [BUG] ethernet:enic: A use after free bug in
 enic_hard_start_xmit

On Tue, 2021-04-27 at 10:55 +0800, lyl2019@...l.ustc.edu.cn wrote:
> 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").

Thank you for reporting this.

One solution is to make enic_queue_wq_skb() return error and goto spin_unlock()
incase of error.

Would you like to send the fix for this?

--
Govind