2021-04-27 02:56:23

by Lv Yunlong

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 <[email protected]>

2021-05-01 00:12:22

by Govindarajulu Varadarajan

Subject: Re: [BUG] ethernet:enic: A use after free bug in enic_hard_start_xmit

On Tue, 2021-04-27 at 10:55 +0800, [email protected] 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