linux-kernel - Re: [PATCH] ethernet:enic: Fix a use after free bug in enic_hard_start

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Date:   Sun, 2 May 2021 01:12:49 +0000
From:   "Govindarajulu Varadarajan (gvaradar)" <gvaradar@...co.com>
To:     "Christian Benvenuti (benve)" <benve@...co.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "lyl2019@...l.ustc.edu.cn" <lyl2019@...l.ustc.edu.cn>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Govindarajulu Varadarajan (gvaradar)" <gvaradar@...co.com>
Subject: Re: [PATCH] ethernet:enic: Fix a use after free bug in
 enic_hard_start_xmit

On Sat, 2021-05-01 at 08:31 -0700, Lv Yunlong wrote:
> 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).
> 
> My patch makes enic_queue_wq_skb() return error and goto spin_unlock()
> incase of error. The solution is provided by Govind.
> See https://lkml.org/lkml/2021/4/30/961.
> 
> Fixes: fb7516d42478e ("enic: add sw timestamp support")
> Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
> ---
>  drivers/net/ethernet/cisco/enic/enic_main.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cisco/enic/enic_main.c
> b/drivers/net/ethernet/cisco/enic/enic_main.c
> index f04ec53544ae..40abc3fdeba6 100644
> --- a/drivers/net/ethernet/cisco/enic/enic_main.c
> +++ b/drivers/net/ethernet/cisco/enic/enic_main.c
> @@ -768,7 +768,7 @@ static inline int enic_queue_wq_skb_encap(struct enic
> *enic, struct vnic_wq *wq,
>         return err;
>  }
>  
> -static inline void enic_queue_wq_skb(struct enic *enic,
> +static inline int enic_queue_wq_skb(struct enic *enic,
>         struct vnic_wq *wq, struct sk_buff *skb)
>  {
>         unsigned int mss = skb_shinfo(skb)->gso_size;
> @@ -813,7 +813,9 @@ static inline void enic_queue_wq_skb(struct enic *enic,
>                 }
>                 wq->to_use = buf->next;
>                 dev_kfree_skb(skb);
> +               return err;

return err seems unnecessary here.

>         }
> +       return err;
>  }
>  
>  /* netif_tx_lock held, process context with BHs disabled, or BH */
> @@ -857,7 +859,8 @@ static netdev_tx_t enic_hard_start_xmit(struct sk_buff
> *skb,
>                 return NETDEV_TX_BUSY;
>         }
>  
> -       enic_queue_wq_skb(enic, wq, skb);
> +       if (enic_queue_wq_skb(enic, wq, skb) < 0)

0 is success, any other value is error. if (enic_queue_wq_skb(enic, wq, skb)).

Otherwise patch looks good.

Thanks
Govind