netdev - Re: [PATCH] p54: add null pointer check before releasing socket buffer

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Date:   Mon, 10 Apr 2017 14:12:54 +0200
From:   Christian Lamparter <chunkeey@...glemail.com>
To:     Myungho Jung <mhjungk@...il.com>
Cc:     netdev@...r.kernel.org, David Miller <davem@...hat.com>,
        linux-wireless@...r.kernel.org
Subject: Re: [PATCH] p54: add null pointer check before releasing socket buffer

(Added linux-wireless, since this is a wireless driver)

On Sunday, April 9, 2017 10:23:20 PM CEST Myungho Jung wrote:
> Kernel panic is caused by trying to dereference null pointer. Check if
> the pointer is null before freeing space.
Do you have the kernel panic somewhere?
I think you have an even bigger problem: You see, in order to get EEPROM
readback and rx_stats feedback you need to sent a request to the firmware
and if the response's req_id cookies don't match, you end up filling up 
the very limited device address space.

As for adding if (!skb) checks. I think kfree, kfree_skb, dev_kfree_skb 
(aka consume_skb) all check for null pointers already. So the logical
thing to do would be to make dev_kfree_skb_irq (which would also fix
dev_kfree_skb_any) consistent with kfree, kfree_skb, dev_kfree_skb and
add the check there.

> Signed-off-by: Myungho Jung <mhjungk@...il.com>
> ---
>  drivers/net/wireless/intersil/p54/txrx.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/intersil/p54/txrx.c b/drivers/net/wireless/intersil/p54/txrx.c
> index 1af7da0..8956061 100644
> --- a/drivers/net/wireless/intersil/p54/txrx.c
> +++ b/drivers/net/wireless/intersil/p54/txrx.c
> @@ -503,7 +503,9 @@ static void p54_rx_eeprom_readback(struct p54_common *priv,
>  
>  	priv->eeprom = NULL;
>  	tmp = p54_find_and_unlink_skb(priv, hdr->req_id);
> -	dev_kfree_skb_any(tmp);
> +	if (unlikely(!tmp))
> +		dev_kfree_skb_any(tmp);
> +
>  	complete(&priv->eeprom_comp);
>  }
>  
> @@ -597,7 +599,9 @@ static void p54_rx_stats(struct p54_common *priv, struct sk_buff *skb)
>  	}
>  
>  	tmp = p54_find_and_unlink_skb(priv, hdr->req_id);
> -	dev_kfree_skb_any(tmp);
> +	if (unlikely(!tmp))
> +		dev_kfree_skb_any(tmp);
> +
>  	complete(&priv->stat_comp);
>  }
>  
>