netdev - Re: [PATCH 1/4] net: check for reference outside of skb

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Date:	Tue, 3 Aug 2010 07:11:14 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/4] net: check for reference outside of skb

On Tue, Aug 3, 2010 at 6:00 AM, Stephen Hemminger <shemminger@...tta.com> wrote:
> It is legitimate for callers of skb_header_pointer to pass a negative
> offset, but the resulting pointer should not go outside the valid
> range of data in the skb.
>
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
>
> --- a/include/linux/skbuff.h    2010-08-01 09:23:01.635121262 -0700
> +++ b/include/linux/skbuff.h    2010-08-01 09:25:27.453901530 -0700
> @@ -1853,6 +1853,9 @@ static inline void *skb_header_pointer(c
>  {
>        int hlen = skb_headlen(skb);
>
> +       if (hlen + offset < 0)
> +               return NULL;
> +

It seems wrong. do you mean

      if (skb_headroom(hlen) + offset < 0)

Nevertheless it is also wrong. skb_header_pointer doesn't know if the
headroom is filled with valid data or not.

Thanks.

>        if (hlen - offset >= len)
>                return skb->data + offset;




-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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