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

From: Stephen Hemminger <[email-masked]>
Date: Mon, 2 Aug 2010 16:21:58 -0700

On Tue, 3 Aug 2010 07:11:14 +0800
Changli Gao <[email-masked]> wrote:

> On Tue, Aug 3, 2010 at 6:00 AM, Stephen Hemminger <[email-masked]> 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 <[email-masked]>
> >
> > --- 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.
>

It should be headroom. It is okay if the request is looking at PAD
area, that is the callers problem. Just don't want wander off into
into unallocated space.

Anyway, I'll fix it in cls_u32.