On Mon, Nov 28, 2016 at 12:49:36AM -0500, David Miller wrote:
> From: Cong Wang <xiyou.wangc...@gmail.com>
> Date: Sun, 27 Nov 2016 21:39:33 -0800
>
> > On Sun, Nov 27, 2016 at 7:58 AM, Amir Vadai <a...@vadai.me> wrote:
> >> Should not allow setting a negative offset that goes below the skb head.
> > ...
> >> diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
> >> index b54d56d4959b..e79e8a88f2d2 100644
> >> --- a/net/sched/act_pedit.c
> >> +++ b/net/sched/act_pedit.c
> >> @@ -154,8 +154,11 @@ static int tcf_pedit(struct sk_buff *skb, const
> >> struct tc_action *a,
> >> }
> >>
> >> ptr = skb_header_pointer(skb, off + offset, 4,
> >> &_data);
> >> - if (!ptr)
> >> + if ((unsigned char *)ptr < skb->head) {
> >
> >
> > ptr returned could be &_data, which is on stack, so why this comparison
> > makes sense for this case?
>
> Indeed, this will definitely do the wrong thing when the on-stack area
> passed back to ptr.
yes - my bad. will correct it and send v1
