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.
