netdev - Re: [PATCH v2,net-next 1/2] ip_gre: fix parsing gre header in ipgre

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Date:   Sat, 15 Sep 2018 09:22:19 +0800
From:   Haishuang Yan <yanhaishuang@...s.chinamobile.com>
To:     Edward Cree <ecree@...arflare.com>
Cc:     David Miller <davem@...emloft.net>, kuznet@....inr.ac.ru,
        jbenc@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2,net-next 1/2] ip_gre: fix parsing gre header in
 ipgre_err



> On 2018年9月14日, at 下午8:44, Edward Cree <ecree@...arflare.com> wrote:
> 
> On 13/09/18 18:58, David Miller wrote:
>> From: Haishuang Yan <yanhaishuang@...s.chinamobile.com>
>> Date: Wed, 12 Sep 2018 17:21:21 +0800
>> 
>>> @@ -86,7 +86,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
>>> 
>>> 	options = (__be32 *)(greh + 1);
>>> 	if (greh->flags & GRE_CSUM) {
>>> -		if (skb_checksum_simple_validate(skb)) {
>>> +		if (csum_err && skb_checksum_simple_validate(skb)) {
>>> 			*csum_err = true;
>>> 			return -EINVAL;
>>> 		}
>> You want to ignore csum errors, but you do not want to elide the side
>> effects of the skb_checksum_simple_validate() call which are to set
>> skb->csum_valid and skb->csum.
>> 
>> Therefore, the skb_checksum_simple_validate() call still needs to be
>> performed. We just wont return -EINVAL in the NULL csum_err case.
> 
> How about just reversing the order of the AND?
> 
> 	if (skb_checksum_simple_validate(skb) && csum_err) {
> 		*csum_err = true;
> 		return -EINVAL;
> 	}
> 
> 

It looks good to me, thanks!

But skb_checksum_try_convert only need to be called after the checksum is 
validated, so I suggested a better solution as following:

   89                 if (!skb_checksum_simple_validate(skb)) {
   90                         skb_checksum_try_convert(skb, IPPROTO_GRE, 0,
   91                                                  null_compute_pseudo);
   92                 } else if (csum_err) {
   93                         *csum_err = true;
   94                         return -EINVAL;
   95                 }