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Subject: Re: [PATCH v2,net-next 1/2] ip_gre: fix parsing gre header in
 ipgre_err
To:     David Miller <davem@davemloft.net>,
        <yanhaishuang@cmss.chinamobile.com>
CC:     <kuznet@ms2.inr.ac.ru>, <jbenc@redhat.com>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <1536744082-3568-1-git-send-email-yanhaishuang@cmss.chinamobile.com>
 <20180913.105840.140151724801067072.davem@davemloft.net>
From:   Edward Cree <ecree@solarflare.com>
Message-ID: <4bd44714-8190-feca-27dc-6f6b254341f8@solarflare.com>
Date:   Fri, 14 Sep 2018 13:44:05 +0100
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On 13/09/18 18:58, David Miller wrote:
> From: Haishuang Yan <yanhaishuang@cmss.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;
	}