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Subject: Re: [PATCH v2] ip6mr: Fix skb_under_panic in ip6mr_cache_report()
To:     Jakub Kicinski <kuba@kernel.org>
CC:     <davem@davemloft.net>, <dsahern@kernel.org>, <edumazet@google.com>,
        <pabeni@redhat.com>, <yoshfuji@linux-ipv6.org>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <simon.horman@corigine.com>
References: <20230728121703.29572-1-yuehaibing@huawei.com>
 <20230731200959.2019cb9c@kernel.org>
From:   YueHaibing <yuehaibing@huawei.com>
Message-ID: <f91c3fd7-8d7a-7a91-8d16-935c90ef9b5d@huawei.com>
Date:   Tue, 1 Aug 2023 14:28:21 +0800
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On 2023/8/1 11:09, Jakub Kicinski wrote:
> On Fri, 28 Jul 2023 20:17:03 +0800 Yue Haibing wrote:
>>  #ifdef CONFIG_IPV6_PIMSM_V2
>> +	int nhoff = skb_network_offset(pkt);
>>  	if (assert == MRT6MSG_WHOLEPKT || assert == MRT6MSG_WRMIFWHOLE)
>> -		skb = skb_realloc_headroom(pkt, -skb_network_offset(pkt)
>> -						+sizeof(*msg));
>> +		skb = skb_realloc_headroom(pkt, -nhoff + sizeof(*msg));
> 
> These changes look unnecessary. You can leave this code be (as ugly as
> it is)...
> 
>>  	else
>>  #endif
>>  		skb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(*msg), GFP_ATOMIC);
>> @@ -1073,7 +1073,7 @@ static int ip6mr_cache_report(const struct mr_table *mrt, struct sk_buff *pkt,
>>  		   And all this only to mangle msg->im6_msgtype and
>>  		   to set msg->im6_mbz to "mbz" :-)
>>  		 */
>> -		skb_push(skb, -skb_network_offset(pkt));
>> +		__skb_pull(skb, nhoff);
> 
> .. and just replace the push here with:
> 
>   __skb_pull(skb, skb_network_offset(pkt));

Thanks， will do this in v3.
>