Re: [PATCH] sit: reload iphdr in ipip6_rcv

[David Miller]

From: äæå <yanhaishuang@xxxxxxxxxxxxxxxxxxxx>
Date: Tue, 6 Jun 2017 10:09:45 +0800

> 
>> On 5 Jun 2017, at 9:03 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>> 
>> On Sun, 2017-06-04 at 14:43 +0800, Haishuang Yan wrote:
>>> Since iptunnel_pull_header() can call pskb_may_pull(),
>>> we must reload any pointer that was related to skb->head.
>>> 
>>> Fixes: a09a4c8dd1ec ("tunnels: Remove encapsulation offloads on decap")
>>> Signed-off-by: Haishuang Yan <yanhaishuang@xxxxxxxxxxxxxxxxxxxx>
>>> ---
>>> net/ipv6/sit.c | 1 +
>>> 1 file changed, 1 insertion(+)
>>> 
>>> diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
>>> index 61e5902..af832e7 100644
>>> --- a/net/ipv6/sit.c
>>> +++ b/net/ipv6/sit.c
>>> @@ -657,6 +657,7 @@ static int ipip6_rcv(struct sk_buff *skb)
>>> 		if (iptunnel_pull_header(skb, 0, htons(ETH_P_IPV6),
>>> 		    !net_eq(tunnel->net, dev_net(tunnel->dev))))
>>> 			goto out;
>>> +		iph = ip_hdr(skb);
>>> 
>>> 		err = IP_ECN_decapsulate(iph, skb);
>>> 		if (unlikely(err)) {
>> 
>> This seems unnecessary.
>> 
>> By the time ipip6_rcv() is called, we already have the guarantee the
>> IPv4 header is in skb linear part.
>> 
>> Otherwise we could not use iph->saddr and iph->daddr in the call to
>> ipip6_tunnel_lookup()
>> 
>> Therefore, the pskb_may_pull() is a nop in this particular case.
> 
> Yes, itâs right. Thanks!

Ok, I reverted, thanks everyone.