Re: [PATCH v3 2/2] ip6_tunnel: fix ip6 tunnel lookup in collect_md mode

[严海双]

> On 2017年9月6日, at 上午11:14, Alexei Starovoitov <ast@xxxxxx> wrote:
> 
> On 9/4/17 1:36 AM, Haishuang Yan wrote:
>> In collect_md mode, if the tun dev is down, it still can call
>> __ip6_tnl_rcv to receive on packets, and the rx statistics increase
>> improperly.
>> 
>> Fixes: 8d79266bc48c ("ip6_tunnel: add collect_md mode to IPv6 tunnels")
>> Cc: Alexei Starovoitov <ast@xxxxxx>
>> Signed-off-by: Haishuang Yan <yanhaishuang@xxxxxxxxxxxxxxxxxxxx>
>> 
>> ---
>> Change since v3:
>>  * Increment rx_dropped if tunnel device is not up, suggested by
>>  Pravin B Shelar
>>  * Fix wrong recipient address
>> ---
>> net/ipv6/ip6_tunnel.c | 7 +++++--
>> 1 file changed, 5 insertions(+), 2 deletions(-)
>> 
>> diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
>> index 10a693a..e91d3b6 100644
>> --- a/net/ipv6/ip6_tunnel.c
>> +++ b/net/ipv6/ip6_tunnel.c
>> @@ -171,8 +171,11 @@ static struct net_device_stats *ip6_get_stats(struct net_device *dev)
>> 	}
>> 
>> 	t = rcu_dereference(ip6n->collect_md_tun);
>> -	if (t)
>> -		return t;
>> +	if (t) {
>> +		if (t->dev->flags & IFF_UP)
>> +			return t;
>> +		t->dev->stats.rx_dropped++;
>> +	}
> 
> Why increment the stats only for this drop case?
Because It was suggested by Pravin on v2 commit of the patch.

> There are plenty of other conditions where packet
> will be dropped in ip6 tunnel. I think it's important
> to present consistent behavior to the users,
> so I'd increment drop stats either for all drop cases
> or for none. And today it's none.
> The ! IFF_UP case should probably be return NULL too
> 
>