linux-kernel - Re: [PATCH] flow_dissector: Fix vlan header offset in __skb_flow

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Date:   Thu, 20 Jun 2019 09:20:09 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Stanislav Fomichev <sdf@...ichev.me>
Cc:     YueHaibing <yuehaibing@...wei.com>, davem@...emloft.net,
        sdf@...gle.com, jianbol@...lanox.com, jiri@...lanox.com,
        mirq-linux@...e.qmqm.pl, willemb@...gle.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] flow_dissector: Fix vlan header offset in
 __skb_flow_dissect

Wed, Jun 19, 2019 at 08:39:38PM CEST, sdf@...ichev.me wrote:
>On 06/20, YueHaibing wrote:
>> We build vlan on top of bonding interface, which vlan offload
>> is off, bond mode is 802.3ad (LACP) and xmit_hash_policy is
>> BOND_XMIT_POLICY_ENCAP34.
>> 
>> __skb_flow_dissect() fails to get information from protocol headers
>> encapsulated within vlan, because 'nhoff' is points to IP header,
>> so bond hashing is based on layer 2 info, which fails to distribute
>> packets across slaves.
>> 
>> Fixes: d5709f7ab776 ("flow_dissector: For stripped vlan, get vlan info from skb->vlan_tci")
>> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
>> ---
>>  net/core/flow_dissector.c | 3 +++
>>  1 file changed, 3 insertions(+)
>> 
>> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
>> index 415b95f..2a52abb 100644
>> --- a/net/core/flow_dissector.c
>> +++ b/net/core/flow_dissector.c
>> @@ -785,6 +785,9 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
>>  		    skb && skb_vlan_tag_present(skb)) {
>>  			proto = skb->protocol;
>>  		} else {
>> +			if (dissector_vlan == FLOW_DISSECTOR_KEY_MAX)
>> +				nhoff -=  sizeof(*vlan);
>> +
>Should we instead fix the place where the skb is allocated to properly
>pull vlan (skb_vlan_untag)? I'm not sure this particular place is

Yes.

>supposed to work with an skb. Having an skb with nhoff pointing to
>IP header but missing skb_vlan_tag_present() when with
>proto==ETH_P_8021xx seems weird.
>
>>  			vlan = __skb_header_pointer(skb, nhoff, sizeof(_vlan),
>>  						    data, hlen, &_vlan);
>>  			if (!vlan) {
>> -- 
>> 2.7.0
>> 
>>