netdev - Re: [PATCH net-next V2 1/5] flow_dissector: For stripped vlan, get vlan info from skb->vlan

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Date:	Thu, 18 Aug 2016 08:46:38 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Hadar Hen Zion <hadarh@....mellanox.co.il>
Cc:	Hadar Hen Zion <hadarh@...lanox.com>,
	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Jiri Pirko <jiri@...lanox.com>,
	Amir Vadai <amirva@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Tom Herbert <tom@...bertland.com>
Subject: Re: [PATCH net-next V2 1/5] flow_dissector: For stripped vlan, get
 vlan info from skb->vlan_tci

Thu, Aug 18, 2016 at 08:22:49AM CEST, hadarh@....mellanox.co.il wrote:
>On Wed, Aug 17, 2016 at 4:02 PM, Jiri Pirko <jiri@...nulli.us> wrote:
>> Wed, Aug 17, 2016 at 01:05:33PM CEST, hadarh@....mellanox.co.il wrote:
>>>On Wed, Aug 17, 2016 at 1:46 PM, Jiri Pirko <jiri@...nulli.us> wrote:
>>>> Wed, Aug 17, 2016 at 12:36:10PM CEST, hadarh@...lanox.com wrote:
>>>>>Early in the datapath skb_vlan_untag function is called, stripped
>>>>>the vlan from the skb and set skb->vlan_tci and skb->vlan_proto fields.
>>>>>
>>>>>The current dissection doesn't handle stripped vlan packets correctly.
>>>>>In some flows, vlan doesn't exist in skb->data anymore when applying
>>>>>flow dissection on the skb, fix that.
>>>>>
>>>>>In case vlan info wasn't stripped before applying flow_dissector (RPS
>>>>>flow for example), or in case of skb with multiple vlans (e.g. 802.1ad),
>>>>>get the vlan info from skb->data. The flow_dissector correctly skips
>>>>>any number of vlans and stores only the first level vlan.
>>>>>
>>>>>Fixes: 0744dd00c1b1 ('net: introduce skb_flow_dissect()')
>>>>>Signed-off-by: Hadar Hen Zion <hadarh@...lanox.com>
>>>>>---
>>>>> net/core/flow_dissector.c | 34 ++++++++++++++++++++++++++--------
>>>>> 1 file changed, 26 insertions(+), 8 deletions(-)
>>>>>
>>>>>diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
>>>>>index 91028ae..362d693 100644
>>>>>--- a/net/core/flow_dissector.c
>>>>>+++ b/net/core/flow_dissector.c
>>>>>@@ -119,12 +119,14 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
>>>>>       struct flow_dissector_key_ports *key_ports;
>>>>>       struct flow_dissector_key_tags *key_tags;
>>>>>       struct flow_dissector_key_keyid *key_keyid;
>>>>>+      bool skip_vlan = false;
>>>>>       u8 ip_proto = 0;
>>>>>       bool ret = false;
>>>>>
>>>>>       if (!data) {
>>>>>               data = skb->data;
>>>>>-              proto = skb->protocol;
>>>>>+              proto = skb_vlan_tag_present(skb) ?
>>>>>+                       skb->vlan_proto : skb->protocol;
>>>>>               nhoff = skb_network_offset(skb);
>>>>>               hlen = skb_headlen(skb);
>>>>>       }
>>>>>@@ -243,23 +245,39 @@ ipv6:
>>>>>       case htons(ETH_P_8021AD):
>>>>>       case htons(ETH_P_8021Q): {
>>>>>               const struct vlan_hdr *vlan;
>>>>>-              struct vlan_hdr _vlan;
>>>>>
>>>>>-              vlan = __skb_header_pointer(skb, nhoff, sizeof(_vlan), data, hlen, &_vlan);
>>>>>-              if (!vlan)
>>>>>-                      goto out_bad;
>>>>>+              if (skb_vlan_tag_present(skb))
>>>>>+                      proto = skb->protocol;
>>>>>+
>>>>>+              if (!skb_vlan_tag_present(skb) ||
>>>>>+                  proto == cpu_to_be16(ETH_P_8021Q) ||
>>>>>+                  proto == cpu_to_be16(ETH_P_8021AD)) {
>>>>
>>>> How this can happen? Could you give me an example?
>>>>
>>>
>>>This can happen in 2 cases:
>>>
>>>1. vlan wasn't stripped yet from the skb.
>>>In RPS flow for example, get_rps_cpu function is using flow-dissector
>>>before vlan_untag is called by __netif_receive_skb_core.
>>
>> right, sigh...
>>
>>
>>>
>>>2. skb with multiple vlan tags.
>>>Only the first vlan is stripped while the inner vlans are still in skb->data.
>>>In this case skb->vlan_proto is 802.1AD and skb->protocol is 802.1Q
>>>(for example) so I have to take the next header from skb->data.
>>
>> Hmm I think that whoever removes the outermost vlan from skb->vlan_*
>> should strip the next header into skb->vlan_*
>
>The outermost vlan isn't removed from skb->vlan_* it stays there.

No I didn't mean in your code. But other code that removes it should
ensure that next vlan header is stripped so the rest of the code (like
yours) can count with it.