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

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Date:	Wed, 17 Aug 2016 15:02:47 +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

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_*