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 09:22:49 +0300
From:	Hadar Hen Zion <hadarh@....mellanox.co.il>
To:	Jiri Pirko <jiri@...nulli.us>
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

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.