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Subject[patch] flow_dissector: Fix wrong vlan header offset in __skb_flow_dissect
Date
We use the openvswitch 2.7.0 and find the issue when ovs use the skb_get_hash() to get the hash of QinQ skb. Because the
__skb_flow_dissect() get the wrong vlan protocol headers.

Someone report bonding driver has the same issue use the
__skb_flow_dissect() to count hash in bond_xmit_hash:
https://lore.kernel.org/netdev/00a5d09f-a23e-661f-60c0-
75fba6227451@huawei.com/T/.

Because in netif_receive_skb, the skb_network_header points to vlan head, but in dev_hard_start_xmit, the skb_network_header points to IP header. So use the skb_network_offset to get the vlan head is not reliable.

Should we use the skb_mac_offset instead the skb_network_offset to get the vlan head when proto is ETH_P_8021AD or ETH_P_8021Q?

Signed-off-by: Feng tiantian <fengtiantian@huawei.com>
---
net/core/flow_dissector.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index 415b95f..9a77d5d 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -629,6 +629,13 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
skb->vlan_proto : skb->protocol;
nhoff = skb_network_offset(skb);
hlen = skb_headlen(skb);
+
+ if (proto == htons(ETH_P_8021AD) ||
+ proto == htons(ETH_P_8021Q)) {
+ if (skb_mac_header_was_set(skb))
+ nhoff = skb_mac_offset(skb) + ETH_HLEN;
+ }
+
#if IS_ENABLED(CONFIG_NET_DSA)
if (unlikely(skb->dev && netdev_uses_dsa(skb->dev))) {
const struct dsa_device_ops *ops;
--
1.8.3.1
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