[PATCH net] net: handle 802.1P vlan 0 packets properly

[Govindarajulu Varadarajan <gvaradar@cisco.com>]

When stack receives pkt: [802.1P vlan 0][802.1AD vlan 100][IPv4],
vlan_do_receive() returns false if it does not find vlan_dev. Later
__netif_receive_skb_core() fails to find packet type handler for
skb->protocol 801.1AD and drops the packet.

801.1P header with vlan id 0 should be handled as untagged packets.
This patch fixes it by checking if vlan_id is 0 and processes next vlan
header.

Signed-off-by: Govindarajulu Varadarajan <gvaradar@cisco.com>
---
 net/8021q/vlan_core.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
index a313165e7a67..0cde54c02c3f 100644
--- a/net/8021q/vlan_core.c
+++ b/net/8021q/vlan_core.c
@@ -9,14 +9,32 @@
 bool vlan_do_receive(struct sk_buff **skbp)
 {
 	struct sk_buff *skb = *skbp;
-	__be16 vlan_proto = skb->vlan_proto;
-	u16 vlan_id = skb_vlan_tag_get_id(skb);
+	__be16 vlan_proto;
+	u16 vlan_id;
 	struct net_device *vlan_dev;
 	struct vlan_pcpu_stats *rx_stats;
 
+again:
+	vlan_proto = skb->vlan_proto;
+	vlan_id = skb_vlan_tag_get_id(skb);
 	vlan_dev = vlan_find_dev(skb->dev, vlan_proto, vlan_id);
-	if (!vlan_dev)
+	if (!vlan_dev) {
+		/* Incase of 802.1P header with vlan id 0, continue if
+		 * vlan_dev is not found.
+		 */
+		if (unlikely(!vlan_id)) {
+			__vlan_hwaccel_clear_tag(skb);
+			if (skb->protocol == cpu_to_be16(ETH_P_8021Q) ||
+			    skb->protocol == cpu_to_be16(ETH_P_8021AD)) {
+				skb = skb_vlan_untag(skb);
+				*skbp = skb;
+				if (unlikely(!skb))
+					return false;
+				goto again;
+			}
+		}
 		return false;
+	}
 
 	skb = *skbp = skb_share_check(skb, GFP_ATOMIC);
 	if (unlikely(!skb))
-- 
2.22.0