vlan: allow null VLAN ID to be used

We currently use a 16 bit field (vlan_tci) to store VLAN ID/PRIO on a skb.

Null value is used as a special value, meaning vlan tagging not enabled.
This forbids use of null vlan ID.

As pointed by David, some drivers use the 3 high order bits (PRIO)

As VLAN ID is 12 bits, we can use the remaining bit (CFI) as a flag, and
allow null VLAN ID.

In case future code really wants to use VLAN_CFI_MASK, we'll have to use
a bit outside of vlan_tci.

#define VLAN_PRIO_MASK         0xe000 /* Priority Code Point */
#define VLAN_PRIO_SHIFT        13
#define VLAN_CFI_MASK          0x1000 /* Canonical Format Indicator */
#define VLAN_TAG_PRESENT       VLAN_CFI_MASK
#define VLAN_VID_MASK          0x0fff /* VLAN Identifier */

Reported-by: Gertjan Hofman <gertjan_hofman@yahoo.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index e7bada1d5ed9..950c13fa60d2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2300,7 +2300,7 @@ int netif_receive_skb(struct sk_buff *skb)
         if (!skb->tstamp.tv64)
                 net_timestamp(skb);
 
-        if (skb->vlan_tci && vlan_hwaccel_do_receive(skb))
+        if (vlan_tx_tag_present(skb) && vlan_hwaccel_do_receive(skb))
                 return NET_RX_SUCCESS;
 
         /* if we've gotten here through NAPI, check netpoll */