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>

2 files changed, 2 insertions, 2 deletions

diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h
index 82570bc2a180..4ade5edf1033 100644
--- a/net/8021q/vlan.h
+++ b/net/8021q/vlan.h
@@ -89,7 +89,7 @@ static inline u32 vlan_get_ingress_priority(struct net_device *dev,
 {
         struct vlan_dev_info *vip = vlan_dev_info(dev);
 
-        return vip->ingress_priority_map[(vlan_tci >> 13) & 0x7];
+        return vip->ingress_priority_map[(vlan_tci >> VLAN_PRIO_SHIFT) & 0x7];
 }
 
 #ifdef CONFIG_VLAN_8021Q_GVRP
diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index 4198ec5c8abc..e3701977f58d 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -393,7 +393,7 @@ int vlan_dev_set_egress_priority(const struct net_device *dev,
         struct vlan_dev_info *vlan = vlan_dev_info(dev);
         struct vlan_priority_tci_mapping *mp = NULL;
         struct vlan_priority_tci_mapping *np;
-        u32 vlan_qos = (vlan_prio << 13) & 0xE000;
+        u32 vlan_qos = (vlan_prio << VLAN_PRIO_SHIFT) & VLAN_PRIO_MASK;
 
         /* See if a priority mapping exists.. */
         mp = vlan->egress_priority_map[skb_prio & 0xF];