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, 9 insertions, 5 deletions

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 7ff9af1d0f05..8898cbebcf34 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -63,7 +63,11 @@ static inline struct vlan_ethhdr *vlan_eth_hdr(const struct sk_buff *skb)
         return (struct vlan_ethhdr *)skb_mac_header(skb);
 }
 
-#define VLAN_VID_MASK   0xfff
+#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 */
 
 /* found in socket.c */
 extern void vlan_ioctl_set(int (*hook)(struct net *, void __user *));
@@ -105,8 +109,8 @@ static inline void vlan_group_set_device(struct vlan_group *vg,
         array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] = dev;
 }
 
-#define vlan_tx_tag_present(__skb)      ((__skb)->vlan_tci)
-#define vlan_tx_tag_get(__skb)          ((__skb)->vlan_tci)
+#define vlan_tx_tag_present(__skb)      ((__skb)->vlan_tci & VLAN_TAG_PRESENT)
+#define vlan_tx_tag_get(__skb)          ((__skb)->vlan_tci & ~VLAN_TAG_PRESENT)
 
 #if defined(CONFIG_VLAN_8021Q) || defined(CONFIG_VLAN_8021Q_MODULE)
 extern struct net_device *vlan_dev_real_dev(const struct net_device *dev);
@@ -231,7 +235,7 @@ static inline struct sk_buff *__vlan_put_tag(struct sk_buff *skb, u16 vlan_tci)
 static inline struct sk_buff *__vlan_hwaccel_put_tag(struct sk_buff *skb,
                                                      u16 vlan_tci)
 {
-        skb->vlan_tci = vlan_tci;
+        skb->vlan_tci = VLAN_TAG_PRESENT | vlan_tci;
         return skb;
 }
 
@@ -284,7 +288,7 @@ static inline int __vlan_hwaccel_get_tag(const struct sk_buff *skb,
                                          u16 *vlan_tci)
 {
         if (vlan_tx_tag_present(skb)) {
-                *vlan_tci = skb->vlan_tci;
+                *vlan_tci = vlan_tx_tag_get(skb);
                 return 0;
         } else {
                 *vlan_tci = 0;