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>

5 files changed, 15 insertions, 10 deletions

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 7ff9af1d0f0..8898cbebcf3 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;
diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h
index 82570bc2a18..4ade5edf103 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 4198ec5c8ab..e3701977f58 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];
diff --git a/net/core/dev.c b/net/core/dev.c
index e7bada1d5ed..950c13fa60d 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 */
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index ff752c60641..33e68f20ec6 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -79,6 +79,7 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/mutex.h>
+#include <linux/if_vlan.h>
 
 #ifdef CONFIG_INET
 #include <net/inet_common.h>
@@ -766,7 +767,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
                         getnstimeofday(&ts);
                 h.h2->tp_sec = ts.tv_sec;
                 h.h2->tp_nsec = ts.tv_nsec;
-                h.h2->tp_vlan_tci = skb->vlan_tci;
+                h.h2->tp_vlan_tci = vlan_tx_tag_get(skb);
                 hdrlen = sizeof(*h.h2);
                 break;
         default:
@@ -1493,7 +1494,7 @@ static int packet_recvmsg(struct kiocb *iocb, struct socket *sock,
                 aux.tp_snaplen = skb->len;
                 aux.tp_mac = 0;
                 aux.tp_net = skb_network_offset(skb);
-                aux.tp_vlan_tci = skb->vlan_tci;
+                aux.tp_vlan_tci = vlan_tx_tag_get(skb);
 
                 put_cmsg(msg, SOL_PACKET, PACKET_AUXDATA, sizeof(aux), &aux);
         }