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>

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;

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

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];

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 */

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);
 	}