net: Always untag vlan-tagged traffic on input.

Currently the functionality to untag traffic on input resides
as part of the vlan module and is build only when VLAN support
is enabled in the kernel.  When VLAN is disabled, the function
vlan_untag() turns into a stub and doesn't really untag the
packets.  This seems to create an interesting interaction
between VMs supporting checksum offloading and some network drivers.

There are some drivers that do not allow the user to change
tx-vlan-offload feature of the driver.  These drivers also seem
to assume that any VLAN-tagged traffic they transmit will
have the vlan information in the vlan_tci and not in the vlan
header already in the skb.  When transmitting skbs that already
have tagged data with partial checksum set, the checksum doesn't
appear to be updated correctly by the card thus resulting in a
failure to establish TCP connections.

The following is a packet trace taken on the receiver where a
sender is a VM with a VLAN configued.  The host VM is running on
doest not have VLAN support and the outging interface on the
host is tg3:
10:12:43.503055 52:54:00:ae:42:3f > 28:d2:44:7d:c2:de, ethertype 802.1Q
(0x8100), length 78: vlan 100, p 0, ethertype IPv4, (tos 0x0, ttl 64, id 27243,
offset 0, flags [DF], proto TCP (6), length 60)
    10.0.100.1.58545 > 10.0.100.10.ircu-2: Flags [S], cksum 0xdc39 (incorrect
-> 0x48d9), seq 1069378582, win 29200, options [mss 1460,sackOK,TS val
4294837885 ecr 0,nop,wscale 7], length 0
10:12:44.505556 52:54:00:ae:42:3f > 28:d2:44:7d:c2:de, ethertype 802.1Q
(0x8100), length 78: vlan 100, p 0, ethertype IPv4, (tos 0x0, ttl 64, id 27244,
offset 0, flags [DF], proto TCP (6), length 60)
    10.0.100.1.58545 > 10.0.100.10.ircu-2: Flags [S], cksum 0xdc39 (incorrect
-> 0x44ee), seq 1069378582, win 29200, options [mss 1460,sackOK,TS val
4294838888 ecr 0,nop,wscale 7], length 0

This connection finally times out.

I've only access to the TG3 hardware in this configuration thus have
only tested this with TG3 driver.  There are a lot of other drivers
that do not permit user changes to vlan acceleration features, and
I don't know if they all suffere from a similar issue.

The patch attempt to fix this another way.  It moves the vlan header
stipping code out of the vlan module and always builds it into the
kernel network core.  This way, even if vlan is not supported on
a virtualizatoin host, the virtual machines running on top of such
host will still work with VLANs enabled.

CC: Patrick McHardy <[email protected]>
CC: Nithin Nayak Sujir <[email protected]>
CC: Michael Chan <[email protected]>
CC: Jiri Pirko <[email protected]>
Signed-off-by: Vladislav Yasevich <[email protected]>
Acked-by: Jiri Pirko <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Vlad Yasevich

include/linux/if_vlan.h

@@ -187,7 +187,6 @@ vlan_dev_get_egress_qos_mask(struct net_device *dev, u32 skprio)
 }
 
 extern bool vlan_do_receive(struct sk_buff **skb);
-extern struct sk_buff *vlan_untag(struct sk_buff *skb);
 
 extern int vlan_vid_add(struct net_device *dev, __be16 proto, u16 vid);
 extern void vlan_vid_del(struct net_device *dev, __be16 proto, u16 vid);
@@ -241,11 +240,6 @@ static inline bool vlan_do_receive(struct sk_buff **skb)
 	return false;
 }
 
-static inline struct sk_buff *vlan_untag(struct sk_buff *skb)
-{
-	return skb;
-}
-
 static inline int vlan_vid_add(struct net_device *dev, __be16 proto, u16 vid)
 {
 	return 0;

include/linux/skbuff.h

@@ -2555,6 +2555,7 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen);
 void skb_scrub_packet(struct sk_buff *skb, bool xnet);
 unsigned int skb_gso_transport_seglen(const struct sk_buff *skb);
 struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features);
+struct sk_buff *skb_vlan_untag(struct sk_buff *skb);
 
 struct skb_checksum_ops {
 	__wsum (*update)(const void *mem, int len, __wsum wsum);

net/8021q/vlan_core.c

@@ -112,59 +112,6 @@ __be16 vlan_dev_vlan_proto(const struct net_device *dev)
 }
 EXPORT_SYMBOL(vlan_dev_vlan_proto);
 
-static struct sk_buff *vlan_reorder_header(struct sk_buff *skb)
-{
-	if (skb_cow(skb, skb_headroom(skb)) < 0) {
-		kfree_skb(skb);
-		return NULL;
-	}
-
-	memmove(skb->data - ETH_HLEN, skb->data - VLAN_ETH_HLEN, 2 * ETH_ALEN);
-	skb->mac_header += VLAN_HLEN;
-	return skb;
-}
-
-struct sk_buff *vlan_untag(struct sk_buff *skb)
-{
-	struct vlan_hdr *vhdr;
-	u16 vlan_tci;
-
-	if (unlikely(vlan_tx_tag_present(skb))) {
-		/* vlan_tci is already set-up so leave this for another time */
-		return skb;
-	}
-
-	skb = skb_share_check(skb, GFP_ATOMIC);
-	if (unlikely(!skb))
-		goto err_free;
-
-	if (unlikely(!pskb_may_pull(skb, VLAN_HLEN)))
-		goto err_free;
-
-	vhdr = (struct vlan_hdr *) skb->data;
-	vlan_tci = ntohs(vhdr->h_vlan_TCI);
-	__vlan_hwaccel_put_tag(skb, skb->protocol, vlan_tci);
-
-	skb_pull_rcsum(skb, VLAN_HLEN);
-	vlan_set_encap_proto(skb, vhdr);
-
-	skb = vlan_reorder_header(skb);
-	if (unlikely(!skb))
-		goto err_free;
-
-	skb_reset_network_header(skb);
-	skb_reset_transport_header(skb);
-	skb_reset_mac_len(skb);
-
-	return skb;
-
-err_free:
-	kfree_skb(skb);
-	return NULL;
-}
-EXPORT_SYMBOL(vlan_untag);
-
-
 /*
  * vlan info and vid list
  */

net/bridge/br_vlan.c

@@ -181,7 +181,7 @@ bool br_allowed_ingress(struct net_bridge *br, struct net_port_vlans *v,
 	 */
 	if (unlikely(!vlan_tx_tag_present(skb) &&
 		     skb->protocol == proto)) {
-		skb = vlan_untag(skb);
+		skb = skb_vlan_untag(skb);
 		if (unlikely(!skb))
 			return false;
 	}

net/core/dev.c

@@ -3602,7 +3602,7 @@ static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc)
 
 	if (skb->protocol == cpu_to_be16(ETH_P_8021Q) ||
 	    skb->protocol == cpu_to_be16(ETH_P_8021AD)) {
-		skb = vlan_untag(skb);
+		skb = skb_vlan_untag(skb);
 		if (unlikely(!skb))
 			goto unlock;
 	}

net/core/skbuff.c

@@ -62,6 +62,7 @@
 #include <linux/scatterlist.h>
 #include <linux/errqueue.h>
 #include <linux/prefetch.h>
+#include <linux/if_vlan.h>
 
 #include <net/protocol.h>
 #include <net/dst.h>
@@ -3973,3 +3974,55 @@ unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
 	return shinfo->gso_size;
 }
 EXPORT_SYMBOL_GPL(skb_gso_transport_seglen);
+
+static struct sk_buff *skb_reorder_vlan_header(struct sk_buff *skb)
+{
+	if (skb_cow(skb, skb_headroom(skb)) < 0) {
+		kfree_skb(skb);
+		return NULL;
+	}
+
+	memmove(skb->data - ETH_HLEN, skb->data - VLAN_ETH_HLEN, 2 * ETH_ALEN);
+	skb->mac_header += VLAN_HLEN;
+	return skb;
+}
+
+struct sk_buff *skb_vlan_untag(struct sk_buff *skb)
+{
+	struct vlan_hdr *vhdr;
+	u16 vlan_tci;
+
+	if (unlikely(vlan_tx_tag_present(skb))) {
+		/* vlan_tci is already set-up so leave this for another time */
+		return skb;
+	}
+
+	skb = skb_share_check(skb, GFP_ATOMIC);
+	if (unlikely(!skb))
+		goto err_free;
+
+	if (unlikely(!pskb_may_pull(skb, VLAN_HLEN)))
+		goto err_free;
+
+	vhdr = (struct vlan_hdr *)skb->data;
+	vlan_tci = ntohs(vhdr->h_vlan_TCI);
+	__vlan_hwaccel_put_tag(skb, skb->protocol, vlan_tci);
+
+	skb_pull_rcsum(skb, VLAN_HLEN);
+	vlan_set_encap_proto(skb, vhdr);
+
+	skb = skb_reorder_vlan_header(skb);
+	if (unlikely(!skb))
+		goto err_free;
+
+	skb_reset_network_header(skb);
+	skb_reset_transport_header(skb);
+	skb_reset_mac_len(skb);
+
+	return skb;
+
+err_free:
+	kfree_skb(skb);
+	return NULL;
+}
+EXPORT_SYMBOL(skb_vlan_untag);