[Bridge] [PATCH v2 1/1] net: bridge: use mac_len in bridge forwarding

Zahari Doychev
2019-08-05T15:37:40Z

The bridge code cannot forward packets from various paths that set up the
SKBs in different ways. Some of these packets get corrupted during the
forwarding as not always is just ETH_HLEN pulled at the front. This happens
e.g. when VLAN tags are pushed bu using tc act_vlan on ingress.

The problem is fixed by using skb->mac_len instead of ETH_HLEN, which makes
sure that the skb headers are correctly restored. This usually does not
change anything, execpt the local bridge transmits which now need to set
the skb->mac_len correctly in br_dev_xmit, as well as the broken case noted
above.

Signed-off-by: Zahari Doychev <zahari.doychev at linux.com>
---
 net/bridge/br_device.c  | 3 ++-
 net/bridge/br_forward.c | 4 ++--
 net/bridge/br_vlan.c    | 3 ++-
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 681b72862c16..aeb77ff60311 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -55,8 +55,9 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device
*dev)
 	BR_INPUT_SKB_CB(skb)->frag_max_size = 0;

 	skb_reset_mac_header(skb);
+	skb_reset_mac_len(skb);
 	eth = eth_hdr(skb);
-	skb_pull(skb, ETH_HLEN);
+	skb_pull(skb, skb->mac_len);

 	if (!br_allowed_ingress(br, br_vlan_group_rcu(br), skb, &vid))
 		goto out;
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index 86637000f275..edb4f3533f05 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -32,7 +32,7 @@ static inline int should_deliver(const struct net_bridge_port
*p,

 int br_dev_queue_push_xmit(struct net *net, struct sock *sk, struct sk_buff
*skb)
 {
-	skb_push(skb, ETH_HLEN);
+	skb_push(skb, skb->mac_len);
 	if (!is_skb_forwardable(skb->dev, skb))
 		goto drop;

@@ -94,7 +94,7 @@ static void __br_forward(const struct net_bridge_port *to,
 		net = dev_net(indev);
 	} else {
 		if (unlikely(netpoll_tx_running(to->br->dev))) {
-			skb_push(skb, ETH_HLEN);
+			skb_push(skb, skb->mac_len);
 			if (!is_skb_forwardable(skb->dev, skb))
 				kfree_skb(skb);
 			else
diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
index 021cc9f66804..88244c9cc653 100644
--- a/net/bridge/br_vlan.c
+++ b/net/bridge/br_vlan.c
@@ -466,13 +466,14 @@ static bool __allowed_ingress(const struct net_bridge *br,
 		/* Tagged frame */
 		if (skb->vlan_proto != br->vlan_proto) {
 			/* Protocol-mismatch, empty out vlan_tci for new tag */
-			skb_push(skb, ETH_HLEN);
+			skb_push(skb, skb->mac_len);
 			skb = vlan_insert_tag_set_proto(skb, skb->vlan_proto,
 							skb_vlan_tag_get(skb));
 			if (unlikely(!skb))
 				return false;

 			skb_pull(skb, ETH_HLEN);
+			skb_reset_network_header(skb);
 			skb_reset_mac_len(skb);
 			*vid = 0;
 			tagged = false;
--
2.22.0