Patch "net: bridge: Fix ethernet header pointer before check skb forwardable" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

net: bridge: Fix ethernet header pointer before check skb forwardable

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-bridge-fix-ethernet-header-pointer-before-check-skb-forwardable.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From foo@baz Sat Jan 26 10:53:10 CET 2019
From: Yunjian Wang <[email protected]>
Date: Thu, 17 Jan 2019 09:46:41 +0800
Subject: net: bridge: Fix ethernet header pointer before check skb forwardable

From: Yunjian Wang <[email protected]>

[ Upstream commit 28c1382fa28f2e2d9d0d6f25ae879b5af2ecbd03 ]

The skb header should be set to ethernet header before using is_skb_forwardable. Because the ethernet header length has been considered in is_skb_forwardable(including dev->hard_header_len length).

To reproduce the issue:
1, add 2 ports on linux bridge br using following commands:

$ brctl addbr br
$ brctl addif br eth0
$ brctl addif br eth1
2, the MTU of eth0 and eth1 is 1500
3, send a packet(Data 1480, UDP 8, IP 20, Ethernet 14, VLAN 4)
from eth0 to eth1

So the expect result is packet larger than 1500 cannot pass through eth0 and eth1. But currently, the packet passes through success, it means eth1's MTU limit doesn't take effect.

---
 net/bridge/br_forward.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

@@ -35,10 +35,10 @@ static inline int should_deliver(const s
 
 int br_dev_queue_push_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
+	skb_push(skb, ETH_HLEN);
 	if (!is_skb_forwardable(skb->dev, skb))
 		goto drop;
 
-	skb_push(skb, ETH_HLEN);
 	br_drop_fake_rtable(skb);
 
 	if (skb->ip_summed == CHECKSUM_PARTIAL &&

@@ -96,12 +96,11 @@ static void __br_forward(const struct ne
 		net = dev_net(indev);
 	} else {
 		if (unlikely(netpoll_tx_running(to->br->dev))) {
-			if (!is_skb_forwardable(skb->dev, skb)) {
+			skb_push(skb, ETH_HLEN);
+			if (!is_skb_forwardable(skb->dev, skb))
 				kfree_skb(skb);
-			} else {
-				skb_push(skb, ETH_HLEN);
+			else
 				br_netpoll_send_skb(to, skb);
-			}
 			return;
 		}
 		br_hook = NF_BR_LOCAL_OUT;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/net-bridge-fix-ethernet-header-pointer-before-check-skb-forwardable.patch