Commit 28c1382f authored Jan 17, 2019 by Yunjian Wang Committed by David S. Miller Jan 17, 2019

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



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.

Fixes: f6367b46 ("bridge: use is_skb_forwardable in forward path")
Cc: bridge@lists.linux-foundation.org
Cc: Nkolay Aleksandrov <nikolay@cumulusnetworks.com>
Cc: Roopa Prabhu <roopa@cumulusnetworks.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent cc5e7107

net/bridge/br_forward.c

+4 −5

Original line number	Diff line number	Diff line
		@@ -36,10 +36,10 @@ 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);
		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 &&
		@@ -98,12 +98,11 @@ static void __br_forward(const struct net_bridge_port *to,
		net = dev_net(indev);
		} else {
		if (unlikely(netpoll_tx_running(to->br->dev))) {
		if (!is_skb_forwardable(skb->dev, skb)) {
		kfree_skb(skb);
		} else {
		skb_push(skb, ETH_HLEN);
		if (!is_skb_forwardable(skb->dev, skb))
		kfree_skb(skb);
		else
		br_netpoll_send_skb(to, skb);
		}
		return;
		}
		br_hook = NF_BR_LOCAL_OUT;

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