netdev - [PATCH net-next] openvswitch: fix vport packet length check.

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Message-Id: <1520387817-11137-1-git-send-email-u9012063@gmail.com>
Date:   Tue,  6 Mar 2018 17:56:57 -0800
From:   William Tu <u9012063@...il.com>
To:     netdev@...r.kernel.org
Cc:     pshelar@....org, jbenc@...hat.com
Subject: [PATCH net-next] openvswitch: fix vport packet length check.

When sending a packet to a tunnel device, the dev's hard_header_len
could be larger than the skb->len in function packet_length().
In the case of ip6gretap/erspan, hard_header_len = LL_MAX_HEADER + t_hlen,
which is around 180, and an ARP packet sent to this tunnel has
skb->len = 42.  This causes the 'unsign int length' to become super
large because it is negative value, causing the later ovs_vport_send
to drop it due to over-mtu size.  The patch fixes it by setting it to 0.

Signed-off-by: William Tu <u9012063@...il.com>
---
 net/openvswitch/vport.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/openvswitch/vport.c b/net/openvswitch/vport.c
index b6c8524032a0..7718d5b4cf8a 100644
--- a/net/openvswitch/vport.c
+++ b/net/openvswitch/vport.c
@@ -467,7 +467,7 @@ int ovs_vport_receive(struct vport *vport, struct sk_buff *skb,
 static unsigned int packet_length(const struct sk_buff *skb,
 				  struct net_device *dev)
 {
-	unsigned int length = skb->len - dev->hard_header_len;
+	int length = skb->len - dev->hard_header_len;

 	if (!skb_vlan_tag_present(skb) &&
 	    eth_type_vlan(skb->protocol))
@@ -478,7 +478,7 @@ static unsigned int packet_length(const struct sk_buff *skb,
 	 * account for 802.1ad. e.g. is_skb_forwardable().
 	 */

-	return length;
+	return length > 0 ? length : 0;
 }

 void ovs_vport_send(struct vport *vport, struct sk_buff *skb, u8 mac_proto)
-- 
2.7.4