[PATCHv2 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 <redacted>
---
v1->v2:
  replace the return type from unsigned int to int
---
 net/openvswitch/vport.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/openvswitch/vport.c b/net/openvswitch/vport.c
index b6c8524032a0..f81c1d0ddff4 100644
--- a/net/openvswitch/vport.c
+++ b/net/openvswitch/vport.c

@@ -464,10 +464,10 @@ int ovs_vport_receive(struct vport *vport, struct sk_buff *skb,
 	return 0;
 }
 
-static unsigned int packet_length(const struct sk_buff *skb,
-				  struct net_device *dev)
+static 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

On Wed, Mar 7, 2018 at 3:38 PM, William Tu [off-list ref] wrote:

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 <redacted>
---
v1->v2:
  replace the return type from unsigned int to int
---

Acked-by: Pravin B Shelar <redacted>

From: William Tu <redacted>
Date: Wed,  7 Mar 2018 15:38:48 -0800

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 <redacted>
---
v1->v2:
  replace the return type from unsigned int to int

Applied, thanks.