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

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Date:   Wed, 7 Mar 2018 13:18:57 -0800
From:   Pravin Shelar <pshelar@....org>
To:     William Tu <u9012063@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Benc <jbenc@...hat.com>
Subject: Re: [PATCH net-next] openvswitch: fix vport packet length check.

On Tue, Mar 6, 2018 at 5:56 PM, William Tu <u9012063@...il.com> 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 <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)
Can you also change return type of this function?

>  {
> -       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
>