On Tue, Sep 25, 2018 at 7:26 AM Jesper Dangaard Brouer
<bro...@redhat.com> wrote:
>
> XDP can modify (and resize) the Ethernet header in the packet.
>
> There is a bug in generic-XDP, because skb->protocol and skb->pkt_type
> are setup before reaching (netif_receive_)generic_xdp.
>
> This bug was hit when XDP were popping VLAN headers (changing
> eth->h_proto), as skb->protocol still contains VLAN-indication
> (ETH_P_8021Q) causing invocation of skb_vlan_untag(skb), which corrupt
> the packet (basically popping the VLAN again).
>
> This patch catch if XDP changed eth header in such a way, that SKB
> fields needs to be updated.
>
> Fixes: d445516966dc ("net: xdp: support xdp generic on virtual devices")
> Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
> ---
> net/core/dev.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index ca78dc5a79a3..db6d89f536cb 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4258,6 +4258,9 @@ static u32 netif_receive_generic_xdp(struct sk_buff
> *skb,
> struct netdev_rx_queue *rxqueue;
> void *orig_data, *orig_data_end;
> u32 metalen, act = XDP_DROP;
> + __be16 orig_eth_type;
> + struct ethhdr *eth;
> + bool orig_bcast;
> int hlen, off;
> u32 mac_len;
>
> @@ -4298,6 +4301,9 @@ static u32 netif_receive_generic_xdp(struct sk_buff
> *skb,
> xdp->data_hard_start = skb->data - skb_headroom(skb);
> orig_data_end = xdp->data_end;
> orig_data = xdp->data;
> + eth = (struct ethhdr *)xdp->data;
> + orig_bcast = is_multicast_ether_addr_64bits(eth->h_dest);
> + orig_eth_type = eth->h_proto;
>
> rxqueue = netif_get_rxqueue(skb);
> xdp->rxq = &rxqueue->xdp_rxq;
> @@ -4321,6 +4327,14 @@ static u32 netif_receive_generic_xdp(struct sk_buff
> *skb,
>
> }
>
> + /* check if XDP changed eth hdr such SKB needs update */
> + eth = (struct ethhdr *)xdp->data;
> + if ((orig_eth_type != eth->h_proto) ||
> + (orig_bcast != is_multicast_ether_addr_64bits(eth->h_dest))) {
Is the actions below always correct for the condition above? Do we need
to confirm the SKB is updated properly?
> + __skb_push(skb, mac_len);
> + skb->protocol = eth_type_trans(skb, skb->dev);
> + }
> +
> switch (act) {
> case XDP_REDIRECT:
> case XDP_TX:
>
