[ ping to Jesper wrt feedback ]
On 09/26/2018 07:36 AM, Song Liu wrote:
> 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:
>>
