On Mon, Apr 8, 2019 at 12:59 PM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>
> commit 868d523535c2 ("bpf: add bpf_skb_adjust_room encap flags")
> introduced support to bpf_skb_adjust_room for GSO-friendly GRE
> and UDP encapsulation.
>
> For GSO to work for skbs, the inner headers (mac and network) need to
> be marked. For L3 encapsulation using bpf_skb_adjust_room, the mac
> and network headers are identical. Here we provide a way of specifying
> the inner mac header length for cases where L2 encap is desired. Such
> an approach can support encapsulated ethernet headers, MPLS headers etc.
> For example to convert from a packet of form [eth][ip][tcp] to
> [eth][ip][udp][inner mac][ip][tcp], something like the following could
> be done:
>
> headroom = sizeof(iph) + sizeof(struct udphdr) + inner_maclen;
>
> ret = bpf_skb_adjust_room(skb, headroom, BPF_ADJ_ROOM_MAC,
> BPF_F_ADJ_ROOM_ENCAP_L4_UDP |
> BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 |
> BPF_F_ADJ_ROOM_ENCAP_L2(inner_maclen));
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> u64 flags)
> {
> + u16 mac_len = 0, inner_mac = 0, inner_net = 0, inner_trans = 0;
> bool encap = flags & BPF_F_ADJ_ROOM_ENCAP_L3_MASK;
> - u16 mac_len = 0, inner_net = 0, inner_trans = 0;
> unsigned int gso_type = SKB_GSO_DODGY;
> + u8 inner_mac_len = flags >> BPF_ADJ_ROOM_ENCAP_L2_SHIFT;
> int ret;
>
> if (skb_is_gso(skb) && !skb_is_gso_tcp(skb)) {
> @@ -3008,6 +3011,9 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
>
> mac_len = skb->network_header - skb->mac_header;
> inner_net = skb->network_header;
> + if (inner_mac_len > len_diff)
> + return -EINVAL;
> + inner_mac = inner_net - inner_mac_len;
nit: variable inner_mac is not needed.
> @@ -3031,7 +3036,7 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> gso_type |= SKB_GSO_GRE;
> else if (flags & BPF_F_ADJ_ROOM_ENCAP_L3_IPV6)
> gso_type |= SKB_GSO_IPXIP6;
> - else
> + else if (flags & BPF_F_ADJ_ROOM_ENCAP_L3_IPV4)
> gso_type |= SKB_GSO_IPXIP4;
Nice catch. L2 encap should also work without L3 encap.
