On Thu, Nov 08, 2018 at 04:11:37PM +0100, Nicolas Dichtel wrote:
> This new mode enables to add or remove an l2 header in a programmatic way
> with cls_bpf.
> For example, it enables to play with mpls headers.
>
> Signed-off-by: Nicolas Dichtel <nicolas.dich...@6wind.com>
> ---
> include/uapi/linux/bpf.h | 3 ++
> net/core/filter.c | 54 ++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 3 ++
> 3 files changed, 60 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 852dc17ab47a..47407fd5162b 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1467,6 +1467,8 @@ union bpf_attr {
> *
> * * **BPF_ADJ_ROOM_NET**: Adjust room at the network layer
> * (room space is added or removed below the layer 3 header).
> + * * **BPF_ADJ_ROOM_DATA**: Adjust room at the beginning of the
> + * packet (room space is added or removed below skb->data).
> *
> * All values for *flags* are reserved for future usage, and must
> * be left at zero.
> @@ -2408,6 +2410,7 @@ enum bpf_func_id {
> /* Mode for BPF_FUNC_skb_adjust_room helper. */
> enum bpf_adj_room_mode {
> BPF_ADJ_ROOM_NET,
> + BPF_ADJ_ROOM_DATA,
> };
>
> /* Mode for BPF_FUNC_skb_load_bytes_relative helper. */
> diff --git a/net/core/filter.c b/net/core/filter.c
> index e521c5ebc7d1..e699849b269d 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2884,6 +2884,58 @@ static int bpf_skb_adjust_net(struct sk_buff *skb, s32
> len_diff)
> return ret;
> }
>
> +static int bpf_skb_data_shrink(struct sk_buff *skb, u32 len)
> +{
> + unsigned short hhlen = skb->dev->header_ops ?
> + skb->dev->hard_header_len : 0;
> + int ret;
> +
> + ret = skb_unclone(skb, GFP_ATOMIC);
> + if (unlikely(ret < 0))
> + return ret;
> +
> + __skb_pull(skb, len);
> + skb_reset_mac_header(skb);
> + skb_reset_network_header(skb);
> + skb->network_header += hhlen;
> + skb_reset_transport_header(skb);
hmm...why transport_header does not need += hhlen here
while network_header does?
> + return 0;
> +}
> +
> +static int bpf_skb_data_grow(struct sk_buff *skb, u32 len)
> +{
> + unsigned short hhlen = skb->dev->header_ops ?
> + skb->dev->hard_header_len : 0;
> + int ret;
> +
> + ret = skb_cow(skb, len);
> + if (unlikely(ret < 0))
> + return ret;
> +
> + skb_push(skb, len);
> + skb_reset_mac_header(skb);
> + return 0;
> +}
> +
> +static int bpf_skb_adjust_data(struct sk_buff *skb, s32 len_diff)
> +{
> + u32 len_diff_abs = abs(len_diff);
> + bool shrink = len_diff < 0;
> + int ret;
> +
> + if (unlikely(len_diff_abs > 0xfffU))
> + return -EFAULT;
> +
> + if (shrink && len_diff_abs >= skb_headlen(skb))
> + return -EFAULT;
> +
> + ret = shrink ? bpf_skb_data_shrink(skb, len_diff_abs) :
> + bpf_skb_data_grow(skb, len_diff_abs);
> +
> + bpf_compute_data_pointers(skb);
> + return ret;
> +}
> +
> BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
> u32, mode, u64, flags)
> {
> @@ -2891,6 +2943,8 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb,
> s32, len_diff,
> return -EINVAL;
> if (likely(mode == BPF_ADJ_ROOM_NET))
> return bpf_skb_adjust_net(skb, len_diff);
> + if (likely(mode == BPF_ADJ_ROOM_DATA))
> + return bpf_skb_adjust_data(skb, len_diff);
>
> return -ENOTSUPP;
> }
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 852dc17ab47a..47407fd5162b 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -1467,6 +1467,8 @@ union bpf_attr {
> *
> * * **BPF_ADJ_ROOM_NET**: Adjust room at the network layer
> * (room space is added or removed below the layer 3 header).
> + * * **BPF_ADJ_ROOM_DATA**: Adjust room at the beginning of the
> + * packet (room space is added or removed below skb->data).
> *
> * All values for *flags* are reserved for future usage, and must
> * be left at zero.
> @@ -2408,6 +2410,7 @@ enum bpf_func_id {
> /* Mode for BPF_FUNC_skb_adjust_room helper. */
> enum bpf_adj_room_mode {
> BPF_ADJ_ROOM_NET,
> + BPF_ADJ_ROOM_DATA,
> };
>
> /* Mode for BPF_FUNC_skb_load_bytes_relative helper. */
> --
> 2.18.0
>
