bpf: add bpf_skb_change_type helper

This work adds a helper for changing skb->pkt_type in a controlled way.
We only allow a subset of possible values and can extend that in future
should other use cases come up. Doing this as a helper has the advantage
that errors can be handeled gracefully and thus helper kept extensible.

It's a write counterpart to pkt_type member we can already read from
struct __sk_buff context. Major use case is to change incoming skbs to
PACKET_HOST in a programmatic way instead of having to recirculate via
redirect(..., BPF_F_INGRESS), for example.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 66cd738a937a..be6ac1291680 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -327,6 +327,15 @@ enum bpf_func_id {
          */
         BPF_FUNC_skb_change_proto,
 
+        /**
+         * bpf_skb_change_type(skb, type)
+         * Change packet type of skb.
+         * @skb: pointer to skb
+         * @type: new skb->pkt_type type
+         * Return: 0 on success or negative error
+         */
+        BPF_FUNC_skb_change_type,
+
         __BPF_FUNC_MAX_ID,
 };