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Commit d2485c42 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller
Browse files

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: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 6578171a

include/uapi/linux/bpf.h

+9 −0
Original line number Diff line number Diff line
@@ -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,

};

net/core/filter.c

+24 −0
Original line number Diff line number Diff line
@@ -1979,6 +1979,28 @@ static const struct bpf_func_proto bpf_skb_change_proto_proto = { 
	.arg3_type	= ARG_ANYTHING,

};



static u64 bpf_skb_change_type(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)

{

	struct sk_buff *skb = (struct sk_buff *) (long) r1;

	u32 pkt_type = r2;



	/* We only allow a restricted subset to be changed for now. */

	if (unlikely(skb->pkt_type > PACKET_OTHERHOST ||

		     pkt_type > PACKET_OTHERHOST))

		return -EINVAL;



	skb->pkt_type = pkt_type;

	return 0;

}



static const struct bpf_func_proto bpf_skb_change_type_proto = {

	.func		= bpf_skb_change_type,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_CTX,

	.arg2_type	= ARG_ANYTHING,

};



bool bpf_helper_changes_skb_data(void *func)

{

	if (func == bpf_skb_vlan_push)
@@ -2278,6 +2300,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id) 
		return &bpf_skb_vlan_pop_proto;

	case BPF_FUNC_skb_change_proto:

		return &bpf_skb_change_proto_proto;

	case BPF_FUNC_skb_change_type:

		return &bpf_skb_change_type_proto;

	case BPF_FUNC_skb_get_tunnel_key:

		return &bpf_skb_get_tunnel_key_proto;

	case BPF_FUNC_skb_set_tunnel_key: