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bpf: add bpf_skb_change_type helper

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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>
This commit is contained in:
Daniel Borkmann 2016-06-28 12:18:28 +02:00 committed by David S. Miller
parent 6578171a7f
commit d2485c4242
2 changed files with 33 additions and 0 deletions
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9
include/uapi/linux/bpf.h
View File

@ -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,
};

24
net/core/filter.c
View File

@ -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: