Commit 12bed760 authored by Eyal Birger's avatar Eyal Birger Committed by Daniel Borkmann
Browse files

bpf: add helper for getting xfrm states 



This commit introduces a helper which allows fetching xfrm state
parameters by eBPF programs attached to TC.

Prototype:
bpf_skb_get_xfrm_state(skb, index, xfrm_state, size, flags)

skb: pointer to skb
index: the index in the skb xfrm_state secpath array
xfrm_state: pointer to 'struct bpf_xfrm_state'
size: size of 'struct bpf_xfrm_state'
flags: reserved for future extensions

The helper returns 0 on success. Non zero if no xfrm state at the index
is found - or non exists at all.

struct bpf_xfrm_state currently includes the SPI, peer IPv4/IPv6
address and the reqid; it can be further extended by adding elements to
its end - indicating the populated fields by the 'size' argument -
keeping backwards compatibility.

Typical usage:

struct bpf_xfrm_state x = {};
bpf_skb_get_xfrm_state(skb, 0, &x, sizeof(x), 0);
...

Signed-off-by: default avatarEyal Birger <eyal.birger@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent fbcf93eb

include/uapi/linux/bpf.h

+24 −1
Original line number Diff line number Diff line
@@ -774,6 +774,15 @@ union bpf_attr { 
 *     @xdp_md: pointer to xdp_md

 *     @delta: A negative integer to be added to xdp_md.data_end

 *     Return: 0 on success or negative on error

 *

 * int bpf_skb_get_xfrm_state(skb, index, xfrm_state, size, flags)

 *     retrieve XFRM state

 *     @skb: pointer to skb

 *     @index: index of the xfrm state in the secpath

 *     @key: pointer to 'struct bpf_xfrm_state'

 *     @size: size of 'struct bpf_xfrm_state'

 *     @flags: room for future extensions

 *     Return: 0 on success or negative error

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -841,7 +850,8 @@ union bpf_attr { 
	FN(msg_cork_bytes),		\

	FN(msg_pull_data),		\

	FN(bind),			\

	FN(xdp_adjust_tail),

	FN(xdp_adjust_tail),		\

	FN(skb_get_xfrm_state),



/* integer value in 'imm' field of BPF_CALL instruction selects which helper

 * function eBPF program intends to call
@@ -947,6 +957,19 @@ struct bpf_tunnel_key { 
	__u32 tunnel_label;

};



/* user accessible mirror of in-kernel xfrm_state.

 * new fields can only be added to the end of this structure

 */

struct bpf_xfrm_state {

	__u32 reqid;

	__u32 spi;	/* Stored in network byte order */

	__u16 family;

	union {

		__u32 remote_ipv4;	/* Stored in network byte order */

		__u32 remote_ipv6[4];	/* Stored in network byte order */

	};

};



/* Generic BPF return codes which all BPF program types may support.

 * The values are binary compatible with their TC_ACT_* counter-part to

 * provide backwards compatibility with existing SCHED_CLS and SCHED_ACT

net/core/filter.c

+48 −0
Original line number Diff line number Diff line
@@ -57,6 +57,7 @@ 
#include <net/sock_reuseport.h>

#include <net/busy_poll.h>

#include <net/tcp.h>

#include <net/xfrm.h>

#include <linux/bpf_trace.h>



/**
@@ -3743,6 +3744,49 @@ static const struct bpf_func_proto bpf_bind_proto = { 
	.arg3_type	= ARG_CONST_SIZE,

};



#ifdef CONFIG_XFRM

BPF_CALL_5(bpf_skb_get_xfrm_state, struct sk_buff *, skb, u32, index,

	   struct bpf_xfrm_state *, to, u32, size, u64, flags)

{

	const struct sec_path *sp = skb_sec_path(skb);

	const struct xfrm_state *x;



	if (!sp || unlikely(index >= sp->len || flags))

		goto err_clear;



	x = sp->xvec[index];



	if (unlikely(size != sizeof(struct bpf_xfrm_state)))

		goto err_clear;



	to->reqid = x->props.reqid;

	to->spi = x->id.spi;

	to->family = x->props.family;

	if (to->family == AF_INET6) {

		memcpy(to->remote_ipv6, x->props.saddr.a6,

		       sizeof(to->remote_ipv6));

	} else {

		to->remote_ipv4 = x->props.saddr.a4;

	}



	return 0;

err_clear:

	memset(to, 0, size);

	return -EINVAL;

}



static const struct bpf_func_proto bpf_skb_get_xfrm_state_proto = {

	.func		= bpf_skb_get_xfrm_state,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_CTX,

	.arg2_type	= ARG_ANYTHING,

	.arg3_type	= ARG_PTR_TO_UNINIT_MEM,

	.arg4_type	= ARG_CONST_SIZE,

	.arg5_type	= ARG_ANYTHING,

};

#endif



static const struct bpf_func_proto *

bpf_base_func_proto(enum bpf_func_id func_id)

{
@@ -3884,6 +3928,10 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_get_socket_cookie_proto;

	case BPF_FUNC_get_socket_uid:

		return &bpf_get_socket_uid_proto;

#ifdef CONFIG_XFRM

	case BPF_FUNC_skb_get_xfrm_state:

		return &bpf_skb_get_xfrm_state_proto;

#endif

	default:

		return bpf_base_func_proto(func_id);

	}

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