Commit b32cc5b9 authored by Nikita V. Shirokov's avatar Nikita V. Shirokov Committed by Daniel Borkmann
Browse files

bpf: adding bpf_xdp_adjust_tail helper 



Adding new bpf helper which would allow us to manipulate
xdp's data_end pointer, and allow us to reduce packet's size
indended use case: to generate ICMP messages from XDP context,
where such message would contain truncated original packet.

Signed-off-by: default avatarNikita V. Shirokov <tehnerd@tehnerd.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 0c90f224

include/uapi/linux/bpf.h

+9 −1
Original line number Diff line number Diff line
@@ -755,6 +755,13 @@ union bpf_attr { 
 *     @addr: pointer to struct sockaddr to bind socket to

 *     @addr_len: length of sockaddr structure

 *     Return: 0 on success or negative error code

 *

 * int bpf_xdp_adjust_tail(xdp_md, delta)

 *     Adjust the xdp_md.data_end by delta. Only shrinking of packet's

 *     size is supported.

 *     @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

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -821,7 +828,8 @@ union bpf_attr { 
	FN(msg_apply_bytes),		\

	FN(msg_cork_bytes),		\

	FN(msg_pull_data),		\

	FN(bind),

	FN(bind),			\

	FN(xdp_adjust_tail),



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

 * function eBPF program intends to call

net/core/filter.c

+28 −1
Original line number Diff line number Diff line
@@ -2725,6 +2725,30 @@ static const struct bpf_func_proto bpf_xdp_adjust_head_proto = { 
	.arg2_type	= ARG_ANYTHING,

};



BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)

{

	void *data_end = xdp->data_end + offset;



	/* only shrinking is allowed for now. */

	if (unlikely(offset >= 0))

		return -EINVAL;



	if (unlikely(data_end < xdp->data + ETH_HLEN))

		return -EINVAL;



	xdp->data_end = data_end;



	return 0;

}



static const struct bpf_func_proto bpf_xdp_adjust_tail_proto = {

	.func		= bpf_xdp_adjust_tail,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

	.arg1_type	= ARG_PTR_TO_CTX,

	.arg2_type	= ARG_ANYTHING,

};



BPF_CALL_2(bpf_xdp_adjust_meta, struct xdp_buff *, xdp, int, offset)

{

	void *meta = xdp->data_meta + offset;
@@ -3074,7 +3098,8 @@ bool bpf_helper_changes_pkt_data(void *func) 
	    func == bpf_l4_csum_replace ||

	    func == bpf_xdp_adjust_head ||

	    func == bpf_xdp_adjust_meta ||

	    func == bpf_msg_pull_data)

	    func == bpf_msg_pull_data ||

	    func == bpf_xdp_adjust_tail)

		return true;



	return false;
@@ -3888,6 +3913,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 
		return &bpf_xdp_redirect_proto;

	case BPF_FUNC_redirect_map:

		return &bpf_xdp_redirect_map_proto;

	case BPF_FUNC_xdp_adjust_tail:

		return &bpf_xdp_adjust_tail_proto;

	default:

		return bpf_base_func_proto(func_id);

	}

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