test_sockmap_change_tail.c

 1// SPDX-License-Identifier: GPL-2.0
 2/* Copyright (c) 2024 ByteDance */
 3#include "vmlinux.h"
 4#include <bpf/bpf_helpers.h>
 5
 6#ifndef PAGE_SIZE
 7#define PAGE_SIZE __PAGE_SIZE
 8#endif
 9#define BPF_SKB_MAX_LEN (PAGE_SIZE << 2)
10
11struct {
12	__uint(type, BPF_MAP_TYPE_SOCKMAP);
13	__uint(max_entries, 1);
14	__type(key, int);
15	__type(value, int);
16} sock_map_rx SEC(".maps");
17
18long change_tail_ret = 1;
19
20SEC("sk_skb")
21int prog_skb_verdict(struct __sk_buff *skb)
22{
23	char *data, *data_end;
24
25	bpf_skb_pull_data(skb, 1);
26	data = (char *)(unsigned long)skb->data;
27	data_end = (char *)(unsigned long)skb->data_end;
28
29	if (data + 1 > data_end)
30		return SK_PASS;
31
32	if (data[0] == 'T') { /* Trim the packet */
33		change_tail_ret = bpf_skb_change_tail(skb, skb->len - 1, 0);
34		return SK_PASS;
35	} else if (data[0] == 'G') { /* Grow the packet */
36		change_tail_ret = bpf_skb_change_tail(skb, skb->len + 1, 0);
37		return SK_PASS;
38	} else if (data[0] == 'E') { /* Error */
39		change_tail_ret = bpf_skb_change_tail(skb, BPF_SKB_MAX_LEN, 0);
40		return SK_PASS;
41	}
42	return SK_PASS;
43}
44
45char _license[] SEC("license") = "GPL";