1// SPDX-License-Identifier: GPL-2.0
2// Copyright (c) 2019 Facebook
3
4#include <stdint.h>
5#include <string.h>
6
7#include <linux/stddef.h>
8#include <linux/bpf.h>
9
10#include <bpf/bpf_helpers.h>
11
12#include "bpf_compiler.h"
13
14#ifndef ARRAY_SIZE
15#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
16#endif
17
18/* tcp_mem sysctl has only 3 ints, but this test is doing TCP_MEM_LOOPS */
19#define TCP_MEM_LOOPS 28  /* because 30 doesn't fit into 512 bytes of stack */
20#define MAX_ULONG_STR_LEN 7
21#define MAX_VALUE_STR_LEN (TCP_MEM_LOOPS * MAX_ULONG_STR_LEN)
22
23const char tcp_mem_name[] = "net/ipv4/tcp_mem/very_very_very_very_long_pointless_string";
24static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
25{
26	unsigned char i;
27	char name[sizeof(tcp_mem_name)];
28	int ret;
29
30	memset(name, 0, sizeof(name));
31	ret = bpf_sysctl_get_name(ctx, name, sizeof(name), 0);
32	if (ret < 0 || ret != sizeof(tcp_mem_name) - 1)
33		return 0;
34
35	__pragma_loop_no_unroll
36	for (i = 0; i < sizeof(tcp_mem_name); ++i)
37		if (name[i] != tcp_mem_name[i])
38			return 0;
39
40	return 1;
41}
42
43SEC("cgroup/sysctl")
44int sysctl_tcp_mem(struct bpf_sysctl *ctx)
45{
46	unsigned long tcp_mem[TCP_MEM_LOOPS] = {};
47	char value[MAX_VALUE_STR_LEN];
48	unsigned char i, off = 0;
49	/* a workaround to prevent compiler from generating
50	 * codes verifier cannot handle yet.
51	 */
52	volatile int ret;
53
54	if (ctx->write)
55		return 0;
56
57	if (!is_tcp_mem(ctx))
58		return 0;
59
60	ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN);
61	if (ret < 0 || ret >= MAX_VALUE_STR_LEN)
62		return 0;
63
64	__pragma_loop_no_unroll
65	for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) {
66		ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0,
67				  tcp_mem + i);
68		if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
69			return 0;
70		off += ret & MAX_ULONG_STR_LEN;
71	}
72
73	return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2];
74}
75
76char _license[] SEC("license") = "GPL";
77