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