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_helpers.h"
11 #include "bpf_util.h"
12 
13 /* Max supported length of a string with unsigned long in base 10 (pow2 - 1). */
14 #define MAX_ULONG_STR_LEN 0xF
15 
16 /* Max supported length of sysctl value string (pow2). */
17 #define MAX_VALUE_STR_LEN 0x40
18 
19 static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
20 {
21 	char tcp_mem_name[] = "net/ipv4/tcp_mem";
22 	unsigned char i;
23 	char name[64];
24 	int ret;
25 
26 	memset(name, 0, sizeof(name));
27 	ret = bpf_sysctl_get_name(ctx, name, sizeof(name), 0);
28 	if (ret < 0 || ret != sizeof(tcp_mem_name) - 1)
29 		return 0;
30 
31 #pragma clang loop unroll(full)
32 	for (i = 0; i < sizeof(tcp_mem_name); ++i)
33 		if (name[i] != tcp_mem_name[i])
34 			return 0;
35 
36 	return 1;
37 }
38 
39 SEC("cgroup/sysctl")
40 int sysctl_tcp_mem(struct bpf_sysctl *ctx)
41 {
42 	unsigned long tcp_mem[3] = {0, 0, 0};
43 	char value[MAX_VALUE_STR_LEN];
44 	unsigned char i, off = 0;
45 	int ret;
46 
47 	if (ctx->write)
48 		return 0;
49 
50 	if (!is_tcp_mem(ctx))
51 		return 0;
52 
53 	ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN);
54 	if (ret < 0 || ret >= MAX_VALUE_STR_LEN)
55 		return 0;
56 
57 #pragma clang loop unroll(full)
58 	for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) {
59 		ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0,
60 				  tcp_mem + i);
61 		if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
62 			return 0;
63 		off += ret & MAX_ULONG_STR_LEN;
64 	}
65 
66 
67 	return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2];
68 }
69 
70 char _license[] SEC("license") = "GPL";
71