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 /* Max supported length of a string with unsigned long in base 10 (pow2 - 1). */
13 #define MAX_ULONG_STR_LEN 0xF
14 
15 /* Max supported length of sysctl value string (pow2). */
16 #define MAX_VALUE_STR_LEN 0x40
17 
18 #ifndef ARRAY_SIZE
19 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
20 #endif
21 
22 const char tcp_mem_name[] = "net/ipv4/tcp_mem";
is_tcp_mem(struct bpf_sysctl * ctx)23 static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
24 {
25 	unsigned char i;
26 	char name[sizeof(tcp_mem_name)];
27 	int ret;
28 
29 	memset(name, 0, sizeof(name));
30 	ret = bpf_sysctl_get_name(ctx, name, sizeof(name), 0);
31 	if (ret < 0 || ret != sizeof(tcp_mem_name) - 1)
32 		return 0;
33 
34 #pragma clang loop unroll(full)
35 	for (i = 0; i < sizeof(tcp_mem_name); ++i)
36 		if (name[i] != tcp_mem_name[i])
37 			return 0;
38 
39 	return 1;
40 }
41 
42 SEC("cgroup/sysctl")
sysctl_tcp_mem(struct bpf_sysctl * ctx)43 int sysctl_tcp_mem(struct bpf_sysctl *ctx)
44 {
45 	unsigned long tcp_mem[3] = {0, 0, 0};
46 	char value[MAX_VALUE_STR_LEN];
47 	unsigned char i, off = 0;
48 	volatile int ret;
49 
50 	if (ctx->write)
51 		return 0;
52 
53 	if (!is_tcp_mem(ctx))
54 		return 0;
55 
56 	ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN);
57 	if (ret < 0 || ret >= MAX_VALUE_STR_LEN)
58 		return 0;
59 
60 #pragma clang loop unroll(full)
61 	for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) {
62 		ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0,
63 				  tcp_mem + i);
64 		if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
65 			return 0;
66 		off += ret & MAX_ULONG_STR_LEN;
67 	}
68 
69 
70 	return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2];
71 }
72 
73 char _license[] SEC("license") = "GPL";
74