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