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
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
is_tcp_mem(struct bpf_sysctl * ctx)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")
sysctl_tcp_mem(struct bpf_sysctl * ctx)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 int ret;
48
49 if (ctx->write)
50 return 0;
51
52 if (!is_tcp_mem(ctx))
53 return 0;
54
55 ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN);
56 if (ret < 0 || ret >= MAX_VALUE_STR_LEN)
57 return 0;
58
59 #pragma clang loop unroll(disable)
60 for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) {
61 ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0,
62 tcp_mem + i);
63 if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
64 return 0;
65 off += ret & MAX_ULONG_STR_LEN;
66 }
67
68 return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2];
69 }
70
71 char _license[] SEC("license") = "GPL";
72
