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
20 const char tcp_mem_name[] = "net/ipv4/tcp_mem/very_very_very_very_long_pointless_string";
21 static __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
40 SEC("cgroup/sysctl")
41 int 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
73 char _license[] SEC("license") = "GPL";
74
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