root/tools/testing/selftests/bpf/progs/test_sysctl_prog.c

DEFINITIONS

1. is_tcp_mem
2. SEC

   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 /* 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 static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
  23 {
  24         char tcp_mem_name[] = "net/ipv4/tcp_mem";
  25         unsigned char i;
  26         char name[64];
  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")
  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         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";