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// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2019 Facebook
#include <stdint.h>
#include <string.h>
#include <linux/stddef.h>
#include <linux/bpf.h>
#include "bpf_helpers.h"
#ifndef ARRAY_SIZE
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
#endif
/* tcp_mem sysctl has only 3 ints, but this test is doing TCP_MEM_LOOPS */
#define TCP_MEM_LOOPS 28 /* because 30 doesn't fit into 512 bytes of stack */
#define MAX_ULONG_STR_LEN 7
#define MAX_VALUE_STR_LEN (TCP_MEM_LOOPS * MAX_ULONG_STR_LEN)
static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
{
volatile char tcp_mem_name[] = "net/ipv4/tcp_mem/very_very_very_very_long_pointless_string";
unsigned char i;
char name[64];
int ret;
memset(name, 0, sizeof(name));
ret = bpf_sysctl_get_name(ctx, name, sizeof(name), 0);
if (ret < 0 || ret != sizeof(tcp_mem_name) - 1)
return 0;
#pragma clang loop unroll(disable)
for (i = 0; i < sizeof(tcp_mem_name); ++i)
if (name[i] != tcp_mem_name[i])
return 0;
return 1;
}
SEC("cgroup/sysctl")
int sysctl_tcp_mem(struct bpf_sysctl *ctx)
{
unsigned long tcp_mem[TCP_MEM_LOOPS] = {};
char value[MAX_VALUE_STR_LEN];
unsigned char i, off = 0;
/* a workaround to prevent compiler from generating
* codes verifier cannot handle yet.
*/
volatile int ret;
if (ctx->write)
return 0;
if (!is_tcp_mem(ctx))
return 0;
ret = bpf_sysctl_get_current_value(ctx, value, MAX_VALUE_STR_LEN);
if (ret < 0 || ret >= MAX_VALUE_STR_LEN)
return 0;
#pragma clang loop unroll(disable)
for (i = 0; i < ARRAY_SIZE(tcp_mem); ++i) {
ret = bpf_strtoul(value + off, MAX_ULONG_STR_LEN, 0,
tcp_mem + i);
if (ret <= 0 || ret > MAX_ULONG_STR_LEN)
return 0;
off += ret & MAX_ULONG_STR_LEN;
}
return tcp_mem[0] < tcp_mem[1] && tcp_mem[1] < tcp_mem[2];
}
char _license[] SEC("license") = "GPL";
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