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