53 lines
1.6 KiB
C
53 lines
1.6 KiB
C
/* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*/
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#include "vmlinux.h"
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#include <string.h>
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#include <linux/version.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_core_read.h>
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struct {
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__uint(type, BPF_MAP_TYPE_HASH);
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__type(key, struct sockaddr_in);
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__type(value, struct sockaddr_in);
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__uint(max_entries, 256);
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} dnat_map SEC(".maps");
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/* kprobe is NOT a stable ABI
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* kernel functions can be removed, renamed or completely change semantics.
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* Number of arguments and their positions can change, etc.
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* In such case this bpf+kprobe example will no longer be meaningful
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*
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* This example sits on a syscall, and the syscall ABI is relatively stable
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* of course, across platforms, and over time, the ABI may change.
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*/
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SEC("ksyscall/connect")
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int BPF_KSYSCALL(bpf_prog1, int fd, struct sockaddr_in *uservaddr,
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int addrlen)
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{
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struct sockaddr_in new_addr, orig_addr = {};
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struct sockaddr_in *mapped_addr;
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if (addrlen > sizeof(orig_addr))
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return 0;
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if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), uservaddr) != 0)
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return 0;
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mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr);
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if (mapped_addr != NULL) {
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memcpy(&new_addr, mapped_addr, sizeof(new_addr));
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bpf_probe_write_user(uservaddr, &new_addr,
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sizeof(new_addr));
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}
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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u32 _version SEC("version") = LINUX_VERSION_CODE;
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