54 lines
1.7 KiB
C
54 lines
1.7 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 <linux/skbuff.h>
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#include <linux/netdevice.h>
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#include <uapi/linux/bpf.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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struct bpf_map_def SEC("maps") dnat_map = {
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.type = BPF_MAP_TYPE_HASH,
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.key_size = sizeof(struct sockaddr_in),
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.value_size = sizeof(struct sockaddr_in),
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.max_entries = 256,
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};
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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("kprobe/sys_connect")
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int bpf_prog1(struct pt_regs *ctx)
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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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void *sockaddr_arg = (void *)PT_REGS_PARM2(ctx);
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int sockaddr_len = (int)PT_REGS_PARM3(ctx);
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if (sockaddr_len > sizeof(orig_addr))
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return 0;
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if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), sockaddr_arg) != 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(sockaddr_arg, &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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