| 1 | /* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me> |
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| 2 | * |
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| 3 | * This program is free software; you can redistribute it and/or |
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| 4 | * modify it under the terms of version 2 of the GNU General Public |
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| 5 | * License as published by the Free Software Foundation. |
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| 6 | */ |
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| 7 | #include "vmlinux.h" |
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| 8 | #include <string.h> |
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| 9 | #include <linux/version.h> |
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| 10 | #include <bpf/bpf_helpers.h> |
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| 11 | #include <bpf/bpf_tracing.h> |
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| 12 | #include <bpf/bpf_core_read.h> |
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| 13 | |
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| 14 | struct { |
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| 15 | __uint(type, BPF_MAP_TYPE_HASH); |
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| 16 | __type(key, struct sockaddr_in); |
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| 17 | __type(value, struct sockaddr_in); |
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| 18 | __uint(max_entries, 256); |
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| 19 | } dnat_map SEC(".maps" ); |
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| 20 | |
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| 21 | /* kprobe is NOT a stable ABI |
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| 22 | * kernel functions can be removed, renamed or completely change semantics. |
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| 23 | * Number of arguments and their positions can change, etc. |
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| 24 | * In such case this bpf+kprobe example will no longer be meaningful |
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| 25 | * |
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| 26 | * This example sits on a syscall, and the syscall ABI is relatively stable |
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| 27 | * of course, across platforms, and over time, the ABI may change. |
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| 28 | */ |
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| 29 | SEC("ksyscall/connect" ) |
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| 30 | int BPF_KSYSCALL(bpf_prog1, int fd, struct sockaddr_in *uservaddr, |
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| 31 | int addrlen) |
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| 32 | { |
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| 33 | struct sockaddr_in new_addr, orig_addr = {}; |
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| 34 | struct sockaddr_in *mapped_addr; |
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| 35 | |
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| 36 | if (addrlen > sizeof(orig_addr)) |
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| 37 | return 0; |
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| 38 | |
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| 39 | if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), uservaddr) != 0) |
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| 40 | return 0; |
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| 41 | |
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| 42 | mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr); |
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| 43 | if (mapped_addr != NULL) { |
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| 44 | memcpy(dest: &new_addr, src: mapped_addr, n: sizeof(new_addr)); |
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| 45 | bpf_probe_write_user(uservaddr, &new_addr, |
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| 46 | sizeof(new_addr)); |
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| 47 | } |
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| 48 | return 0; |
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| 49 | } |
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| 50 | |
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| 51 | char _license[] SEC("license" ) = "GPL" ; |
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| 52 | u32 _version SEC("version" ) = LINUX_VERSION_CODE; |
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| 53 | |
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