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Alexey Novikov 2025-02-07 13:32:34 +03:00
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3
.gitignore vendored Normal file
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pinger_bpf*
cursed-ping
result

60
flake.lock generated Normal file
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{
"nodes": {
"flake-utils": {
"inputs": {
"systems": "systems"
},
"locked": {
"lastModified": 1731533236,
"narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
"owner": "numtide",
"repo": "flake-utils",
"rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
"type": "github"
},
"original": {
"owner": "numtide",
"repo": "flake-utils",
"type": "github"
}
},
"nixpkgs": {
"locked": {
"lastModified": 1738680400,
"narHash": "sha256-ooLh+XW8jfa+91F1nhf9OF7qhuA/y1ChLx6lXDNeY5U=",
"owner": "NixOS",
"repo": "nixpkgs",
"rev": "799ba5bffed04ced7067a91798353d360788b30d",
"type": "github"
},
"original": {
"id": "nixpkgs",
"ref": "nixos-unstable",
"type": "indirect"
}
},
"root": {
"inputs": {
"flake-utils": "flake-utils",
"nixpkgs": "nixpkgs"
}
},
"systems": {
"locked": {
"lastModified": 1681028828,
"narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
"owner": "nix-systems",
"repo": "default",
"rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
"type": "github"
},
"original": {
"owner": "nix-systems",
"repo": "default",
"type": "github"
}
}
},
"root": "root",
"version": 7
}

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flake.nix Normal file
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{
description = "cursed ping";
inputs = {
nixpkgs.url = "nixpkgs/nixos-unstable";
flake-utils.url = "github:numtide/flake-utils";
};
outputs = {
self,
nixpkgs,
flake-utils,
...
}:
{
overlays.default = final: prev: {
inherit (self.packages.${prev.system}) bpf2go;
};
} // flake-utils.lib.eachDefaultSystem (system: let
pkgs = import nixpkgs {
inherit system;
overlays = [ self.overlays.default ];
};
in {
packages = {
bpf2go = pkgs.buildGoModule rec {
pname = "bpf2go";
version = "0.17.2";
src = pkgs.fetchFromGitHub {
owner = "cilium";
repo = "ebpf";
rev = "v${version}";
hash = "sha256-lIJsITwdt6PuTMEHXJekBKM2rgCdPJF+i+QHt0jBgp8=";
};
vendorHash = "sha256-Ygljpp5GVM2EbD51q1ufqA6z5yJnrXVEfVLIPrxfm18=";
subPackages = [ "cmd/bpf2go" ];
doCheck = false;
};
pinger = pkgs.buildGoModule rec {
pname = "cursed-ping";
version = "1";
src = ./.;
vendorHash = "sha256-RxmMgiMATpO31VP85dlkOXl/nLbVD5W1dfWHhuGKcME=";
deleteVendor = true;
ldflags = ["-s -w"];
env.CGO_ENABLED = 0;
nativeBuildInputs = with pkgs; [clang bpftools libllvm linuxHeaders bpf2go glibc_multi libbpf];
hardeningDisable = [ "all" ];
buildInputs = nativeBuildInputs;
postConfigure = ''
go generate ./...
'';
meta = with pkgs.lib; {
description = "cursed ping";
license = licenses.wtfpl;
};
};
};
formatter = pkgs.alejandra;
});
}

3
gen.go Normal file
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package main
//go:generate bpf2go pinger xdp.c

8
go.mod Normal file
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module github.com/x3lfyn/cursed-ping
go 1.23.3
require (
github.com/cilium/ebpf v0.17.1 // indirect
golang.org/x/sys v0.26.0 // indirect
)

4
go.sum Normal file
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github.com/cilium/ebpf v0.17.1 h1:G8mzU81R2JA1nE5/8SRubzqvBMmAmri2VL8BIZPWvV0=
github.com/cilium/ebpf v0.17.1/go.mod h1:vay2FaYSmIlv3r8dNACd4mW/OCaZLJKJOo+IHBvCIO8=
golang.org/x/sys v0.26.0 h1:KHjCJyddX0LoSTb3J+vWpupP9p0oznkqVk/IfjymZbo=
golang.org/x/sys v0.26.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=

56
main.go Normal file
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package main
import (
"errors"
"fmt"
"log"
"net"
"os"
"os/signal"
"github.com/cilium/ebpf"
"github.com/cilium/ebpf/link"
)
func main() {
if len(os.Args) < 2 {
log.Fatalf("specify a network interface")
}
ifaceName := os.Args[1]
iface, err := net.InterfaceByName(ifaceName)
if err != nil {
log.Fatalf("lookup network iface %q: %s", ifaceName, err)
}
var objs pingerObjects
if err := loadPingerObjects(&objs, nil); err != nil {
var verr *ebpf.VerifierError
if errors.As(err, &verr) {
fmt.Printf("%+v\n", verr)
}
}
defer objs.Close()
link, err := link.AttachXDP(link.XDPOptions{
Program: objs.Pinger,
Interface: iface.Index,
})
if err != nil {
log.Fatal("attaching XDP:", err)
}
defer link.Close()
log.Printf("attached to %s", ifaceName)
stop := make(chan os.Signal, 5)
signal.Notify(stop, os.Interrupt)
for {
select {
case <-stop:
log.Print("received signal, exiting..")
return
}
}
}

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xdp.c Normal file
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#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/bpf.h>
#include <linux/icmp.h>
#include <bpf/bpf_helpers.h>
#include <linux/in.h>
#include <bpf/bpf_endian.h>
#define bpf_memcpy __builtin_memcpy
__attribute__((__always_inline__)) static inline __u16 csum_fold_helper(
__u64 csum) {
int i;
#pragma unroll
for (i = 0; i < 4; i++) {
if (csum >> 16)
csum = (csum & 0xffff) + (csum >> 16);
}
return ~csum;
}
// https://github.com/AirVantage/sbulb/blob/master/sbulb/bpf/checksum.c#L21
__attribute__((__always_inline__))
static inline void update_csum(__u64 *csum, __be32 old_addr,__be32 new_addr ) {
// ~HC
*csum = ~*csum;
*csum = *csum & 0xffff;
// + ~m
__u32 tmp;
tmp = ~old_addr;
*csum += tmp;
// + m
*csum += new_addr;
// then fold and complement result !
*csum = csum_fold_helper(*csum);
}
__attribute__((__always_inline__))
static inline void recalc_icmp_csum(struct icmphdr* hdr, __be32 old_value, __be32 new_value) {
__u64 csum = hdr->checksum;
update_csum(&csum, old_value, new_value);
hdr->checksum = csum;
}
__attribute__((__always_inline__))
static inline void recalc_ip_csum(struct iphdr* hdr, __be32 old_value, __be32 new_value) {
__u64 csum = hdr->check;
update_csum(&csum, old_value, new_value);
hdr->check = csum;
}
SEC("xdp")
int pinger(struct xdp_md* ctx) {
void *data_end = (void *)(long)ctx->data_end;
void *data = (void *)(long)ctx->data;
struct ethhdr *eth = data;
if ((void *)(eth + 1) > data_end) {
return XDP_PASS;
}
if (bpf_ntohs(eth->h_proto) != ETH_P_IP) {
return XDP_PASS;
}
struct iphdr *iph = (void*)(eth + 1);
if ((void*)(iph + 1) > data_end) {
return XDP_PASS;
}
if (iph->protocol != IPPROTO_ICMP) {
return XDP_PASS;
}
struct icmphdr* icmphdr = (void*)(iph + 1);
if ((void*)(icmphdr + 1) > data_end) {
return XDP_PASS;
}
if (icmphdr->type != 8) {
return XDP_PASS;
}
__u8 tmp_mac[ETH_ALEN];
bpf_memcpy(tmp_mac, eth->h_dest, ETH_ALEN);
bpf_memcpy(eth->h_dest, eth->h_source, ETH_ALEN);
bpf_memcpy(eth->h_source, tmp_mac, ETH_ALEN);
__u32 tmp_ip = iph->daddr;
iph->daddr = iph->saddr;
iph->saddr = tmp_ip;
icmphdr->type = 0;
recalc_icmp_csum(icmphdr, 8, icmphdr->type);
__u64* ts_secs = (void*)(icmphdr + 1);
__u64* ts_nsecs = (void*)(icmphdr + 1) + sizeof(__u64);
if ((void*)ts_nsecs + sizeof(__u64) <= data_end) {
__u64 old_secs = *ts_secs;
__u64 old_nsecs = *ts_nsecs;
*ts_secs -= bpf_get_prandom_u32() % 500;
*ts_nsecs -= bpf_get_prandom_u32();
recalc_icmp_csum(icmphdr, old_secs, *ts_secs);
recalc_icmp_csum(icmphdr, old_nsecs, *ts_nsecs);
}
__u8 old_ttl = iph->ttl;
iph->ttl = bpf_get_prandom_u32() % 200 + 40;
recalc_ip_csum(iph, old_ttl, iph->ttl);
__be16 old_seq = icmphdr->un.echo.sequence;
icmphdr->un.echo.sequence = bpf_htons(bpf_get_prandom_u32() % 1000);
recalc_icmp_csum(icmphdr, old_seq, icmphdr->un.echo.sequence);
return XDP_TX;
}
char LICENSE[] SEC("license") = "GPL";