fntlnz

ELF Format Cheatsheet

Introduction

Executable and Linkable Format (ELF), is the default binary format on Linux-based systems.

Compilation

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Compile with gcc
gcc -nostdlib main.c 

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The eBPF verifier

Important: This article was written by Github Copilot, while it's not entirely accurate, it's quite good to see what it ended up with.

The bpf verifier is a tool that can be used to check the correctness of eBPF programs. It is implemented in C and is used by the kernel. When the kernel is built with CONFIG_BPF_JIT, it does further optimization on the BPF programs.

To write a valid eBPF program you need to follow a few rules:

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Flux as a Library Example

Flux is a lightweight scripting language for querying databases (like InfluxDB) and working with data. It's part of InfluxDB 1.7 and 2.0, but can be run independently of those.

This gist contains a main.go file that shows how flux can be used as a library in your programs.

Components

The main components you need are:

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Seccomp BPF filter example

Use bpf programs as filters for seccomp, the one in the example will block all the write syscalls after it's loaded.

Usage

Compile it with just

gcc main.c

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#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/ip.h>

#define SEC(NAME) __attribute__((section(NAME), used))

SEC("dropper_main")
int dropper(struct xdp_md *ctx) {
  int ipsize = 0;

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[[constraint]]
  name = "k8s.io/api"
  version = "kubernetes-1.11.0"

[[constraint]]
  name = "k8s.io/apimachinery"
  version = "kubernetes-1.11.0"

[[constraint]]
  name = "k8s.io/client-go"

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InfluxDB and Chronograf in Kubernetes

1. Create the namespace

kubectl create ns monitoring

2. Deploy influxdb

kubectl apply -f influxdb.yml

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1. Calculate the offset

offset(fn) = virtual_address(fn) - virtual_address(.text) + offset(.text)


2. Virtual address: 
readelf -S /home/fntlnz/go/bin/influx | grep -i text
  [ 1] .text             PROGBITS         0000000000401000  00001000

So, virtual address= 0x0000000000401000

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docker service create --mode global --mount type=volume,volume-opt=o=addr=10.3.20.25,volume-opt=device=:/share/poc1/pluto,volume-opt=type=nfs,source=pluto,target=/pluto --name nfstest alpine top