/*
**  Copyright (C) 2013 - Jonathan Salwan - http://twitter.com/JonathanSalwan
** 
**  This program is free software: you can redistribute it and/or modify
**  it under the terms of the GNU General Public License as published by
**  the Free Software Foundation, either version 3 of the License, or
**  (at your option) any later version.
** 
**  This program is distributed in the hope that it will be useful,
**  but WITHOUT ANY WARRANTY; without even the implied warranty of
**  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
**  GNU General Public License for more details.
**
**  You should have received a copy of the GNU General Public License
**  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
#include <elf.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <stdlib.h>
Elf32_Ehdr    *pElf_Header;
Elf32_Phdr    *pElf32_Phdr;
Elf32_Shdr    *pElf32_Shdr;
char          *pMapElf;
struct stat   filestat;
static unsigned char *set_header(char *file)
{
  int fd;
  unsigned char *data;
  fd = open(file, O_RDONLY, 0644);
  stat(file, &filestat);
  printf("[+] Binary size : %d octets\n", (int)filestat.st_size);
  data = malloc(filestat.st_size * sizeof(char));
  read(fd, data, filestat.st_size);
  pMapElf = mmap(0, filestat.st_size, PROT_READ, MAP_SHARED, fd, 0);
  pElf_Header = (Elf32_Ehdr *)data;
  pElf32_Shdr = (Elf32_Shdr *)((char *)data + pElf_Header->e_shoff);
  pElf32_Phdr = (Elf32_Phdr *)((char *)data + pElf_Header->e_phoff);
  close(fd);
  return (data);
}
int main(int argc, char **argv)
{
  unsigned char *data;
  unsigned nb_section;
  Elf32_Shdr *current;
  int i, fd;
  if (argc < 2){
    printf("Syntax: ./%s <bin>\n", argv[0]);
    return -1;
  }
  data = set_header(argv[1]);
  printf("--- Step 1 ---\n");
  printf("[+] Clean sections...\n");
  nb_section = pElf_Header->e_shnum;
  for (i = 0 ; i < nb_section ; i++){
    pElf32_Shdr->sh_name = 0;
    pElf32_Shdr->sh_type = 0;
    pElf32_Shdr->sh_flags = 0;
    pElf32_Shdr->sh_addr = 0;
    pElf32_Shdr->sh_offset = 0;
    pElf32_Shdr->sh_size = 0;
    pElf32_Shdr->sh_link = 0;
    pElf32_Shdr->sh_info = 0;
    pElf32_Shdr->sh_addralign = 0;
    pElf32_Shdr->sh_entsize = 0;
    pElf32_Shdr++;
  }
  printf("[+] Clean section [DONE]\n");
  printf("--- Step 2 ---\n");
  printf("[+] Clean elf header...\n");
  pElf_Header->e_shnum = 0;
  pElf_Header->e_shstrndx = 0;
  pElf_Header->e_shentsize = 0;
  pElf_Header->e_version = 0;
  pElf_Header->e_ehsize = 0;
  pElf_Header->e_shoff = 123;
  printf("[+] Clean elf header [DONE]\n");
  printf("--- Step 3 ---\n");
  printf("[+] Writting binary...\n");
  fd = open(argv[1], O_WRONLY, 0644);
  write(fd, data, filestat.st_size);
  close(fd);
  printf("[+] Writting binary [DONE]\n");
  free(data);
  return 0;
}

#include <stdio.h>
int main()
{
	printf("Hello World\n");
	return 0;
}

./hello_world
Hello World
file hello_world
hello_world: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=0x76996acaebdeb479499ffdafe8dc7392c907a342, not stripped
readelf -t hello_world
There are 30 section headers, starting at offset 0x113c:
Section Headers:
  [Nr] Name
       Type            Addr     Off    Size   ES   Lk Inf Al
       Flags
  [ 0] 
       NULL            00000000 000000 000000 00   0   0  0
       [00000000]: 
  [ 1] .interp
       PROGBITS        08048154 000154 000013 00   0   0  1
       [00000002]: ALLOC
  [ 2] .note.ABI-tag
       NOTE            08048168 000168 000020 00   0   0  4
       [00000002]: ALLOC
  [ 3] .note.gnu.build-id
       NOTE            08048188 000188 000024 00   0   0  4
       [00000002]: ALLOC
  [ 4] .gnu.hash
       GNU_HASH        080481ac 0001ac 000020 04   5   0  4
       [00000002]: ALLOC
...
ELF HEADER:
e_ident:		7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
e_ident[EI_CLASS]:	ELFCLASS32
e_ident[EI_DATA]:	ELFDATA2LSB
e_ident[EI_VERSION]:	EV_CURRENT
e_ident[EI_OSABI]:	ELFOSABI_SYSV
e_ident[EI_ABIVERSION]:	0x0
e_type:			ET_EXEC
e_machine:		EM_386
e_version:		EV_CURRENT
e_entry:		0x08048320
e_phoff:		0x00000034	(52)
e_shoff:		0x0000113c	(4412)
e_ehsize:		0x00000034	(52)
e_phentsize:		0x00000020	(32)
e_phnum:		0x00000009	(9)
e_shentsize:		0x00000028	(40)
e_shnum:		0x0000001e	(30)
e_shstrndx:		0x0000001b	(27)

./hello_world
Hello World
file hello_world 
hello_world_2: ELF 32-bit LSB executable, Intel 80386, invalid version (SYSV), for GNU/Linux 2.6.24, dynamically linked (uses shared libs), corrupted section header size
readelf -t hello_world
There are no sections in this file.
ELF HEADER:
e_ident:		7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
e_ident[EI_CLASS]:	ELFCLASS32
e_ident[EI_DATA]:	ELFDATA2LSB
e_ident[EI_VERSION]:	EV_CURRENT
e_ident[EI_OSABI]:	ELFOSABI_SYSV
e_ident[EI_ABIVERSION]:	0x0
e_type:			ET_EXEC
e_machine:		EM_386
e_version:		EV_NONE
e_entry:		0x08048320
e_phoff:		0x00000034	(52)
e_shoff:		0x00000000	(0)
e_ehsize:		0x00000000	(0)
e_phentsize:		0x00000020	(32)
e_phnum:		0x00000009	(9)
e_shentsize:		0x00000000	(0)
e_shnum:		0x00000000	(0)
e_shstrndx:		0x00000000	(0)