[SOLVED] Assembly Ubuntu x86 segmentation fault

Issue

I've got the following assembly piece of code:

section .text
  global _start
    _start:
      ; Store the argument string on stack
      xor  eax, eax 
      push eax          ; Use 0 to terminate the string
      push "bash"
      mov al, 0x2f      ; Set "/" to the least significant byte of eax
      push eax          ; Add "/" onto the stack
      push "/bin"
      mov  ebx, esp     ; Get the string address

      ; Construct the argument array argv[]
      xor eax, eax      ; eax = 0x00000000
      push eax          ; argv[1] = 0
      push ebx          ; argv[0] points "/bin/bash"
      mov  ecx, esp     ; Get the address of argv[]
   
      ; For environment variable 
      xor  edx, edx     ; No env variables 

      ; Invoke execve()
      mov   al, 0x0b    ; eax = 0x0000000b
      int 0x80

It's supposed to call bash shell but it gives a segmentation fault after compiling to object code and linking to generate binary. OS Ubuntu x86. Thanks in advance!

Adding extra shashes is forbidden to complete this task.

Solution

Problem is the mov al, 0x2f; push eax which will push 4 bytes not 1. Try:

  push "h"
  push "/bas"
  push "/bin"
  mov  ebx, esp     ; Get the string address

Also make sure you create 32 bit binary.

Answered By - Jester

Answer Checked By - David Goodson (WPSolving Volunteer)