Dilemma with Buffer overflow

Question

I was experimenting with a code described in the "Shell coders handbook" where you overflow a buffer and cause the same code to be executed twice...

void return_input (void)
{ char array[5]; 
  gets (array); 
  printf(“%s\n”, array); 
}
 main() 
 { 
  return_input();
  return 0; 
 }

The task was to overwrite the buffer and to replace the address of 'return 0' with the address of 'return_input()' so that the entered string is printed twice..

i compiled it as follows

gcc -fno-stack-protector overflow.c

to override the protection mechanisms. The problem is i cant get it to execute twice. in this case the address of the function ri() is at 0x08048440 . I gave the input as follows

./a.out
aaaaaaaaaaaaa\x40\x84\x04\x08

shouldnt this cause the function to be called twice?? It always returns

aaaaaaaaaaaaaaaa�� 
Segmentation fault (core dumped)

How can i overflow the buffer to call the function twice?

@BenGreen i am trying to learn by myself. If this question was assigned as a homework, the tutors would have already taught me how to run a basic exploit and then try out it on my own. or in english - I wouldnt have asked this question in the first place :) — Ray
– Ray, Commented Jun 1, 2013 at 11:37
@BenGreen the homework tag has been deprecated months ago and is now removed: meta.stackexchange.com/questions/147100/… — l4mpi
– l4mpi, Commented Jun 1, 2013 at 11:45

Community · Accepted Answer · 2017-05-23 12:11:20Z

1

\x40\x84\x04\x08 is not supported. You should use some other program to translate the hex input to bytes.

If you are using bash, you can try echo -e '\x40\x84\x04\x08' | ./a.out. I found that solution at linux shell scripting: hex string to bytes

edited May 23, 2017 at 12:11

CommunityBot

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answered Jun 1, 2013 at 11:23

Jiaming Lu

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Comments

Lee Daniel Crocker · Accepted Answer · 2013-06-01 11:21:47Z

0

By definition, the behavior of a buffer overflow is unpredictable. You will only get the same behavior if you happen to be using the same version of the same compiler with the same settings on the same OS, etc., etc.

answered Jun 1, 2013 at 11:21

Lee Daniel Crocker

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VAT69 · Accepted Answer · 2013-06-01 11:56:26Z

0

based on your machine type , you might need to adjust. http://www.tenouk.com/Bufferoverflowc/Bufferoverflow4.html

answered Jun 1, 2013 at 11:56

VAT69

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3 Comments

Ray Over a year ago

Thank you so very much for this information . It works!!!! I would like to learn more about this subject and would be greatly indebted to you if you can share more resource. Hope you would help. Thanka again ! :)

VAT69 Over a year ago

If the information was relevant , Please mark it as the answer.

VAT69 Over a year ago

This link should allow you to experiment and correct your code :users.ece.cmu.edu/~jprimero/Simulator.html. Copy paste your code above and see the execution in action.

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