[SOLVED] Bash question

goodhombre · 06-25-2017, 11:39 AM

Hi Guys,

I wonder if somebody can help me to figure this out. A program receives some input from the user and spawns a bash shell.

Code:

#include <stdlib.h>
#include <stdio.h>

/*
gcc -m32 -o test_shell  test_shell.c  
*/


int main()
{
  char buf[40];
  printf("\nGive the input:");
  fgets(buf,40,stdin);
  printf("\n[buf]: %s\n", buf);
  system("/bin/bash");
  printf("Shell closed! Bye.\n");
  return 0;
}

the problem I cannot sort out is that I cannot interact wit the new shell when I'm providing user input using pipes :

Code:

echo aaa |  ./test_shell

It just open the new shell and close it right away .

Code:

root@kali:/tmp# echo -n 'aaa' |  ./test_shell

Give the input:
[buf]: aaa

Shell closed! Bye.

The C code cannot be changed.

Thanks.

NevemTeve · 06-25-2017, 12:36 PM

What do you wish to happen? What do you wish to achieve with this program?

Laserbeak · 06-25-2017, 12:45 PM

Yes, please explain further what your goal is.

In any case, I think the C has to be changed.

rigor · 06-25-2017, 12:48 PM

Hi goodhombre!

Generally:

when bash is run interactively, there's often some sort of terminal emulation session associated with it; when the terminal emulator is closed, the bash session ends.
With your test, the input to the bash is closed after the "aaa" is sent to bash.

It will stay open, if instead it is tested like this:

Code:

while read a_line; do echo $a_line; done | test_shell

Hi!
Give the input:
[buf]: Hi!

Shell is still open, but C program won't echo any more lines because it is not looping, looking for additional input.

I compiled your test_shell.c program, and the above is the actual output, the shell session stays open.

But I do have to wonder what you think you will be able to accomplish with the C program, exactly as it is. The C program isn't going to be able to read any more input, unless it loops, or some such, looking for more input.

goodhombre · 06-25-2017, 02:26 PM

Thanks rigor a lot,

I adjusted a little bit and it worked perfectly.

Code:

root@kali:b="aaaaaa";while read a_line; do printf $b; echo $a_line;b=''; done | ./test_shell


Give the input:
[buf]: aaaaaa

whoami
printf: usage: printf [-v var] format [arguments]
root
cat test_shell.c
printf: usage: printf [-v var] format [arguments]
#include <stdlib.h>
#include <stdio.h>

/*
gcc -m32 -o test_shell  test_shell.c  
*/


int main()
{...........................

The C program was a simplified version I wrote to be easier to explain what I need to do.

The idea was the I had to feed the input for fgets from command line so I can format it properly, there were some dodgy chars I had to write them in hex .

Thanks rigor a lot .