Passing Commands into a Binary that runs a shell using a bash script

Question

New to bash scripting so having a little teething problem and was wondering if someone could clear up some trouble I'm having, I have a simple C file called test that creates a shell as seen below:

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

int main()
{
  execl("/bin/sh", "/bin/sh", (void *) NULL);
  perror("exec");
 return 1;
}

I want to create a bash script to execute this file which I have done below, but then on execution I then wish to send commands to the shell that the binary creates - is this possible I am trying the following to no avail:

#!bin/bash
/var/testfolder/test; # execute the test c file to spawn the shell
??? #don't know how to pass commands to the new shell created :(

This approach seems odd; a shell script that executes a C program that opens a different shell. What problem are you trying to solve? Maybe someone can suggest a better approach. — Hunter McMillen
– Hunter McMillen, Commented Mar 22, 2015 at 18:46
its for a piece of work at uni lecturer wants a script that shows how we exploited a program - I have run a series of Linux commands separately I want to consolidate them all into 1 script to automatically run the commands I used. In this case - the program provided creates a shell I then need to run appropriate commands in this shell and was hoping I could do this using a single script (I know its easier not to) — TIMMY
– TIMMY, Commented Mar 22, 2015 at 18:53
Where does the C program come into that equation? A script to run a series of commands in sequence is just the commands in sequence in the file. Why involve this C program at all? — Etan Reisner
– Etan Reisner, Commented Mar 22, 2015 at 18:59
Are you trying to generate a shell commands into a file and then execute generated shell file? You just have to chmod u+x <generated script file> and then execute it with ./<generated script file>if it's generated in the current directory. This script will run on a child shell process. — Sylvain Bugat
– Sylvain Bugat, Commented Mar 22, 2015 at 18:59
Forget my previous comment I think this explains better: I have been given a C program with root permissions for example, it runs a shell - I want a bash script to firstly run the C program (which I can do) and then pass commands to the bash shell it generates (which I cannot seem to work out) — TIMMY
– TIMMY, Commented Mar 22, 2015 at 19:04

Sylvain Bugat · Accepted Answer · 2015-03-22 19:59:28Z

1

Your compiled C binary has the SETUID permission i suppose? With the binary and arguments you can execute any shell like this with this binary permission:

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

int main( int argc, char ** argv )
{
    execv("/bin/sh", argv );
    perror("exec");
    return 1;
}

Output of a test script to print arguments and current process:

$ ./test_execv ./test.sh foo bar
Executing $0: ./test.sh
Args $*: foo bar
process:
  PID TTY          TIME CMD
 3300 pts/1    00:00:08 bash
 3498 pts/1    00:00:00 sh
 3499 pts/1    00:00:00 ps

Security issue
If you can execute a script to a root shell, anyone can do this. I think you just have to add some of your scripts (only those needed) with a sudo permission to be run as root from your the needed account.

answered Mar 22, 2015 at 19:59

Sylvain Bugat

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Comments

Danogentili · Accepted Answer · 2015-03-22 22:26:37Z

0

Try this:

#!/bin/bash
/var/testfolder/test <<EOF
cmdtopass1
cmdtopass2
cmdtopass3
EOF

answered Mar 22, 2015 at 22:26

Danogentili

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