Python: raw_input leaves stuff in input buffer?

Question

I have a python script that reads using raw_input and then opens a shell using system("sh"), e.g

r_input = raw_input('Enter the key\n')
system("sh")

I need to feed this script some binary data, which I do using print or sys.stdout.write, e.g.

python -c "import sys; sys.stdout.write('\x02\x03\x04')" | python ./input_parse.py

The problem is that despite that the input is read entirely, the shell exits immediately, as if it gets some leftover from the stdin. When I feed the script from the keyboard, it works, but I can't put binary data there, it is interpreted as string...

I tried subprocess, like this (but not much difference):

 python -c "import subprocess; process = subprocess.Popen(['python', 'input_parse.py], shell=False, stdin=subprocess.PIPE);process.stdin.write('hi')" | python ./py_deobf_input_parse.py

How can I get this to work?

Update: I have found a solution, maybe not ideal, but worked. Basically I used the same subprocess model, but had to add the \n to the end of my input. Then I did another process.stdin.write to pass the command to the opened shell. I had to add asleep between them, otherwise it was exiting immediately. I still will give a credit if someone finds a nicer answer.

python -c "import subprocess; import time; process = subprocess.Popen(['./py_input_parse'], stdin=subprocess.PIPE); process.stdin.write('\x02\x02\x02\x02\n'); process.stdin.flush(); time.sleep(2); process.stdin.write('cat ./flag.txt \n');

I don't know if this can help you, but I can do the following using the shell builtin printf: printf '\x02\x03\x04' | awk '{print length($0)}' -> 3 — gboffi
– gboffi, Commented Nov 23, 2014 at 15:07

Daniel · Accepted Answer · 2014-11-23 15:45:08Z

1

What do you expect? The stdin of your input_parse.py is the stdout of the writing script. As soon as you've read all your binary data, the stdin is finished. So calling a shell afterwards detects a closed stdin and terminates.

answered Nov 23, 2014 at 15:45

Daniel

42.9k4 gold badges57 silver badges82 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Moshe Kravchik Over a year ago

Thanks for the insight. Do you have a suggestion how to make it work? I've tried process.wait(), but it does not help

Eryk Sun Over a year ago

You want the shell's stdin to be the terminal instead of the pipe? Try p = subprocess.Popen(["sh"], stdin=open('/dev/tty')); p.wait()

Moshe Kravchik Over a year ago

I need to send the binary string to the script first.

Eryk Sun Over a year ago

My suggestion doesn't affect the incoming data on the pipe and raw_input statement. It replaces the subsequent system("sh") with a Popen instance in which stdin is redirected back to the terminal. But based on your last update I don't understand why you need to run sh. Surely it can't be just to execute cat.

Collectives™ on Stack Overflow

Python: raw_input leaves stuff in input buffer?

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related