CODEWITHSUNDEEP
c++pythonwebipc
Wingston Sharon
Wingston Sharon

Reputation: 1060

Python server script and C program communication Error

The objective of my application is to control some LEDs on my embedded target from the ethernet link. My embedded board supports lighttpd web server. From this web server, I can run python scripts that read to devices on my board no problem. The problem comes when I am trying to write to those devices. The lighttpd server is running as "www" group. My board's root user has no password. Any attempt i make to force the lighttpd server to run as root results in lighttpd not starting at all. So I made a C program to be called as a subprocess elevated to root via sudo from the python script.

my C program that controls the LEDs:

int main(int argc, char* args[]){   
string python_message = "";
bool quit = false;

while (!quit)
{
    cin >> python_message;  
    if (python_message == "quit"){
    quit = true;
    }else if (python_message == "1"){
        ledn(1,"1");    
    }else if (python_message == "2"){
        ledn(1,"0");
    }else {
    cout << "Huh?" << endl;
    }   
}   
return 0;
}

The python script that is in cgi-bin

import sys
import time

print "Blinking User LED Program"

import subprocess
proc = subprocess.Popen(["sudo","/usr/bin/slave"], stdin=subprocess.PIPE, stdout=subprocess.PIPE)

print "1"
proc.stdin.write("1\n")
time.sleep(.5)
print "0"
proc.stdin.write("0\n")
time.sleep(.5)

If i comment the proc.stdin and proc.stdout lines my program runs and gives me all the print statement outputs. When those lines are there i get a 500 server error.

Upvotes: 1

Views: 312

Answers (1)

John Zwinck
John Zwinck

Reputation: 249404

Ricardo Cárdenes's suggestion to change the ownership or permissions of the device is a good one, but if you can't do that, just make the Python script that lighttpd calls be a "setuid" script, meaning that lighttpd will invoke it as www but it will run as root.

I normally would not suggest making a script setuid (making a compiled C program setuid is a little less dangerous, maybe). But in your case you don't seem to be concerned about security (since you mentioned trying to run lighttpd as root), so I'd give it a shot. Just don't forget that your setuid script can then do anything it wants!

Upvotes: 1

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