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Secure coding 2

Written by:	dimport
Published by:	Nightscript
Published on:	2003-06-21 07:19:46
Topic:	C

Search OSI about C.

More articles by dimport.

viewed 8278 times

Continuation of the Secure coding article that was published earlier.

system() vs exec()It is always more secure to use the exec command insted of the system call, becuse system spawns a shell that executes the whole string while exec only executes the first argument. Lets look at some source code:

int main(int argc, char *argv[]) {

  char buffer[30];

  snprintf(buffer, sizeof(buffer), "cat %s", argv[1]);

  system(buffer); }

Now, think about what would happen if they input "/etc/hosts ; rm -rf /etc/passwd" as argv[1] that would fuck things up a little right ? lets look at this:

...

execl("cat", "cat", argv[1], NULL);

Now whatever string we get it end up as an argument to cat, handy.Check the PATH/IFSConsider the code from the above example with a modified PATH and a modified cat, that could get kinda messy. So therefore you should always check the path before doing anything.The IFS is not very much better, here take a look at this example:

sol# cat > /tmp/bin

#!/bin/sh

IFS=" "

export IFS

echo "gotcha! i'm actually in /tmp"

sol# IFS="/"

sol# export IFS

sol# /bin/csh

gotcha! i'm actually in /tmp

sol#

I think you see the danger now.Keep it randomIf your program ever generates something random that will be used for something important, make sure it's really random and that you use a really good seed. Most def. random generations isn't really random numbers so, be carefull and BE paranoid it's never wrong ;)A great article of random number can be found

here

KEEP THE SETUID AWAYAnd if you really have to make sure you run as little code as necessary in setuid mode.

This article was originally written by shab

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Comments:

nomzz
2009-06-06 10:21:22

Thx for providing all that!
u may get some information from hdi certification
That data may help many people!

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