Re: "random" number seeds vs. Netscape

Perry said:
> 
> Also be especially careful about how you run the thing! Don't use
> popen or anything like it!

There's nothing inherently wrong with using popen or system.  The problem
arises when you use information given to you from outside as the argument
to popen or system without checking it.  You should have an awareness that
whatever you pass to system or popen is essentially being passed as the
commandstring to a:

    execl("/bin/sh", "sh", "-c", commandstring, (char *)0);

Make sure you know the implications of this.  If you know that what you're
passing can happily be exec'd directly, it's more efficient to do an exec 
yourself instead of (effectively) having a sh exec'd to exec your code.
Of course you can see that you shouldn't do something like:

    cout << "Enter the directory to list: " 
    cin >> buffer;
    system(buffer);

especially if you're running with any sort of priviledges.  Suppose someone
entered:

    / ; echo >>/etc/passwd "gotcha::0:0:Intruder Man:/:/sbin/sh

Obviously if this program was being run as root you'd be in trouble.
If it was running as a user it would let them do something like add
an .rhosts for the user that would let them get on the machine.  Once
on a machine it's often fairly easy to leverage that access into root
access.

Oh well, I could talk about security all day:)

Patrick
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Patrick Horgan writes:
> Perry said:
> > 
> > Also be especially careful about how you run the thing! Don't use
> > popen or anything like it!
> 
> There's nothing inherently wrong with using popen or system.

Nor is there anything inherently wrong with having sex without the use
of a condom.

However, it is very difficult -- VERY DIFFICULT -- to prove to
yourself that there is never an instance in which your system() or
popen() can be abused. In any case, I find its often more prudent just
to strip all these things out of my code. If you don't use them, you
don't have to prove they are done properly. Paranoia is your
friend. No one can ever break you for doing something you don't do.

> The problem arises when you use information given to you from
> outside as the argument to popen or system without checking it.

Yup, but often, you'd be suprised what turns out to be outside data.

In any case, you obviously also understand why this is bad, but I hope
that people out there understan -- always make sure that you are
double extra careful about the use of such calls.

Perry