Guide to writing secure setuid programs?

[Patrick Barron]

In article <127 at heart-of-gold> jc at heart-of-gold (John M Chambers x7780 1E342) writes:
>Lest people think I am being facetious, I'd like to point out that there
>is an important point at work here.  When writing a program, I don't know
>whether it will be setuid.  So how can I follow the above advice? (Obviously, 
>by not writing any programs! :-)  When I write a line of code, how do I 
>determine whether it is in a setuid program?

   On the contrary, normally when one writes a program that is going to
have the set-uid bit set, one knows that for a fact before starting.  Taking
random programs that you know little or nothing about, and making them
set-uid, is an exceptionally bad idea.

>Can anyone show me the source for setuid()?  I suspect that you can't,

  No, I can't show you the source for setuid(), but only because my Ultrix
license agreement prohibits it.... :-)  Seriously, there really is a setuid()
system call.  It doesn't do what you want, though.

--Pat.