getlogin() is not secure

[idallen () FREENET CARLETON CA (Ian! D. Allen [NCFreeNet])]

> From: Thamer Al-Herbish <shadows () WHITEFANG COM>  Jan  8, 17:36
> To be extra pedantic use getlogin() to double check. getlogin cannot
> lie unless you are root and did a setlogin().

> From "man getlogin" on my SuSE 5.2 Linux system:

   "getlogin returns a pointer to a string containing the name of the user
    logged in on the controlling terminal  of  the process,  or  a null
    pointer if this information cannot be determined."

I haven't tried this in years, but I used to be able to send mail from
anyone who was logged in by writing a little script that disconnected the
controlling terminal of my process and then pointed at the writable
terminal of someone currently online (thus adopting that terminal as the
controlling terminal of my process).  Then getlogin() would think I was them.

Terminals are less writable these days, of course, but I still won't
use getlogin() for anything.

I couldn't find "setlogin" under Linux or Solaris 2.6.

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-IAN!  Ian! D. Allen   Ottawa, Ontario, Canada   idallen () freenet carleton ca
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