[1485] in SIPB_Linux_Development
Re: /bin/athena/login
daemon@ATHENA.MIT.EDU (Theodore Y. Ts'o)
Mon Oct 21 10:49:16 1996
Date: Mon, 21 Oct 1996 10:48:35 -0400
From: "Theodore Y. Ts'o" <tytso@MIT.EDU>
To: Salvatore Valente <svalente@MIT.EDU>
Cc: warlord@MIT.EDU, linux-dev@MIT.EDU
In-Reply-To: Salvatore Valente's message of Sun, 20 Oct 1996 21:45:11 -0400,
<199610210145.VAA12182@cutter-john.mit.edu>
Date: Sun, 20 Oct 1996 21:45:11 -0400
Cc: linux-dev@MIT.EDU
From: Salvatore Valente <svalente@MIT.EDU>
I have no idea why vhangup() would cause login to exit. (The
documentation I've managed to find about vhangup() is unimpressive.)
(I didn't put that call into login, it was there in the source code
for Linux /bin/login at the time I added the Athena hacks to it.)
Vhangup() is a BSD 4.3-ism. What it does is force a virtual hangup on
the process's controlling tty. That means *all* filedescriptors on that
tty become revoked (reads return EOF, writes return EIO) and all
processes belonging to the tty's session receive a SIGHUP.
This is done to prevent trojan horse programs from retaining access to
the tty after the user logs out (to try to steal the next user's
passsword, etc.). Usually it's getty/telnetd/rlogind that calls
vhangup(), since they're the programs that initially get the tty,
chown/chmod it appropriately, etc.
- Ted
