Path: utzoo!attcan!lsuc!sickkids!mark
From: mark@sickkids.UUCP (Mark Bartelt)
Newsgroups: comp.bugs.4bsd
Subject: Bug in chsh / passwd -s
Message-ID: <130@sickkids.UUCP>
Date: 9 Dec 88 18:04:32 GMT
Reply-To: mark@sickkids.UUCP (Mark Bartelt)
Organization: Hospital for Sick Children, Toronto
Lines: 23

A bug in passwd.c has the effect of making it possible to change one's
login shell from /bin/sh to /bin/csh, but not vice-versa.  (Unless one
swaps the order of /bin/sh and /bin/csh in /etc/shells, in which case
one has the reverse problem!)

In getloginshell(), there are two loops which call getusershell():

  for (valid = getusershell(); valid; valid = getusershell()) {

The first loop is used to confirm that the user who is invoking chsh (or
its equivalent, passwd -s) has an (old) login shell listed in /etc/shells;
the second is used to verify that the new shell chosen is valid.  The bug
and fix are obvious; change the second loop to begin:

  for (setusershell(), valid=getusershell(); valid; valid=getusershell()) {

Well, maybe not; setusershell() doesn't work as distributed with 4.3bsd.
One can either fix *that* bug first, or use endusershell() in place of
setusershell() above.

Mark Bartelt                          UUCP: {utzoo,decvax}!sickkids!mark
Hospital for Sick Children, Toronto   BITNET: mark@sickkids.utoronto
416/598-6442                          INTERNET: mark@sickkids.toronto.edu