#!/bin/sh -
#
# visudopw:  Edit the password file
#



# Create a directory for temporary files
#
# Because we only want to allow one instance to edit the file at
# at one time, we will use a common directory as a locking
# mechanism.  If this fails, the superuser may have to recover
# the lock manually.

TMPDIR=/tmp/vipw.lock
TMPFILE=$TMPDIR/passwd
ORIGFILE=$TMPDIR/passwd.orig


umask 077
if ! mkdir $TMPDIR ; then
     echo "Password file is locked.  Try back later"
     exit 255
fi
 
# Copy the password file to a temporary file for editing by
# the user "nobody".  It must be owned and writable by nobody.

cp /etc/passwd $TMPFILE
chown nobody $TMPFILE

# Copy the password file to a non-writable file for later comparison
cp /etc/passwd $ORIGFILE


# Set a default editor if one is not already specified
: ${EDITOR:=/bin/vi}


# Now let the user edit the file as user "nobody"
su nobody -c "$EDITOR $TMPFILE"

# Now that the user edits are complete, apply the sanity checks
# This is left as a reader exercise...
#
# 1. Check to see if modifications have been made?
#    Compare /tmp/vipw.lock/passwd to /tmp/vipw.lock/passwd.orig
#         and exit if no change.
# 2. Check that no system accounts have been modified.
# 3. Check that no system accounts have been added.
# 4. Check that no system accounts have been deleted.
# 5. Perform formatting checking to insure a working file
# 6. Check to see if modifications have been made to the real file
#    Compare /etc/passwd to /tmp/vipw.lock/passwd.orig
#         and exit with an error if changes present.

# Finally, install the new password file.
cat /tmp/vipw.lock/passwd > /etc/passwd

rm $ORIGFILE $TMPFILE
rmdir $TMPDIR