I'd really need more of your code to understand what's happening, but cleaning up your indentation revealed that you were missing a curly brace. Also, you want to push the passwords onto the list. Assigning a password to the list would simply overwrite the last password.

#!/usr/local/bin/perl
use strict;
use warnings;

my @listOfPass;
                                                                      
+                                                
open(INPUT , "<$input_file" ) or die "couldn't open ($input_file) :$!"
+;
                                                                      
+                                                
my ($section,%passwds);
while(<CONFILE>) {
    chomp;
    if (/^\[(.*?)\]$/) { $section = $1; next; }
    if ($section eq 'PASSWORDS') {
        my ($mkt,$pass) = split;
        $passwds{$mkt} = $pass;
        $passwds{$pass} = $mkt;
        push @listOfPass, $pass;
    }
}#end while loop
close (INPUT);
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