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+# Wallet::ACL::LDAP::Attribute -- Wallet LDAP attribute ACL verifier.
+#
+# Written by Russ Allbery
+# Copyright 2012, 2013, 2014
+#     The Board of Trustees of the Leland Stanford Junior University
+#
+# See LICENSE for licensing terms.
+
+##############################################################################
+# Modules and declarations
+##############################################################################
+
+package Wallet::ACL::LDAP::Attribute;
+require 5.006;
+
+use strict;
+use warnings;
+use vars qw(@ISA $VERSION);
+
+use Authen::SASL ();
+use Net::LDAP qw(LDAP_COMPARE_TRUE);
+use Wallet::ACL::Base;
+use Wallet::Config;
+
+@ISA = qw(Wallet::ACL::Base);
+
+# This version should be increased on any code change to this module.  Always
+# use two digits for the minor version with a leading zero if necessary so
+# that it will sort properly.
+$VERSION = '0.01';
+
+##############################################################################
+# Interface
+##############################################################################
+
+# Create a new persistant verifier.  Load the Net::LDAP module and open a
+# persistant LDAP server connection that we'll use for later calls.
+sub new {
+    my $type = shift;
+    my $host = $Wallet::Config::LDAP_HOST;
+    my $base = $Wallet::Config::LDAP_BASE;
+    unless ($host and defined ($base) and $Wallet::Config::LDAP_CACHE) {
+        die "LDAP attribute ACL support not configured\n";
+    }
+
+    # Ensure the required Perl modules are available and bind to the directory
+    # server.  Catch any errors with a try/catch block.
+    my $ldap;
+    eval {
+        local $ENV{KRB5CCNAME} = $Wallet::Config::LDAP_CACHE;
+        my $sasl = Authen::SASL->new (mechanism => 'GSSAPI');
+        $ldap = Net::LDAP->new ($host, onerror => 'die');
+        my $mesg = eval { $ldap->bind (undef, sasl => $sasl) };
+    };
+    if ($@) {
+        my $error = $@;
+        chomp $error;
+        1 while ($error =~ s/ at \S+ line \d+\.?\z//);
+        die "LDAP attribute ACL support not available: $error\n";
+    }
+
+    # We successfully bound, so create our object and return it.
+    my $self = { ldap => $ldap };
+    bless ($self, $type);
+    return $self;
+}
+
+# Check whether a given principal has the required LDAP attribute.  We first
+# map the principal to a DN by doing a search for that principal (and bailing
+# if we get more than one entry).  Then, we do a compare to see if that DN has
+# the desired attribute and value.
+#
+# If the ldap_map_principal sub is defined in Wallet::Config, call it on the
+# principal first to map it to the value for which we'll search.
+#
+# The connection is configured to die on any error, so we do all the work in a
+# try/catch block to report errors.
+sub check {
+    my ($self, $principal, $acl) = @_;
+    undef $self->{error};
+    unless ($principal) {
+        $self->error ('no principal specified');
+        return;
+    }
+    my ($attr, $value);
+    if ($acl) {
+        ($attr, $value) = split ('=', $acl, 2);
+    }
+    unless (defined ($attr) and defined ($value)) {
+        $self->error ('malformed ldap-attr ACL');
+        return;
+    }
+    my $ldap = $self->{ldap};
+
+    # Map the principal name to an attribute value for our search if we're
+    # doing a custom mapping.
+    if (defined &Wallet::Config::ldap_map_principal) {
+        eval { $principal = Wallet::Config::ldap_map_principal ($principal) };
+        if ($@) {
+            $self->error ("mapping principal to LDAP failed: $@");
+            return;
+        }
+    }
+
+    # Now, map the user to a DN by doing a search.
+    my $entry;
+    eval {
+        my $fattr = $Wallet::Config::LDAP_FILTER_ATTR || 'krb5PrincipalName';
+        my $filter = "($fattr=$principal)";
+        my $base = $Wallet::Config::LDAP_BASE;
+        my @options = (base => $base, filter => $filter, attrs => [ 'dn' ]);
+        my $search = $ldap->search (@options);
+        if ($search->count == 1) {
+            $entry = $search->pop_entry;
+        } elsif ($search->count > 1) {
+            die $search->count . " LDAP entries found for $principal";
+        }
+    };
+    if ($@) {
+        $self->error ("cannot search for $principal in LDAP: $@");
+        return;
+    }
+    return 0 unless $entry;
+
+    # We have a user entry.  We can now check whether that user has the
+    # desired attribute and value.
+    my $result;
+    eval {
+        my $mesg = $ldap->compare ($entry, attr => $attr, value => $value);
+        $result = $mesg->code;
+    };
+    if ($@) {
+        $self->error ("cannot check LDAP attribute $attr for $principal: $@");
+        return;
+    }
+    return ($result == LDAP_COMPARE_TRUE) ? 1 : 0;
+}
+
+1;
+
+##############################################################################
+# Documentation
+##############################################################################
+
+=for stopwords
+ACL Allbery verifier LDAP PRINCIPAL's DN ldap-attr
+
+=head1 NAME
+
+Wallet::ACL::LDAP::Attribute - Wallet ACL verifier for LDAP attribute compares
+
+=head1 SYNOPSIS
+
+    my $verifier = Wallet::ACL::LDAP::Attribute->new;
+    my $status = $verifier->check ($principal, "$attr=$value");
+    if (not defined $status) {
+        die "Something failed: ", $verifier->error, "\n";
+    } elsif ($status) {
+        print "Access granted\n";
+    } else {
+        print "Access denied\n";
+    }
+
+=head1 DESCRIPTION
+
+Wallet::ACL::LDAP::Attribute checks whether the LDAP record for the entry
+corresponding to a principal contains an attribute with a particular
+value.  It is used to verify ACL lines of type C<ldap-attr>.  The value of
+such an ACL is an attribute followed by an equal sign and a value, and the
+ACL grants access to a given principal if and only if the LDAP entry for
+that principal has that attribute set to that value.
+
+To use this object, several configuration parameters must be set.  See
+L<Wallet::Config> for details on those configuration parameters and
+information about how to set wallet configuration.
+
+=head1 METHODS
+
+=over 4
+
+=item new()
+
+Creates a new ACL verifier.  Opens and binds the connection to the LDAP
+server.
+
+=item check(PRINCIPAL, ACL)
+
+Returns true if PRINCIPAL is granted access according to ACL, false if
+not, and undef on an error (see L<"DIAGNOSTICS"> below).  ACL must be an
+attribute name and a value, separated by an equal sign (with no
+whitespace).  PRINCIPAL will be granted access if its LDAP entry contains
+that attribute with that value.
+
+=item error()
+
+Returns the error if check() returned undef.
+
+=back
+
+=head1 DIAGNOSTICS
+
+The new() method may fail with one of the following exceptions:
+
+=over 4
+
+=item LDAP attribute ACL support not available: %s
+
+Attempting to connect or bind to the LDAP server failed.
+
+=item LDAP attribute ACL support not configured
+
+The required configuration parameters were not set.  See Wallet::Config(3)
+for the required configuration parameters and how to set them.
+
+=back
+
+Verifying an LDAP attribute ACL may fail with the following errors
+(returned by the error() method):
+
+=over 4
+
+=item cannot check LDAP attribute %s for %s: %s
+
+The LDAP compare to check for the required attribute failed.  The
+attribute may have been misspelled, or there may be LDAP directory
+permission issues.  This error indicates that PRINCIPAL's entry was
+located in LDAP, but the check failed during the compare to verify the
+attribute value.
+
+=item cannot search for %s in LDAP: %s
+
+Searching for PRINCIPAL (possibly after ldap_map_principal() mapping)
+failed.  This is often due to LDAP directory permissions issues.  This
+indicates a failure during the mapping of PRINCIPAL to an LDAP DN.
+
+=item malformed ldap-attr ACL
+
+The ACL parameter to check() was malformed.  Usually this means that
+either the attribute or the value were empty or the required C<=> sign
+separating them was missing.
+
+=item mapping principal to LDAP failed: %s
+
+There was an ldap_map_principal() function defined in the wallet
+configuration, but calling it for the PRINCIPAL argument failed.
+
+=item no principal specified
+
+The PRINCIPAL parameter to check() was undefined or the empty string.
+
+=back
+
+=head1 SEE ALSO
+
+Wallet::ACL(3), Wallet::ACL::Base(3), Wallet::Config(3), wallet-backend(8)
+
+This module is part of the wallet system.  The current version is
+available from L<http://www.eyrie.org/~eagle/software/wallet/>.
+
+=head1 AUTHOR
+
+Russ Allbery <eagle@eyrie.org>
+
+=cut