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Add CNAME followage in Recursor
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This commit makes Engine able to follow CNAMEs when doing recursive lookups.
Currently CNAMEs will be followed when all of the following are true:
	- the response has RCODE "NoError"
	- the response does not contain records of the queried type, but does contain at least one CNAME record for the name
	- the response does not contain multiple CNAME records for the same name
	- the target of the CNAME record has not been followed before (case-insensitive)

Three system, debug level messages are created: 'CNAME_LOOP_INNER', 'CNAME_LOOP_OUTER' and 'CNAME_MULTIPLE_FOR_NAME'.

Some test cases have been modified to account for this new behavior.

Unitary tests have also been updated.
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@tgreenx
tgreenx committed Oct 31, 2023
1 parent 5fd6423 commit 6a32b4c
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Showing 11 changed files with 572 additions and 335 deletions.
2 changes: 2 additions & 0 deletions MANIFEST
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Original file line number Diff line number Diff line change
Expand Up @@ -143,6 +143,8 @@ t/profiles/Test-syntax-all.json
t/profiles/Test-zone-all.json
t/recursor.data
t/recursor.t
t/recursor-A.data
t/recursor-A.t
t/Test-address.data
t/Test-address.t
t/Test-basic.data
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65 changes: 60 additions & 5 deletions lib/Zonemaster/Engine/Recursor.pm
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Original file line number Diff line number Diff line change
Expand Up @@ -99,7 +99,7 @@ sub recurse {

my ( $p, $state ) =
$class->_recurse( $name, $type, $dns_class,
{ ns => [ root_servers() ], count => 0, common => 0, seen => {}, glue => {} } );
{ ns => [ root_servers() ], count => 0, common => 0, seen => {}, cseen => {}, glue => {} } );
$recurse_cache{$name}{$type}{$dns_class} = $p;

return $p;
Expand All @@ -111,7 +111,7 @@ sub parent {

my ( $p, $state ) =
$class->_recurse( $name, 'SOA', 'IN',
{ ns => [ root_servers() ], count => 0, common => 0, seen => {}, glue => {} } );
{ ns => [ root_servers() ], count => 0, common => 0, seen => {}, cseen => {}, glue => {} } );

my $pname;
if ( name( $state->{trace}[0][0] ) eq name( $name ) ) {
Expand Down Expand Up @@ -193,8 +193,63 @@ sub _recurse {
return ( $p, $state );
}

if ( $class->_is_answer( $p ) ) { # Return answer
return ( $p, $state );
if ( $class->_is_answer( $p ) ) { # Return answer, or follow CNAME
if ( not $p->has_rrs_of_type_for_name( $type, $name ) and $p->has_rrs_of_type_for_name( 'CNAME', $name ) ) {
my @cname_rrs_for_name = $p->get_records_for_name( 'CNAME', $name, 'answer');

if ( scalar @cname_rrs_for_name > 1 ) {
Zonemaster::Engine->logger->add( CNAME_MULTIPLE_FOR_NAME => { name => $name } );
return ( undef, $state );
}
else {
my %cnames;
my %tseen;

for my $rr ( $p->get_records( 'CNAME', 'answer' ) ) {
my $rr_owner = name( $rr->owner );
my $rr_target = name( $rr->cname );

if ( scalar $p->has_rrs_of_type_for_name( 'CNAME', $rr_owner ) > 1 ) {
Zonemaster::Engine->logger->add( CNAME_MULTIPLE_FOR_NAME => { name => $rr_owner->string } );
return ( undef, $state );
}

if ( lc( $rr_owner ) eq lc( $rr_target ) or exists $tseen{lc( $rr_target )} ) {
Zonemaster::Engine->logger->add( CNAME_LOOP_INNER => { name => $rr_owner->string, target => $rr_target->string } );
return ( undef, $state );
}

$tseen{lc( $rr_target )} = 1;
$cnames{$rr_owner} = $rr_target;
}

my $target = $name;
$target = $cnames{$target} while $cnames{$target};

if ( $state->{cseen}{lc( $target )} ) {
Zonemaster::Engine->logger->add( CNAME_LOOP_OUTER => { name => $name, target => $target, cnames => join( ';', keys %{ $state->{cseen} } ) } );
return ( undef, $state );
}

$state->{cseen}{lc( $target )} = 1;

if ( lc( $target ) eq lc( $name ) ) {
Zonemaster::Engine->logger->add( CNAME_LOOP_INNER => { name => $name, target => $target } );
return ( undef, $state );
}

$state->{count} += 1;
return ( undef, $state ) if $state->{count} > 100; # Loop protection

( $p, $state ) = $class->_recurse( $target, $type, $dns_class,
{ ns => [ root_servers() ], count => $state->{count}, common => 0, seen => {}, cseen => $state->{cseen}, glue => {} });

return ( $p, $state );
}
}
else {
return ( $p, $state );
}
}

# So it's not an error, not an empty response and not an answer
Expand Down Expand Up @@ -297,7 +352,7 @@ sub get_addresses_for {
my ( $class, $name, $state ) = @_;
my @res;
$state //=
{ ns => [ root_servers() ], count => 0, common => 0, seen => {} };
{ ns => [ root_servers() ], count => 0, common => 0, seen => {}, cseen => {} };

my ( $pa ) = $class->_recurse(
"$name", 'A', 'IN',
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10 changes: 4 additions & 6 deletions lib/Zonemaster/Engine/Test/Syntax.pm
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Original file line number Diff line number Diff line change
Expand Up @@ -918,16 +918,15 @@ sub syntax06 {

my $domain = ( $rname =~ s/.*@//r );
my $p_mx = Zonemaster::Engine::Recursor->recurse( $domain, q{MX} );

if ( not $p_mx or $p_mx->rcode ne 'NOERROR' ) {
push @results, info( RNAME_MAIL_DOMAIN_INVALID => { domain => $domain } );
next;
}

# Follow CNAMEs in the MX response
my %cnames =
map { $_->owner => $_->cname } $p_mx->get_records( q{CNAME}, q{answer} );
$domain .= q{.}; # Add back final dot
$domain = $cnames{$domain} while $cnames{$domain};
# Retrieve followed CNAME, if any
my @p_question_sec = $p_mx->question;
$domain = $p_question_sec[0]->owner;

# Determine mail domain(s)
my @mail_domains;
Expand All @@ -939,7 +938,6 @@ sub syntax06 {
}

for my $mail_domain ( @mail_domains ) {

# Assume mail domain is invalid until we see an actual IP address
my $exchange_valid = 0;

Expand Down
10 changes: 8 additions & 2 deletions lib/Zonemaster/Engine/Test/Zone.pm
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Original file line number Diff line number Diff line change
Expand Up @@ -1056,13 +1056,18 @@ sub zone07 {
my $soa_mname = $soa->mname;
$soa_mname =~ s/[.]\z//smx;
my $addresses_nb = 0;

foreach my $address_type ( q{A}, q{AAAA} ) {
my $p_mname = Zonemaster::Engine::Recursor->recurse( $soa_mname, $address_type );
if ( $p_mname ) {
if ( $p_mname->has_rrs_of_type_for_name( $address_type, $soa_mname ) ) {
my @p_question_sec = $p_mname->question;
my $final_name = name( $p_question_sec[0]->owner );

if ( $p_mname->has_rrs_of_type_for_name( $address_type, $final_name ) ) {
$addresses_nb++;
}
if ( $p_mname->has_rrs_of_type_for_name( q{CNAME}, $soa_mname ) ) {

if ( $final_name ne $soa_mname ) {
push @results,
info(
MNAME_IS_CNAME => {
Expand All @@ -1080,6 +1085,7 @@ sub zone07 {
}
} ## end if ( $p_mname )
} ## end foreach my $address_type ( ...)

if ( not $addresses_nb ) {
push @results,
info(
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3 changes: 3 additions & 0 deletions share/profile.json
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Original file line number Diff line number Diff line change
Expand Up @@ -407,6 +407,9 @@
"CACHE_FETCHED" : "DEBUG2",
"CACHED_RETURN" : "DEBUG3",
"CANNOT_CONTINUE" : "CRITICAL",
"CNAME_LOOP_INNER" : "DEBUG",
"CNAME_LOOP_OUTER" : "DEBUG",
"CNAME_MULTIPLE_FOR_NAME" : "DEBUG",
"DEPENDENCY_VERSION" : "DEBUG",
"EMPTY_RETURN" : "DEBUG3",
"EXTERNAL_RESPONSE" : "DEBUG3",
Expand Down
3 changes: 3 additions & 0 deletions share/profile.yaml
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Original file line number Diff line number Diff line change
Expand Up @@ -445,6 +445,9 @@ test_levels:
CACHE_CREATED: DEBUG2
CACHE_FETCHED: DEBUG2
CANNOT_CONTINUE: CRITICAL
CNAME_LOOP_INNER : DEBUG
CNAME_LOOP_OUTER : DEBUG
CNAME_MULTIPLE_FOR_NAME : DEBUG
DEPENDENCY_VERSION: DEBUG
EMPTY_RETURN: DEBUG3
EXTERNAL_RESPONSE: DEBUG3
Expand Down
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