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The Basics
Id: 131498
Status: new
Priority: 0/
Queue: XML-LibXML

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Owner: Nobody in particular
Requestors: ppisar [...] redhat.com
Cc:
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Bug Information
Severity: (no value)
Broken in: 2.0202
Fixed in: (no value)

Attachments
XML-LibXML-2.0202-Parse-an-ampersand-entity-in-SAX-interface.patch



Subject: XML::LibXML::SAX stopped parsing & in an attribute value
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2.0202 stopped expanding external entities. But it also broke parsing internal &#38; entity that is located in an attribute value and when it is parsed with XML::LibXML::SAX. Reproducer: #!/usr/bin/perl use XML::LibXML::SAX; XML::LibXML::SAX->new(Handler => 'Handler')->parse_string(<<'END'); <?xml version="1.0"?> <root> <predefined param="&quot;">&quot;</predefined> <numeric param="&#65;">&#65;</numeric> <numericampersand param="&#38;">&#38;</numericampersand> </root> END package Handler; my $text = ''; sub start_element { my ($self, $node) = @_; print "STARTELEM name=$node->{LocalName}\n"; for my $key (sort keys %{$node->{Attributes}}) { printf "\tATTR name=%s value=%s\n", $node->{Attributes}->{$key}->{Name}, $node->{Attributes}->{$key}->{Value}; } $text = ''; } sub end_element { print "\tTEXT $text\n" if $text ne ''; $text = ''; } sub characters { my ($self, $node) = @_; $text .= $node->{Data}; } Output with old XML-LibXML: $ perl -I/home/test/fedora/perl-XML-LibXML/XML-LibXML-2.0201/blib/{lib,arch} ./saxent STARTELEM name=root STARTELEM name=predefined ATTR name=param value=" TEXT " STARTELEM name=numeric ATTR name=param value=A TEXT A STARTELEM name=numericampersand ATTR name=param value=& TEXT & TEXT Ouput with new XML-LibXML: $ perl -I/home/test/fedora/perl-XML-LibXML/XML-LibXML-2.0202/blib/{lib,arch} ./saxent STARTELEM name=root STARTELEM name=predefined ATTR name=param value=" TEXT " STARTELEM name=numeric ATTR name=param value=A TEXT A STARTELEM name=numericampersand ATTR name=param value=&#38; TEXT & TEXT See the difference in parsing <numericampersand param="&#38;">. Please note that XML::LibXML parser does not suffer from it. This bug causes RDF-Trine tests to fail <https://github.com/kasei/perlrdf/issues/167>. By the way I looked into XML::LibXML::SAX and XML::LibXML::SAX::Parser and I cannot see how a user can enable parsing external entities and DTDs when using XML::SAX. I think XML::LibXML::SAX could use a SAX feature for enabling it.
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Dne Pá 17.led.2020 08:19:15, ppisar napsal(a): Show quoted text
> 2.0202 stopped expanding external entities. But it also broke parsing > internal &#38; entity that is located in an attribute value and when > it is parsed with XML::LibXML::SAX. > > Reproducer: > > #!/usr/bin/perl > use XML::LibXML::SAX; > XML::LibXML::SAX->new(Handler => 'Handler')->parse_string(<<'END'); > <?xml version="1.0"?> > <root> > <predefined param="&quot;">&quot;</predefined> > <numeric param="&#65;">&#65;</numeric> > <numericampersand param="&#38;">&#38;</numericampersand> > </root> > END > package Handler; > my $text = ''; > sub start_element { > my ($self, $node) = @_; > print "STARTELEM name=$node->{LocalName}\n"; > for my $key (sort keys %{$node->{Attributes}}) { > printf "\tATTR name=%s value=%s\n", > $node->{Attributes}->{$key}->{Name}, > $node->{Attributes}->{$key}->{Value}; > } > $text = ''; > } > sub end_element { > print "\tTEXT $text\n" if $text ne ''; > $text = ''; > } > sub characters { > my ($self, $node) = @_; > $text .= $node->{Data}; > } > > Output with old XML-LibXML: > > $ perl -I/home/test/fedora/perl-XML-LibXML/XML-LibXML- > 2.0201/blib/{lib,arch} ./saxent > STARTELEM name=root > STARTELEM name=predefined > ATTR name=param value=" > TEXT " > STARTELEM name=numeric > ATTR name=param value=A > TEXT A > STARTELEM name=numericampersand > ATTR name=param value=& > TEXT & > TEXT > > Ouput with new XML-LibXML: > > $ perl -I/home/test/fedora/perl-XML-LibXML/XML-LibXML- > 2.0202/blib/{lib,arch} ./saxent > STARTELEM name=root > STARTELEM name=predefined > ATTR name=param value=" > TEXT " > STARTELEM name=numeric > ATTR name=param value=A > TEXT A > STARTELEM name=numericampersand > ATTR name=param value=&#38; > TEXT & > TEXT > > See the difference in parsing <numericampersand param="&#38;">. > > Please note that XML::LibXML parser does not suffer from it. This bug > causes RDF-Trine tests to fail > <https://github.com/kasei/perlrdf/issues/167>. > > By the way I looked into XML::LibXML::SAX and XML::LibXML::SAX::Parser > and I cannot see how a user can enable parsing external entities and > DTDs when using XML::SAX. I think XML::LibXML::SAX could use a SAX > feature for enabling it.
I added sum debugging (print attr argument) into PmmGenAttributeHashSV() function and it seems that libxml2 ignores that one entity in attributes: $ perl -Iblib/{lib,arch} /tmp/reproducer parse_string(): self=XML::LibXML=HASH(0x55a9fd53dfd0) string=|<?xml version="1.0"?> <root> <predefined param="&quot;">&quot;</predefined> <numeric param="&#65;">&#65;</numeric> <numericampersand param="&#38;">&#38;</numericampersand> </root> | at blib/lib/XML/LibXML.pm line 845. STARTELEM name=root PmmGenAttributeHashSV() attrname=param attrvalue=" STARTELEM name=predefined ATTR name=param value=" TEXT " PmmGenAttributeHashSV() attrname=param attrvalue=A STARTELEM name=numeric ATTR name=param value=A TEXT A PmmGenAttributeHashSV() attrname=param attrvalue=&#38; STARTELEM name=numericampersand ATTR name=param value=&#38; TEXT & TEXT
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Dne St 22.led.2020 06:29:21, ppisar napsal(a): Show quoted text
> I added sum debugging (print attr argument) into > PmmGenAttributeHashSV() function and it seems that libxml2 ignores > that one entity in attributes: >
And it seems to be known libxml2 bug <https://bugzilla.gnome.org/show_bug.cgi?id=316487>.
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Dne Pá 17.led.2020 08:19:15, ppisar napsal(a): Show quoted text
> 2.0202 stopped expanding external entities. But it also broke parsing > internal &#38; entity that is located in an attribute value and when > it is parsed with XML::LibXML::SAX. >
An attached patch fixes it for me. It basically works around the libxml2 misfeature by unconditionally expanding "&#38;" entity. This is not currently an issue because XML::LibXML::SAX does not allow disabling predefined entities, neither to hook a callback for a parsed entity.
Subject: XML-LibXML-2.0202-Parse-an-ampersand-entity-in-SAX-interface.patch
From 3d0adda7560137309be8b10c63ff41e41dfb1516 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <ppisar@redhat.com> Date: Tue, 28 Jan 2020 17:05:32 +0100 Subject: [PATCH] Parse an ampersand entity in SAX interface MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit After disabling parsing external entities in XML-LibXML-2.0202, XML::LibXML::SAX interface stopped expanding &amp; and &#38; entities in attribute values (often found in href XHTML attributes) and returned "&#38;" instead. This was discovered by a RDF-Trine test suite failure <https://github.com/kasei/perlrdf/issues/167>. First, I suspected XML-LibXML <https://rt.cpan.org/Ticket/Display.html?id=131498>, but it turned out that the unexpanded entity comes from libxml2 C library itself. And that it's not just an ommitted expansion, but that it's actually an escape sequence for "&" characters. Other XML metacharacters (like "<") are not affeced. Also text nodes are also not affected. My finding was confirmed by an old libxml2 bug report <https://bugzilla.gnome.org/show_bug.cgi?id=316487>. This patch "fixes" this discepancy by replacing all "&#38;" subtstrings with a literal "&" in SAX interface of start_element() callbacks. Signed-off-by: Petr Písař <ppisar@redhat.com> --- MANIFEST | 1 + perl-libxml-sax.c | 44 ++++++++++++++++++++++++++++++++++++++++++-- t/52_sax_intent.t | 40 ++++++++++++++++++++++++++++++++++++++++ 3 files changed, 83 insertions(+), 2 deletions(-) create mode 100755 t/52_sax_intent.t diff --git a/MANIFEST b/MANIFEST index 5248ea5..ccc3410 100644 --- a/MANIFEST +++ b/MANIFEST @@ -174,6 +174,7 @@ t/49callbacks_returning_undef.t t/49global_extent.t t/50devel.t t/51_parse_html_string_rt87089.t +t/52_sax_intent.t t/60error_prev_chain.t t/60struct_error.t t/61error.t diff --git a/perl-libxml-sax.c b/perl-libxml-sax.c index b949d3c..232a879 100644 --- a/perl-libxml-sax.c +++ b/perl-libxml-sax.c @@ -20,6 +20,7 @@ extern "C" { #include "ppport.h" #include <stdlib.h> +#include <string.h> #include <libxml/xmlmemory.h> #include <libxml/parser.h> #include <libxml/parserInternals.h> @@ -639,6 +640,34 @@ PmmGenNsName( const xmlChar * name, const xmlChar * nsURI ) return retval; } +/* If a value argument does not contain "&#38;", the value pointer is returned. + * Otherwise a new xmlChar * string is allocated, the value copied there and + * "&#38;" occurences replaced with "&". Then the caller must free it. */ +static +xmlChar * +_expandAmp( const xmlChar *value ) +{ + xmlChar *expanded = NULL; + const xmlChar *entity; + int length; + + if (value == NULL || + (NULL == (entity = (const xmlChar *)strstr((const char *)value, "&#38;")))) { + return (xmlChar *)value; + } + + do { + length = entity - value; + expanded = xmlStrncat(expanded, value, length); + expanded = xmlStrncat(expanded, (const xmlChar *)"&", 1); + value += length + 5; /* "&#38;" */ + } while (NULL != (entity = (const xmlChar*)strstr((const char *)value, "&#38;"))); + + expanded = xmlStrcat(expanded, value); + + return expanded; +} + HV * PmmGenAttributeHashSV( pTHX_ PmmSAXVectorPtr sax, const xmlChar **attr, SV * handler ) @@ -653,8 +682,8 @@ PmmGenAttributeHashSV( pTHX_ PmmSAXVectorPtr sax, const xmlChar * nsURI = NULL; const xmlChar **ta = attr; const xmlChar * name = NULL; - const xmlChar * value = NULL; + xmlChar * value = NULL; xmlChar * keyname = NULL; xmlChar * localname = NULL; xmlChar * prefix = NULL; @@ -665,7 +694,13 @@ PmmGenAttributeHashSV( pTHX_ PmmSAXVectorPtr sax, while ( *ta != NULL ) { atV = newHV(); name = *ta; ta++; - value = *ta; ta++; + /* XXX: libxml2 SAX2 interface does not expand &#38; + * entity in the attribute values + * <https://bugzilla.gnome.org/show_bug.cgi?id=316487> + * resulting in stray "&#38;" sequences after disabling + * external entity expansion + * <https://rt.cpan.org/Ticket/Display.html?id=131498>. */ + value = _expandAmp(*ta); if ( name != NULL && XML_STR_NOT_EMPTY( name ) ) { localname = xmlSplitQName(NULL, name, &prefix); @@ -754,6 +789,11 @@ PmmGenAttributeHashSV( pTHX_ PmmSAXVectorPtr sax, prefix = NULL; } + + if (value != *ta) { + xmlFree(value); + } + ta++; } } diff --git a/t/52_sax_intent.t b/t/52_sax_intent.t new file mode 100755 index 0000000..a45b4d1 --- /dev/null +++ b/t/52_sax_intent.t @@ -0,0 +1,40 @@ +use strict; +use warnings; +use Test::More; + +my %tests = ( + # attribte name raw attrib. value expected parsed value + predefined => ['&quot;', '"'], # alawys worked + numeric => ['&#65;', 'A'], # always worked + numericampersand => ['&#38;', '&'], # a regression + ampA => ['&#38;A', '&A'], # a corner case + Aamp => ['A&#38;', 'A&'], # a corner case + AampBampC => ['A&#38;B&#38;C', 'A&B&C'], # a corner case +); +plan tests => scalar (keys %tests); + +my $input = '<?xml version="1.0"?><root'; +for my $test (sort keys %tests) { + $input .= sprintf(" %s='%s'", $test, $tests{$test}->[0]); +} +$input .= '/>'; + +diag("Parsing $input"); +use XML::LibXML::SAX; + +XML::LibXML::SAX->new(Handler => 'Handler')->parse_string($input); + + +package Handler; +sub start_element { + my ($self, $node) = @_; + for my $attribute (sort keys %{$node->{Attributes}}) { + my $name = $node->{Attributes}->{$attribute}->{Name}; + Test::More::is( + $node->{Attributes}->{$attribute}->{Value}, + $tests{$name}->[1], + sprintf("%s='%s' attribute", $name, $tests{$name}->[0]) + ); + } +} + -- 2.21.1


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