Memory access bug in XMLString2Perl()

[Chris Cheung]

Dear all,

  I am currently using Xerces-C 2.3.0 and Xerces-Perl 2.3.0-4.

  When I use valgrind (a popular memory debugger, 
(http://valgrind.kde.org/) to check the following simple program:

------------------------------------------
#!/usr/bin/perl -w

use strict;

use XML::Xerces;

my $xmlString = '<?xml version="1.0"?><A><B>Hello</B></A>';

my $parser = XML::Xerces::XercesDOMParser->new();
$parser->parse(XML::Xerces::MemBufInputSource->new($xmlString));

my $doc = $parser->getDocument();

my $root = $doc->getDocumentElement;
print $root->getAttribute("notExist");
-----------------------------------------

$ valgrind ./parse.pl

valgrind detected invalid memory access like:

==24771== Invalid write of size 1
==24771==    at 0x42F06DEA: XMLString2Perl(unsigned short const*) 
(Xerces.cpp:1004)
==24771==    by 0x4306E53B: _wrap_DOMElement_getAttribute 
(Xerces.cpp:59286)
==24771==    by 0x402ACCD5: Perl_pp_entersub (in 
/usr/lib/perl5/5.8.0/i386-linux-thread-multi/CORE/libperl.so)
==24771==    by 0x402A62E8: Perl_runops_standard (in 
/usr/lib/perl5/5.8.0/i386-linux-thread-multi/CORE/libperl.so)
==24771==    Address 0x418CD8FC is 0 bytes after a block of size 0 alloc'd
==24771==    at 0x40026268: __builtin_vec_new (in 
/usr/lib/valgrind/vgskin_memcheck.so)
==24771==    by 0x400262C0: operator new[](unsigned) (in 
/usr/lib/valgrind/vgskin_memcheck.so)
==24771==    by 0x42F06DAE: XMLString2Perl(unsigned short const*) 
(Xerces.cpp:995)
==24771==    by 0x4306E53B: _wrap_DOMElement_getAttribute 
(Xerces.cpp:59286)

I used -ggdb3 in building Xerces-Perl and hence line number is displayed 
in the error message. It seems that

in line 995 of Xerces.cpp:

SV*
XMLString2Perl(const XMLCh* input) {
    SV *output;
  unsigned int charsEaten = 0;
  int length  = XMLString::stringLen(input);      // string length

  XMLByte* res = new XMLByte[length * UTF8_MAXLEN];          
     // output string

  unsigned int total_chars =
    UTF8_TRANSCODER->transcodeTo((const XMLCh*) input,
                   (unsigned int) length,
                   (XMLByte*) res,
                   (unsigned int) length*UTF8_MAXLEN,
                   charsEaten,
                   XMLTranscoder::UnRep_Throw
                   );
  res[total_chars] = '\0';

The memory to malloc should be (length * UTF8_MAXLEN + 1):

  XMLByte* res = new XMLByte[length * UTF8_MAXLEN + 1];          // output 

so that the memory for the ending '\0' is not missed.

Thank you for your attention.


-- 
Best Regards,

Chris Cheung
Center for Large-Scale Computation

Have a nice day!


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