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bug in Math::BigInt with undef #13283

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p5pRT opened this issue Sep 17, 2013 · 6 comments

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@p5pRT
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commented Sep 17, 2013

Migrated from rt.perl.org#119863 (status was 'rejected')

Searchable as RT119863$

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commented Sep 17, 2013

From hb-perlbug@bsws.de

Created by hb-perlbug@bsws.de

This is a bug report for perl from hb-perlbug@​bsws.de,
generated with the help of perlbug 1.39 running under perl 5.16.3.

-----------------------------------------------------------------
Math​::BigInt got broken when one component is undef. Unfortunately
the I can only reproduce teh bug in a big custome webapp, but it
comes down to BigInt.pm's objectify() being called with an undef
param, which it won't objectify, due to the check on line 2673ff

  # Don't do anything with undefs.

  unless (defined($a[$i])) {
  next;
  }

callers, i. e. badd(), don't deal with any component being undef.

sub badd
  {
  # add second arg (BINT or string) to first (BINT) (modifies first)
  # return result as BINT

  # set up parameters
  my ($self,$x,$y,@​r) = (ref($_[0]),@​_);
  # objectify is costly, so avoid it
  if ((!ref($_[0])) || (ref($_[0]) ne ref($_[1])))
  {
  ($self,$x,$y,@​r) = objectify(2,@​_);
  }

  return $x if $x->modify('badd');
  return $upgrade->badd($upgrade->new($x),$upgrade->new($y),@​r) if defined $upgrade &&
  ((!$x->isa($self)) || (!$y->isa($self)));

in my case $y ends up being undef, objectify doesn't do anything to it,
and the $y->isa call chokes.
[error] Can't call method "isa" on an undefined value at /usr/libdata/perl5/Math/BigInt.pm line 1131.\n

crude (and almost certainly not correct) fix​:

Inline Patch
--- BigInt.pm.orig	Tue Sep 17 10:37:09 2013
+++ BigInt.pm	Tue Sep 17 10:32:12 2013
@@ -2670,11 +2670,12 @@ sub objectify {
             next;
         }
 
-        # Don't do anything with undefs.
-
-        unless (defined($a[$i])) {
-            next;
-        }
+#        # Don't do anything with undefs.
+#
+#        unless (defined($a[$i])) {
+#            next;
+#        }
+        $a[$i] //= 0;
 
         # Perl scalars are fed to the appropriate constructor.
 
Perl Info

Flags:
    category=library
    severity=high
    module=Math::BigInt

Site configuration information for perl 5.16.3:

Configured by root at Thu Jan  1  0:00:00 UTC 1970.

Summary of my perl5 (revision 5 version 16 subversion 3) configuration:
   
  Platform:
    osname=openbsd, osvers=5.4, archname=amd64-openbsd
    uname='openbsd'
    config_args='-dsE -Dopenbsd_distribution=defined -Dccflags=-DNO_LOCALE_NUMERIC -DNO_LOCALE_COLLATE -Dmksymlinks'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-DNO_LOCALE_NUMERIC -DNO_LOCALE_COLLATE -fno-strict-aliasing -fno-delete-null-pointer-checks -pipe -fstack-protector -I/usr/local/include',
    optimize='-O2',
    cppflags='-DNO_LOCALE_NUMERIC -DNO_LOCALE_COLLATE -fno-strict-aliasing -fno-delete-null-pointer-checks -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.2.1 20070719 ', gccosandvers='openbsd5.4'
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags ='-Wl,-E  -fstack-protector'
    libpth=/usr/lib
    libs=-lm -lutil -lc
    perllibs=-lm -lutil -lc
    libc=/usr/lib/libc.a, so=so, useshrplib=true, libperl=libperl.so.14.0
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-R/usr/libdata/perl5/amd64-openbsd/5.16.3/CORE'
    cccdlflags='-DPIC -fPIC ', lddlflags='-shared -fPIC  -fstack-protector'

Locally applied patches:
    


@INC for perl 5.16.3:
    /usr/local/libdata/perl5/site_perl/amd64-openbsd
    /usr/libdata/perl5/site_perl/amd64-openbsd
    /usr/local/libdata/perl5/site_perl
    /usr/libdata/perl5/site_perl
    /usr/libdata/perl5/amd64-openbsd/5.16.3
    /usr/local/libdata/perl5/amd64-openbsd/5.16.3
    /usr/libdata/perl5
    /usr/local/libdata/perl5
    .


Environment for perl 5.16.3:
    HOME=/home/brahe
    LANG (unset)
    LANGUAGE (unset)
    LC_CTYPE=en_US.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/brahe/bin:/sbin:/usr/sbin:/bin:/usr/bin:/sbin:/usr/sbin:/usr/X11R6/bin:/usr/local/bin:/usr/local/sbin:/usr/local/sbin
    PERL_BADLANG (unset)
    SHELL=/bin/ksh

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commented Sep 17, 2013

From @cpansprout

On Tue Sep 17 07​:23​:11 2013, hb-perlbug@​bsws.de wrote​:

Math​::BigInt got broken when one component is undef. Unfortunately
the I can only reproduce teh bug in a big custome webapp, but it
comes down to BigInt.pm's objectify() being called with an undef
param, which it won't objectify, due to the check on line 2673ff

    \# Don't do anything with undefs\.

    unless \(defined\($a\[$i\]\)\) \{
        next;
    \}

That appears to be by design. I suspect your code is buggy in giving it
undef to begin with.

Could you try to reduce your big webapp to something smaller that can
reproduce the bug?

--

Father Chrysostomos

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commented Sep 17, 2013

The RT System itself - Status changed from 'new' to 'open'

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commented Sep 19, 2013

From hb@bsws.de

* Father Chrysostomos via RT <perlbug-followup@​perl.org> [2013-09-17 17​:38]​:

On Tue Sep 17 07​:23​:11 2013, hb-perlbug@​bsws.de wrote​:

Math​::BigInt got broken when one component is undef. Unfortunately
the I can only reproduce teh bug in a big custome webapp, but it
comes down to BigInt.pm's objectify() being called with an undef
param, which it won't objectify, due to the check on line 2673ff

    \# Don't do anything with undefs\.

    unless \(defined\($a\[$i\]\)\) \{
        next;
    \}

That appears to be by design. I suspect your code is buggy in giving it
undef to begin with.

no, it is not, your statement last not least contradicts perlop​:

  "undef" is always treated as numeric, and in particular is
  changed to 0 before incrementing (so that a post-increment of
  an undef value will return 0 rather than "undef").

and this has worked for ages, up until the upgrade to OpenBSD 5.4 and
thus perl 5.16.3.

the bug was introduced in
http​://perl5.git.perl.org/perl.git/commitdiff/66a0495875e8130c45cac4fabd5f8d05f2;3Cf4c372?hp=7833bfdd94cb7b5afbbc1b18e75e664482f529d5

the trigger is sth like

my %foo;
$foo{nonexistantmember} += $somenumber;

that code is under "use warnings;" and doesn't trigger any, fwiw.

Could you try to reduce your big webapp to something smaller that can
reproduce the bug?

I tried, of course, but haven't been able to, i must miss some bit
that gets to that codepath. it should be obvious enough tho.

--
Henning Brauer, hb@​bsws.de, henning@​openbsd.org
BS Web Services GmbH, AG Hamburg HRB 128289, http​://bsws.de
Full-Service ISP - Secure Hosting, Mail and DNS Services
Dedicated Servers, Rootservers, Application Hosting

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commented Dec 15, 2017

From zefram@fysh.org

Math-BigInt is maintained primarily as a CPAN distribution, so this
is the wrong place to report bugs in it. If the problem described
still occurs, you should report it to <bug-Math-BigInt@​rt.cpan.org>.
This ticket in the perl5 queue should be closed.

-zefram

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commented Dec 15, 2017

@iabyn - Status changed from 'open' to 'rejected'

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