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[perl #131192] panic: attempt to copy freed scalar via @ARGV onstack, Getopt::Long + Carp::longmess

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From:
niels @ thykier . net
Date:
April 23, 2017 03:54
Subject:
[perl #131192] panic: attempt to copy freed scalar via @ARGV onstack, Getopt::Long + Carp::longmess
Message ID:
rt-4.0.24-13248-1492852186-1680.131192-75-0@perl.org
# New Ticket Created by  niels@thykier.net 
# Please include the string:  [perl #131192]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=131192 >



This is a bug report for perl from niels@thykier.net,
generated with the help of perlbug 1.40 running under perl 5.26.0.


-----------------------------------------------------------------
[Please describe your issue here]

Hi,

I discovered that after a change to a project of mine, perl started
throwing Bizarre Copy errors.  I eventually reproduced it to the
following test case (included below).  As I reduced the test case, the
error eventually turned into "panic: attempt to copy freed scalar"
(although, tweaks to the test case sometimes flip it back to a Bizarre
copy).

Some observations:

 * @ARGV must be passed to a sub and @ARGV must be non-empty
 * That sub (or something it calls) must call Getopt::Long::GetOptions
 * Carp::longmess() is required to trigger the bug
 * Originally discovered on Debian stretch's perl 5.24, but is also
   reproducible in blead.

Running the test case:

  """
  ./perl -Ilib run.pl --state-dir foo
  panic: attempt to copy freed scalar 55a956c38168 to 55a956c59510 at lib/Carp.pm line 229.
  """

The definition of run.pl:

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

use strict;
use warnings;
use Carp qw(longmess);

use Getopt::Long();
use Errno qw(ENOENT);

my %OPT;
# If the %OPT_HASH is changed, I some times see
my %OPT_HASH= (
    'state-dir=s'	=> \$OPT{'state-dir'},
    'mirror-path=s'	=> \$OPT{'mirror-path'},
    # Comma-separated lists
    'distributions=s@'	=>
      sub { push(@{$OPT{'distributions'}}, split(m/,/, $_[1])); },
    'mirror-areas=s@'	=>
      sub { push(@{$OPT{'mirror-areas'}},  split(m/,/, $_[1])); },
    'architectures=s@'	=>
      sub { push(@{$OPT{'architectures'}}, split(m/,/, $_[1])); },
    'desired-version=s' => \$OPT{'desired-version'},
    'lintian-lab=s'	=> \$OPT{'lintian-lab'},
    'reschedule-all'	=> \$OPT{'reschedule-all'},
    'help|h'		=> \&usage,
    'debug|d'		=> \$OPT{'debug'},
    'dry-run'		=> \$OPT{'dry-run'},
);

sub tool_main {
    # We have to call GetOptions to reproduce the issue - plus we need
    # at least one argument consumed.
    die("Usage: $0 --state-dir does-not-matter\n") if not @ARGV;
    Getopt::Long::config('bundling', 'no_getopt_compat', 'no_auto_abbrev');
    Getopt::Long::GetOptions(%OPT_HASH) or die("error parsing options\n");
    load_state_cache();
    exit(0);
}

sub load_state_cache {
    my ($state_dir) = @_;
    my $state_file = "./file-that-does-not-exist";
    my $fd;
    if (not open($fd, '<:raw', $state_file)) {
	my $err = $!;
	# Originally reproduced with autodie, but it was reproducible by
	# simply calling longmess (which autodie does to collect a stack
	# trace for its exception)
	Carp::longmess(); # <-- Triggers a "attempt to copy freed scalar"
			  #	OR a Bizarre copy of X
	die("open ($state_file): $err") if $err != ENOENT;
	# Not present; presume empty
	return;
    }
    # We wanted to get here because of ENOENT
    ...;
    close($fd);
    return;
}

sub usage {
    print <<EOF;
Random usage message
EOF

    exit(0);
}

tool_main(@ARGV);  # Has to be here to trigger the error

# Local Variables:
# indent-tabs-mode: nil
# cperl-indent-level: 4
# End:
# vim: syntax=perl sw=4 sts=4 sr et

"""

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=low
---
Site configuration information for perl 5.26.0:

Configured by moon at Sat Apr 22 10:20:49 CEST 2017.

Summary of my perl5 (revision 5 version 26 subversion 0) configuration:
  Commit id: 78d5fac03632a8c05a3e3e954b0cb9dfa0be4f36
  Platform:
    osname=linux
    osvers=4.9.0-2-amd64
    archname=x86_64-linux
    uname='linux hostname 4.9.0-2-amd64 #1 smp debian 4.9.18-1 (2017-03-30) x86_64 gnulinux '
    config_args='-des -DDEBUG'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
    bincompat5005=undef
  Compiler:
    cc='cc'
    ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
    optimize='-O2'
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='6.3.0 20170406'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/6/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
    libs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.24.so
    so=so
    useshrplib=false
    libperl=libperl.a
    gnulibc_version='2.24'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'


---
@INC for perl 5.26.0:
    lib
    /usr/local/lib/perl5/site_perl/5.26.0/x86_64-linux
    /usr/local/lib/perl5/site_perl/5.26.0
    /usr/local/lib/perl5/5.26.0/x86_64-linux
    /usr/local/lib/perl5/5.26.0

---
Environment for perl 5.26.0:
    HOME=/home/user
    LANG=en_DK.UTF-8
    LANGUAGE=en_GB:en
    LC_NUMERIC=C.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/bash

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