-Di switch is now required for PerlIO debugging output¶

Previously PerlIO debugging output would be sent to the file specified by the "PERLIO_DEBUG" environment variable if perl wasn't running setuid and the -T or -t switches hadn't been parsed yet.

If perl performed output at a point where it hadn't yet parsed its switches this could result in perl creating or overwriting the file named by "PERLIO_DEBUG" even when the -T switch had been supplied.

Perl now requires the -Di switch to produce PerlIO debugging output. By default this is written to "stderr", but can optionally be redirected to a file by setting the "PERLIO_DEBUG" environment variable.

If perl is running setuid or the -T switch was supplied "PERLIO_DEBUG" is ignored and the debugging output is sent to "stderr" as for any other -D switch.

Core modules and tools no longer search "." for optional modules¶

The tools and many modules supplied in core no longer search the default current directory entry in @INC for optional modules. For example, Storable will remove the final "." from @INC before trying to load Log::Agent.

This prevents an attacker injecting an optional module into a process run by another user where the current directory is writable by the attacker, e.g. the /tmp directory.

In most cases this removal should not cause problems, but difficulties were encountered with base, which treats every module name supplied as optional. These difficulties have not yet been resolved, so for this release there are no changes to base. We hope to have a fix for base in Perl 5.22.4.

To protect your own code from this attack, either remove the default "." entry from @INC at the start of your script, so:

  #!/usr/bin/perl
  use strict;
  ...

becomes:

  #!/usr/bin/perl
  BEGIN { pop @INC if $INC[-1] eq '.' }
  use strict;
  ...

or for modules, remove "." from a localized @INC, so:

  my $can_foo = eval { require Foo; }

becomes:

  my $can_foo = eval {
      local @INC = @INC;
      pop @INC if $INC[-1] eq '.';
      require Foo;
  };

Updated Modules and Pragmata¶

• Archive::Tar has been upgraded from version 2.04 to 2.04_01.
• bignum has been upgraded from version 0.39 to 0.39_01.
• CPAN has been upgraded from version 2.11 to 2.11_01.
• Digest has been upgraded from version 1.17 to 1.17_01.
• Digest::SHA has been upgraded from version 5.95 to 5.95_01.
• Encode has been upgraded from version 2.72 to 2.72_01.
• ExtUtils::Command has been upgraded from version 1.20 to 1.20_01.
• ExtUtils::MakeMaker has been upgraded from version 7.04_01 to 7.04_02.
• File::Fetch has been upgraded from version 0.48 to 0.48_01.
• File::Spec has been upgraded from version 3.56_01 to 3.56_02.
• HTTP::Tiny has been upgraded from version 0.054 to 0.054_01.
• IO has been upgraded from version 1.35 to 1.35_01.
• The IO-Compress modules have been upgraded from version 2.068 to 2.068_001.
• IPC::Cmd has been upgraded from version 0.92 to 0.92_01.
• JSON::PP has been upgraded from version 2.27300 to 2.27300_01.
• Locale::Maketext has been upgraded from version 1.26 to 1.26_01.
• Locale::Maketext::Simple has been upgraded from version 0.21 to 0.21_01.
• Memoize has been upgraded from version 1.03 to 1.03_01.
• Module::CoreList has been upgraded from version 5.20160429 to 5.20170114_22.
• Net::Ping has been upgraded from version 2.43 to 2.43_01.
• Parse::CPAN::Meta has been upgraded from version 1.4414 to 1.4414_001.
• Pod::Html has been upgraded from version 1.22 to 1.2201.
• Pod::Perldoc has been upgraded from version 3.25 to 3.25_01.
• Storable has been upgraded from version 2.53_01 to 2.53_02.
• Sys::Syslog has been upgraded from version 0.33 to 0.33_01.
• Test has been upgraded from version 1.26 to 1.26_01.
• Test::Harness has been upgraded from version 3.35 to 3.35_01.
• XSLoader has been upgraded from version 0.20 to 0.20_01, fixing a security hole in which binary files could be loaded from a path outside of @INC. [perl #128528] <https://rt.perl.org/Public/Bug/Display.html?id=128528>

Changes to Existing Documentation¶

perlapio

•

The documentation of "PERLIO_DEBUG" has been updated.

perlrun

•

The new -Di switch has been documented, and the documentation of "PERLIO_DEBUG" has been updated.