#! /usr/bin/perl -ws
# written April 1996, tale@isc.org (David C Lawrence)
# Version 1.11, 14 Oct 1998
#
# NOTICE TO INN MAINTAINERS:  The version that is shipped with INN
# is the same as the version that I make available to the rest of the
# world (including non-INN sites), so please make all changes through me.
#
# This program is intended to be compatible with Perl 4 and Perl 5.
#
# Changes from 1.10 -> 1.11
# -- code to log error messages to syslog.
#    See $syslog and $syslog_method configurable variables.
# -- configurably allow date stamp on stderr error messages.
# -- added locking for multiple concurrent pgp instances.
# -- more clear error message if pgp exits abnormally.
# -- identify PGP 5 "BAD signature" string.
# -- minor diddling for INN (path to innshellvars.pl changed)
#
# Changes from 1.9 -> 1.10
# -- minor diddling for INN 2.0: use $inn'pathtmp if it exists, and
#    work with the new subst method to find innshellvars.pl
# -- do not truncate the tmp file when opening, in case it is really linked
#    to another file
#
# Changes from 1.8 -> 1.9
# -- match 'Bad signature' pgp output to return exit status 3 by removing
#    '^' in regexp matched on multiline string.
#
# Changes from 1.7 -> 1.8
# -- ignore final dot-CRLF if article is in NNTP format
#
# Changes from 1.6 -> 1.7
# -- parse PGP 5.0 'good signature' lines.
# -- allow -test swtich; prints pgp input and output
# -- look for pgp in INN's innshellvars.pl
# -- changed regexp delimiters for stripping $0 to be compatible with old perl
#
# Changes from 1.5 -> 1.6
# -- handle articles encoded in NNTP format ('.' starting line is doubled,
#    \r\n at line end) by stripping NNTP encoding.
# -- exit 255 with pointer to $HOME or $PGPPATH if pgp can't find key ring.
#    (probably doesn't match the necessary error message with ViaCrypt PGP)
# -- failures also report message-id so the article can be looked up to retry.
#
# Changes from 1.4 -> 1.5
# -- force English lanugage for 'Good signature from user' by passing
#    +language=en on pgp command line, rather than setting the
#    environment variable LANGUAGE to 'en'.
#
# Changes from 1.3 -> 1.4
# -- now handles wrapped headers that have been unfolded.
#    (though I do believe news software oughtn't be unfolding them.)
# -- checks to ensure that the temporary file is really a file, and
#    not a link or some other weirdness

# Path to pgp binary; for PGP 5.0, set the path to the pgpv binary.
$pgp = '/usr/local/bin/pgp';

# if you keep your keyring somewhere that is not the default used by pgp,
# uncomment the next line and set appropriately.
# $ENV{'PGPPATH'} = '/path/to/your/pgp/config';

$tmpdir = "/tmp";
$lockdir = $tmpdir;

# Set to have the script use syslog for errors instead of stderr.
# Value should be the facility and level to use, as would be found
# in syslog.conf; ie, "news.err" is the "news" facility and "err" level.
# For various reasons, it is impossible to economically have the script
# figure out how to do syslogging correctly on the machine.
#
$syslog = 'news.err';
# $syslog = '';  # an empty value means don't try to do syslogging.

# How should syslog be accessed?
# As it turns out, syslogging is very hard to do portably in all
# versions of perl up to and including 5.005_02. 'inet' is all that
# was available in perl up to version 5.004_03. If your syslog does
# not accept UDP log packets, such as when syslogd runs with the -l flag,
# 'inet' will not work.  A value of 'unix' will try to contact syslogd
# directly over a Unix domain socket built entirely in perl code
# (no subprocesses).  If that is not working for you, and you have
# the 'logger' program on your system, set this variable to its full
# path name to have a subprocess contact syslogd.  If the method is just
# "logger", the script will search some known directories for that program.
# If it can't be found & used, everything falls back on stderr logging.
#
# You can test the script's syslogging by running "pgpverify < /some/text/file"
# on a file that is not a valid news article.  The "non-header at line #"
# error should be syslogged.
#
# $syslog_method = 'unix';    # Unix doman socket, perl5.004_03 or higher
# $syslog_method = 'inet';    # UDP to port 514 of localhost
$syslog_method = 'logger';

# Prepend the error message with a timestamp?
# This is only relevant if not syslogging, when errors go to stderr.
#
# $log_date = 0;  # zero means don't do it.
# $log_date = 1;  # non-zero means do it.
$log_date = -t STDOUT; # do it if STDOUT is to a terminal

### Exit value:
### 0  good signature
### 1  no signature
### 2  unknown signature
### 3  bad signature
### 255 problem not directly related to pgp analysis of signature

# not syslogged, such an error is almost certainly from someone running
# the script manually.
die "Usage: $0 < message\n" if @ARGV != 0;

$0 =~ s%^.*/%%;                 # trim /path/to/prog to prog

do '@LIBDIR@/innshellvars.pl';
$pgp = $inn'pgp if $inn'pgp && $inn'pgp ne "no-pgp-found-during-configure";
$tmp = ($inn'pathtmp ? $inn'pathtmp : $tmpdir) . "/pgp$$";
$lockdir = $inn'locks if $inn'locks;
#
# ... and it is expected some day that an INN variable will let perl
# scripts know how syslogging should be done.

# the call to pgp needs to be locked because it tries to both read and write
# a file named randseed.bin but doesn't do its own locking as it should,
# and the consequences of a multiprocess conflict is failure to verify.
#
$lock = "$lockdir/LOCK.$0";

if (! -x $pgp) {
  &fail("$0: $pgp: " . (-e _ ? "cannot execute" : "no such file") . "\n");
}

# this is, by design, case-sensitive with regards to the headers it checks.
# it's also insistent about the colon-space rule.
while (<>) {
  # if a header line ends with \r\n, this article is in the encoding
  # it would be in during an NNTP session.  some article storage
  # managers keep them this way for efficiency.
  $nntp_format = /\r\n$/ if $. == 1;
  s/\r?\n$//;

  last if /^$/;
  if (/^(\S+):[ \t](.+)/) {
    ($label, $value) = ($1, $2);
    $dup{$label} = 1 if $header{$label};
    $header{$label} = $value;
  } elsif (/^\s/) {
    &fail("$0: non-header at line $.: $_\n") unless $label;
    $header{$label} .= "\n$_";
  } else {
    &fail("$0: non-header at line $.: $_\n");
  }
}

$pgpheader = "X-PGP-Sig";
exit 1 unless $_ = $header{$pgpheader}; # no signature

# the regexp below might be too strict about the structure of pgp sig lines

# the $sep value means the separator between the radix64 signature lines
# can have any amount of spaces or tabs, but must have at least one space
# or tab, if there is a newline then the space or tab has to follow the
# newline.  any number of newlines can appear as long as each is followed
# by at least one space or tab.   *phew*
$sep = "[ \t]*(\n?[ \t]+)+";

# match all of the characters in a radix64 string
$r64 = '[a-zA-Z0-9+/]';

&fail("$0: $pgpheader not in expected format\n")
  unless /^(\S+)$sep(\S+)(($sep$r64{64})+$sep$r64+=?=?$sep=$r64{4})$/;

($version, $signed_headers, $signature) = ($1, $3, $4);
$signature =~ s/$sep/\n/g;

$message  = "-----BEGIN PGP SIGNED MESSAGE-----\n\n";
$message .= "X-Signed-Headers: $signed_headers\n";
foreach $label (split(",", $signed_headers)) {
  &fail("$0: duplicate signed $label header, can't verify\n")
    if $dup{$label};
  $message .= "$label: ";
  $message .= "$header{$label}" if $header{$label};
  $message .= "\n";
}
$message .= "\n";               # end of headers

while (<>) {                    # read body lines
  if ($nntp_format) {
    # check for end of article; some news servers (eg, Highwind's "Breeze")
    # include the dot-CRLF of the NNTP protocol in the article data passed
    # to this script
    last if $_ eq ".\r\n";

    # remove NNTP encoding
    s/^\.\./\./;
    s/\r\n$/\n/;
  }

  s/^-/- -/;                    # pgp quote ("ASCII armor") dashes
  $message .= $_;               # append to output string
}

$message .= "\n-----BEGIN PGP SIGNATURE-----\n";
$message .= "Version: $version\n";
$message .= $signature;
$message .= "\n-----END PGP SIGNATURE-----\n";

open(TMP,">> $tmp") || &fail("$0: open > $tmp: $!\n");

-f TMP ||
  &fail("$0: $tmp not a plain file, possible security violation attempt\n");
(stat(_))[3] == 1 ||
  &fail("$0: $tmp has hard links, possible security violation attempt\n");

seek(TMP, 0, 0);                # make sure pointer is at beginning of file
truncate(TMP, 0);               # make sure file is zero length

print TMP $message;
close(TMP) || &errmsg("$0: close > $tmp: $!\n");
&fail("$0: write error for message to check\n")
  if -s $tmp != length($message);

print $message if $test;

until (&shlock($lock) > 0) {
  sleep(2);
}

open(PGP,"$pgp -f +language=en < $tmp 2>&1 >/dev/null |") ||
  &fail("$0: failed to execute pgp: $!\n");

undef $/;
$_ = <PGP>;

unlink($lock) || &errmsg("$0: unlink $lock: $!\n");
unlink($tmp)  || &errmsg("$0: unlink $tmp: $!\n");

unless (close(PGP)) {
  if ($? >> 8) {
    &errmsg("$0: pgp exited status " . $? >> 8 . "\n");
  } else {
    &errmsg("$0: pgp died on signal " . $? &255 . "\n");
  }
}

print if $test;

# MIT PGP 2.6.2:
#   Good signature from user "Robert Braver <rbraver@ohww.norman.ok.us>".
# ViaCrypt PGP 4.0:
#   Good signature from user:  Robert Braver <rbraver@ohww.norman.ok.us>
# PGP 5.0i:
#   Good signature made 1997-07-09 21:57 GMT by key:
#     1024 bits, Key ID B88DA9C1, Created 1996-04-10
#      "news.announce.newgroups"

$ok = 2;                        # unknown signature result is default
if (/B[Aa][Dd] signature /) {
  $ok = 3;
} elsif (/Good signature from user(:  (.*)| "(.*)"\.)/ ||
         /Good signature made .* by key:\n.+\n +"(.*)"/) {
  $ok = 0;
  $signer = $+;
} elsif (/Keyring file '(.*)' does not exist/) {
  &fail("$0: couldn't access $1.  Bad \$HOME or \$PGPPATH?\n");
}

print "$signer\n" if $signer;
exit $ok;

sub
errmsg

{
  $_[0] =~ s/\n$//;

  $date = '';
  if ($log_date) {
    eval "require 'ctime.pl'";
    ($date = &ctime(time)) =~ s/\d{4}\n//
      unless $@;
  }

  if ($syslog_method eq "logger") {
    @loggers = ('/usr/bin/logger', '/usr/local/bin/logger');
    foreach $try (@loggers) {
      if (-x $try) {
        $syslog_method = $try;
        last;
      }
    }
    $syslog = '' if $syslog_method eq 'logger';
  }

  if ($syslog && $syslog_method !~ m%/logger$%) {
    if ($] >= 5) {
      eval "use Sys::Syslog";
    } else { 
      eval "require 'syslog.pl'";
    }
  }

  if ($@ || $syslog eq '') {
    warn $date, "$0: trying to use perl's syslog: $@\n" if $@;
    warn $date, $_[0], "\n";
    warn $date, "... while processing $header{'Message-ID'}\n"
      if $header{'Message-ID'};

  } else {
    $_[0] .= " processing $header{'Message-ID'}"
      if $header{'Message-ID'};

    if ($syslog_method =~ m%/logger$%) {
      unless (system($syslog_method, "-i", "-p", $syslog, $_[0]) == 0) {
        if ($? >> 8) {
          warn $date, "$0: $syslog_method exited status ",  $? >>  8, "\n";
        } else {
          warn $date, "$0: $syslog_method died on signal ", $? & 255, "\n";
        }
        $syslog = '';
        &errmsg($_[0]);
      }

    } else {
      # setlogsock arrived in perl 5.004_03 to enable Sys::Syslog
      # to use a Unix domain socket to talk to syslogd, which is
      # the only way to do it when syslog runs with the -l switch.
      if ($syslog_method eq "unix") {
        if ($] <= 5.00403 || ! eval "setlogsock('unix')") {
          warn $date, "$0: cannot use syslog_method 'unix' on this system\n";
          $syslog = '';
          &errmsg($_[0]);
        }
      }
      
      ($facility, $level) = ($syslog =~ /^(w+)\.(\w+)$/);

      # unfortunately, there is no way to definitively know in this program if
      # the message was logged.  I wish there were a way to send a message
      # to stderr if and only if the syslog attempt failed.
      &openlog($0, 'pid', $facility);
      &syslog($level, $_[0]);
      &closelog();
    }
  }

}

sub
fail

{
  unlink($tmp);

  &errmsg($_[0]);

  exit 255;
}

# get a lock in essentially the same fashion as INN's shlock.
# return 1 on success, 0 for normal failure, -1 for abnormal failure.
# "normal failure" is that a lock is apparently in use by someone else.
sub shlock {
  local($file) = @_;
  local($ltmp, $pid);

  unless (defined(&ENOENT)) {
    eval "require POSIX qw(:errno_h)";
    if ($@) {
      # values taken from BSD/OS 3.1
      sub ENOENT {  2 }
      sub ESRCH  {  3 }
      sub EEXIST { 17 }
    }
  }

  $ltmp = ($file =~ m#(.*/)#)[0] . "shlock$$";

  # this should really attempt to use another temp name
  -e $ltmp && (unlink($ltmp) || return -1);

  open(LTMP, ">$ltmp") || return -1;
  print LTMP "$$\n" || (unlink($ltmp), return -1);
  close(LTMP) || (unlink($ltmp), return -1);

  if (!link($ltmp, $file)) {
    if ($! == &EEXIST) {
      if (open(LOCK, "<$file")) {
        $pid = <LOCK>;
        if ($pid =~ /^\d+$/ && (kill(0, $pid) == 1 || $! != &ESRCH)) { 
          unlink($ltmp);
          return 0;
        }

        # ok, the pid in the lockfile is not a number or no longer exists.
        close(LOCK);            # silent failure is ok here

        # unlink failed 
        if (unlink($file) != 1 && $! != &ENOENT) {
          unlink($ltmp);
          return 0;
        }

      # check if open failed for reason other than file no longer present
      } elsif ($! != &ENOENT) { 
        unlink($ltmp);
        return -1;
      }

      # either this process unlinked the lockfile because it was bogus,
      # or between this process's link() and open() the other process
      # holding the lock unlinked it.  This process can now try to aquire.
      if (! link($ltmp, $file)) {
        unlink($ltmp);
        return $! == &EEXIST ? 0 : -1; # maybe another proc grabbed the lock
      }

    } else {                    # first attempt to link failed
      unlink($ltmp);
      return 0;
    }
  }
  unlink($ltmp);
  return 1;
}

# Our lawyer told me to include the following.  The upshot of it is
# that you can use the software for free as much as you like.

# Copyright (c) 1996 UUNET Technologies, Inc.
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
# 3. All advertising materials mentioning features or use of this software
#    must display the following acknowledgement:
#      This product includes software developed by UUNET Technologies, Inc.
# 4. The name of UUNET Technologies ("UUNET") may not be used to endorse or
#    promote products derived from this software without specific prior
#    written permission.
#
# THIS SOFTWARE IS PROVIDED BY UUNET ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED.  IN NO EVENT SHALL UUNET BE LIABLE FOR ANY DIRECT,
# INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
# STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
# OF THE POSSIBILITY OF SUCH DAMAGE.