/usr/share/perl5/Mail/SpamAssassin/Locker/UnixNFSSafe.pm is in spamassassin 3.4.0-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements. See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to you under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License. You may obtain a copy of the License at:
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# </@LICENSE>
package Mail::SpamAssassin::Locker::UnixNFSSafe;
use strict;
use warnings;
use bytes;
use re 'taint';
use Mail::SpamAssassin;
use Mail::SpamAssassin::Locker;
use Mail::SpamAssassin::Util;
use Mail::SpamAssassin::Logger;
use File::Spec;
use Time::Local;
use Fcntl qw(:DEFAULT :flock);
use vars qw{
@ISA
};
@ISA = qw(Mail::SpamAssassin::Locker);
###########################################################################
sub new {
my $class = shift;
my $self = $class->SUPER::new(@_);
$self;
}
###########################################################################
# NFS-safe locking (I hope!):
# Attempt to create a file lock, using NFS-safe locking techniques.
#
# Locking code adapted from code by Alexis Rosen <alexis@panix.com>
# by Kelsey Cummings <kgc@sonic.net>, with mods by jm and quinlan
#
# A good implementation of Alexis' code, for reference, is here:
# http://mail-index.netbsd.org/netbsd-bugs/1996/04/17/0002.html
use constant LOCK_MAX_AGE => 600; # seconds
sub safe_lock {
my ($self, $path, $max_retries, $mode) = @_;
my $is_locked = 0;
my @stat;
$max_retries ||= 30;
$mode ||= "0700";
$mode = (oct $mode) & 0666;
dbg ("locker: mode is $mode");
my $lock_file = "$path.lock";
my $hname = Mail::SpamAssassin::Util::fq_hostname();
my $lock_tmp = Mail::SpamAssassin::Util::untaint_file_path
($path.".lock.".$hname.".".$$);
# keep this for unlocking
$self->{lock_tmp} = $lock_tmp;
my $umask = umask(~$mode);
if (!open(LTMP, ">$lock_tmp")) {
umask $umask; # just in case
die "locker: safe_lock: cannot create tmp lockfile $lock_tmp for $lock_file: $!\n";
}
umask $umask;
autoflush LTMP 1;
dbg("locker: safe_lock: created $lock_tmp");
for (my $retries = 0; $retries < $max_retries; $retries++) {
if ($retries > 0) { $self->jittery_one_second_sleep(); }
print LTMP "$hname.$$\n" or warn "Error writing to $lock_tmp: $!";
dbg("locker: safe_lock: trying to get lock on $path with $retries retries");
if (link($lock_tmp, $lock_file)) {
dbg("locker: safe_lock: link to $lock_file: link ok");
$is_locked = 1;
last;
}
# link _may_ return false even if the link _is_ created
@stat = lstat($lock_tmp);
@stat or warn "locker: error accessing $lock_tmp: $!";
if (defined $stat[3] && $stat[3] > 1) {
dbg("locker: safe_lock: link to $lock_file: stat ok");
$is_locked = 1;
last;
}
# check age of lockfile ctime
my $now = ($#stat < 11 ? undef : $stat[10]);
@stat = lstat($lock_file);
@stat or warn "locker: error accessing $lock_file: $!";
my $lock_age = ($#stat < 11 ? undef : $stat[10]);
if (defined($lock_age) && defined($now) && ($now - $lock_age) > LOCK_MAX_AGE)
{
# we got a stale lock, break it
dbg("locker: safe_lock: breaking stale $lock_file: age=" .
(defined $lock_age ? $lock_age : "undef") . " now=$now");
unlink($lock_file)
or warn "locker: safe_lock: unlink of lock file $lock_file failed: $!\n";
}
}
close LTMP or die "error closing $lock_tmp: $!";
unlink($lock_tmp)
or warn "locker: safe_lock: unlink of temp lock $lock_tmp failed: $!\n";
# record this for safe unlocking
if ($is_locked) {
@stat = lstat($lock_file);
@stat or warn "locker: error accessing $lock_file: $!";
my $lock_ctime = ($#stat < 11 ? undef : $stat[10]);
$self->{lock_ctimes} ||= { };
$self->{lock_ctimes}->{$path} = $lock_ctime;
}
return $is_locked;
}
###########################################################################
sub safe_unlock {
my ($self, $path) = @_;
my $lock_file = "$path.lock";
my $lock_tmp = $self->{lock_tmp};
if (!$lock_tmp) {
dbg("locker: safe_unlock: $path.lock never locked");
return;
}
# 1. Build a temp file and stat that to get an idea of what the server
# thinks the current time is (our_tmp.st_ctime). note: do not use time()
# directly because the server's clock may be out of sync with the client's.
my @stat_ourtmp;
if (!defined sysopen(LTMP, $lock_tmp, O_CREAT|O_WRONLY|O_EXCL, 0700)) {
warn "locker: safe_unlock: failed to create lock tmpfile $lock_tmp: $!";
return;
} else {
autoflush LTMP 1;
print LTMP "\n" or warn "Error writing to $lock_tmp: $!";
if (!(@stat_ourtmp = stat(LTMP)) || (scalar(@stat_ourtmp) < 11)) {
@stat_ourtmp or warn "locker: error accessing $lock_tmp: $!";
warn "locker: safe_unlock: failed to create lock tmpfile $lock_tmp";
close LTMP or die "error closing $lock_tmp: $!";
unlink($lock_tmp)
or warn "locker: safe_lock: unlink of lock file failed: $!\n";
return;
}
}
my $ourtmp_ctime = $stat_ourtmp[10]; # paranoia
if (!defined $ourtmp_ctime) {
die "locker: safe_unlock: stat failed on $lock_tmp";
}
close LTMP or die "error closing $lock_tmp: $!";
unlink($lock_tmp)
or warn "locker: safe_lock: unlink of lock file failed: $!\n";
# 2. If the ctime hasn't been modified, unlink the file and return. If the
# lock has expired, sleep the usual random interval before returning. If we
# didn't sleep, there could be a race if the caller immediately tries to
# relock the file.
my $lock_ctime = $self->{lock_ctimes}->{$path};
if (!defined $lock_ctime) {
warn "locker: safe_unlock: no ctime recorded for $lock_file";
return;
}
my @stat_lock = lstat($lock_file);
@stat_lock or warn "locker: error accessing $lock_file: $!";
my $now_ctime = $stat_lock[10];
if (defined $now_ctime && $now_ctime == $lock_ctime)
{
# things are good: the ctimes match so it was our lock
unlink($lock_file)
or warn "locker: safe_unlock: unlink failed: $lock_file\n";
dbg("locker: safe_unlock: unlink $lock_file");
if ($ourtmp_ctime >= $lock_ctime + LOCK_MAX_AGE) {
# the lock has expired, so sleep a bit; use some randomness
# to avoid race conditions.
dbg("locker: safe_unlock: lock expired on $lock_file expired safely; sleeping");
my $i; for ($i = 0; $i < 5; $i++) {
$self->jittery_one_second_sleep();
}
}
return;
}
# 4. Either ctime has been modified, or the entire lock file is missing.
# If the lock should still be ours, based on the ctime of the temp
# file, warn it was stolen. If not, then our lock is expired and
# someone else has grabbed the file, so warn it was lost.
if ($ourtmp_ctime < $lock_ctime + LOCK_MAX_AGE) {
warn "locker: safe_unlock: lock on $lock_file was stolen";
} else {
warn "locker: safe_unlock: lock on $lock_file was lost due to expiry";
}
}
###########################################################################
sub refresh_lock {
my($self, $path) = @_;
return unless $path;
# this could arguably read the lock and make sure the same process
# owns it, but this shouldn't, in theory, be an issue.
# TODO: in NFS, it definitely may be one :(
my $lock_file = "$path.lock";
utime time, time, $lock_file;
# update the lock_ctimes entry
my @stat = lstat($lock_file);
@stat or warn "locker: error accessing $lock_file: $!";
my $lock_ctime = ($#stat < 11 ? undef : $stat[10]);
$self->{lock_ctimes}->{$path} = $lock_ctime;
dbg("locker: refresh_lock: refresh $path.lock");
}
###########################################################################
1;
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