#!/usr/bin/perl
#============================================================= -*-perl-*-
#
# BackupPC_Admin_SCGI: An SCGI implementation of the BackupPC
#                      admin interface.
#
# DESCRIPTION
#
#   BackupPC_Admin_SCGI runs as the BackupPC user, and spawns one
#   or more children to hangle requests from apache.  Apache needs
#   the mod_scgi plugin, and communicates with BackupPC_Admin_SCGI
#   over a designated TCP port.
#
#   IMPORTANT SECURITY WARNING: the scgi protocol doesn't support any
#   mutual authentication between apache and BackupPC_Admin_SCGI
#   (ie: the SCGI server).  Since apache handles access control,
#   the SCGI server assumes that every request is valid.
#
#   So *anyone* who can connect TCP port $Conf{SCGIServerPort} that
#   BackupPC_Admin_SCGI is listening on has full access to all the
#   BackupPC backups by spoofing SCGI requests.  So if you use
#   BackupPC_Admin_SCGI, you must block the $Conf{SCGIServerPort}
#   TCP port from any remote machines, and only allow trusted users
#   to access the machine that BackupPC_Admin_SCGI is running on.
#
#   BackupPC_Admin_SCGI should refuse connections from non-localhost
#   machines, but it is still recommended you configure your BackupPC
#   host to block port $Conf{SCGIServerPort}.
#
# AUTHOR
#   Craig Barratt  <cbarratt@users.sourceforge.net>
#
# COPYRIGHT
#   Copyright (C) 2013  Craig Barratt
#
#   This program is free software: you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation, either version 3 of the License, or
#   (at your option) any later version.
#
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU General Public License for more details.
#
#   You should have received a copy of the GNU General Public License
#   along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
#========================================================================
#
# Version 4.4.0, released 20 Jun 2020.
#
# See http://backuppc.sourceforge.net.
#
#========================================================================

use strict;
no utf8;

use lib "/usr/share/backuppc/lib";

use IO::Socket;
use Data::Dumper;
use POSIX ":sys_wait_h";
use CGI;

use BackupPC::Lib;
use BackupPC::XS;
use BackupPC::CGI::Lib qw(:all);
use BackupPC::CGI::AdminOptions;
use BackupPC::CGI::Archive;
use BackupPC::CGI::ArchiveInfo;
use BackupPC::CGI::Browse;
use BackupPC::CGI::DeleteBackup;
use BackupPC::CGI::DirHistory;
use BackupPC::CGI::EditConfig;
use BackupPC::CGI::EmailSummary;
use BackupPC::CGI::GeneralInfo;
use BackupPC::CGI::HostInfo;
use BackupPC::CGI::LOGlist;
use BackupPC::CGI::Metrics;
use BackupPC::CGI::Queue;
use BackupPC::CGI::ReloadServer;
use BackupPC::CGI::Restore;
use BackupPC::CGI::RestoreFile;
use BackupPC::CGI::RestoreInfo;
use BackupPC::CGI::StartServer;
use BackupPC::CGI::StartStopBackup;
use BackupPC::CGI::StopServer;
use BackupPC::CGI::Summary;
use BackupPC::CGI::View;

my %ActionDispatch = (
    "summary"              => "Summary",
    "Start_Incr_Backup"    => "StartStopBackup",
    "Start_Full_Backup"    => "StartStopBackup",
    "Stop_Dequeue_Backup"  => "StartStopBackup",
    "Stop_Dequeue_Archive" => "StartStopBackup",
    "queue"                => "Queue",
    "view"                 => "View",
    "LOGlist"              => "LOGlist",
    "emailSummary"         => "EmailSummary",
    "browse"               => "Browse",
    "dirHistory"           => "DirHistory",
    "Restore"              => "Restore",
    "RestoreFile"          => "RestoreFile",
    "hostInfo"             => "HostInfo",
    "generalInfo"          => "GeneralInfo",
    "restoreInfo"          => "RestoreInfo",
    "archiveInfo"          => "ArchiveInfo",
    "Start_Archive"        => "Archive",
    "Archive"              => "Archive",
    "Reload"               => "ReloadServer",
    "startServer"          => "StartServer",
    "Stop"                 => "StopServer",
    "adminOpts"            => "AdminOptions",
    "editConfig"           => "EditConfig",
    "deleteBackup"         => "DeleteBackup",
    "keepBackup"           => "HostInfo",
    "rss"                  => "Metrics",
    "metrics"              => "Metrics",
);
my %ChildPid2Num;

BEGIN {
    eval "use SCGI;";
    if ( $@ ) {
        print("BackupPC_Admin_SCGI: can't load perl SCGI module - install via CPAN; exiting in 60 seconds\n");
        #
        # if we exit immediately, BackupPC will restart us immediately
        #
        sleep(60);
        exit(1);
    }
}

#
# Edit this if you want to get more information about each request
#
my $LogLevel = 0;

$Cgi = new CGI;

die("BackupPC::Lib->new failed\n") if ( !($bpc = BackupPC::Lib->new) );
$TopDir      = $bpc->TopDir();
$LogDir      = $bpc->LogDir();
$BinDir      = $bpc->BinDir();
%Conf        = $bpc->Conf();
$Lang        = $bpc->Lang();
$ConfigMTime = $bpc->ConfigMTime();
umask($Conf{UmaskMode});

my $LockFile    = "$LogDir/scgi_lock";
my $LockFileSz  = 2048;
my $ChildExited = 0;

$SIG{INT}  = \&childKill;
$SIG{CHLD} = \&childCleanup;
my $socket = IO::Socket::INET->new(
    Listen    => 5,
    ReuseAddr => 1,
    LocalAddr => 'localhost',
    LocalPort => $Conf{SCGIServerPort} || 8199
) or die "cannot bind to port $Conf{SCGIServerPort}: $!";

my $scgi = SCGI->new($socket, blocking => 1);

#
# Clean up %ENV for taint checking
#
delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
$ENV{PATH} = $Conf{MyPath};

#
# We use a lock file with $MaxChild + 1 number of bytes to serialize the multiple
# children responding to requests, and to allow the parent to detect when all the
# children are busy (meaning we need more). We create a dummy file with $LockFileSz
# bytes.  The bytes are used as follows:
#
#  - Bytes 1..$MaxChild are locked by each child to indicate they are idle
#    (which generally means they are blocking on locking byte #0).
#
#  - Byte #0 is used to serialize the child's accepts().  Each child tries to lock
#    byte #0.  After one gets the lock, it does an accept().  Once the accept()
#    returns, it unlocks byte #0, and also unlocks byte #child to indicate it is
#    busy processing the request.
#
#  - the parent blocks trying to lock bytes 1..$MaxChild.  If it succeeds, it means
#    all the children are busy, so it forks a new child.
#
my $LockFd;
if ( !open($LockFd, ">", $LockFile) ) {
    print("BackupPC_Admin_SCGI: can't open/create $LockFile; exiting in 60 seconds\n");
    sleep(60);
    exit(1);
}
if ( syswrite($LockFd, chr(0) x $LockFileSz) != $LockFileSz ) {
    print("BackupPC_Admin_SCGI: can't write $LockFileSz bytes to $LockFile; exiting in 60 seconds\n");
    sleep(60);
    exit(1);
}
close($LockFd);

my $MaxChild = 1;
for ( my $i = 0 ; $i < $MaxChild ; $i++ ) {
    childRun($i);
}

#
# This is the parent.  We try to get an exclusive lock on bytes 1..$MaxChild of the
# lock file.  If we succeed in getting the lock, it means all the children are busy
# servicing requests, so we need to spawn another child to service new requests.
#
if ( !open($LockFd, "+<", $LockFile) ) {
    print("BackupPC_Admin_SCGI: can't open $LockFile; exiting in 60 seconds\n");
    sleep(60);
    exit(1);
}
my $LockFdNum = fileno($LockFd);
while ( 1 ) {
    if ( BackupPC::XS::DirOps::lockRangeFd($LockFdNum, 1, $MaxChild, 1) ) {
        if ( $ChildExited ) {
            $ChildExited = 0;
            #
            # If a second child dies while in the signal handler caused by the
            # first death, we won't get another signal. So we must do a non-blocking
            # loop here else we will leave the unreaped child as a zombie. And
            # the next time two children die we get another zombie. And so on.
            #
            # As we reap each child, we start another one in the same slot.
            #
            while ( (my $child = waitpid(-1, WNOHANG)) > 0 ) {
                print("BackupPC_Admin_SCGI: child $child exited ($!)\n")
                  if ( $LogLevel >= 3 );
                if ( defined($ChildPid2Num{$child}) ) {
                    childRun($ChildPid2Num{$child});
                }
            }
            next;
        }
        print("BackupPC_Admin_SCGI: parent lock failed ($!)... continuing\n")
          if ( $LogLevel >= 3 );
        sleep(1);
        next;
    }
    BackupPC::XS::DirOps::unlockRangeFd($LockFdNum, 1, $MaxChild);
    print("BackupPC_Admin_SCGI: all children busy... starting a new child $MaxChild\n")
      if ( $LogLevel >= 5 );
    if ( $MaxChild >= $LockFileSz - 2 ) {
        #
        # Need to extend the lock file size, since we need a lock byte for
        # every child, plus one.
        #
        $LockFileSz *= 2;
        print("BackupPC_Admin_SCGI: extending $LockFile to length $LockFileSz\n");
        sysseek($LockFd, 0, 0);
        if ( syswrite($LockFd, chr(0) x $LockFileSz) != $LockFileSz ) {
            print(
                "BackupPC_Admin_SCGI: can't write $LockFileSz bytes to $LockFile; terminating children and exiting...\n"
            );
            kill 2, keys(%ChildPid2Num);
            sleep(1);
            kill 9, keys(%ChildPid2Num);
            exit(1);
        }
        sysseek($LockFd, 0, 0);
    }
    childRun($MaxChild++);
}

sub childRun
{
    my($childNum) = @_;
    my($pid, $fhRead, $fhWrite);

    #
    # There is a race condition that we have to avoid when we fork a new child.
    # If the parent returns quickly before the child has secured its idle lock,
    # then the parent will immediately think all children are busy, and will
    # start another child.
    #
    # So we create a pipe.  The parent waits for the child to close the pipe,
    # which it does after it has secured its idle lock.  The parent can then
    # continue, trying to lock bytes 1..$MaxChild, which will initially block
    # due to the new child being idle.
    #
    pipe($fhRead, $fhWrite);
    $pid = fork();
    if ( $pid ) {
        #
        # Parent remembers the child's pid, and waits for the child
        # to grab its idle lock.  Then we're done.
        #
        $ChildPid2Num{$pid} = $childNum;
        print("BackupPC_Admin_SCGI: Parent about to read pipe\n") if ( $LogLevel >= 5 );
        close($fhWrite);
        sysread($fhRead, my $dummy, 1);
        close($fhRead);
        print("BackupPC_Admin_SCGI: Parent closing pipe\n") if ( $LogLevel >= 5 );
        return;
    }
    #
    # This is the child.
    #
    $SIG{INT} = "DEFAULT";
    close($fhRead);
    close($LockFd);
    print("BackupPC_Admin_SCGI: child $childNum starting (pid $$)\n") if ( $LogLevel >= 3 );
    if ( !open($LockFd, "+<", $LockFile) ) {
        print("BackupPC_Admin_SCGI: child $childNum can't open $LockFile; exiting\n");
        exit(1);
    }
    $LockFdNum = fileno($LockFd);
    while ( 1 ) {
        #
        # Grab a lock on byte #$childNum to indicate we are idle.
        #
        if ( BackupPC::XS::DirOps::lockRangeFd($LockFdNum, 1 + $childNum, 1, 1) ) {
            print("BackupPC_Admin_SCGI: child $childNum failed to get idle lock ($!)\n")
              if ( $LogLevel >= 3 );
            sleep(1);
            next;
        }
        print("BackupPC_Admin_SCGI: child $childNum got idle lock\n")
          if ( $LogLevel >= 5 );

        if ( defined($fhWrite) ) {
            #
            # Now close the pipe write side, so the parent can safely continue.
            #
            close($fhWrite);
            $fhWrite = undef;
        }

        #
        # We use an exclusive lock on byte 0 of the lock file to make sure
        # only one child does an accept at a time.  As we process the
        # request, another child will get the lock on byte 0 and will accept
        # the next request.
        #
        if ( BackupPC::XS::DirOps::lockRangeFd($LockFdNum, 0, 1, 1) ) {
            print("BackupPC_Admin_SCGI: child $childNum lock failed ($!)... continuing\n")
              if ( $LogLevel >= 3 );
            sleep(1);
            next;
        }
        print("BackupPC_Admin_SCGI: child $childNum got accept lock\n")
          if ( $LogLevel >= 5 );
        my $request = $scgi->accept;
        BackupPC::XS::DirOps::unlockRangeFd($LockFdNum, 0,             1);
        BackupPC::XS::DirOps::unlockRangeFd($LockFdNum, 1 + $childNum, 1);

        my $iaddr = $request->connection->peeraddr();
        if ( ord($iaddr) != 127 ) {
            #
            # peer is not a localhost address (ie: 127.0.0.1/8); ignore it
            #
            my $addrStr = join(".", unpack("C*", $iaddr));
            printf("BackupPC_Admin_SCGI: unexpected connection from $addrStr (%s) ignored\n",
                gethostbyaddr($iaddr, AF_INET));
            $request = undef;
            next;
        }
        print("BackupPC_Admin_SCGI: child $childNum processing request\n")
          if ( $LogLevel >= 5 );
        handleRequest($request);
        $request = undef;
        select(STDOUT);
        print("BackupPC_Admin_SCGI: child $childNum finished request\n")
          if ( $LogLevel >= 5 );
    }
}

sub handleRequest
{
    my($request) = @_;

    $request->read_env;
    my $con = $request->connection;
    read($con, my $body, $request->env->{CONTENT_LENGTH});

    select($con);
    NewRequest($request, $body);

    if ( $LogLevel >= 4 ) {
        my $fdDebug;
        open($fdDebug, ">", "$LogDir/request.txt");
        print $fdDebug "Environment: ", Dumper($request->env), "\n\n";
        print $fdDebug "Body: ", $body, "\n\n";
        print $fdDebug "Other: ", "User = $User, MyURL = $MyURL, PID = $$, In = ", Dumper(\%In), "Conf = ",
          Dumper(\%Conf), "\n\n";
        close($fdDebug);
    }
    if ( !defined($ActionDispatch{$In{action}}) ) {
        $In{action} = defined($In{host}) ? "hostInfo" : "generalInfo";
    }
    my $action = $ActionDispatch{$In{action}};
    $BackupPC::CGI::{"${action}::"}{action}();
}

sub NewRequest
{
    my($request, $body) = @_;
    my($queryStr);

    %In = ();
    if ( $request->env->{REQUEST_METHOD} eq "POST" ) {
        $queryStr = $body;
    } else {
        $queryStr = $request->env->{QUERY_STRING};
    }
    foreach my $p ( split(/&/, $queryStr) ) {
        next if ( $p !~ /^([^=]*)=(.*)/ );
        my $name = $1;
        $In{$name} = $2;
        $In{$name} =~ s/\+/ /g;
        $In{$name} =~ s{%(..)}{chr(hex($1))}eg;
    }
    $ENV{SCRIPT_NAME} = $request->env->{SCRIPT_NAME};
    $ENV{REMOTE_USER} = $request->env->{REMOTE_USER};
    $ENV{REQUEST_URI} = $request->env->{REQUEST_URI};

    if ( $bpc->ConfigMTime() != $ConfigMTime ) {
        $bpc->ConfigRead();
        $TopDir      = $bpc->TopDir();
        $LogDir      = $bpc->LogDir();
        $BinDir      = $bpc->BinDir();
        %Conf        = $bpc->Conf();
        $Lang        = $bpc->Lang();
        $ConfigMTime = $bpc->ConfigMTime();
        umask($Conf{UmaskMode});
    }

    #
    # Default REMOTE_USER so in a miminal installation the user
    # has a sensible default.
    #
    $ENV{REMOTE_USER} = $Conf{BackupPCUser} if ( $ENV{REMOTE_USER} eq "" );

    #
    # We require that Apache pass in $ENV{SCRIPT_NAME} and $ENV{REMOTE_USER}.
    # The latter requires .ht_access style authentication.  Replace this
    # code if you are using some other type of authentication, and have
    # a different way of getting the user name.
    #
    $MyURL = $ENV{SCRIPT_NAME};
    $User  = $ENV{REMOTE_USER};

    #
    # Handle LDAP uid=user when using mod_authz_ldap and otherwise untaint
    #
    $User = $1 if ( $User =~ /uid=([^,]+)/i || $User =~ /(.*)/ );

    if ( !defined($Hosts) || $bpc->HostsMTime() != $HostsMTime ) {
        $HostsMTime = $bpc->HostsMTime();
        $Hosts      = $bpc->HostInfoRead();

        # turn moreUsers list into a hash for quick lookups
        foreach my $host ( keys %$Hosts ) {
            $Hosts->{$host}{moreUsers} =
              {map { $_, 1 } split(",", $Hosts->{$host}{moreUsers})};
        }
    }

    #
    # Untaint the host name
    #
    if ( $In{host} =~ /^([\w.\s-]+)$/ ) {
        $In{host} = $1;
    } else {
        delete($In{host});
    }
}

sub childCleanup
{
    $ChildExited = 1;
    $SIG{CHLD} = \&childCleanup;
}

sub childKill
{
    #print("childKill: ", join(",", keys(%ChildPid2Num)), "\n");
    kill 2, keys(%ChildPid2Num);
    sleep(1);
    kill 9, keys(%ChildPid2Num);
    exit(0);
}
