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Filename : linux-check-removal
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#!/usr/bin/perl

# Copyright 1996-2006 Manoj Srivastava
# Copyright 2016 Ben Hutchings
#
# 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 2 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, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

use strict;
use warnings;
use FileHandle;
use POSIX ();

sub usage {
    my $fh = shift;
    print $fh (<< "EOT");
Usage: $0 VERSION

This command is intended to be called from the prerm maintainer scripts
of Linux kernel packages.

The VERSION argument must be the kernel version string as shown by
'uname -r' and used in filenames.

If the currently running kernel matches VERSION, linux-check-removal
will normally prompt the user to confirm this potentially dangerous
action and will fail if the user chooses to abort.  However, if the
current environment is in a chroot or container, or if debconf
prompts are disabled, it will always succeed without prompting.
EOT
}

sub usage_error {
    usage(*STDERR{IO});
    exit 2;
}

# Check usage early, before Debconf::Client::ConfModule initialises and
# adds its complaints about permissions
BEGIN {
    if (@ARGV != 1) {
	usage_error();
    }
    if ($ARGV[0] eq 'help' or grep({$_ eq '--help'} @ARGV)) {
	usage(*STDOUT{IO});
	exit 0;
    }
}

# Are we in a container?  Check for $container in pid 1's environment.
sub in_container {
    my $res = 0;
    if (my $fh = new FileHandle('/proc/1/environ', 'r')) {
	local $/ = "\0";
	$res = grep(/^container=/, <$fh>);
	close($fh);
    }
    return $res;
}

# Are we in in a chroot?  Compare root device and inode numbers with pid 1.
sub in_chroot {
    my @my_root_st = stat('/');
    my @pid1_root_st = stat('/proc/1/root');

    return @my_root_st && @pid1_root_st &&
	($my_root_st[0] != $pid1_root_st[0] || $my_root_st[1] != $pid1_root_st[1]);
}

sub check {
    my ($version) = @_;
    my (undef, undef, $running, undef, undef) = POSIX::uname();

    if ($running ne $version || in_chroot() || in_container()) {
	exit 0;
    }

    if (!exists($ENV{'DEBIAN_FRONTEND'}) ||
	$ENV{'DEBIAN_FRONTEND'} ne 'noninteractive') {
	use Debconf::Client::ConfModule qw(:all);

	my $title = 'linux-base/removing-title';
	my $question = "linux-base/removing-running-kernel";
	my ($ret, $seen, $answer);

	# debconf only generates a title automatically when used directly
	# from a maintainer script.  Also, the automatic title says we are
	# 'configuring' a package but we're not.
	($ret) = subst($title, 'package', $ENV{DPKG_MAINTSCRIPT_PACKAGE});
	if ($ret) {
	    die "Failed to substitute package name in title: $ret";
	}
	($ret) = settitle($title);
	if ($ret) {
	    die "Failed to set title: $ret";
	}
	($ret) = fset($question, 'seen', 'false');
	if ($ret) {
	    die "Failed to reset seen flag for $question: $ret";
	}
	($ret) = reset($question);
	if ($ret) {
	    die "Failed to reset answer for $question: $ret";
	}
	($ret) = subst($question, 'running', $running);
	if ($ret) {
	    die "Failed to substitute version in $question: $ret";
	}
	($ret, $seen) = input('critical', $question);
	if ($ret && $ret != 30) {
	    die "Failed to prepare question $question: $ret $seen";
	}
	($ret, $seen) = go();
	if ($ret && $ret != 30) {
	    die "Failed to ask question $question: $ret $seen";
	}
	($ret, $answer) = get($question);
	if ($ret) {
	    die "Failed to retrieve answer for $question: $ret $answer";
	}

	if ($answer eq 'true') {
	    print STDERR "E: Aborting removal of the running kernel\n";
	    exit 1;
	}
    }

    print STDERR "W: Removing the running kernel\n";
    exit 0;
}

check(@ARGV);