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#! /usr/bin/perl
# Copyright (C) 2013 Sergey Poznyakoff <gray@gnu.org>
#
# 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, 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/>.

use strict;
use File::Spec;
use Pod::Man;
use Pod::Usage;

=head1 NAME

gitaclhook - control access to git repositories

=head1 SYNOPSIS

B<gitaclhook> I<refname> I<old-sha1> I<new-sha1>

B<gitaclhook --help>     

=head1 DESCRIPTION
    
This program is intended to be run as an "update" hook by git.
It is called by B<git-receive-pack> with arguments:
I<refname> I<old-sha1> I<new-sha1>.

If the B<hooks.aclfile> keyword is defined in the repository's config file,
this hook will parse the file and allow or deny update depending on
its settings.  If B<hooks.aclfile> is not defined, update is allowed
unconditionally.

=head1 ACL FILE
    
The ACL file has the usual line-oriented syntax.  Comments are introduced
by the # sign and extend to the end of the physical line.  Comments and
empty lines are ignored.

Non-empty lines introduce ACL rules.  The syntax is:

=over 4
    
I<VERB> I<PROJECT> I<USER> [I<OP> I<REF>]

=back

where brackets denote optional parts.  The parts of an ACL are:

=over 4

=item I<VERB>

Either B<allow> or B<deny>, to allow or deny the operation, correspondingly.

=item I<PROJECT>

The name of the project.  It is obtained by removing the directory
and suffix parts of the repository pathname.  Thus, if the repository
is located in B</var/gitroot/foobar.git>, then the corresponding name of
the project is B<foobar>.

An asterisk matches any project name.

=item I<USER>

Name of the user.  The word B<all> stands for any user, the word B<none>
matches no one at all.  Otherwise, if this part begins with a percent
sign (B<%>), the rest of characters are treated as the name of the UNIX
group to check and the rule matches any user in that group.  Otherwise,
the literal match is assumed.

=back

The optional parts are:

=over 4

=item I<OP>

Requested operation codes.  It is a string consisting of one or more
of the following letters (case-insensitive):

=over 8

=item B<C>

Create new ref.

=item B<D>

Delete existing ref.

=item B<U>

Fast-forward existing ref (no commit loss).

=item B<R>

Rewind or rebase existing ref (commit loss).

=back    
    
=item I<REF>

Affected ref, relative to the git B<refs/> directory.  If it begins with
a caret (B<^>), it is treated as a Perl regular expression (with the B<^>
being its part).  If it ends with a B</>, it is treated as a prefix match,
so, e.g., B<heads/baz/> matches B<refs/heads/baz> and anything below.
Otherwise, it must match exactly the affected ref.

=back

=head1 RULE MATCHING
    
The rule applies only if its I<PROJECT> and I<USER> parts match the project
which is being updated and the user who requests the update, its I<OP>
contains the opcode of the requested operation and I<REF> matches the affected
ref.  Missing I<REF> and/or I<OP> are treated as a match.

If no rule applies, the operation is allowed.

For example, assume you have the following ACL file:

    allow myprog %devel   U    heads/master
    allow myprog %pm      CDUR heads/
    allow myprog %pm      C    ^heads/tags/v\\d+$
    allow myprog admin    CDUR
    deny myprog all

Then the users from the B<devel> group will be able to push updates to
B<refs/heads/master>, the users from the B<pm> group will be allowed to do
anything with refs under B<refs/heads> and to create tags with names beginning
with B<v> and containing only digits afterwards, and the user B<admin> will
be allowed to do anything he pleases.  No other users will be allowed to
update that repository.

=head1 CONFIGURATION SETTINGS

=over 4

=item B<hooks.aclfile>    STRING

Name of the ACL file.

=item B<hooks.acllog>     STRING

Send log info to this file.

=item B<hooks.acldebug>   BOOL

Enable debugging.

=item B<hooks.aclquiet>   BOOL

Suppress diagnostics on stderr.

=item B<hooks.httpd-user> STRING

Name of the user httpd runs as.  Define it if the repository can be
accessed via HTTP(S).  If B<gitaclhook> is run as this user, it will
get the name of the user on behalf of which the update is performed
from the environment variable B<REMOTE_USER>.

=back

=head1 SEE ALSO

B<git-receive-pack>(1).     
    
=head1 AUTHOR

Sergey Poznyakoff, <gray@gno.org>    
    
=cut

my $debug = $ENV{GIT_UPDATE_DEBUG} > 0;
my $logfile;
my $quiet;
my ($user_name) = getpwuid $<;
my $git_dir = $ENV{GIT_DIR};
my $ref = $ARGV[0];
my $old = $ARGV[1];
my $new = $ARGV[2];

my $project_name;
my $op;

my %opstr = ('C' => 'create',
	     'D' => 'delete',
	     'U' => 'update',
	     'R' => 'rewind/rebase');

sub logmsg($$;$) {
    return 0 unless $logfile;

    my $status = shift;
    my $message = shift;
    my $loc = shift;
    my $fd;

    open($fd, $logfile);
    if ($loc) {
	print $fd "$status:$loc: $message\n";
    } else {
	print $fd "$status: $message\n";
    }
    close($fd);
}

sub deny($;$) {
    my $msg = shift;
    my $loc = shift;

    logmsg("DENY",
	   "$project_name:$user_name:$opstr{$op}:$ref:$old:$new: $msg",
	   $loc);

    print STDERR "debug: denied by $loc\n" if ($debug and $loc);
    print STDERR "denied: $msg\n" unless $quiet;
    exit 1;
}

sub allow($) {
    logmsg("ALLOW",
	   "$project_name:$user_name:$opstr{$op}:$ref:$old:$new",
	   $_[0]);
    print STDERR "debug: allow $_[0]\n" if $debug;
    exit 0;
}

sub info($) {
    logmsg("INFO", $_[0]);
    print STDERR "info: $_[0]\n" if $debug;
}

sub git_value(@) {
    my $fd;
    
    open($fd,'-|','git',@_);
    local $_ = <$fd>;
    chop;
    close($fd);
    return $_;
}

sub match_user($) {
    my $user = shift;
    return 1 if ($user eq 'all');
    return 0 if ($user eq 'none');
    if ($user =~ /^%(.+)/) {
	my ($name,$passwd,$gid,$members) = getgrnam($1) or return 0;
	my @a = split(/\s+/,$members);
	for (my $i = 0; $i <= $#a; $i++) {
	    return 1 if $a[$i] eq $user_name;
	}
    } elsif ($user eq $user_name) {
	return 1;
    }
    return 0;
}

sub match_ref($) {
    my $expr = shift;
    return ($ref =~ /$expr/) if ($expr =~ /^\^/);
    return ("$ref/" eq $expr or index($ref, $expr) == 0) if ($expr =~ /\/$/);
    return $ref eq $expr;
}

sub check_acl($$$) {
    my $project = shift;
    my $op = shift;
    my $ref = shift;
    my $fd;
    my $line = 0;
    my @ret;
    
    my $filename = git_value('config', 'hooks.aclfile');
    allow("no ACL configured for $project")
	unless defined($filename);

    open($fd, "<", $filename) or deny("cannot open configuration file: $!");
    while (<$fd>) {
	++$line;
	chomp;
	s/^\s+//;
	s/\s+$//;
	s/#.*//;
	next if ($_ eq "");
	my @x = split(/\s+/, $_, 5);
	
	deny("unknown keyword", "$filename:$line")
	    unless ($x[0] eq 'allow' || $x[0] eq 'deny');
	deny("malformed line", "$filename:$line")
	    unless $#x >= 2;
	
	next if ($x[1] ne "*" and $x[1] ne $project);
	next unless match_user($x[2]);
	next if ($#x >= 3 && index(uc $x[3], $op) == -1);
	next if ($#x == 4 && !match_ref($x[4]));

	allow("$filename:$line") if ($x[0] eq 'allow');
	deny("you are not permitted to " . $opstr{$op} . " $ref",
	     "$filename:$line");
    }
    close($fd);
    allow("default rule");
}

####

# Sanity checks
unless ($git_dir) {
    pod2usage(-exitstatus => 0, -verbose => 2) if ($ref eq "--help");
    deny "try \"$0 --help\" for fore info"
}

$debug = git_value('config', '--bool', 'hooks.acldebug') unless ($debug);
$logfile = git_value('config', 'hooks.acllog');
if ($logfile && $logfile !~ /[>|]/) {
    $logfile = ">>$logfile";
}
$quiet = git_value('config', 'hooks.aclquiet') unless ($debug);

my $httpdusr = git_value('config', 'hooks.httpd-user');
if (defined($httpdusr) and $user_name eq $httpdusr) {
    deny "need authenticated user" unless defined($ENV{AUTH_TYPE});
    $user_name = $ENV{REMOTE_USER};
}

deny "need a ref name" unless $ref;
deny "bogus ref $ref" unless $ref =~ s,^refs/,,;
deny "bad old value $old" unless $old =~ /^[a-z0-9]{40}$/;
deny "bad new value $new" unless $new =~ /^[a-z0-9]{40}$/;
deny "no such user" unless $user_name;
allow "no change requested" if $old eq $new;

$project_name = File::Spec->rel2abs($git_dir);
$project_name =~ m,/([^/]+)(?:\.git|/\.git)$,;
$project_name = $1;

if ($old =~ /^0{40}$/) {
    $op = 'C';
} elsif ($new =~ /^0{40}$/) {
    $op = 'D';
} elsif ($ref =~ m,^heads/, && $old eq git_value('merge-base',$old,$new)) {
    $op = 'U';
} else {
    $op = 'R';
}

info "$user_name requested $opstr{$op} on $ref in $project_name";

check_acl($project_name, $op, $ref);

# Finis






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