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Merge pull request #237 from briandfoy/briandfoy/symbolic-mode
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(WIP) Recover SymbolicMode.pm
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@briandfoy
briandfoy authored Sep 13, 2023
2 parents 9c53c92 + f6708b1 commit 5d0c940
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207 changes: 204 additions & 3 deletions bin/chmod
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Original file line number Diff line number Diff line change
Expand Up @@ -64,7 +64,6 @@ my $mode = shift;

my $symbolic = 0;
if ($mode =~ /[^0-7]/) {
require SymbolicMode;
$symbolic = 1;
}
elsif ($mode !~ /^[0-7]{1,4}$/) {
Expand Down Expand Up @@ -113,14 +112,216 @@ sub modify_file {
}
my $realmode = $mode;
if ($symbolic) {
$realmode = SymbolicMode::mod ($mode, $file) or
$realmode = mod($mode, $file) or
die "invalid mode: $mode\n";
}
chmod oct ($realmode), $file or warn "$!\n";
}

exit $warnings;

#
# $Id: SymbolicMode.pm,v 1.1 2004/07/23 20:10:01 cwest Exp $
#
# $Log: SymbolicMode.pm,v $
# Revision 1.1 2004/07/23 20:10:01 cwest
# initial import
#
# Revision 1.1 1999/03/07 12:03:54 abigail
# Initial revision
#
#

sub mod ($$) {
my $symbolic = shift;
my $file = shift;

# Initialization.
# The 'user', 'group' and 'other' groups.
my @ugo = qw /u g o/;
# Bit masks for '[sg]uid', 'sticky', 'read', 'write' and 'execute'.
# Can't use qw // cause silly Perl doesn't know '2' is a number
# when dealing with &= ~$bit.
my %bits = (s => 8, t => 8, r => 4, w => 2, x => 1);


# For parsing.
my $who_re = '[augo]*';
my $action_re = '[-+=][rstwxXugo]*';


# Find the current permissions. This is what we start with.
my $mode = sprintf "%04o" => (stat $file) [2] || 0;
my $current = substr $mode => -3; # rwx permissions for ugo.

my %perms;
@perms {@ugo} = split // => $current;

# Handle the suid, guid and sticky bits.
# It looks like permission are 4 groups of 3 bits, groups for user,
# group and others, and a group for the special flags, but they are
# really 3 groups of 4 bits. Or maybe not.
# Anyway, this function is greatly simplified by treating them as
# 3 4-bit groups. The highest bit will be "special" one. suid for
# the users group, guid for the group group, and the sticky bit
# for the others group.
my $special = substr $mode => -4, 1;
my $bit = 1;
foreach my $c (reverse @ugo) {
$perms {$c} |= 8 if $special & $bit;
$bit <<= 1;
}

# Keep track of the original permissions.
my %orig = %perms;

# Find the umask setting, and store the bits for each group
# in a hash.
my %umask; # umask bits.
@umask {@ugo} = split // => sprintf "%03o" => umask;


# Time to parse...
foreach my $clause (split /,/ => $symbolic) {

# Perhaps we should die if we can't parse it?
return undef unless
my ($who, $actions) =
$clause =~ /^($who_re)((?:$action_re)+)$/o;
# We would rather split the different actions out here,
# but there doesn't seem to be a way to collect them.
# /^($who_re)($action_re)+/ only gets the last one.
# Now, we have to reparse in later.

my %who;
if ($who) {
$who =~ s/a/ugo/; # Ignore multiple 'a's.
@who {split // => $who} = undef;
}

# @who will contain who these settings applies to.
# if who isn't set, it might be masked with the umask,
# hence, this isn't the final decision.
# Maybe we don't need this.
my @who = $who ? keys %who : @ugo;

foreach my $action (split /(?=$action_re)/o => $actions) {
# The first character has to be the operator.
my $operator = substr $action, 0, 1;
# And the rest are the permissions.
my $perms = substr $action, 1;

# BSD documentation says 'X' is to be ignored unless
# the operator is '-'. GNU, HP, SunOS and Solaris handle
# '-' and '=', while OpenBSD ignores only '-'.
# Solaris, HP and OpenBSD all turn a file with permission
# 666 to a file with permission 000 if chmod =X is
# is applied on it. SunOS and GNU act as if chmod = was
# applied to it. I cannot find out what the reasoning
# behind the choices of Solaris, HP and OpenBSD is.
# GNU and SunOS seem to ignore the 'X', which, after
# careful studying of the documentation seems to be
# the right choice.
# Therefore, remove any 'X' if the operator ain't '+';
$perms =~ s/X+//g unless $operator eq '+';

# If there are no permissions, things are simple.
unless ($perms) {
# Things like u+ and go- are ignored; only = makes sense.
next unless $operator eq '=';
# Clear permissions on u= and go=.
if ($who) {@perms {keys %who} = (0) x 3;}
# '=' is special. Sets permissions to the umask.
else {%perms = %umask;}
next;
}

# If we arrive here, $perms is a string.
# We can iterate over the characters.
foreach (split // => $perms) {
if ($_ eq 'X') {
# We know the operator eq '+'.
# Permission of `X' is special. If used on a regular file,
# the execution bit will only be turned on if any of the
# execution bits of the _unmodified_ file are turned on.
# That is,
# chmod 600 file; chmod u+x,a+X file;
# should result in the file having permission 700, not 711.
# GNU and SunOS get this wrong;
# Solaris, HP and OpenBSD get it right.
next unless -d $file || grep {$orig {$_} & 1} @ugo;
# Now, do as if it's an x.
$_ = 'x';
}

if (/[st]/) {
# BSD man page says operations on 's' and 't' are to
# be ignored if they operate only on the "other" group.
# GNU and HP happely accept 'o+t'. Sun rejects 'o+t',
# but also rejects 'g+t', accepting only 'u+t'.
# OpenBSD acceps both 'u+t' and 'g+t', ignoring 'o+t'.
# We do too.
# OpenBSD however, accepts 'o=t', clearing all the bits
# of the "other" group.
# We don't, as that doesn't make any sense, and doesn't
# confirm to the documentation.
next if $who =~ /^o+$/;
}

# Determine the $bit for the mask.
my $bit = /[ugo]/ ? $orig {$_} & ~8 : $bits {$_};

die "Weird permission `$_' found\n" unless defined $bit;
# Should not happen.

# Determine the set on which to operate.
my @set = $who ? @who : grep {!($umask {$_} & $bit)} @ugo;

# If the permission is 's', don't operate on the other group.
# Unless the operator was '='. But in that case, don't set
# the 8 bit for 'other'.
my $equal_s;
if (/s/) {
if ($operator eq '=') {$equal_s = 1;}
else {@set = grep {!/o/} @set or next;}
}
# If the permission is 't', only operate on the other group;
# regardless what the 'who' settings are.
# Note that for a directory with permissions 1777, and a
# umask of 002, a chmod =t on HP and Solaris turn the
# permissions to 1000, GNU and SunOS turn the permissiosn
# to 1020, while OpenBSD keeps 1777.
/t/ and @set = qw /o/;

# Apply.
foreach my $s (@set) {
do {$perms {$s} |= $bit; next} if $operator eq '+';
do {$perms {$s} &= ~$bit; next} if $operator eq '-';
do {$perms {$s} = $bit; next} if $operator eq '=';
die "Weird operator `$operator' found\n";
# Should not happen.
}

# Special case '=s'.
$perms {o} &= ~$bit if $equal_s;
}
}
}

# Now, translate @perms to an *octal* number.

# First, deal with the suid, guid, and sticky bits by collecting
# the high bits of the ugo permissions.
my $first = 0;
$bit = 1;
for my $c (reverse @ugo) {
if ($perms {$c} & 8) {$first |= $bit; $perms {$c} &= ~8;}
$bit <<= 1;
}

join "" => $first, @perms {@ugo};
}

__END__
=pod
Expand Down Expand Up @@ -385,7 +586,7 @@ The OpenBSD documentation does not match the OpenBSD implementation.
Furthermore, the implementations of Solaris, SunOS, HP, and GNU all differ
from each other, and from OpenBSD.
This manual page needs work. The module I<SymbolicMode> needs to be
This manual page needs work. The module I<PerlPowerTools::SymbolicMode> needs to be
documented.
B<chmod> parses a symbolic mode once for each file. That is too much
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