I'm trying to add a feature to a legacy script. The script is suid, and uses perl -T (taint mode: man perlsec), for extra security. The feature I need to add is implemented in Python.
My problem is that I can't convince perlsec to preserve the suid permissions, no matter how much I launder the environment and my command lines.
This is frustrating, since it preserves the suid for other binaries (such as /bin/id). Is there a undocumented special case for /usr/bin/perl? This seems unlikely.
Does anyone know a way to make this work? (As-is: We don't have the resources to re-architect this whole thing.)
Solution: (as per @gbacon)
# use the -p option to bash
system('/bin/bash', '-p', '-c', '/usr/bin/id -un');
# or set real user and group ids
$< = $>;
$( = $);
system('/usr/bin/python', '-c', 'import os; os.system("/usr/bin/id -un")');
Gives the desired results!
Here's a cut-down version of my script, which still shows my problem.
#!/usr/bin/perl -T
## This is an SUID script: man perlsec
%ENV = ( "PATH" => "" );
##### PERLSEC HELPERS #####
sub tainted (@) {
# Prevent errors, stringifying
local(@_, $@, $^W) = @_;
#let eval catch the DIE signal
$SIG{__DIE__} = '';
my $retval = not eval { join("",@_), kill 0; 1 };
$SIG{__DIE__} = 'myexit';
return $retval
}
sub show_taint {
foreach (@_) {
my $arg = $_; #prevent "read-only variable" nonsense
chomp $arg;
if ( tainted($arg) ) {
print "TAINT:'$arg'";
} else {
print "ok:'$arg'";
}
print ", ";
}
print "\n";
}
### END PERLSEC HELPERS ###
# Are we SUID ? man perlsec
my $uid = `/usr/bin/id --user` ;
chomp $uid;
my $reluser = "dt-pdrel";
my $reluid = `/usr/bin/id --user $reluser 2> /dev/null`;
chomp $reluid;
if ( $uid ne $reluid ) {
# what ? we are not anymore SUID ? somebody must do a chmod u+s $current_script
print STDERR "chmod 4555 $myname\n";
exit(14);
}
# comment this line if you don't want to autoflush after every print
$| = 1;
# now, we're safe, single & SUID
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# BEGIN of main code itself
print "\nENVIRON UNDER BASH:\n";
run('/bin/bash', '-c', '/bin/env');
print "\nTAINT DEMO:\n";
print "\@ARGV: ";
show_taint(@ARGV);
print "\%ENV: ";
show_taint(values %ENV);
print "`cat`: ";
show_taint(`/bin/cat /etc/host.conf`);
print "\nworks:\n";
run('/usr/bin/id', '-un');
run('/usr/bin/id -un');
print "\ndoesn't work:\n";
run('/bin/bash', '-c', '/usr/bin/id -un');
run('/bin/bash', '-c', '/bin/date >> /home/dt-pdrel/date');
run('/bin/date >> /home/dt-pdrel/date');
run('/usr/bin/python', '-c', 'import os; os.system("/usr/bin/id -un")');
run('/usr/bin/python', '-c', 'import os; os.system("/usr/bin/id -un")');
sub run {
my @cmd = @_;
print "\tCMD: '@cmd'\n";
print "\tSEC: ";
show_taint(@cmd);
print "\tOUT: ";
system @cmd ;
print "\n";
}
And here's the output:
$ id -un
bukzor
$ ls -l /proj/test/test.pl
-rwsr-xr-x 1 testrel asic 1976 Jul 22 14:34 /proj/test/test.pl*
$ /proj/test/test.pl foo bar
ENVIRON UNDER BASH:
CMD: '/bin/bash -c /bin/env'
SEC: ok:'/bin/bash', ok:'-c', ok:'/bin/env',
OUT: PATH=
PWD=/proj/test2/bukzor/test_dir/
SHLVL=1
_=/bin/env
TAINT DEMO:
@ARGV: TAINT:'foo', TAINT:'bar',
%ENV: ok:'',
`cat`: TAINT:'order hosts,bind',
works:
CMD: '/usr/bin/id -un'
SEC: ok:'/usr/bin/id', ok:'-un',
OUT: testrel
CMD: '/usr/bin/id -un'
SEC: ok:'/usr/bin/id -un',
OUT: testrel
doesn't work:
CMD: '/bin/bash -c /usr/bin/id -un'
SEC: ok:'/bin/bash', ok:'-c', ok:'/usr/bin/id -un',
OUT: bukzor
CMD: '/bin/bash -c /bin/date >> /home/testrel/date'
SEC: ok:'/bin/bash', ok:'-c', ok:'/bin/date >> /home/testrel/date',
OUT: /bin/bash: /home/testrel/date: Permission denied
CMD: '/bin/date >> /home/testrel/date'
SEC: ok:'/bin/date >> /home/testrel/date',
OUT: sh: /home/testrel/date: Permission denied
CMD: '/usr/bin/python -c import os; os.system("/usr/bin/id -un")'
SEC: ok:'/usr/bin/python', ok:'-c', ok:'import os; os.system("/usr/bin/id -un")',
OUT: bukzor
CMD: '/usr/bin/python -c import os; os.system("/usr/bin/id -un")'
SEC: ok:'/usr/bin/python', ok:'-c', ok:'import os; os.system("/usr/bin/id -un")',
OUT: bukzor