Beefy Boxes and Bandwidth Generously Provided by pair Networks
good chemistry is complicated,
and a little bit messy -LW
 
PerlMonks  

Re^4: Passing argument into STDIN inside safe.pm reval (Update: which opcodes to enable)

by Dallaylaen (Scribe)
on Feb 14, 2013 at 21:14 UTC ( #1018795=note: print w/ replies, xml ) Need Help??


in reply to Re^3: Passing argument into STDIN inside safe.pm reval
in thread Passing argument into STDIN inside safe.pm reval

Thanks for pointing out Opcode.

So here's my opcode hunter:

#!/usr/bin/perl -w use strict; use Opcode qw(opset opmask_add opset_to_ops invert_opset); my $code = shift; defined $code or die "Usage: $0 <code> <permitted_opcode> <permitted_opcode> ...\n" +; # skip some masks from prev operations my %skip; $skip{$_}++ for @ARGV; my @all = opset_to_ops(invert_opset(opset())); # Try all opcodes, print error if eval failed foreach ( @all ) { $skip{$_} and next; opmask_add(opset($_)); eval $code and next; print "Eval failed on opcode: $_ with error: $@\n"; exit 1; }; print "Eval OK\n";

For input "my $x; 1" it requires four operators - const padany lineseq leaveeval

padany is the one responsible for the "private vatriable" error observable in this thread.

Now how come private variable is needed in "eval 1"? SIGDIE is my friend! Sooo... Let's get a stack trace:

#!/usr/bin/perl -w use strict; use warnings; use 5.012; use Safe; use Carp; my $code = shift; die "Usage: $0 <code> <premitted op> <permitted op> ..." unless define +d $code; my @perm = @ARGV; print "Trying: $code\n"; my $compartment = Safe->new; $compartment->share('*STDIN'); $compartment->share('&Dumper'); $compartment->permit_only(@perm); # Trap detailed stack trace my $stack; local $SIG{__DIE__} = sub { $stack = Carp::longmess(shift) }; print $compartment->reval($code); if ($@) { print "Unsafe code detected: $@"; print "At: $stack"; }

Here's my stack trace (note Carp complaining).

bash$ perl safe2.pl 1 Trying: 1 Unsafe code detected: 'private value' trapped by operation mask at (ev +al 5) line 1. At: 'private value' trapped by operation mask at (eval 5) line 1. at (eval 5) line 1 eval 'my $__ExPr__;1 ;' called at (eval 4) line 1 main::__ANON__(** Incomplete caller override detected; @DB::args w +ere not set **) called at /usr/share/perl/5.14/Safe.pm line 358 eval {...} called at /usr/share/perl/5.14/Safe.pm line 358 Safe::reval(** Incomplete caller override detected; @DB::args were + not set **) called at safe2.pl line 26

Aha, so Safe has added a "my" to my code before executing it. Finally, let's enable opcodes found by first script:

bash$ perl safe2.pl 1 padany const leaveeval lineseq Trying: 1 1
Conclusion: No sensible code will be ever executed by a compartment w/o these four opcodes.


Comment on Re^4: Passing argument into STDIN inside safe.pm reval (Update: which opcodes to enable)
Select or Download Code

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1018795]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others taking refuge in the Monastery: (4)
As of 2014-09-22 02:18 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    How do you remember the number of days in each month?











    Results (177 votes), past polls