David Helgason wrote:
On 14. okt 2004, at 21:09, Andrew Dunstan wrote:
It has just been brought to my attention that we are being very restrictive about what we allow to be done in trusted plperl. Basically we allow the :default and :base_math set of operations (run perldoc Opcode or see http://www.perldoc.com/perl5.8.0/lib/Opcode.html for details of what these mean). In particular, we do not allow calls to perl's builtin sort, which is unpleasant, and on reviewing the list it seems to me we could quite reasonably allow access to pack and unpack also. bless and sprintf are also likely candidates for inclusion - I have not finished reviewing the list, and would welcome advice from perl gurus on this.
pack and unpack are unfortunately not safe. Very useful, but they allow write/read access to random memory. It's really a shame perl doesn't have a pragma to make them safe or have safe versions of them.
Bless should be OK, unless sensitive objects are provided to the procedures.
A postgres question I don't know the answer to is whether allowing the user to trigger a segfault is a security problem. If it isn't, several opcodes may probably be allowed, including sort and sprintf. If it is, well, you need only follow the perl5-porters list to know that there's banal perl structures are continuously being found that will segfault perl, some at compile time, other at runtime.
OK, based on this and some further thought, I have prepared the attached patch which does the right thing, I think, both in terms of what we allow and what we don't.
First, we tighten security by disallowing access to srand and IO functions on existing filehandles (other IO ops are already disallowed).
The we relax the restrictions by allowing access to perl's sort, sprintf and time routines. I decided against pack/unpack based on the above, and also decided that I couldn't think of any case where bless would have any practical use - although that might change later. I'm trying to keep changes minimal here. I don't believe that "time" carries any significant security implications, and I think the dangers from "sort" and "sprintf" are not so great as to disallow them. They might cause a SEGV in a pathological case, but that doesn't give the user access to the machine - if they can login to postgres they can probably mount any number of DOS attacks anyway.
To answer David's question, the man says this about trusted functions: "the TRUSTED flag should only be given for languages that do not allow access to database server internals or the file system". I think the changes I propose fit in with that statement.
The patch also does some other inconsequential tidying of overlong lines, and removes some unnecessary ops in the unsafe case. These are basically cosmetic - the only significant part is replacing this:
$PLContainer->permit(':base_math');with this:
$PLContainer->permit(qw[:base_math !:base_io !srand sort sprintf time]);
I have tested and it appears to do the right thing, both for the things excluded and those included.
cheers
andrew
Index: src/pl/plperl/plperl.c
===================================================================
RCS file: /home/cvsmirror/pgsql/src/pl/plperl/plperl.c,v
retrieving revision 1.54
diff -c -r1.54 plperl.c
*** src/pl/plperl/plperl.c 7 Oct 2004 19:01:09 -0000 1.54
--- src/pl/plperl/plperl.c 15 Oct 2004 14:48:18 -0000
***************
*** 250,266 ****
static char *safe_ok =
"use vars qw($PLContainer); $PLContainer = new Safe('PLPerl');"
! "$PLContainer->permit_only(':default');$PLContainer->permit(':base_math');"
! "$PLContainer->share(qw[&elog &spi_exec_query &DEBUG &LOG &INFO &NOTICE &WARNING &ERROR %SHARED ]);"
"sub ::mksafefunc { return $PLContainer->reval(qq[sub { $_[0] $_[1]}]); }"
;
static char *safe_bad =
"use vars qw($PLContainer); $PLContainer = new Safe('PLPerl');"
! "$PLContainer->permit_only(':default');$PLContainer->permit(':base_math');"
! "$PLContainer->share(qw[&elog &DEBUG &LOG &INFO &NOTICE &WARNING &ERROR %SHARED ]);"
"sub ::mksafefunc { return $PLContainer->reval(qq[sub { "
! "elog(ERROR,'trusted perl functions disabled - please upgrade perl Safe module to at least 2.09');}]); }"
;
SV *res;
--- 250,269 ----
static char *safe_ok =
"use vars qw($PLContainer); $PLContainer = new Safe('PLPerl');"
! "$PLContainer->permit_only(':default');"
! "$PLContainer->permit(qw[:base_math !:base_io !srand sort sprintf time]);"
! "$PLContainer->share(qw[&elog &spi_exec_query &DEBUG &LOG "
! "&INFO &NOTICE &WARNING &ERROR %SHARED ]);"
"sub ::mksafefunc { return $PLContainer->reval(qq[sub { $_[0] $_[1]}]); }"
;
static char *safe_bad =
"use vars qw($PLContainer); $PLContainer = new Safe('PLPerl');"
! "$PLContainer->permit_only(':default');"
! "$PLContainer->share(qw[&elog &ERROR ]);"
"sub ::mksafefunc { return $PLContainer->reval(qq[sub { "
! "elog(ERROR,'trusted perl functions disabled - "
! "please upgrade perl Safe module to at least 2.09');}]); }"
;
SV *res;
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