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Thread: plperl and sqrt.

plperl and sqrt.

From
Travis Bauer
Date:
I have plperl compiled, installed, and generally working on
Solaris.  But when I try to execute the sqrt function, an error
is issued:

ERROR: creation of function failed: sqrt trapped by operation
mask at (eval 10) line 4.

The number after eval changes depending on where I put the line
of code which calls sqrt. Can someone tell me how to get around
this?

Thanks,


--
----------------------------------------------------------------
Travis Bauer | CS Grad Student | IU |www.cs.indiana.edu/~trbauer
----------------------------------------------------------------

Re: plperl and sqrt.

From
Tom Lane
Date:
Travis Bauer <trbauer@indiana.edu> writes:
> I have plperl compiled, installed, and generally working on
> Solaris.  But when I try to execute the sqrt function, an error
> is issued:
> ERROR: creation of function failed: sqrt trapped by operation
> mask at (eval 10) line 4.

There's an "operation mask" inside plperl that defines which Perl
opcodes it thinks are safe to allow the user to execute.  I think
the mask is set pretty conservatively at the moment ... definitely
too conservatively, if it rejects sqrt :-(.  But no one's gotten
round to looking at the situation more closely to decide what's
safe and what's not.  Feel free to look at the documentation for
Perl's Opcode module and propose a more reasonable mask.

            regards, tom lane

Re: plperl and sqrt.

From
Travis Bauer
Date:
 Tom Lane (tgl@sss.pgh.pa.us) wrote:

 >
 > There's an "operation mask" inside plperl that defines which Perl
 > opcodes it thinks are safe to allow the user to execute.  I think
 > the mask is set pretty conservatively at the moment ... definitely
 > too conservatively, if it rejects sqrt :-(.  But no one's gotten
 > round to looking at the situation more closely to decide what's
 > safe and what's not.  Feel free to look at the documentation for
 > Perl's Opcode module and propose a more reasonable mask.
 >
 >             regards, tom lane

 The existing mask seems the most reasonable.  The mast is :default,
 which is not the most strict, but reasonably so.  It allows users to
 write scripts that would consume system resources, tying up the
 system, but prevents them (probably) from getting too much access to
 the host system.  sqrt is disables because you can use it to produce
 floating point exceptions which would call $SIG{??}.  I'm not sure
 why this is bad, but it seems that this would violate the comparment
 somehow.

 Anyway, it would be nice to have a commandline switch for the
 Makefile.PL script which would allow people to customize the
 operation mask that plperl.so uses.  I have to use the :base_math
 mask because I need sqrt.  When plperl is re-enabled in the
 configure script, it should be added there too.

--
----------------------------------------------------------------
Travis Bauer | CS Grad Student | IU |www.cs.indiana.edu/~trbauer
----------------------------------------------------------------

Re: Re: plperl and sqrt.

From
Tom Lane
Date:
Travis Bauer <trbauer@indiana.edu> writes:
> ... sqrt is disables because you can use it to produce
> floating point exceptions which would call $SIG{??}.

That seems a little silly, unless they also lock out *all* floating
point ops plus integer division (what about divide by zero?).

> I'm not sure why this is bad, but it seems that this would violate the
> comparment somehow.

Offhand I think this is not reasonable or necessary for Postgres' use.
I'd support adding base_math to our standard mask.

> Anyway, it would be nice to have a commandline switch for the
> Makefile.PL script which would allow people to customize the
> operation mask that plperl.so uses.

Submit a patch (and more importantly, documentation patches so that
people will know about this issue).

            regards, tom lane