Re: plperl sigfpe reset can crash the server

On Thursday, August 23, 2012 12:17:22 PM Andres Freund wrote:
> Hi,
>
> While debugging an instance of this bug I noticed that plperlu always
> removes the SIGFPE handler and sets it to ignore:
>
>
> andres(at)awork2:~$ psql -p 5435 -U postgres -h /var/run/postgresql test
> Timing is on.
> psql (9.1devel, server 9.1.5)
> Type "help" for help.
>
> test=# SELECT pg_backend_pid();
> pg_backend_pid
> ----------------
> 9287
>
> root(at)awork2:/home/andres# grep -E '^Sig(Cgt|Ign)' /proc/9287/status|awk
> '{print $2}'
> 0000000001301800
> 0000000180006287
>
> test=# DO LANGUAGE plperlu $$$$;
>
> root(at)awork2:/home/andres# grep -E '^Sig(Cgt|Ign)' /proc/9287/status|awk
> '{print $2}'
> 0000000001301880
> 0000000180006207
>
> Note the 8'th bit being unset in SigCgt and set in SigIgn. Thats SIGFPE...
>
> Not sure how relevant this really is, but it could cause errors to be
> ignored...

In fact it can be used to crash the server:
test=# SELECT (-2^31)::int/-1;
ERROR: floating-point exception
DETAIL: An invalid floating-point operation was signaled. This probably means
an out-of-range result or an invalid operation, such as division by zero.
test=# DO LANGUAGE plperl $$$$;
DO
Time: 172.235 ms
test=# SELECT (-2^31)::int/-1;
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.

Greetings,

Andres
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services