Thread

1. Autovacuum worker does not set stack_base_ptr

   Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> — 2012-04-01T16:31:46Z

   Currently, only regular backends set the stack base pointer, for the 
   check_stack_depth() mechanism, in PostgresMain. We don't have stack 
   overrun protection in auxiliary processes. However, autovacuum workers 
   at least can run arbitrary user code, and if that overruns the stack, 
   you get a segfault.
   
   Here's a little script to reproduce that:
   
   begin;
   create table atable(id int4);
   insert into atable select generate_series(1,10000);
   
   /* not recursive yet */
   create or replace function recfunc(i int4) returns bool AS $$begin
      return true;
   end;
   $$ language plpgsql immutable;
   
   /* Create index using the function. */
   create index recindex on atable((recfunc(id)));
   
   /* make the function recursive */
   create or replace function recfunc(i int4) returns bool AS $$begin
      perform recfunc(i);
   end;
   $$ language plpgsql immutable;
   
   commit;
   
   /* Now wait for autoanalyze to kick in, and crash */
   
   The fix is quite straightforward, we just need to set the stack base 
   pointer. I think we should set it in all processes, even though most 
   auxiliary processes like bgwriter can't execute arbitrary code. There's 
   no harm in doing so, anyway. I'm thinking that we should set the base 
   pointer in PostmasterMain(), so that it is inherited by all forked 
   processes, and in SubPostmasterMain() for EXEC_BACKEND.
   
   Proposed patch attached. The comment changes regarding PL/Java are in 
   anticipation for a fix for the Itanium-issue mentioned here: 
   http://lists.pgfoundry.org/pipermail/pljava-dev/2012/001906.html. 
   Nothing has yet been done in PL/Java, but I am assuming it will start 
   using the set/restore_stack_base() functions introduced in this patch. 
   However, we might need to do something more complicated to fix the first 
   PL/Java issue I explain in that email.
   
   I suppose this needs to be backpatched all the way to 8.3.
   
   -- 
      Heikki Linnakangas
      EnterpriseDB   http://www.enterprisedb.com
   

2. Re: Autovacuum worker does not set stack_base_ptr

   Robert Haas <robertmhaas@gmail.com> — 2012-04-03T02:57:19Z

   On Sun, Apr 1, 2012 at 12:31 PM, Heikki Linnakangas
   <heikki.linnakangas@enterprisedb.com> wrote:
   > Currently, only regular backends set the stack base pointer, for the
   > check_stack_depth() mechanism, in PostgresMain. We don't have stack overrun
   > protection in auxiliary processes. However, autovacuum workers at least can
   > run arbitrary user code, and if that overruns the stack, you get a segfault.
   
   The *Main functions for the various auxiliary processes seem to have a
   bad case of cut-and-paste-itis.  Consolidating some of that logic
   would help to avoid bugs of this type.
   
   -- 
   Robert Haas
   EnterpriseDB: http://www.enterprisedb.com
   The Enterprise PostgreSQL Company