Fix type-safety problem with parallel aggregate serial/deserialization.

The original specification for this called for the deserialization function
to have signature "deserialize(serialtype) returns transtype", which is a
security violation if transtype is INTERNAL (which it always would be in
practice) and serialtype is not (which ditto).  The patch blithely overrode
the opr_sanity check for that, which was sloppy-enough work in itself,
but the indisputable reason this cannot be allowed to stand is that CREATE
FUNCTION will reject such a signature and thus it'd be impossible for
extensions to create parallelizable aggregates.

The minimum fix to make the signature type-safe is to add a second, dummy
argument of type INTERNAL.  But to lock it down a bit more and make misuse
of INTERNAL-accepting functions less likely, let's get rid of the ability
to specify a "serialtype" for an aggregate and just say that the only
useful serialtype is BYTEA --- which, in practice, is the only interesting
value anyway, due to the usefulness of the send/recv infrastructure for
this purpose.  That means we only have to allow "serialize(internal)
returns bytea" and "deserialize(bytea, internal) returns internal" as
the signatures for these support functions.

In passing fix bogus signature of int4_avg_combine, which I found thanks
to adding an opr_sanity check on combinefunc signatures.

catversion bump due to removing pg_aggregate.aggserialtype and adjusting
signatures of assorted built-in functions.

David Rowley and Tom Lane

Discussion: <27247.1466185504@sss.pgh.pa.us>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/include/parser/parse_agg.h b/src/include/parser/parse_agg.h
index 1408d4e9fd2..28fc354a424 100644
--- a/src/include/parser/parse_agg.h
+++ b/src/include/parser/parse_agg.h
@@ -51,12 +51,12 @@ extern void build_aggregate_combinefn_expr(Oid agg_state_type,
 							   Oid combinefn_oid,
 							   Expr **combinefnexpr);
 
-extern void build_aggregate_serialfn_expr(Oid agg_state_type,
-							  Oid agg_serial_type,
-							  Oid agg_input_collation,
-							  Oid serialfn_oid,
+extern void build_aggregate_serialfn_expr(Oid serialfn_oid,
 							  Expr **serialfnexpr);
 
+extern void build_aggregate_deserialfn_expr(Oid deserialfn_oid,
+								Expr **deserialfnexpr);
+
 extern void build_aggregate_finalfn_expr(Oid *agg_input_types,
 							 int num_finalfn_inputs,
 							 Oid agg_state_type,