Properly initialize SortSupport for ORDER BY rechecks in nodeIndexscan.c.

Fix still another bug in commit 35fcb1b3d: it failed to fully initialize
the SortSupport states it introduced to allow the executor to re-check
ORDER BY expressions containing distance operators.  That led to a null
pointer dereference if the sortsupport code tried to use ssup_cxt.  The
problem only manifests in narrow cases, explaining the lack of previous
field reports.  It requires a GiST-indexable distance operator that lacks
SortSupport and is on a pass-by-ref data type, which among core+contrib
seems to be only btree_gist's interval opclass; and it requires the scan
to be done as an IndexScan not an IndexOnlyScan, which explains how
btree_gist's regression test didn't catch it.  Per bug #14134 from
Jihyun Yu.

Peter Geoghegan

Report: <[email protected]>

1 files changed, 13 insertions, 2 deletions

diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index bf16cb1b57e..3143bd94ec4 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -967,9 +967,20 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 			Oid			orderbyop = lfirst_oid(lco);
 			Node	   *orderbyexpr = (Node *) lfirst(lcx);
 			Oid			orderbyType = exprType(orderbyexpr);
+			Oid			orderbyColl = exprCollation(orderbyexpr);
+			SortSupport orderbysort = &indexstate->iss_SortSupport[i];
+
+			/* Initialize sort support */
+			orderbysort->ssup_cxt = CurrentMemoryContext;
+			orderbysort->ssup_collation = orderbyColl;
+			/* See cmp_orderbyvals() comments on NULLS LAST */
+			orderbysort->ssup_nulls_first = false;
+			/* ssup_attno is unused here and elsewhere */
+			orderbysort->ssup_attno = 0;
+			/* No abbreviation */
+			orderbysort->abbreviate = false;
+			PrepareSortSupportFromOrderingOp(orderbyop, orderbysort);
 
-			PrepareSortSupportFromOrderingOp(orderbyop,
-											 &indexstate->iss_SortSupport[i]);
 			get_typlenbyval(orderbyType,
 							&indexstate->iss_OrderByTypLens[i],
 							&indexstate->iss_OrderByTypByVals[i]);