Fix mishandling of resjunk columns in ON CONFLICT ... UPDATE tlists.

It's unusual to have any resjunk columns in an ON CONFLICT ... UPDATE
list, but it can happen when MULTIEXPR_SUBLINK SubPlans are present.
If it happens, the ON CONFLICT UPDATE code path would end up storing
tuples that include the values of the extra resjunk columns.  That's
fairly harmless in the short run, but if new columns are added to
the table then the values would become accessible, possibly leading
to malfunctions if they don't match the datatypes of the new columns.

This had escaped notice through a confluence of missing sanity checks,
including

* There's no cross-check that a tuple presented to heap_insert or
heap_update matches the table rowtype.  While it's difficult to
check that fully at reasonable cost, we can easily add assertions
that there aren't too many columns.

* The output-column-assignment cases in execExprInterp.c lacked
any sanity checks on the output column numbers, which seems like
an oversight considering there are plenty of assertion checks on
input column numbers.  Add assertions there too.

* We failed to apply nodeModifyTable's ExecCheckPlanOutput() to
the ON CONFLICT UPDATE tlist.  That wouldn't have caught this
specific error, since that function is chartered to ignore resjunk
columns; but it sure seems like a bad omission now that we've seen
this bug.

In HEAD, the right way to fix this is to make the processing of
ON CONFLICT UPDATE tlists work the same as regular UPDATE tlists
now do, that is don't add "SET x = x" entries, and use
ExecBuildUpdateProjection to evaluate the tlist and combine it with
old values of the not-set columns.  This adds a little complication
to ExecBuildUpdateProjection, but allows removal of a comparable
amount of now-dead code from the planner.

In the back branches, the most expedient solution seems to be to
(a) use an output slot for the ON CONFLICT UPDATE projection that
actually matches the target table, and then (b) invent a variant of
ExecBuildProjectionInfo that can be told to not store values resulting
from resjunk columns, so it doesn't try to store into nonexistent
columns of the output slot.  (We can't simply ignore the resjunk columns
altogether; they have to be evaluated for MULTIEXPR_SUBLINK to work.)
This works back to v10.  In 9.6, projections work much differently and
we can't cheaply give them such an option.  The 9.6 version of this
patch works by inserting a JunkFilter when it's necessary to get rid
of resjunk columns.

In addition, v11 and up have the reverse problem when trying to
perform ON CONFLICT UPDATE on a partitioned table.  Through a
further oversight, adjust_partition_tlist() discarded resjunk columns
when re-ordering the ON CONFLICT UPDATE tlist to match a partition.
This accidentally prevented the storing-bogus-tuples problem, but
at the cost that MULTIEXPR_SUBLINK cases didn't work, typically
crashing if more than one row has to be updated.  Fix by preserving
resjunk columns in that routine.  (I failed to resist the temptation
to add more assertions there too, and to do some minor code
beautification.)

Per report from Andres Freund.  Back-patch to all supported branches.

Security: CVE-2021-32028

1 files changed, 47 insertions, 35 deletions

diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
index 8fe4fc57bf6..4698f74f910 100644
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -788,6 +788,7 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 		 */
 		if (node->onConflictAction == ONCONFLICT_UPDATE)
 		{
+			OnConflictSetState *onconfl = makeNode(OnConflictSetState);
 			TupleConversionMap *map;
 
 			map = leaf_part_rri->ri_PartitionInfo->pi_RootToPartitionMap;
@@ -795,14 +796,14 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 			Assert(node->onConflictSet != NIL);
 			Assert(rootResultRelInfo->ri_onConflict != NULL);
 
-			leaf_part_rri->ri_onConflict = makeNode(OnConflictSetState);
+			leaf_part_rri->ri_onConflict = onconfl;
 
 			/*
 			 * Need a separate existing slot for each partition, as the
 			 * partition could be of a different AM, even if the tuple
 			 * descriptors match.
 			 */
-			leaf_part_rri->ri_onConflict->oc_Existing =
+			onconfl->oc_Existing =
 				table_slot_create(leaf_part_rri->ri_RelationDesc,
 								  &mtstate->ps.state->es_tupleTable);
 
@@ -822,17 +823,16 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 				 * Projections and where clauses themselves don't store state
 				 * / are independent of the underlying storage.
 				 */
-				leaf_part_rri->ri_onConflict->oc_ProjSlot =
+				onconfl->oc_ProjSlot =
 					rootResultRelInfo->ri_onConflict->oc_ProjSlot;
-				leaf_part_rri->ri_onConflict->oc_ProjInfo =
+				onconfl->oc_ProjInfo =
 					rootResultRelInfo->ri_onConflict->oc_ProjInfo;
-				leaf_part_rri->ri_onConflict->oc_WhereClause =
+				onconfl->oc_WhereClause =
 					rootResultRelInfo->ri_onConflict->oc_WhereClause;
 			}
 			else
 			{
 				List	   *onconflset;
-				TupleDesc	tupDesc;
 				bool		found_whole_row;
 
 				/*
@@ -842,7 +842,7 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 				 * pseudo-relation (INNER_VAR), and second to handle the main
 				 * target relation (firstVarno).
 				 */
-				onconflset = (List *) copyObject((Node *) node->onConflictSet);
+				onconflset = copyObject(node->onConflictSet);
 				if (part_attnos == NULL)
 					part_attnos =
 						convert_tuples_by_name_map(RelationGetDescr(partrel),
@@ -865,20 +865,19 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 										&found_whole_row);
 				/* We ignore the value of found_whole_row. */
 
-				/* Finally, adjust this tlist to match the partition. */
+				/* Finally, reorder the tlist to match the partition. */
 				onconflset = adjust_partition_tlist(onconflset, map);
 
 				/* create the tuple slot for the UPDATE SET projection */
-				tupDesc = ExecTypeFromTL(onconflset);
-				leaf_part_rri->ri_onConflict->oc_ProjSlot =
-					ExecInitExtraTupleSlot(mtstate->ps.state, tupDesc,
-										   &TTSOpsVirtual);
+				onconfl->oc_ProjSlot =
+					table_slot_create(partrel,
+									  &mtstate->ps.state->es_tupleTable);
 
 				/* build UPDATE SET projection state */
-				leaf_part_rri->ri_onConflict->oc_ProjInfo =
-					ExecBuildProjectionInfo(onconflset, econtext,
-											leaf_part_rri->ri_onConflict->oc_ProjSlot,
-											&mtstate->ps, partrelDesc);
+				onconfl->oc_ProjInfo =
+					ExecBuildProjectionInfoExt(onconflset, econtext,
+											   onconfl->oc_ProjSlot, false,
+											   &mtstate->ps, partrelDesc);
 
 				/*
 				 * If there is a WHERE clause, initialize state where it will
@@ -907,7 +906,7 @@ ExecInitPartitionInfo(ModifyTableState *mtstate, EState *estate,
 											RelationGetForm(partrel)->reltype,
 											&found_whole_row);
 					/* We ignore the value of found_whole_row. */
-					leaf_part_rri->ri_onConflict->oc_WhereClause =
+					onconfl->oc_WhereClause =
 						ExecInitQual((List *) clause, &mtstate->ps);
 				}
 			}
@@ -1498,18 +1497,15 @@ ExecBuildSlotPartitionKeyDescription(Relation rel,
 
 /*
  * adjust_partition_tlist
- *		Adjust the targetlist entries for a given partition to account for
- *		attribute differences between parent and the partition
+ *		Re-order the targetlist entries for a given partition to account for
+ *		column position differences between the parent and the partition.
  *
- * The expressions have already been fixed, but here we fix the list to make
- * target resnos match the partition's attribute numbers.  This results in a
- * copy of the original target list in which the entries appear in resno
- * order, including both the existing entries (that may have their resno
- * changed in-place) and the newly added entries for columns that don't exist
- * in the parent.
+ * The expressions have already been fixed, but we must now re-order the
+ * entries in case the partition has different column order, and possibly
+ * add or remove dummy entries for dropped columns.
  *
- * Scribbles on the input tlist, so callers must make sure to make a copy
- * before passing it to us.
+ * Although a new List is returned, this feels free to scribble on resno
+ * fields of the given tlist, so that should be a working copy.
  */
 static List *
 adjust_partition_tlist(List *tlist, TupleConversionMap *map)
@@ -1518,31 +1514,35 @@ adjust_partition_tlist(List *tlist, TupleConversionMap *map)
 	TupleDesc	tupdesc = map->outdesc;
 	AttrNumber *attrMap = map->attrMap;
 	AttrNumber	attrno;
+	ListCell   *lc;
 
 	for (attrno = 1; attrno <= tupdesc->natts; attrno++)
 	{
 		Form_pg_attribute att_tup = TupleDescAttr(tupdesc, attrno - 1);
+		AttrNumber	parentattrno = attrMap[attrno - 1];
 		TargetEntry *tle;
 
-		if (attrMap[attrno - 1] != InvalidAttrNumber)
+		if (parentattrno != InvalidAttrNumber)
 		{
-			Assert(!att_tup->attisdropped);
-
 			/*
 			 * Use the corresponding entry from the parent's tlist, adjusting
-			 * the resno the match the partition's attno.
+			 * the resno to match the partition's attno.
 			 */
-			tle = (TargetEntry *) list_nth(tlist, attrMap[attrno - 1] - 1);
+			Assert(!att_tup->attisdropped);
+			tle = (TargetEntry *) list_nth(tlist, parentattrno - 1);
+			Assert(!tle->resjunk);
+			Assert(tle->resno == parentattrno);
 			tle->resno = attrno;
 		}
 		else
 		{
-			Const	   *expr;
-
 			/*
 			 * For a dropped attribute in the partition, generate a dummy
-			 * entry with resno matching the partition's attno.
+			 * entry with resno matching the partition's attno.  This should
+			 * match what expand_targetlist() does.
 			 */
+			Const	   *expr;
+
 			Assert(att_tup->attisdropped);
 			expr = makeConst(INT4OID,
 							 -1,
@@ -1560,6 +1560,18 @@ adjust_partition_tlist(List *tlist, TupleConversionMap *map)
 		new_tlist = lappend(new_tlist, tle);
 	}
 
+	/* Finally, attach any resjunk entries to the end of the new tlist */
+	foreach(lc, tlist)
+	{
+		TargetEntry *tle = (TargetEntry *) lfirst(lc);
+
+		if (tle->resjunk)
+		{
+			tle->resno = list_length(new_tlist) + 1;
+			new_tlist = lappend(new_tlist, tle);
+		}
+	}
+
 	return new_tlist;
 }