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

7 files changed, 81 insertions, 17 deletions

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 0c59ff11e54..25fcd4c5241 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -2414,6 +2414,10 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid,
 	Buffer		vmbuffer = InvalidBuffer;
 	bool		all_visible_cleared = false;
 
+	/* Cheap, simplistic check that the tuple matches the rel's rowtype. */
+	Assert(HeapTupleHeaderGetNatts(tup->t_data) <=
+		   RelationGetNumberOfAttributes(relation));
+
 	/*
 	 * Fill in tuple header fields, assign an OID, and toast the tuple if
 	 * necessary.
@@ -3515,6 +3519,10 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
 
 	Assert(ItemPointerIsValid(otid));
 
+	/* Cheap, simplistic check that the tuple matches the rel's rowtype. */
+	Assert(HeapTupleHeaderGetNatts(newtup->t_data) <=
+		   RelationGetNumberOfAttributes(relation));
+
 	/*
 	 * Forbid this during a parallel operation, lest it allocate a combocid.
 	 * Other workers might need that combocid for visibility checks, and we
diff --git a/src/backend/executor/execExpr.c b/src/backend/executor/execExpr.c
index 7496189fabf..2a2741352af 100644
--- a/src/backend/executor/execExpr.c
+++ b/src/backend/executor/execExpr.c
@@ -304,6 +304,32 @@ ExecBuildProjectionInfo(List *targetList,
 						PlanState *parent,
 						TupleDesc inputDesc)
 {
+	return ExecBuildProjectionInfoExt(targetList,
+									  econtext,
+									  slot,
+									  true,
+									  parent,
+									  inputDesc);
+}
+
+/*
+ *		ExecBuildProjectionInfoExt
+ *
+ * As above, with one additional option.
+ *
+ * If assignJunkEntries is true (the usual case), resjunk entries in the tlist
+ * are not handled specially: they are evaluated and assigned to the proper
+ * column of the result slot.  If assignJunkEntries is false, resjunk entries
+ * are evaluated, but their result is discarded without assignment.
+ */
+ProjectionInfo *
+ExecBuildProjectionInfoExt(List *targetList,
+						   ExprContext *econtext,
+						   TupleTableSlot *slot,
+						   bool assignJunkEntries,
+						   PlanState *parent,
+						   TupleDesc inputDesc)
+{
 	ProjectionInfo *projInfo = makeNode(ProjectionInfo);
 	ExprState  *state;
 	ExprEvalStep scratch;
@@ -337,7 +363,8 @@ ExecBuildProjectionInfo(List *targetList,
 		 */
 		if (tle->expr != NULL &&
 			IsA(tle->expr, Var) &&
-			((Var *) tle->expr)->varattno > 0)
+			((Var *) tle->expr)->varattno > 0 &&
+			(assignJunkEntries || !tle->resjunk))
 		{
 			/* Non-system Var, but how safe is it? */
 			variable = (Var *) tle->expr;
@@ -401,6 +428,10 @@ ExecBuildProjectionInfo(List *targetList,
 			ExecInitExprRec(tle->expr, parent, state,
 							&state->resvalue, &state->resnull);
 
+			/* This makes it easy to discard resjunk results when told to. */
+			if (!assignJunkEntries && tle->resjunk)
+				continue;
+
 			/*
 			 * Column might be referenced multiple times in upper nodes, so
 			 * force value to R/O - but only if it could be an expanded datum.
diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index b5f5b735f81..de515617695 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -564,6 +564,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 			 * care of at compilation time.  But see EEOP_INNER_VAR comments.
 			 */
 			Assert(attnum >= 0 && attnum < innerslot->tts_nvalid);
+			Assert(resultnum >= 0 && resultnum < resultslot->tts_tupleDescriptor->natts);
 			resultslot->tts_values[resultnum] = innerslot->tts_values[attnum];
 			resultslot->tts_isnull[resultnum] = innerslot->tts_isnull[attnum];
 
@@ -580,6 +581,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 			 * care of at compilation time.  But see EEOP_INNER_VAR comments.
 			 */
 			Assert(attnum >= 0 && attnum < outerslot->tts_nvalid);
+			Assert(resultnum >= 0 && resultnum < resultslot->tts_tupleDescriptor->natts);
 			resultslot->tts_values[resultnum] = outerslot->tts_values[attnum];
 			resultslot->tts_isnull[resultnum] = outerslot->tts_isnull[attnum];
 
@@ -596,6 +598,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 			 * care of at compilation time.  But see EEOP_INNER_VAR comments.
 			 */
 			Assert(attnum >= 0 && attnum < scanslot->tts_nvalid);
+			Assert(resultnum >= 0 && resultnum < resultslot->tts_tupleDescriptor->natts);
 			resultslot->tts_values[resultnum] = scanslot->tts_values[attnum];
 			resultslot->tts_isnull[resultnum] = scanslot->tts_isnull[attnum];
 
@@ -606,6 +609,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 		{
 			int			resultnum = op->d.assign_tmp.resultnum;
 
+			Assert(resultnum >= 0 && resultnum < resultslot->tts_tupleDescriptor->natts);
 			resultslot->tts_values[resultnum] = state->resvalue;
 			resultslot->tts_isnull[resultnum] = state->resnull;
 
@@ -616,6 +620,7 @@ ExecInterpExpr(ExprState *state, ExprContext *econtext, bool *isnull)
 		{
 			int			resultnum = op->d.assign_tmp.resultnum;
 
+			Assert(resultnum >= 0 && resultnum < resultslot->tts_tupleDescriptor->natts);
 			resultslot->tts_isnull[resultnum] = state->resnull;
 			if (!resultslot->tts_isnull[resultnum])
 				resultslot->tts_values[resultnum] =
@@ -1747,8 +1752,10 @@ ExecJustAssignInnerVar(ExprState *state, ExprContext *econtext, bool *isnull)
 	 *
 	 * Since we use slot_getattr(), we don't need to implement the FETCHSOME
 	 * step explicitly, and we also needn't Assert that the attnum is in range
-	 * --- slot_getattr() will take care of any problems.
+	 * --- slot_getattr() will take care of any problems.  Nonetheless, check
+	 * that resultnum is in range.
 	 */
+	Assert(resultnum >= 0 && resultnum < outslot->tts_tupleDescriptor->natts);
 	outslot->tts_values[resultnum] =
 		slot_getattr(inslot, attnum, &outslot->tts_isnull[resultnum]);
 	return 0;
@@ -1765,6 +1772,7 @@ ExecJustAssignOuterVar(ExprState *state, ExprContext *econtext, bool *isnull)
 	TupleTableSlot *outslot = state->resultslot;
 
 	/* See comments in ExecJustAssignInnerVar */
+	Assert(resultnum >= 0 && resultnum < outslot->tts_tupleDescriptor->natts);
 	outslot->tts_values[resultnum] =
 		slot_getattr(inslot, attnum, &outslot->tts_isnull[resultnum]);
 	return 0;
@@ -1781,6 +1789,7 @@ ExecJustAssignScanVar(ExprState *state, ExprContext *econtext, bool *isnull)
 	TupleTableSlot *outslot = state->resultslot;
 
 	/* See comments in ExecJustAssignInnerVar */
+	Assert(resultnum >= 0 && resultnum < outslot->tts_tupleDescriptor->natts);
 	outslot->tts_values[resultnum] =
 		slot_getattr(inslot, attnum, &outslot->tts_isnull[resultnum]);
 	return 0;
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 2f6a1102cda..54bb2cb5723 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -2135,7 +2135,6 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	if (node->onConflictAction == ONCONFLICT_UPDATE)
 	{
 		ExprContext *econtext;
-		TupleDesc	tupDesc;
 
 		/* insert may only have one plan, inheritance is not expanded */
 		Assert(nplans == 1);
@@ -2155,16 +2154,25 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 		mtstate->mt_excludedtlist = node->exclRelTlist;
 
 		/* create target slot for UPDATE SET projection */
-		tupDesc = ExecTypeFromTL((List *) node->onConflictSet,
-								 resultRelInfo->ri_RelationDesc->rd_rel->relhasoids);
 		mtstate->mt_conflproj = ExecInitExtraTupleSlot(mtstate->ps.state);
-		ExecSetSlotDescriptor(mtstate->mt_conflproj, tupDesc);
+		ExecSetSlotDescriptor(mtstate->mt_conflproj,
+							  resultRelInfo->ri_RelationDesc->rd_att);
+
+		/*
+		 * The onConflictSet tlist should already have been adjusted to emit
+		 * the table's exact column list.  It could also contain resjunk
+		 * columns, which should be evaluated but not included in the
+		 * projection result.
+		 */
+		ExecCheckPlanOutput(resultRelInfo->ri_RelationDesc,
+							node->onConflictSet);
 
 		/* build UPDATE SET projection state */
 		resultRelInfo->ri_onConflictSetProj =
-			ExecBuildProjectionInfo(node->onConflictSet, econtext,
-									mtstate->mt_conflproj, &mtstate->ps,
-									resultRelInfo->ri_RelationDesc->rd_att);
+			ExecBuildProjectionInfoExt(node->onConflictSet, econtext,
+									   mtstate->mt_conflproj, false,
+									   &mtstate->ps,
+									   resultRelInfo->ri_RelationDesc->rd_att);
 
 		/* build DO UPDATE WHERE clause expression */
 		if (node->onConflictWhere)
diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
index 379e7c77a18..da6ec7cab3d 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -263,6 +263,12 @@ extern ProjectionInfo *ExecBuildProjectionInfo(List *targetList,
 						TupleTableSlot *slot,
 						PlanState *parent,
 						TupleDesc inputDesc);
+extern ProjectionInfo *ExecBuildProjectionInfoExt(List *targetList,
+												  ExprContext *econtext,
+												  TupleTableSlot *slot,
+												  bool assignJunkEntries,
+												  PlanState *parent,
+												  TupleDesc inputDesc);
 extern ExprState *ExecPrepareExpr(Expr *node, EState *estate);
 extern ExprState *ExecPrepareQual(List *qual, EState *estate);
 extern ExprState *ExecPrepareCheck(List *qual, EState *estate);
diff --git a/src/test/regress/expected/update.out b/src/test/regress/expected/update.out
index 1778023600e..54166727fba 100644
--- a/src/test/regress/expected/update.out
+++ b/src/test/regress/expected/update.out
@@ -199,7 +199,7 @@ SELECT a, b, char_length(c) FROM update_test;
 (4 rows)
 
 -- Test ON CONFLICT DO UPDATE
-INSERT INTO upsert_test VALUES(1, 'Boo');
+INSERT INTO upsert_test VALUES(1, 'Boo'), (3, 'Zoo');
 -- uncorrelated  sub-select:
 WITH aaa AS (SELECT 1 AS a, 'Foo' AS b) INSERT INTO upsert_test
   VALUES (1, 'Bar') ON CONFLICT(a)
@@ -210,22 +210,24 @@ WITH aaa AS (SELECT 1 AS a, 'Foo' AS b) INSERT INTO upsert_test
 (1 row)
 
 -- correlated sub-select:
-INSERT INTO upsert_test VALUES (1, 'Baz') ON CONFLICT(a)
+INSERT INTO upsert_test VALUES (1, 'Baz'), (3, 'Zaz') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b || ', Correlated', a from upsert_test i WHERE i.a = upsert_test.a)
   RETURNING *;
  a |        b        
 ---+-----------------
  1 | Foo, Correlated
-(1 row)
+ 3 | Zoo, Correlated
+(2 rows)
 
 -- correlated sub-select (EXCLUDED.* alias):
-INSERT INTO upsert_test VALUES (1, 'Bat') ON CONFLICT(a)
+INSERT INTO upsert_test VALUES (1, 'Bat'), (3, 'Zot') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b || ', Excluded', a from upsert_test i WHERE i.a = excluded.a)
   RETURNING *;
  a |             b             
 ---+---------------------------
  1 | Foo, Correlated, Excluded
-(1 row)
+ 3 | Zoo, Correlated, Excluded
+(2 rows)
 
 DROP TABLE update_test;
 DROP TABLE upsert_test;
diff --git a/src/test/regress/sql/update.sql b/src/test/regress/sql/update.sql
index 4cfb8ac7bef..d8ff0bc6ff6 100644
--- a/src/test/regress/sql/update.sql
+++ b/src/test/regress/sql/update.sql
@@ -100,17 +100,17 @@ UPDATE update_test t
 SELECT a, b, char_length(c) FROM update_test;
 
 -- Test ON CONFLICT DO UPDATE
-INSERT INTO upsert_test VALUES(1, 'Boo');
+INSERT INTO upsert_test VALUES(1, 'Boo'), (3, 'Zoo');
 -- uncorrelated  sub-select:
 WITH aaa AS (SELECT 1 AS a, 'Foo' AS b) INSERT INTO upsert_test
   VALUES (1, 'Bar') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b, a FROM aaa) RETURNING *;
 -- correlated sub-select:
-INSERT INTO upsert_test VALUES (1, 'Baz') ON CONFLICT(a)
+INSERT INTO upsert_test VALUES (1, 'Baz'), (3, 'Zaz') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b || ', Correlated', a from upsert_test i WHERE i.a = upsert_test.a)
   RETURNING *;
 -- correlated sub-select (EXCLUDED.* alias):
-INSERT INTO upsert_test VALUES (1, 'Bat') ON CONFLICT(a)
+INSERT INTO upsert_test VALUES (1, 'Bat'), (3, 'Zot') ON CONFLICT(a)
   DO UPDATE SET (b, a) = (SELECT b || ', Excluded', a from upsert_test i WHERE i.a = excluded.a)
   RETURNING *;