Guard against table-AM-less relations in planner.

The executor will dump core if it's asked to execute a seqscan on
a relation having no table AM, such as a view.  While that shouldn't
really happen, it's possible to get there via catalog corruption,
such as a missing ON SELECT rule.  It seems worth installing a defense
against that.  There are multiple plausible places for such a defense,
but I picked the planner's get_relation_info().

Per discussion of bug #17646 from Kui Liu.  Back-patch to v12 where
the tableam APIs were introduced; in older versions you won't get a
SIGSEGV, so it seems less pressing.

Discussion: https://postgr.es/m/17646-70c93cfa40365776@postgresql.org

diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 6d5718ee4cb09cccbd5bd8963d0e6bb21d555db8..9defe378362d3f1cba0e682145313d0438ea3b89 100644 (file)
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -127,6 +127,24 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
         */
        relation = table_open(relationObjectId, NoLock);
 
+       /*
+        * Relations without a table AM can be used in a query only if they are of
+        * special-cased relkinds.  This check prevents us from crashing later if,
+        * for example, a view's ON SELECT rule has gone missing.  Note that
+        * table_open() already rejected indexes and composite types; spell the
+        * error the same way it does.
+        */
+       if (!relation->rd_tableam)
+       {
+               if (!(relation->rd_rel->relkind == RELKIND_FOREIGN_TABLE ||
+                         relation->rd_rel->relkind == RELKIND_PARTITIONED_TABLE))
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_WRONG_OBJECT_TYPE),
+                                        errmsg("cannot open relation \"%s\"",
+                                                       RelationGetRelationName(relation)),
+                                        errdetail_relkind_not_supported(relation->rd_rel->relkind)));
+       }
+
        /* Temporary and unlogged relations are inaccessible during recovery. */
        if (!RelationIsPermanent(relation) && RecoveryInProgress())
                ereport(ERROR,