Fix a crash in logical replication

petere · petere · commit 452253eae95a · 2019-01-30T11:17:05.000+01:00
The bug was that determining which columns are part of the replica identity index using RelationGetIndexAttrBitmap() would run eval_const_expressions() on index expressions and predicates across all indexes of the table, which in turn might require a snapshot, but there wasn't one set, so it crashes. There were actually two separate bugs, one on the publisher and one on the subscriber. To trigger the bug, a table that is part of a publication or subscription needs to have an index with a predicate or expression that lends itself to constant expressions simplification. The fix is to avoid the constant expressions simplification in RelationGetIndexAttrBitmap(), so that it becomes safe to call in these contexts. The constant expressions simplification comes from the calls to RelationGetIndexExpressions()/RelationGetIndexPredicate() via BuildIndexInfo(). But RelationGetIndexAttrBitmap() calling BuildIndexInfo() is overkill. The latter just takes pg_index catalog information, packs it into the IndexInfo structure, which former then just unpacks again and throws away. We can just do this directly with less overhead and skip the troublesome calls to eval_const_expressions(). This also removes the awkward cross-dependency between relcache.c and index.c. Bug: #15114 Reported-by: Петър Славов <pet.slavov@gmail.com> Reviewed-by: Noah Misch <noah@leadboat.com> Reviewed-by: Michael Paquier <michael@paquier.xyz> Discussion: https://www.postgresql.org/message-id/flat/152110589574.1223.17983600132321618383@wrigleys.postgresql.org/
diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
@@ -37,7 +37,6 @@
 #include "access/transam.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
-#include "catalog/index.h"
 #include "catalog/indexing.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_amproc.h"
@@ -4201,28 +4200,51 @@ RelationGetIndexAttrBitmap(Relation relation, IndexAttrBitmapKind attrKind)
 	{
 		Oid			indexOid = lfirst_oid(l);
 		Relation	indexDesc;
-		IndexInfo  *indexInfo;
+		Datum		datum;
+		bool		isnull;
+		Node	   *indexExpressions;
+		Node	   *indexPredicate;
 		int			i;
 		bool		isKey;		/* candidate key */
 		bool		isIDKey;	/* replica identity index */
 
 		indexDesc = index_open(indexOid, AccessShareLock);
 
-		/* Extract index key information from the index's pg_index row */
-		indexInfo = BuildIndexInfo(indexDesc);
+		/*
+		 * Extract index expressions and index predicate.  Note: Don't use
+		 * RelationGetIndexExpressions()/RelationGetIndexPredicate(), because
+		 * those might run constant expressions evaluation, which needs a
+		 * snapshot, which we might not have here.  (Also, it's probably more
+		 * sound to collect the bitmaps before any transformations that might
+		 * eliminate columns, but the practical impact of this is limited.)
+		 */
+
+		datum = heap_getattr(indexDesc->rd_indextuple, Anum_pg_index_indexprs,
+							 GetPgIndexDescriptor(), &isnull);
+		if (!isnull)
+			indexExpressions = stringToNode(TextDatumGetCString(datum));
+		else
+			indexExpressions = NULL;
+
+		datum = heap_getattr(indexDesc->rd_indextuple, Anum_pg_index_indpred,
+							 GetPgIndexDescriptor(), &isnull);
+		if (!isnull)
+			indexPredicate = stringToNode(TextDatumGetCString(datum));
+		else
+			indexPredicate = NULL;
 
 		/* Can this index be referenced by a foreign key? */
-		isKey = indexInfo->ii_Unique &&
-			indexInfo->ii_Expressions == NIL &&
-			indexInfo->ii_Predicate == NIL;
+		isKey = indexDesc->rd_index->indisunique &&
+			indexExpressions == NULL &&
+			indexPredicate == NULL;
 
 		/* Is this index the configured (or default) replica identity? */
 		isIDKey = (indexOid == relreplindex);
 
 		/* Collect simple attribute references */
-		for (i = 0; i < indexInfo->ii_NumIndexAttrs; i++)
+		for (i = 0; i < indexDesc->rd_index->indnatts; i++)
 		{
-			int			attrnum = indexInfo->ii_KeyAttrNumbers[i];
+			int			attrnum = indexDesc->rd_index->indkey.values[i];
 
 			if (attrnum != 0)
 			{
@@ -4240,10 +4262,10 @@ RelationGetIndexAttrBitmap(Relation relation, IndexAttrBitmapKind attrKind)
 		}
 
 		/* Collect all attributes used in expressions, too */
-		pull_varattnos((Node *) indexInfo->ii_Expressions, 1, &indexattrs);
+		pull_varattnos(indexExpressions, 1, &indexattrs);
 
 		/* Collect all attributes in the index predicate, too */
-		pull_varattnos((Node *) indexInfo->ii_Predicate, 1, &indexattrs);
+		pull_varattnos(indexPredicate, 1, &indexattrs);
 
 		index_close(indexDesc, AccessShareLock);
 	}
