Fix contrib/pgstattuple and contrib/pageinspect to prevent attempts to read

temporary tables of other sessions; that is unsafe because of the way our
buffer management works.  Per report from Stuart Bishop.
This is redundant with the bufmgr.c checks in HEAD, but not at all redundant
in the back branches.

contrib/pgstattuple/pgstatindex.c

@@ -247,6 +247,16 @@ pgstatindex(PG_FUNCTION_ARGS)
 	if (!IS_INDEX(rel) || !IS_BTREE(rel))
 		elog(ERROR, "pgstatindex() can be used only on b-tree index.");
 
+	/*
+	 * Reject attempts to read non-local temporary relations; we would
+	 * be likely to get wrong data since we have no visibility into the
+	 * owning session's local buffers.
+	 */
+	if (isOtherTempNamespace(RelationGetNamespace(rel)))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot access temporary tables of other sessions")));
+
 	/*-------------------
 	 * Read a metapage
 	 *-------------------
@@ -405,16 +415,26 @@ bt_page_stats(PG_FUNCTION_ARGS)
 	relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
 	rel = relation_openrv(relrv, AccessShareLock);
 
-	CHECK_RELATION_BLOCK_RANGE(rel, blkno);
-
-	buffer = ReadBuffer(rel, blkno);
-
 	if (!IS_INDEX(rel) || !IS_BTREE(rel))
 		elog(ERROR, "bt_page_stats() can be used only on b-tree index.");
 
+	/*
+	 * Reject attempts to read non-local temporary relations; we would
+	 * be likely to get wrong data since we have no visibility into the
+	 * owning session's local buffers.
+	 */
+	if (isOtherTempNamespace(RelationGetNamespace(rel)))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot access temporary tables of other sessions")));
+
 	if (blkno == 0)
 		elog(ERROR, "Block 0 is a meta page.");
 
+	CHECK_RELATION_BLOCK_RANGE(rel, blkno);
+
+	buffer = ReadBuffer(rel, blkno);
+
 	{
 		HeapTuple	tuple;
 		TupleDesc	tupleDesc;
@@ -513,9 +533,6 @@ bt_page_items(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 				 (errmsg("must be superuser to use pgstattuple functions"))));
 
-	if (blkno == 0)
-		elog(ERROR, "Block 0 is a meta page.");
-
 	if (SRF_IS_FIRSTCALL())
 	{
 		fctx = SRF_FIRSTCALL_INIT();
@@ -529,13 +546,26 @@ bt_page_items(PG_FUNCTION_ARGS)
 		relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
 		uargs->rel = relation_openrv(relrv, AccessShareLock);
 
+		if (!IS_INDEX(uargs->rel) || !IS_BTREE(uargs->rel))
+			elog(ERROR, "bt_page_items() can be used only on b-tree index.");
+
+		/*
+		 * Reject attempts to read non-local temporary relations; we would
+		 * be likely to get wrong data since we have no visibility into the
+		 * owning session's local buffers.
+		 */
+		if (isOtherTempNamespace(RelationGetNamespace(uargs->rel)))
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot access temporary tables of other sessions")));
+
+		if (blkno == 0)
+			elog(ERROR, "Block 0 is a meta page.");
+
 		CHECK_RELATION_BLOCK_RANGE(uargs->rel, blkno);
 
 		uargs->buffer = ReadBuffer(uargs->rel, blkno);
 
-		if (!IS_INDEX(uargs->rel) || !IS_BTREE(uargs->rel))
-			elog(ERROR, "bt_page_items() can be used only on b-tree index.");
-
 		uargs->page = BufferGetPage(uargs->buffer);
 
 		opaque = (BTPageOpaque) PageGetSpecialPointer(uargs->page);
@@ -651,6 +681,16 @@ bt_metap(PG_FUNCTION_ARGS)
 	if (!IS_INDEX(rel) || !IS_BTREE(rel))
 		elog(ERROR, "bt_metap() can be used only on b-tree index.");
 
+	/*
+	 * Reject attempts to read non-local temporary relations; we would
+	 * be likely to get wrong data since we have no visibility into the
+	 * owning session's local buffers.
+	 */
+	if (isOtherTempNamespace(RelationGetNamespace(rel)))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot access temporary tables of other sessions")));
+
 	buffer = ReadBuffer(rel, 0);
 
 	{
@@ -720,6 +760,8 @@ pg_relpages(PG_FUNCTION_ARGS)
 	relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
 	rel = relation_openrv(relrv, AccessShareLock);
 
+	/* note: this will work OK on non-local temp tables */
+
 	relpages = RelationGetNumberOfBlocks(rel);
 
 	relation_close(rel, AccessShareLock);

contrib/pgstattuple/pgstattuple.c

@@ -1,5 +1,5 @@
 /*
- * $PostgreSQL: pgsql/contrib/pgstattuple/pgstattuple.c,v 1.25.2.1 2007/08/28 23:11:12 tgl Exp $
+ * $PostgreSQL: pgsql/contrib/pgstattuple/pgstattuple.c,v 1.25.2.2 2009/03/31 22:55:41 tgl Exp $
  *
  * Copyright (c) 2001,2002	Tatsuo Ishii
  *
@@ -201,6 +201,16 @@ pgstat_relation(Relation rel, FunctionCallInfo fcinfo)
 {
 	const char *err;
 
+	/*
+	 * Reject attempts to read non-local temporary relations; we would
+	 * be likely to get wrong data since we have no visibility into the
+	 * owning session's local buffers.
+	 */
+	if (isOtherTempNamespace(RelationGetNamespace(rel)))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot access temporary tables of other sessions")));
+
 	switch (rel->rd_rel->relkind)
 	{
 		case RELKIND_RELATION: