Fix brin_summarize_new_values() to check index type and ownership.

brin_summarize_new_values() did not check that the passed OID was for
an index at all, much less that it was a BRIN index, and would fail in
obscure ways if it wasn't (possibly damaging data first?).  It also
lacked any permissions test; by analogy to VACUUM, we should only allow
the table's owner to summarize.

Noted by Jeff Janes, fix by Michael Paquier and me

src/backend/access/brin/brin.c

@@ -787,14 +787,50 @@ Datum
 brin_summarize_new_values(PG_FUNCTION_ARGS)
 {
 	Oid			indexoid = PG_GETARG_OID(0);
+	Oid			heapoid;
 	Relation	indexRel;
 	Relation	heapRel;
 	double		numSummarized = 0;
 
-	heapRel = heap_open(IndexGetRelation(indexoid, false),
+	/*
-						ShareUpdateExclusiveLock);
+	 * We must lock table before index to avoid deadlocks.  However, if the
+	 * passed indexoid isn't an index then IndexGetRelation() will fail.
+	 * Rather than emitting a not-very-helpful error message, postpone
+	 * complaining, expecting that the is-it-an-index test below will fail.
+	 */
+	heapoid = IndexGetRelation(indexoid, true);
+	if (OidIsValid(heapoid))
+		heapRel = heap_open(heapoid, ShareUpdateExclusiveLock);
+	else
+		heapRel = NULL;
+
 	indexRel = index_open(indexoid, ShareUpdateExclusiveLock);
 
+	/* Must be a BRIN index */
+	if (indexRel->rd_rel->relkind != RELKIND_INDEX ||
+		indexRel->rd_rel->relam != BRIN_AM_OID)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("\"%s\" is not a BRIN index",
+						RelationGetRelationName(indexRel))));
+
+	/* User must own the index (comparable to privileges needed for VACUUM) */
+	if (!pg_class_ownercheck(indexoid, GetUserId()))
+		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
+					   RelationGetRelationName(indexRel));
+
+	/*
+	 * Since we did the IndexGetRelation call above without any lock, it's
+	 * barely possible that a race against an index drop/recreation could have
+	 * netted us the wrong table.  Recheck.
+	 */
+	if (heapRel == NULL || heapoid != IndexGetRelation(indexoid, false))
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_TABLE),
+				 errmsg("could not open parent table of index %s",
+						RelationGetRelationName(indexRel))));
+
+	/* OK, do it */
 	brinsummarize(indexRel, heapRel, &numSummarized, NULL);
 
 	relation_close(indexRel, ShareUpdateExclusiveLock);

src/test/regress/expected/brin.out

@@ -407,3 +407,14 @@ FROM tenk1 ORDER BY unique2 LIMIT 5 OFFSET 5;
 VACUUM brintest;  -- force a summarization cycle in brinidx
 UPDATE brintest SET int8col = int8col * int4col;
 UPDATE brintest SET textcol = '' WHERE textcol IS NOT NULL;
+-- Tests for brin_summarize_new_values
+SELECT brin_summarize_new_values('brintest'); -- error, not an index
+ERROR:  "brintest" is not an index
+SELECT brin_summarize_new_values('tenk1_unique1'); -- error, not a BRIN index
+ERROR:  "tenk1_unique1" is not a BRIN index
+SELECT brin_summarize_new_values('brinidx'); -- ok, no change expected
+ brin_summarize_new_values 
+---------------------------
+                         0
+(1 row)
+

src/test/regress/sql/brin.sql

@@ -416,3 +416,8 @@ VACUUM brintest;  -- force a summarization cycle in brinidx
 
 UPDATE brintest SET int8col = int8col * int4col;
 UPDATE brintest SET textcol = '' WHERE textcol IS NOT NULL;
+
+-- Tests for brin_summarize_new_values
+SELECT brin_summarize_new_values('brintest'); -- error, not an index
+SELECT brin_summarize_new_values('tenk1_unique1'); -- error, not a BRIN index
+SELECT brin_summarize_new_values('brinidx'); -- ok, no change expected