pageinspect: Fix crash with gist_page_items()

Attempting to use this function with a raw page not coming from a GiST
index would cause a crash, as it was missing the same sanity checks as
gist_page_items_bytea().  This slightly refactors the code so as all the
basic validation checks for GiST pages are done in a single routine,
in the same fashion as the pageinspect functions for hash and BRIN.

This fixes an issue similar to 076f4d9.  A test is added to stress for
this case.  While on it, I have added a similar test for
brin_page_items() with a combination make of a valid GiST index and a
raw btree page.  This one was already protected, but it was not tested.

Reported-by: Egor Chindyaskin
Author: Dmitry Koval
Discussion: https://postgr.es/m/17815-fc4a2d3b74705703@postgresql.org
Backpatch-through: 14

1 files changed, 40 insertions, 42 deletions

diff --git a/contrib/pageinspect/gistfuncs.c b/contrib/pageinspect/gistfuncs.c
index d1c3c321f83..0ae8f7459c1 100644
--- a/contrib/pageinspect/gistfuncs.c
+++ b/contrib/pageinspect/gistfuncs.c
@@ -34,29 +34,20 @@ PG_FUNCTION_INFO_V1(gist_page_items_bytea);
 #define ItemPointerGetDatum(X)	 PointerGetDatum(X)
 
 
-Datum
-gist_page_opaque_info(PG_FUNCTION_ARGS)
+static Page verify_gist_page(bytea *raw_page);
+
+/*
+ * Verify that the given bytea contains a GIST page or die in the attempt.
+ * A pointer to the page is returned.
+ */
+static Page
+verify_gist_page(bytea *raw_page)
 {
-	bytea	   *raw_page = PG_GETARG_BYTEA_P(0);
-	TupleDesc	tupdesc;
-	Page		page;
+	Page		page = get_page_from_raw(raw_page);
 	GISTPageOpaque opaq;
-	HeapTuple	resultTuple;
-	Datum		values[4];
-	bool		nulls[4];
-	Datum		flags[16];
-	int			nflags = 0;
-	uint16		flagbits;
-
-	if (!superuser())
-		ereport(ERROR,
-				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-				 errmsg("must be superuser to use raw page functions")));
-
-	page = get_page_from_raw(raw_page);
 
 	if (PageIsNew(page))
-		PG_RETURN_NULL();
+		return page;
 
 	/* verify the special space has the expected size */
 	if (PageGetSpecialSize(page) != MAXALIGN(sizeof(GISTPageOpaqueData)))
@@ -76,12 +67,38 @@ gist_page_opaque_info(PG_FUNCTION_ARGS)
 							   GIST_PAGE_ID,
 							   opaq->gist_page_id)));
 
+	return page;
+}
+
+Datum
+gist_page_opaque_info(PG_FUNCTION_ARGS)
+{
+	bytea	   *raw_page = PG_GETARG_BYTEA_P(0);
+	TupleDesc	tupdesc;
+	Page		page;
+	HeapTuple	resultTuple;
+	Datum		values[4];
+	bool		nulls[4];
+	Datum		flags[16];
+	int			nflags = 0;
+	uint16		flagbits;
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("must be superuser to use raw page functions")));
+
+	page = verify_gist_page(raw_page);
+
+	if (PageIsNew(page))
+		PG_RETURN_NULL();
+
 	/* Build a tuple descriptor for our result type */
 	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
 		elog(ERROR, "return type must be a row type");
 
 	/* Convert the flags bitmask to an array of human-readable names */
-	flagbits = opaq->flags;
+	flagbits = GistPageGetOpaque(page)->flags;
 	if (flagbits & F_LEAF)
 		flags[nflags++] = CStringGetTextDatum("leaf");
 	if (flagbits & F_DELETED)
@@ -103,7 +120,7 @@ gist_page_opaque_info(PG_FUNCTION_ARGS)
 
 	values[0] = LSNGetDatum(PageGetLSN(page));
 	values[1] = LSNGetDatum(GistPageGetNSN(page));
-	values[2] = Int64GetDatum(opaq->rightlink);
+	values[2] = Int64GetDatum(GistPageGetOpaque(page)->rightlink);
 	values[3] = PointerGetDatum(construct_array(flags, nflags,
 												TEXTOID,
 												-1, false, TYPALIGN_INT));
@@ -124,7 +141,6 @@ gist_page_items_bytea(PG_FUNCTION_ARGS)
 	Tuplestorestate *tupstore;
 	MemoryContext oldcontext;
 	Page		page;
-	GISTPageOpaque opaq;
 	OffsetNumber offset;
 	OffsetNumber maxoff = InvalidOffsetNumber;
 
@@ -157,29 +173,11 @@ gist_page_items_bytea(PG_FUNCTION_ARGS)
 
 	MemoryContextSwitchTo(oldcontext);
 
-	page = get_page_from_raw(raw_page);
+	page = verify_gist_page(raw_page);
 
 	if (PageIsNew(page))
 		PG_RETURN_NULL();
 
-	/* verify the special space has the expected size */
-	if (PageGetSpecialSize(page) != MAXALIGN(sizeof(GISTPageOpaqueData)))
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("input page is not a valid %s page", "GiST"),
-					 errdetail("Expected special size %d, got %d.",
-							   (int) MAXALIGN(sizeof(GISTPageOpaqueData)),
-							   (int) PageGetSpecialSize(page))));
-
-	opaq = (GISTPageOpaque) PageGetSpecialPointer(page);
-	if (opaq->gist_page_id != GIST_PAGE_ID)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("input page is not a valid %s page", "GiST"),
-					 errdetail("Expected %08x, got %08x.",
-							   GIST_PAGE_ID,
-							   opaq->gist_page_id)));
-
 	/* Avoid bogus PageGetMaxOffsetNumber() call with deleted pages */
 	if (GistPageIsDeleted(page))
 		elog(NOTICE, "page is deleted");
@@ -276,7 +274,7 @@ gist_page_items(PG_FUNCTION_ARGS)
 				 errmsg("\"%s\" is not a %s index",
 						RelationGetRelationName(indexRel), "GiST")));
 
-	page = get_page_from_raw(raw_page);
+	page = verify_gist_page(raw_page);
 
 	if (PageIsNew(page))
 	{