pageinspect: Fix handling of page sizes and AM types

This commit fixes a set of issues related to the use of the SQL
functions in this module when the caller is able to pass down raw page
data as input argument:
- The page size check was fuzzy in a couple of places, sometimes
looking after only a sub-range, but what we are looking for is an exact
match on BLCKSZ.  After considering a few options here, I have settled
down to do a generalization of get_page_from_raw().  Most of the SQL
functions already used that, and this is not strictly required if not
accessing an 8-byte-wide value from a raw page, but this feels safer in
the long run for alignment-picky environment, particularly if a code
path begins to access such values.  This also reduces the number of
strings that need to be translated.
- The BRIN function brin_page_items() uses a Relation but it did not
check the access method of the opened index, potentially leading to
crashes.  All the other functions in need of a Relation already did
that.
- Some code paths could fail on elog(), but we should to use ereport()
for failures that can be triggered by the user.

Tests are added to stress all the cases that are fixed as of this
commit, with some junk raw pages (\set VERBOSITY ensures that this works
across all page sizes) and unexpected index types when functions open
relations.

Author: Michael Paquier, Justin Prysby
Discussion: https://postgr.es/m/20220218030020.GA1137@telsasoft.com
Backpatch-through: 10

1 files changed, 13 insertions, 23 deletions

diff --git a/contrib/pageinspect/brinfuncs.c b/contrib/pageinspect/brinfuncs.c
index b7c83652180..bd0ea8b18c1 100644
--- a/contrib/pageinspect/brinfuncs.c
+++ b/contrib/pageinspect/brinfuncs.c
@@ -16,6 +16,7 @@
 #include "access/brin_tuple.h"
 #include "access/htup_details.h"
 #include "catalog/index.h"
+#include "catalog/pg_am_d.h"
 #include "catalog/pg_type.h"
 #include "funcapi.h"
 #include "lib/stringinfo.h"
@@ -31,6 +32,8 @@ PG_FUNCTION_INFO_V1(brin_page_items);
 PG_FUNCTION_INFO_V1(brin_metapage_info);
 PG_FUNCTION_INFO_V1(brin_revmap_data);
 
+#define IS_BRIN(r) ((r)->rd_rel->relam == BRIN_AM_OID)
+
 typedef struct brin_column_state
 {
 	int			nstored;
@@ -45,8 +48,7 @@ Datum
 brin_page_type(PG_FUNCTION_ARGS)
 {
 	bytea	   *raw_page = PG_GETARG_BYTEA_P(0);
-	Page		page = VARDATA(raw_page);
-	int			raw_page_size;
+	Page		page;
 	char	   *type;
 
 	if (!superuser())
@@ -54,14 +56,7 @@ brin_page_type(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 				 errmsg("must be superuser to use raw page functions")));
 
-	raw_page_size = VARSIZE(raw_page) - VARHDRSZ;
-
-	if (raw_page_size != BLCKSZ)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("input page too small"),
-				 errdetail("Expected size %d, got %d",
-						   BLCKSZ, raw_page_size)));
+	page = get_page_from_raw(raw_page);
 
 	switch (BrinPageType(page))
 	{
@@ -89,19 +84,7 @@ brin_page_type(PG_FUNCTION_ARGS)
 static Page
 verify_brin_page(bytea *raw_page, uint16 type, const char *strtype)
 {
-	Page		page;
-	int			raw_page_size;
-
-	raw_page_size = VARSIZE(raw_page) - VARHDRSZ;
-
-	if (raw_page_size != BLCKSZ)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("input page too small"),
-				 errdetail("Expected size %d, got %d",
-						   BLCKSZ, raw_page_size)));
-
-	page = VARDATA(raw_page);
+	Page		page = get_page_from_raw(raw_page);
 
 	/* verify the special space says this page is what we want */
 	if (BrinPageType(page) != type)
@@ -143,6 +126,13 @@ brin_page_items(PG_FUNCTION_ARGS)
 	SetSingleFuncCall(fcinfo, 0);
 
 	indexRel = index_open(indexRelid, AccessShareLock);
+
+	if (!IS_BRIN(indexRel))
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("\"%s\" is not a %s index",
+						RelationGetRelationName(indexRel), "BRIN")));
+
 	bdesc = brin_build_desc(indexRel);
 
 	/* minimally verify the page we got */