From 27d384441851fe28ced962665632f2d1b914f11b Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Sun, 27 Mar 2022 17:53:51 +0900
Subject: pageinspect: Add more sanity checks to prevent out-of-bound reads

A couple of code paths use the special area on the page passed by the
function caller, expecting to find some data in it.  However, feeding
an incorrect page can lead to out-of-bound reads when trying to access
the page special area (like a heap page that has no special area,
leading PageGetSpecialPointer() to grab a pointer outside the allocated
page).

The functions used for hash and btree indexes have some protection
already against that, while some other functions using a relation OID
as argument would make sure that the access method involved is correct,
but functions taking in input a raw page without knowing the relation
the page is attached to would run into problems.

This commit improves the set of checks used in the code paths of BRIN,
btree (including one check if a leaf page is found with a non-zero
level), GIN and GiST to verify that the page given in input has a
special area size that fits with each access method, which is done
though PageGetSpecialSize(), becore calling PageGetSpecialPointer().

The scope of the checks done is limited to work with pages that one
would pass after getting a block with get_raw_page(), as it is possible
to craft byteas that could bypass existing code paths.  Having too many
checks would also impact the usability of pageinspect, as the existing
code is very useful to look at the content details in a corrupted page,
so the focus is really to avoid out-of-bound reads as this is never a
good thing even with functions whose execution is limited to
superusers.

The safest approach could be to rework the functions so as these fetch a
block using a relation OID and a block number, but there are also cases
where using a raw page is useful.

Tests are added to cover all the code paths that needed such checks, and
an error message for hash indexes is reworded to fit better with what
this commit adds.

Reported-By: Alexander Lakhin
Author: Julien Rouhaud, Michael Paquier
Discussion: https://postgr.es/m/16527-ef7606186f0610a1@postgresql.org
Discussion: https://postgr.es/m/561e187b-3549-c8d5-03f5-525c14e65bd0@postgrespro.ru
Backpatch-through: 10
---
 contrib/pageinspect/sql/gist.sql | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

(limited to 'contrib/pageinspect/sql/gist.sql')

diff --git a/contrib/pageinspect/sql/gist.sql b/contrib/pageinspect/sql/gist.sql
index 0d3eed9a19e..58f4c35d1d3 100644
--- a/contrib/pageinspect/sql/gist.sql
+++ b/contrib/pageinspect/sql/gist.sql
@@ -30,13 +30,18 @@ SELECT itemoffset, ctid, itemlen FROM gist_page_items_bytea(get_raw_page('test_g
 CREATE INDEX test_gist_btree on test_gist(t);
 SELECT gist_page_items(get_raw_page('test_gist_btree', 0), 'test_gist_btree');
 
--- Failure with incorrect page size
+-- Failure with various modes.
 -- Suppress the DETAIL message, to allow the tests to work across various
--- page sizes.
+-- page sizes and architectures.
 \set VERBOSITY terse
+-- invalid page size
 SELECT gist_page_items_bytea('aaa'::bytea);
 SELECT gist_page_items('aaa'::bytea, 'test_gist_idx'::regclass);
 SELECT gist_page_opaque_info('aaa'::bytea);
+-- invalid special area size
+SELECT * FROM gist_page_opaque_info(get_raw_page('test_gist', 0));
+SELECT gist_page_items_bytea(get_raw_page('test_gist', 0));
+SELECT gist_page_items_bytea(get_raw_page('test_gist_btree', 0));
 \set VERBOSITY default
 
 DROP TABLE test_gist;
-- 
cgit v1.2.3

