From 8e137b075dc79997d621c7442c0eb299efed7ed7 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Fri, 3 Oct 2014 12:07:10 +0300
Subject: [PATCH] Check for GiST index tuples that don't fit on a page.

The page splitting code would go into infinite recursion if you try to
insert an index tuple that doesn't fit even on an empty page.

Per analysis and suggested fix by Andrew Gierth. Fixes bug #11555, reported
by Bryan Seitz (analysis happened over IRC). Backpatch to all supported
versions.
---
 src/backend/access/gist/gist.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
index 240813898a9..97eee905aac 100644
--- a/src/backend/access/gist/gist.c
+++ b/src/backend/access/gist/gist.c
@@ -1255,6 +1255,23 @@ gistSplit(Relation r,
 	int			i;
 	SplitedPageLayout *res = NULL;
 
+	/* this should never recurse very deeply, but better safe than sorry */
+	check_stack_depth();
+
+	/* there's no point in splitting an empty page */
+	Assert(len > 0);
+
+	/*
+	 * If a single tuple doesn't fit on a page, no amount of splitting will
+	 * help.
+	 */
+	if (len == 1)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+			errmsg("index row size %zu exceeds maximum %zu for index \"%s\"",
+				   IndexTupleSize(itup[0]), GiSTPageSize,
+				   RelationGetRelationName(r))));
+
 	memset(v.spl_lisnull, TRUE, sizeof(bool) * giststate->tupdesc->natts);
 	memset(v.spl_risnull, TRUE, sizeof(bool) * giststate->tupdesc->natts);
 	gistSplitByKey(r, page, itup, len, giststate, &v, 0);