v2-0001-Fix-various-instances-of-undefined-behavior.patch

From d10cbcaabfdb62cf6565a1fa8c697827db94c79a Mon Sep 17 00:00:00 2001
From: John Naylor <john.naylor@postgresql.org>
Date: Wed, 21 Jan 2026 16:44:46 +0700
Subject: [PATCH v2 1/2] Fix various instances of undefined behavior

Mostly this involves checking for NULL pointer before doing operations
that add a non-zero offset.

The exception is an overflow warning in heap_fetch_toast_slice().
XXX WIP

Per clang 21 undefined behavior sanitizer.

Coauthored-by: Alexander Lakhin <exclusion@gmail.com>
Reported-by: Alexander Lakhin <exclusion@gmail.com>
Tested-by:
Discussion: https://postgr.es/m/777bd201-6e3a-4da0-a922-4ea9de46a3ee@gmail.com
Backpatch-through: 14
---
 contrib/pg_trgm/trgm_gist.c               | 5 ++++-
 src/backend/access/heap/heaptoast.c       | 2 +-
 src/backend/utils/adt/multirangetypes.c   | 5 +++--
 src/backend/utils/sort/sharedtuplestore.c | 3 ++-
 4 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/contrib/pg_trgm/trgm_gist.c b/contrib/pg_trgm/trgm_gist.c
index 2f0d61985a5..685275a0f9b 100644
--- a/contrib/pg_trgm/trgm_gist.c
+++ b/contrib/pg_trgm/trgm_gist.c
@@ -701,10 +701,13 @@ gtrgm_penalty(PG_FUNCTION_ARGS)
 	if (ISARRKEY(newval))
 	{
 		char	   *cache = (char *) fcinfo->flinfo->fn_extra;
-		TRGM	   *cachedVal = (TRGM *) (cache + MAXALIGN(siglen));
+		TRGM	   *cachedVal = NULL;
 		Size		newvalsize = VARSIZE(newval);
 		BITVECP		sign;
 
+		if (cache != NULL)
+			cachedVal = (TRGM *) (cache + MAXALIGN(siglen));
+
 		/*
 		 * Cache the sign data across multiple calls with the same newval.
 		 */
diff --git a/src/backend/access/heap/heaptoast.c b/src/backend/access/heap/heaptoast.c
index e28fe47a449..6ddf6c6cf9f 100644
--- a/src/backend/access/heap/heaptoast.c
+++ b/src/backend/access/heap/heaptoast.c
@@ -768,7 +768,7 @@ heap_fetch_toast_slice(Relation toastrel, Oid valueid, int32 attrsize,
 			chcpyend = (sliceoffset + slicelength - 1) % TOAST_MAX_CHUNK_SIZE;
 
 		memcpy(VARDATA(result) +
-			   (curchunk * TOAST_MAX_CHUNK_SIZE - sliceoffset) + chcpystrt,
+			   curchunk * TOAST_MAX_CHUNK_SIZE - sliceoffset + chcpystrt,
 			   chunkdata + chcpystrt,
 			   (chcpyend - chcpystrt) + 1);
 
diff --git a/src/backend/utils/adt/multirangetypes.c b/src/backend/utils/adt/multirangetypes.c
index 07e2a81d46a..08b6549f77e 100644
--- a/src/backend/utils/adt/multirangetypes.c
+++ b/src/backend/utils/adt/multirangetypes.c
@@ -485,8 +485,9 @@ multirange_canonicalize(TypeCacheEntry *rangetyp, int32 input_range_count,
 	int32		output_range_count = 0;
 
 	/* Sort the ranges so we can find the ones that overlap/meet. */
-	qsort_arg(ranges, input_range_count, sizeof(RangeType *), range_compare,
-			  rangetyp);
+	if (ranges != NULL)
+		qsort_arg(ranges, input_range_count, sizeof(RangeType *),
+				  range_compare, rangetyp);
 
 	/* Now merge where possible: */
 	for (i = 0; i < input_range_count; i++)
diff --git a/src/backend/utils/sort/sharedtuplestore.c b/src/backend/utils/sort/sharedtuplestore.c
index 8f35a255263..04189f708fa 100644
--- a/src/backend/utils/sort/sharedtuplestore.c
+++ b/src/backend/utils/sort/sharedtuplestore.c
@@ -323,7 +323,8 @@ sts_puttuple(SharedTuplestoreAccessor *accessor, void *meta_data,
 
 	/* Do we have space? */
 	size = accessor->sts->meta_data_size + tuple->t_len;
-	if (accessor->write_pointer + size > accessor->write_end)
+	if (accessor->write_pointer == NULL ||
+		accessor->write_pointer + size > accessor->write_end)
 	{
 		if (accessor->write_chunk == NULL)
 		{
-- 
2.52.0