From: Michael Paquier <michael@paquier.xyz>
Date: Thu, 4 Jun 2026 22:50:15 +0000 (+0900)
Subject: Fix off-by-one with NFC recomposition for Hangul U+11A7 (TBASE)
X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=82116023e424cba4ac7adefd261bd382ad6e40c8;p=thirdparty%2Fpostgresql.git

Fix off-by-one with NFC recomposition for Hangul U+11A7 (TBASE)

The NFC recomposition incorrectly included TBASE as a valid T syllable,
which is incorrect based on the Unicode specification (TBASE is one
below the start of the range, range beginning at U+11A8).

This would cause the TBASE to be silently swallowed in the
normalization, leading to an incorrect result.

A couple of regression tests are added to check more patterns with
Hangul recomposition and decomposition, on top of a test to check the
problem with TBASE.  Diego has submitted the code fix, and I have
written the tests.

Author: Diego Frias <mail@dzfrias.dev>
Co-authored-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/B92ED640-7D4A-4505-B09F-3548F58CBB16@dzfrias.dev
Backpatch-through: 14
---

diff --git a/src/common/unicode_norm.c b/src/common/unicode_norm.c
index a7d0261aaf0..b5b629b8b6c 100644
--- a/src/common/unicode_norm.c
+++ b/src/common/unicode_norm.c
@@ -236,7 +236,7 @@ recompose_code(uint32 start, uint32 code, uint32 *result)
 	/* Check if two current characters are LV and T */
 	else if (start >= SBASE && start < (SBASE + SCOUNT) &&
 			 ((start - SBASE) % TCOUNT) == 0 &&
-			 code >= TBASE && code < (TBASE + TCOUNT))
+			 code > TBASE && code < (TBASE + TCOUNT))
 	{
 		/* make syllable of form LVT */
 		uint32		tindex = code - TBASE;
diff --git a/src/test/regress/expected/unicode.out b/src/test/regress/expected/unicode.out
index f2713a23268..ab0081165d2 100644
--- a/src/test/regress/expected/unicode.out
+++ b/src/test/regress/expected/unicode.out
@@ -87,3 +87,81 @@ ORDER BY num;
 
 SELECT is_normalized('abc', 'def');  -- run-time error
 ERROR:  invalid normalization form: def
+-- Hangul NFC recomposition tests
+-- L+V -> LV composition (first and last)
+SELECT normalize(U&'\1100\1161', NFC) = U&'\AC00' COLLATE "C" AS hangul_lv_first;
+ hangul_lv_first 
+-----------------
+ t
+(1 row)
+
+SELECT normalize(U&'\1112\1175', NFC) = U&'\D788' COLLATE "C" AS hangul_lv_last;
+ hangul_lv_last 
+----------------
+ t
+(1 row)
+
+-- LV+T -> LVT composition
+SELECT normalize(U&'\AC00\11A8', NFC) = U&'\AC01' COLLATE "C" AS hangul_lvt_first_t;
+ hangul_lvt_first_t 
+--------------------
+ t
+(1 row)
+
+SELECT normalize(U&'\AC00\11C2', NFC) = U&'\AC1B' COLLATE "C" AS hangul_lvt_last_t;
+ hangul_lvt_last_t 
+-------------------
+ t
+(1 row)
+
+SELECT normalize(U&'\D788\11A8', NFC) = U&'\D789' COLLATE "C" AS hangul_lvt_last_lv;
+ hangul_lvt_last_lv 
+--------------------
+ t
+(1 row)
+
+-- L+V+T -> LVT composition
+SELECT normalize(U&'\1100\1161\11A8', NFC) = U&'\AC01' COLLATE "C" AS hangul_full_lvt;
+ hangul_full_lvt 
+-----------------
+ t
+(1 row)
+
+SELECT normalize(U&'\1112\1175\11C2', NFC) = U&'\D7A3' COLLATE "C" AS hangul_full_lvt;
+ hangul_full_lvt 
+-----------------
+ t
+(1 row)
+
+-- TBASE invalid T syllable
+SELECT normalize(U&'\AC00\11A7', NFC) = U&'\AC00\11A7' COLLATE "C" AS hangul_tbase_not_combined;
+ hangul_tbase_not_combined 
+---------------------------
+ t
+(1 row)
+
+SELECT normalize(U&'\1100\1161\11A7', NFC) = U&'\AC00\11A7' COLLATE "C" AS hangul_lv_tbase_separate;
+ hangul_lv_tbase_separate 
+--------------------------
+ t
+(1 row)
+
+-- Hangul NFD decomposition tests
+SELECT normalize(U&'\AC00', NFD) = U&'\1100\1161' COLLATE "C" AS hangul_nfd_lv;
+ hangul_nfd_lv 
+---------------
+ t
+(1 row)
+
+SELECT normalize(U&'\AC01', NFD) = U&'\1100\1161\11A8' COLLATE "C" AS hangul_nfd_lvt;
+ hangul_nfd_lvt 
+----------------
+ t
+(1 row)
+
+SELECT normalize(U&'\D7A3', NFD) = U&'\1112\1175\11C2' COLLATE "C" AS hangul_nfd_last;
+ hangul_nfd_last 
+-----------------
+ t
+(1 row)
+
diff --git a/src/test/regress/sql/unicode.sql b/src/test/regress/sql/unicode.sql
index 63cd523f85f..95c5a7ac184 100644
--- a/src/test/regress/sql/unicode.sql
+++ b/src/test/regress/sql/unicode.sql
@@ -32,3 +32,23 @@ FROM
 ORDER BY num;
 
 SELECT is_normalized('abc', 'def');  -- run-time error
+
+-- Hangul NFC recomposition tests
+-- L+V -> LV composition (first and last)
+SELECT normalize(U&'\1100\1161', NFC) = U&'\AC00' COLLATE "C" AS hangul_lv_first;
+SELECT normalize(U&'\1112\1175', NFC) = U&'\D788' COLLATE "C" AS hangul_lv_last;
+-- LV+T -> LVT composition
+SELECT normalize(U&'\AC00\11A8', NFC) = U&'\AC01' COLLATE "C" AS hangul_lvt_first_t;
+SELECT normalize(U&'\AC00\11C2', NFC) = U&'\AC1B' COLLATE "C" AS hangul_lvt_last_t;
+SELECT normalize(U&'\D788\11A8', NFC) = U&'\D789' COLLATE "C" AS hangul_lvt_last_lv;
+-- L+V+T -> LVT composition
+SELECT normalize(U&'\1100\1161\11A8', NFC) = U&'\AC01' COLLATE "C" AS hangul_full_lvt;
+SELECT normalize(U&'\1112\1175\11C2', NFC) = U&'\D7A3' COLLATE "C" AS hangul_full_lvt;
+-- TBASE invalid T syllable
+SELECT normalize(U&'\AC00\11A7', NFC) = U&'\AC00\11A7' COLLATE "C" AS hangul_tbase_not_combined;
+SELECT normalize(U&'\1100\1161\11A7', NFC) = U&'\AC00\11A7' COLLATE "C" AS hangul_lv_tbase_separate;
+
+-- Hangul NFD decomposition tests
+SELECT normalize(U&'\AC00', NFD) = U&'\1100\1161' COLLATE "C" AS hangul_nfd_lv;
+SELECT normalize(U&'\AC01', NFD) = U&'\1100\1161\11A8' COLLATE "C" AS hangul_nfd_lvt;
+SELECT normalize(U&'\D7A3', NFD) = U&'\1112\1175\11C2' COLLATE "C" AS hangul_nfd_last;