Fix buffer overrun in unicode string normalization with empty input

PostgreSQL 13 and newer versions are directly impacted by that through
the SQL function normalize(), which would cause a call of this function
to write one byte past its allocation if using in input an empty
string after recomposing the string with NFC and NFKC.  Older versions
(v10~v12) are not directly affected by this problem as the only code
path using normalization is SASLprep in SCRAM authentication that
forbids the case of an empty string, but let's make the code more robust
anyway there so as any out-of-core callers of this function are covered.

The solution chosen to fix this issue is simple, with the addition of a
fast-exit path if the decomposed string is found as empty.  This would
only happen for an empty string as at its lowest level a codepoint would
be decomposed as itself if it has no entry in the decomposition table or
if it has a decomposition size of 0.

Some tests are added to cover this issue in v13~.  Note that an empty
string has always been considered as normalized (grammar "IS NF[K]{C,D}
NORMALIZED", through the SQL function is_normalized()) for all the
operations allowed (NFC, NFD, NFKC and NFKD) since this feature has been
introduced as of 2991ac5.  This behavior is unchanged but some tests are
added in v13~ to check after that.

I have also checked "make normalization-check" in src/common/unicode/,
while on it (works in 13~, and breaks in older stable branches
independently of this commit).

The release notes should just mention this commit for v13~.

Reported-by: Matthijs van der Vleuten
Discussion: https://postgr.es/m/17277-0c527a373794e802@postgresql.org
Backpatch-through: 10

diff --git a/src/common/unicode_norm.c b/src/common/unicode_norm.c
index 36ff2aab218ea25247689560f91a4a50d7b8967d..06bf921e4586dc24169245f2710870de2c407e3a 100644 (file)
--- a/src/common/unicode_norm.c
+++ b/src/common/unicode_norm.c
@@ -439,6 +439,10 @@ unicode_normalize(UnicodeNormalizationForm form, const pg_wchar *input)
    decomp_chars[decomp_size] = '\0';
    Assert(decomp_size == current_size);
 
+   /* Leave if there is nothing to decompose */
+   if (decomp_size == 0)
+       return decomp_chars;
+
    /*
     * Now apply canonical ordering.
     */

diff --git a/src/test/regress/expected/unicode.out b/src/test/regress/expected/unicode.out
index 2a1e903696681e625368117b070c2e7bb58898c8..f2713a232688b5c3bc009a39436578b4e13d2d65 100644 (file)
--- a/src/test/regress/expected/unicode.out
+++ b/src/test/regress/expected/unicode.out
@@ -8,6 +8,12 @@ SELECT U&'\0061\0308bc' <> U&'\00E4bc' COLLATE "C" AS sanity_check;
  t
 (1 row)
 
+SELECT normalize('');
+ normalize 
+-----------
+ 
+(1 row)
+
 SELECT normalize(U&'\0061\0308\24D1c') = U&'\00E4\24D1c' COLLATE "C" AS test_default;
  test_default 
 --------------
@@ -67,7 +73,8 @@ FROM
   (VALUES (1, U&'\00E4bc'),
           (2, U&'\0061\0308bc'),
           (3, U&'\00E4\24D1c'),
-          (4, U&'\0061\0308\24D1c')) vals (num, val)
+          (4, U&'\0061\0308\24D1c'),
+          (5, '')) vals (num, val)
 ORDER BY num;
  num | val | nfc | nfd | nfkc | nfkd 
 -----+-----+-----+-----+------+------
@@ -75,7 +82,8 @@ ORDER BY num;
    2 | äbc | f   | t   | f    | t
    3 | äⓑc | t   | f   | f    | f
    4 | äⓑc | f   | t   | f    | f
-(4 rows)
+   5 |     | t   | t   | t    | t
+(5 rows)
 
 SELECT is_normalized('abc', 'def');  -- run-time error
 ERROR:  invalid normalization form: def

diff --git a/src/test/regress/sql/unicode.sql b/src/test/regress/sql/unicode.sql
index ccfc6fa77ab4b2b1f8ef6ada5e51b2723a7fad42..63cd523f85f7996c2fe978549dc293c254da7084 100644 (file)
--- a/src/test/regress/sql/unicode.sql
+++ b/src/test/regress/sql/unicode.sql
@@ -5,6 +5,7 @@ SELECT getdatabaseencoding() <> 'UTF8' AS skip_test \gset
 
 SELECT U&'\0061\0308bc' <> U&'\00E4bc' COLLATE "C" AS sanity_check;
 
+SELECT normalize('');
 SELECT normalize(U&'\0061\0308\24D1c') = U&'\00E4\24D1c' COLLATE "C" AS test_default;
 SELECT normalize(U&'\0061\0308\24D1c', NFC) = U&'\00E4\24D1c' COLLATE "C" AS test_nfc;
 SELECT normalize(U&'\00E4bc', NFC) = U&'\00E4bc' COLLATE "C" AS test_nfc_idem;
@@ -26,7 +27,8 @@ FROM
   (VALUES (1, U&'\00E4bc'),
           (2, U&'\0061\0308bc'),
           (3, U&'\00E4\24D1c'),
-          (4, U&'\0061\0308\24D1c')) vals (num, val)
+          (4, U&'\0061\0308\24D1c'),
+          (5, '')) vals (num, val)
 ORDER BY num;
 
 SELECT is_normalized('abc', 'def');  -- run-time error