From d3e1d6f9ea497bd1b6bb258c6d078f06b8cd4338 Mon Sep 17 00:00:00 2001
From: Philip Withnall <pwithnall@gnome.org>
Date: Sat, 11 Apr 2026 14:42:57 +0100
Subject: [PATCH] gkeyfile: Fix a one-byte heap under-read with
 g_key_file_get_locale_string_list()

If this method was called on a key file key which has an empty value,
`len == 0` and this leads to a one-byte under-read off the start of the
key file buffer.

Spotted by linhlhq as #YWH-PGM9867-200. The suggested fix is theirs, and
the unit test is adapted from their report. I added the fuzzing test.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Fixes: #3930
---
 glib/gkeyfile.c      |  2 +-
 glib/tests/keyfile.c | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/glib/gkeyfile.c b/glib/gkeyfile.c
index ae3bbbc1d..0ddde22db 100644
--- a/glib/gkeyfile.c
+++ b/glib/gkeyfile.c
@@ -2391,7 +2391,7 @@ g_key_file_get_locale_string_list (GKeyFile     *key_file,
     }
 
   len = strlen (value);
-  if (value[len - 1] == key_file->list_separator)
+  if (len > 0 && value[len - 1] == key_file->list_separator)
     value[len - 1] = '\0';
 
   list_separator[0] = key_file->list_separator;
diff --git a/glib/tests/keyfile.c b/glib/tests/keyfile.c
index 16f3b788b..d7c648260 100644
--- a/glib/tests/keyfile.c
+++ b/glib/tests/keyfile.c
@@ -751,6 +751,27 @@ test_locale_string (void)
   g_free (old_locale);
 }
 
+static void
+test_locale_string_empty (void)
+{
+  GKeyFile *keyfile = NULL;
+  GError *local_error = NULL;
+  const char *data =
+    "[valid]\n"
+    "key1=\n";
+
+  g_test_bug ("https://gitlab.gnome.org/GNOME/glib/-/issues/3930");
+
+  keyfile = g_key_file_new ();
+
+  g_key_file_load_from_data (keyfile, data, -1, G_KEY_FILE_NONE, &local_error);
+  g_assert_no_error (local_error);
+
+  check_locale_string_list_value (keyfile, "valid", "key1", NULL, NULL);
+
+  g_key_file_free (keyfile);
+}
+
 static void
 test_lists (void)
 {
@@ -1745,6 +1766,7 @@ main (int argc, char *argv[])
   g_test_add_func ("/keyfile/boolean", test_boolean);
   g_test_add_func ("/keyfile/number", test_number);
   g_test_add_func ("/keyfile/locale-string", test_locale_string);
+  g_test_add_func ("/keyfile/locale-string/empty", test_locale_string_empty);
   g_test_add_func ("/keyfile/lists", test_lists);
   g_test_add_func ("/keyfile/lists-set-get", test_lists_set_get);
   g_test_add_func ("/keyfile/group-remove", test_group_remove);