From: aizu-m <aizumusheer2@gmail.com>
Date: Fri, 19 Jun 2026 06:53:03 +0000 (+0530)
Subject: wc: fix out-of-bounds read for single-byte wide characters
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;p=thirdparty%2Fcoreutils.git

wc: fix out-of-bounds read for single-byte wide characters

In legacy CJK locales a single input byte can decode to a wide character
above UCHAR_MAX, e.g. SHIFT-JIS bytes 0xA1..0xDF become U+FF61..U+FF9F.
wc then indexed its 256-entry wc_isprint/wc_isspace tables with that
value and read past their end.
* src/wc.c (wc): Take the byte-indexed fast path only when the decoded
character fits in a byte; wider values fall through to c32width and
c32isspace.
* tests/wc/wc-sjis.sh: New test.
* tests/local.mk (all_tests): Add it.
* NEWS: Mention the fix.

Link: https://github.com/coreutils/coreutils/pull/298
---

diff --git a/NEWS b/NEWS
index 58beb738ee..4ffd690def 100644
--- a/NEWS
+++ b/NEWS
@@ -36,6 +36,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   'uniq -w' no longer overruns the read buffer in multibyte locales.
   [bug introduced in coreutils-9.5]
 
+  'wc' no longer reads past the end of a lookup table in legacy multibyte
+  locales like SHIFT-JIS where a single byte can decode to a wide character.
+  [bug introduced in coreutils-9.5]
+
 ** Changes in behavior
 
   'ls' -w,--width no longer includes '\n' in the width of a line.
diff --git a/src/wc.c b/src/wc.c
index 2e2a9b03cb..4a31189e64 100644
--- a/src/wc.c
+++ b/src/wc.c
@@ -581,7 +581,7 @@ wc (int fd, char const *file_x, struct fstatus *fstatus)
 
                 default:;
                   bool in_word2;
-                  if (single_byte)
+                  if (single_byte && wide_char <= UCHAR_MAX)
                     {
                       linepos += wc_isprint[wide_char];
                       in_word2 = !wc_isspace[wide_char];
diff --git a/tests/local.mk b/tests/local.mk
index b56e5dcfb6..154b591cea 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -308,6 +308,7 @@ all_tests =					\
   tests/wc/wc-nbsp.sh				\
   tests/wc/wc-parallel.sh			\
   tests/wc/wc-proc.sh				\
+  tests/wc/wc-sjis.sh				\
   tests/wc/wc-total.sh				\
   tests/cat/cat-E.sh				\
   tests/cat/cat-proc.sh				\
diff --git a/tests/wc/wc-sjis.sh b/tests/wc/wc-sjis.sh
new file mode 100755
index 0000000000..39ca1358f4
--- /dev/null
+++ b/tests/wc/wc-sjis.sh
@@ -0,0 +1,54 @@
+#!/bin/sh
+# A single input byte that decodes to a wide character must not overrun
+# wc's byte-indexed isprint/isspace tables.
+
+# Copyright (C) 2026 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ wc printf
+
+# In SHIFT-JIS the bytes 0xA1..0xDF are half-width katakana: each is a
+# single input byte, yet it decodes to U+FF61..U+FF9F, i.e., > UCHAR_MAX.
+# In coreutils v9.5 to 9.11 on glibc where SHIFT_JIS is available,
+# wc indexed its 256-entry wc_isprint[]/wc_isspace[] tables with the
+# decoded value, so reading past their end and crashed.
+
+export LC_ALL=ja_JP.SHIFT_JIS
+
+# Try to generate the locale if not available
+# as it's generally not available by default.
+if test "$(locale charmap 2>/dev/null)" != SHIFT_JIS; then
+  mkdir locale || framework_failure_
+  localedef --no-archive --no-warnings=ascii \
+    -f SHIFT_JIS -i ja_JP "$PWD/locale/ja_JP.SHIFT_JIS" \
+    >/dev/null 2>&1 || skip_ "SHIFT-JIS locale not available"
+  export LOCPATH="$PWD/locale"
+fi
+
+test "$(locale charmap 2>/dev/null)" = SHIFT_JIS \
+  || skip_ "SHIFT-JIS locale not available"
+
+env printf 'a\xa1b\n' > in || framework_failure_
+
+# 0xA1 is one byte and one non-space character: 1 line, 1 word, 4 bytes.
+wc in > out || fail=1
+printf '1 1 4 in\n' > exp || framework_failure_
+compare exp out || fail=1
+
+# -L reaches the same table through wc_isprint; ensure it too completes.
+wc -L in > /dev/null || fail=1
+
+Exit $fail