[PATCH 5.15 025/935] lib/ucs2_string.c: fix out-of-bounds read in ucs2_strnlen()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vincent Mailhol <mailhol@kernel.org>

commit cec0d03fe785380540dc1b4d07c80f67ae2ffc78 upstream.

Patch series "lib/ucs2_string.c: fix out-of-bounds read in
ucs2_strnlen()", v2.

This series fixes an off-by-one out-of-bounds read in ucs2_strnlen().

The first patch is the real fix, the second patch comes as a bonus and
fixes the code indentation.


This patch (of 2):

ucs2_strnlen() checks the current character before checking whether the
caller-provided maximum length has been reached.  If the input is not
NUL-terminated within that bound, the loop can read one ucs2_char_t past
the limit.

Test the length before dereferencing to prevent an off-by-one
out-of-bounds read.

Link: https://lore.kernel.org/20260723-fix-ucs2_strnlen-v2-0-9ea94e32a358@kernel.org
Link: https://lore.kernel.org/20260723-fix-ucs2_strnlen-v2-1-9ea94e32a358@kernel.org
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 lib/ucs2_string.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/lib/ucs2_string.c
+++ b/lib/ucs2_string.c
@@ -8,7 +8,7 @@ ucs2_strnlen(const ucs2_char_t *s, size_
 {
         unsigned long length = 0;
 
-        while (*s++ != 0 && length < maxlength)
+	while (length < maxlength && *s++ != 0)
                 length++;
         return length;
 }