udf: Fix leak of UTF-16 surrogates into encoded strings

OSTA UDF specification does not mention whether the CS0 charset in case
of two bytes per character encoding should be treated in UTF-16 or
UCS-2. The sample code in the standard does not treat UTF-16 surrogates
in any special way but on systems such as Windows which work in UTF-16
internally, filenames would be treated as being in UTF-16 effectively.
In Linux it is more difficult to handle characters outside of Base
Multilingual plane (beyond 0xffff) as NLS framework works with 2-byte
characters only. Just make sure we don't leak UTF-16 surrogates into the
resulting string when loading names from the filesystem for now.

CC: stable@vger.kernel.org # >= v4.6
Reported-by: Mingye Wang <arthur200126@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/udf/unicode.c b/fs/udf/unicode.c
index f897e55f2cd0..16a8ad21b77e 100644
--- a/fs/udf/unicode.c
+++ b/fs/udf/unicode.c
@@ -28,6 +28,9 @@
 
 #include "udf_sb.h"
 
+#define SURROGATE_MASK 0xfffff800
+#define SURROGATE_PAIR 0x0000d800
+
 static int udf_uni2char_utf8(wchar_t uni,
                              unsigned char *out,
                              int boundlen)
@@ -37,6 +40,9 @@ static int udf_uni2char_utf8(wchar_t uni,
         if (boundlen <= 0)
                 return -ENAMETOOLONG;
 
+        if ((uni & SURROGATE_MASK) == SURROGATE_PAIR)
+                return -EINVAL;
+
         if (uni < 0x80) {
                 out[u_len++] = (unsigned char)uni;
         } else if (uni < 0x800) {