udf: Make udf_get_filename() return error instead of 0 length file name

Zero length file name isn't really valid. So check the length of the
final file name generated by udf_translate_to_linux() and return -EINVAL
instead of zero length file name. Update caller of udf_get_filename() to
not check for 0 return value.
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/dir.c

@@ -168,7 +168,7 @@ static int udf_readdir(struct file *file, struct dir_context *ctx)
 		}
 
 		flen = udf_get_filename(sb, nameptr, lfi, fname, UDF_NAME_LEN);
-		if (flen <= 0)
+		if (flen < 0)
 			continue;
 
 		tloc = lelb_to_cpu(cfi.icb.extLocation);

fs/udf/unicode.c

@@ -333,7 +333,7 @@ int udf_get_filename(struct super_block *sb, uint8_t *sname, int slen,
 		     uint8_t *dname, int dlen)
 {
 	struct ustr *filename, *unifilename;
-	int ret = 0;
+	int ret;
 
 	if (!slen)
 		return -EIO;
@@ -370,6 +370,9 @@ int udf_get_filename(struct super_block *sb, uint8_t *sname, int slen,
 	ret = udf_translate_to_linux(dname, dlen,
 				     filename->u_name, filename->u_len,
 				     unifilename->u_name, unifilename->u_len);
+	/* Zero length filename isn't valid... */
+	if (ret == 0)
+		ret = -EINVAL;
 out2:
 	kfree(unifilename);
 out1: