ksmbd: fix the warning from __kernel_write_iter

[ 2110.972290] ------------[ cut here ]------------
[ 2110.972301] WARNING: CPU: 3 PID: 735 at fs/read_write.c:599 __kernel_write_iter+0x21b/0x280

This patch doesn't allow writing to directory.

Cc: stable@vger.kernel.org
Reported-by: Norbert Szetei <norbert@doyensec.com>
Tested-by: Norbert Szetei <norbert@doyensec.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/server/vfs.c

@@ -479,7 +479,8 @@ int ksmbd_vfs_write(struct ksmbd_work *work, struct ksmbd_file *fp,
 	int err = 0;
 
 	if (work->conn->connection_type) {
-		if (!(fp->daccess & (FILE_WRITE_DATA_LE | FILE_APPEND_DATA_LE))) {
+		if (!(fp->daccess & (FILE_WRITE_DATA_LE | FILE_APPEND_DATA_LE)) ||
+		    S_ISDIR(file_inode(fp->filp)->i_mode)) {
 			pr_err("no right to write(%pD)\n", fp->filp);
 			err = -EACCES;
 			goto out;