ksmbd: fix Null pointer dereferences in ksmbd_update_fstate()

Coverity Scan report the following one. This report is a false alarm.
Because fp is never NULL when rc is zero. This patch add null check for fp
in ksmbd_update_fstate to make alarm silence.

*** CID 1568583b:  Null pointer dereferences  (FORWARD_NULL)
/fs/smb/server/smb2pdu.c: 3408 in smb2_open()
3402                    path_put(&path);
3403                    path_put(&parent_path);
3404            }
3405            ksmbd_revert_fsids(work);
3406     err_out1:
3407            if (!rc) {
>>>     CID 1568583b:  Null pointer dereferences  (FORWARD_NULL)
>>>     Passing null pointer "fp" to "ksmbd_update_fstate", which dereferences it.
3408                    ksmbd_update_fstate(&work->sess->file_table, fp, FP_INITED);
3409                    rc = ksmbd_iov_pin_rsp(work, (void *)rsp, iov_len);
3410            }
3411            if (rc) {
3412                    if (rc == -EINVAL)
3413                            rsp->hdr.Status = STATUS_INVALID_PARAMETER;

Fixes: e2b76ab8 ("ksmbd: add support for read compound")
Reported-by: Coverity Scan <scan-admin@coverity.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/server/vfs_cache.c

@@ -603,6 +603,9 @@ struct ksmbd_file *ksmbd_open_fd(struct ksmbd_work *work, struct file *filp)
 void ksmbd_update_fstate(struct ksmbd_file_table *ft, struct ksmbd_file *fp,
 			 unsigned int state)
 {
+	if (!fp)
+		return;
+
 	write_lock(&ft->lock);
 	fp->f_state = state;
 	write_unlock(&ft->lock);