ublk: Validate SQE128 flag before accessing the cmd

ublk_ctrl_cmd_dump() accesses (header *)sqe->cmd before
IO_URING_F_SQE128 flag check. This could cause out of boundary memory
access.

Move the SQE128 flag check earlier in ublk_ctrl_uring_cmd() to return
-EINVAL immediately if the flag is not set.

Fixes: 71f28f3136 ("ublk_drv: add io_uring based userspace block driver")
Signed-off-by: Govindarajulu Varadarajan <govind.varadar@gmail.com>
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -5221,10 +5221,10 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
 	    issue_flags & IO_URING_F_NONBLOCK)
 		return -EAGAIN;
 
-	ublk_ctrl_cmd_dump(cmd);
-
 	if (!(issue_flags & IO_URING_F_SQE128))
-		goto out;
+		return -EINVAL;
+
+	ublk_ctrl_cmd_dump(cmd);
 
 	ret = ublk_check_cmd_op(cmd_op);
 	if (ret)