ublk: Limit dev_id/ub_number values

The dev_id/ub_number is used for the ublk dev's char device's minor
number so it has to fit into MINORMASK. This patch adds checks to prevent
userspace from passing a number that's too large and limits what can be
allocated by the ublk_index_idr for the case where userspace has the
kernel allocate the dev_id/ub_number.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20231012150600.6198-2-michael.christie@oracle.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -470,6 +470,7 @@ static DEFINE_MUTEX(ublk_ctl_mutex);
  * It can be extended to one per-user limit in future or even controlled
  * by cgroup.
  */
+#define UBLK_MAX_UBLKS UBLK_MINORS
 static unsigned int ublks_max = 64;
 static unsigned int ublks_added;	/* protected by ublk_ctl_mutex */
 
@@ -2026,7 +2027,8 @@ static int ublk_alloc_dev_number(struct ublk_device *ub, int idx)
 		if (err == -ENOSPC)
 			err = -EEXIST;
 	} else {
-		err = idr_alloc(&ublk_index_idr, ub, 0, 0, GFP_NOWAIT);
+		err = idr_alloc(&ublk_index_idr, ub, 0, UBLK_MAX_UBLKS,
+				GFP_NOWAIT);
 	}
 	spin_unlock(&ublk_idr_lock);
 
@@ -2305,6 +2307,12 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd)
 		return -EINVAL;
 	}
 
+	if (header->dev_id != U32_MAX && header->dev_id >= UBLK_MAX_UBLKS) {
+		pr_warn("%s: dev id is too large. Max supported is %d\n",
+			__func__, UBLK_MAX_UBLKS - 1);
+		return -EINVAL;
+	}
+
 	ublk_dump_dev_info(&info);
 
 	ret = mutex_lock_killable(&ublk_ctl_mutex);