[PATCH V2 5/6] ublk_drv: add module parameter of ublks_max for limiting max allowed ublk dev

Ming Lei
2022-11-24T03:06:41Z

Prepare for supporting unprivileged ublk device by limiting max number
ublk devices added. Otherwise too many ublk devices could be added by
un-trusted user, which can be thought as one DoS.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/block/ublk_drv.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 04a28a2f2e1f..b12dd5ebe975 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -186,6 +186,15 @@ static wait_queue_head_t ublk_idr_wq; /* wait until one idr is freed */

static DEFINE_MUTEX(ublk_ctl_mutex);

+/*
+ * Max ublk devices allowed to add
+ *
+ * It can be extended to one per-user limit in future or even controlled
+ * by cgroup.
+ */
+static unsigned int ublks_max = 64;
+static unsigned int ublks_added; /* protected by ublk_ctl_mutex */
+
static struct miscdevice ublk_misc;

static void ublk_dev_param_basic_apply(struct ublk_device *ub)
@@ -1441,6 +1450,8 @@ static int ublk_add_chdev(struct ublk_device *ub)
ret = cdev_device_add(&ub->cdev, dev);
if (ret)
goto fail;
+
+ ublks_added++;
return 0;
fail:
put_device(dev);
@@ -1483,6 +1494,7 @@ static void ublk_remove(struct ublk_device *ub)
cancel_work_sync(&ub->quiesce_work);
cdev_device_del(&ub->cdev, &ub->cdev_dev);
put_device(&ub->cdev_dev);
+ ublks_added--;
}

static struct ublk_device *ublk_get_device_from_id(int idx)
@@ -1642,6 +1654,10 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd)
if (ret)
return ret;

+ ret = -EACCES;
+ if (ublks_added >= ublks_max)
+ goto out_unlock;
+
ret = -ENOMEM;
ub = kzalloc(sizeof(*ub), GFP_KERNEL);
if (!ub)
@@ -2093,5 +2109,8 @@ static void __exit ublk_exit(void)
module_init(ublk_init);
module_exit(ublk_exit);

+module_param(ublks_max, int, 0444);
+MODULE_PARM_DESC(ublks_max, "max number of ublk devices allowed to add(default: 64)");
+
MODULE_AUTHOR("Ming Lei <ming.lei@redhat.com>");
MODULE_LICENSE("GPL");
--
2.31.1