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ublk: enforce ublks_max only for unprivileged devices

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Commit 403ebc8778 ("ublk_drv: add module parameter of ublks_max for
limiting max allowed ublk dev"), claimed ublks_max was added to prevent
a DoS situation with an untrusted user creating too many ublk devices.
If that's the case, ublks_max should only restrict the number of
unprivileged ublk devices in the system. Enforce the limit only for
unprivileged ublk devices, and rename variables accordingly. Leave the
external-facing parameter name unchanged, since changing it may break
systems which use it (but still update its documentation to reflect its
new meaning).

As a result of this change, in a system where there are only normal
(non-unprivileged) devices, the maximum number of such devices is
increased to 1 << MINORBITS, or 1048576. That ought to be enough for
anyone, right?

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250228-ublks_max-v1-1-04b7379190c0@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Uday Shankar
2025-02-28 21:31:48 -07:00
committed by Jens Axboe
parent 3aab938c93
commit 80bdfbb354
1 changed files with 27 additions and 15 deletions
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42
drivers/block/ublk_drv.c
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@@ -490,15 +490,17 @@ static wait_queue_head_t ublk_idr_wq; /* wait until one idr is freed */
static DEFINE_MUTEX(ublk_ctl_mutex);
#define UBLK_MAX_UBLKS UBLK_MINORS
/*
* Max ublk devices allowed to add
* Max unprivileged ublk devices allowed to add
*
* 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 */
static unsigned int unprivileged_ublks_max = 64;
static unsigned int unprivileged_ublks_added; /* protected by ublk_ctl_mutex */
static struct miscdevice ublk_misc;
@@ -2203,7 +2205,8 @@ static int ublk_add_chdev(struct ublk_device *ub)
if (ret)
goto fail;
ublks_added++;
if (ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV)
unprivileged_ublks_added++;
return 0;
fail:
put_device(dev);
@@ -2232,11 +2235,16 @@ static int ublk_add_tag_set(struct ublk_device *ub)
static void ublk_remove(struct ublk_device *ub)
{
bool unprivileged;
ublk_stop_dev(ub);
cancel_work_sync(&ub->nosrv_work);
cdev_device_del(&ub->cdev, &ub->cdev_dev);
unprivileged = ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV;
ublk_put_device(ub);
ublks_added--;
if (unprivileged)
unprivileged_ublks_added--;
}
static struct ublk_device *ublk_get_device_from_id(int idx)
@@ -2501,7 +2509,8 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd)
return ret;
ret = -EACCES;
if (ublks_added >= ublks_max)
if ((info.flags & UBLK_F_UNPRIVILEGED_DEV) &&
unprivileged_ublks_added >= unprivileged_ublks_max)
goto out_unlock;
ret = -ENOMEM;
@@ -3138,23 +3147,26 @@ static void __exit ublk_exit(void)
module_init(ublk_init);
module_exit(ublk_exit);
static int ublk_set_max_ublks(const char *buf, const struct kernel_param *kp)
static int ublk_set_max_unprivileged_ublks(const char *buf,
const struct kernel_param *kp)
{
return param_set_uint_minmax(buf, kp, 0, UBLK_MAX_UBLKS);
}
static int ublk_get_max_ublks(char *buf, const struct kernel_param *kp)
static int ublk_get_max_unprivileged_ublks(char *buf,
const struct kernel_param *kp)
{
return sysfs_emit(buf, "%u\n", ublks_max);
return sysfs_emit(buf, "%u\n", unprivileged_ublks_max);
}
static const struct kernel_param_ops ublk_max_ublks_ops = {
.set = ublk_set_max_ublks,
.get = ublk_get_max_ublks,
static const struct kernel_param_ops ublk_max_unprivileged_ublks_ops = {
.set = ublk_set_max_unprivileged_ublks,
.get = ublk_get_max_unprivileged_ublks,
};
module_param_cb(ublks_max, &ublk_max_ublks_ops, &ublks_max, 0644);
MODULE_PARM_DESC(ublks_max, "max number of ublk devices allowed to add(default: 64)");
module_param_cb(ublks_max, &ublk_max_unprivileged_ublks_ops,
&unprivileged_ublks_max, 0644);
MODULE_PARM_DESC(ublks_max, "max number of unprivileged ublk devices allowed to add(default: 64)");
MODULE_AUTHOR("Ming Lei <ming.lei@redhat.com>");
MODULE_DESCRIPTION("Userspace block device");