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ublk: enforce ublks_max only for unprivileged devices

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[ Upstream commit 80bdfbb3545b6f16680a72c825063d08a6b44c7a ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Uday Shankar
2025-02-28 21:31:48 -07:00
committed by Greg Kroah-Hartman
parent c4f025a58e
commit af73c8fd73
1 changed files with 27 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files
drivers/block/ublk_drv.c
+27 -15
View File
@@ -484,15 +484,17 @@ static wait_queue_head_t ublk_idr_wq; /* wait until one idr is freed */
static DEFINE_MUTEX(ublk_ctl_mutex); 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 * It can be extended to one per-user limit in future or even controlled
* by cgroup. * by cgroup.
*/ */
#define UBLK_MAX_UBLKS UBLK_MINORS static unsigned int unprivileged_ublks_max = 64;
static unsigned int ublks_max = 64; static unsigned int unprivileged_ublks_added; /* protected by ublk_ctl_mutex */
static unsigned int ublks_added; /* protected by ublk_ctl_mutex */
static struct miscdevice ublk_misc; static struct miscdevice ublk_misc;
@@ -2203,7 +2205,8 @@ static int ublk_add_chdev(struct ublk_device *ub)
if (ret) if (ret)
goto fail; goto fail;
ublks_added++; if (ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV)
unprivileged_ublks_added++;
return 0; return 0;
fail: fail:
put_device(dev); put_device(dev);
@@ -2241,12 +2244,17 @@ static int ublk_add_tag_set(struct ublk_device *ub)
static void ublk_remove(struct ublk_device *ub) static void ublk_remove(struct ublk_device *ub)
{ {
bool unprivileged;
ublk_stop_dev(ub); ublk_stop_dev(ub);
cancel_work_sync(&ub->stop_work); cancel_work_sync(&ub->stop_work);
cancel_work_sync(&ub->quiesce_work); cancel_work_sync(&ub->quiesce_work);
cdev_device_del(&ub->cdev, &ub->cdev_dev); cdev_device_del(&ub->cdev, &ub->cdev_dev);
unprivileged = ub->dev_info.flags & UBLK_F_UNPRIVILEGED_DEV;
ublk_put_device(ub); ublk_put_device(ub);
ublks_added--;
if (unprivileged)
unprivileged_ublks_added--;
} }
static struct ublk_device *ublk_get_device_from_id(int idx) static struct ublk_device *ublk_get_device_from_id(int idx)
@@ -2495,7 +2503,8 @@ static int ublk_ctrl_add_dev(struct io_uring_cmd *cmd)
return ret; return ret;
ret = -EACCES; ret = -EACCES;
if (ublks_added >= ublks_max) if ((info.flags & UBLK_F_UNPRIVILEGED_DEV) &&
unprivileged_ublks_added >= unprivileged_ublks_max)
goto out_unlock; goto out_unlock;
ret = -ENOMEM; ret = -ENOMEM;
@@ -3123,23 +3132,26 @@ static void __exit ublk_exit(void)
module_init(ublk_init); module_init(ublk_init);
module_exit(ublk_exit); 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); 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 = { static const struct kernel_param_ops ublk_max_unprivileged_ublks_ops = {
.set = ublk_set_max_ublks, .set = ublk_set_max_unprivileged_ublks,
.get = ublk_get_max_ublks, .get = ublk_get_max_unprivileged_ublks,
}; };
module_param_cb(ublks_max, &ublk_max_ublks_ops, &ublks_max, 0644); module_param_cb(ublks_max, &ublk_max_unprivileged_ublks_ops,
MODULE_PARM_DESC(ublks_max, "max number of ublk devices allowed to add(default: 64)"); &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_AUTHOR("Ming Lei <ming.lei@redhat.com>");
MODULE_DESCRIPTION("Userspace block device"); MODULE_DESCRIPTION("Userspace block device");