From: Uday Shankar ushankar@purestorage.com
[ Upstream commit 80bdfbb3545b6f16680a72c825063d08a6b44c7a ]
Commit 403ebc877832 ("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.c... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/ublk_drv.c | 42 ++++++++++++++++++++++++++-------------- 1 file changed, 27 insertions(+), 15 deletions(-)
diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index ab06a7a064fbf..fb770b8b09412 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -499,15 +499,17 @@ 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;
@@ -2294,7 +2296,8 @@ 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); @@ -2323,11 +2326,16 @@ 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) @@ -2589,7 +2597,8 @@ 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; @@ -3227,23 +3236,26 @@ 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");