Re: [PATCH V4 7/8] ublk_drv: allow new process to open ublk chardev with recovery feature enabled

Ming Lei
2022-09-22T02:39:08Z

On Wed, Sep 21, 2022 at 05:58:48PM +0800, ZiyangZhang wrote:
> With recovery feature enabled, if ublk chardev is ready to be released
> and quiesce_work has been scheduled, we:
> (1) cancel monitor_work to avoid UAF on ubq && ublk_io.
> (2) reinit all ubqs, including:
> (a) put the task_struct and reset ->ubq_daemon to NULL.
> (b) reset all ublk_io.
> (3) reset ub->mm to NULL.
> Then ublk chardev is released and new process can open it.
>
> RESTART_DEV is introduced as a new ctrl-cmd for recovery feature.
> After the chardev is opened and all ubqs are ready, user should send
> RESTART_DEV to:
> (1) wait until all new ubq_daemons getting ready.
> (2) update ublksrv_pid
> (3) unquiesce the request queue and expect incoming ublk_queue_rq()
> (4) convert ub's state to UBLK_S_DEV_LIVE
> (5) reschedule monitor_work
>
> Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>
> ---
> drivers/block/ublk_drv.c | 109 +++++++++++++++++++++++++++++++++-
> include/uapi/linux/ublk_cmd.h | 1 +
> 2 files changed, 109 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index dc33ebc20c01..871cd48503a2 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -912,10 +912,67 @@ static int ublk_ch_open(struct inode *inode, struct file *filp)
> return 0;
> }
>
> +static void ublk_queue_reinit(struct ublk_device *ub, struct ublk_queue *ubq)
> +{
> + int i;
> +
> + WARN_ON_ONCE(!(ubq->ubq_daemon && ubq_daemon_is_dying(ubq)));
> + pr_devel("%s: prepare for recovering qid %d\n", __func__, ubq->q_id);
> + /* old daemon is PF_EXITING, put it now */
> + put_task_struct(ubq->ubq_daemon);
> + /* We have to reset it to NULL, otherwise ub won't accept new FETCH_REQ */
> + ubq->ubq_daemon = NULL;

Then we can kill the task put & reset in ublk_deinit_queue(), and call
ublk_queue_reinit() unconditionally in ublk_ch_release().

> +
> + for (i = 0; i < ubq->q_depth; i++) {
> + struct ublk_io *io = &ubq->ios[i];
> +
> + /* forget everything now and be ready for new FETCH_REQ */
> + io->flags = 0;
> + io->cmd = NULL;
> + io->addr = 0;
> + }
> + ubq->nr_io_ready = 0;

I guess the above line should have been WARN_ON_ONCE(!ubq->nr_io_ready)?

> +}
> +
> static int ublk_ch_release(struct inode *inode, struct file *filp)
> {
> struct ublk_device *ub = filp->private_data;
> + int i;
> +
> + /* lockless fast path */
> + if (!unlikely(ublk_can_use_recovery(ub) && ub->dev_info.state == UBLK_S_DEV_QUIESCED))
> + goto out_clear;
> +
> + mutex_lock(&ub->mutex);
> + /*
> + * USER_RECOVERY is only allowd after UBLK_S_DEV_QUIESCED is set,
> + * which means that:
> + * (a) request queue has been quiesced
> + * (b) no inflight rq exists
> + * (c) all ioucmds owned by ther dying process are completed
> + */
> + if (!(ublk_can_use_recovery(ub) && ub->dev_info.state == UBLK_S_DEV_QUIESCED))
> + goto out_unlock;
> + pr_devel("%s: reinit queues for dev id %d.\n", __func__, ub->dev_info.dev_id);
> + /* we are going to release task_struct of ubq_daemon and resets
> + * ->ubq_daemon to NULL. So in monitor_work, check on ubq_daemon causes UAF.
> + * Besides, monitor_work is not necessary in QUIESCED state since we have
> + * already scheduled quiesce_work and quiesced all ubqs.
> + *
> + * Do not let monitor_work schedule itself if state it QUIESCED. And we cancel
> + * it here and re-schedule it in RESTART_DEV to avoid UAF.
> + */
> + cancel_delayed_work_sync(&ub->monitor_work);

monitor_work isn't supposed to be done here, which should be called after
ublk_wait_tagset_rqs_idle(ub) returns.

>
> + for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
> + ublk_queue_reinit(ub, ublk_get_queue(ub, i));
> + /* set to NULL, otherwise new ubq_daemon cannot mmap the io_cmd_buf */
> + ub->mm = NULL;
> + ub->nr_queues_ready = 0;
> + init_completion(&ub->completion);

The above can be done as generic code for both non-recovery and recovery
code.

> + out_unlock:
> + mutex_unlock(&ub->mutex);
> + out_clear:
> clear_bit(UB_STATE_OPEN, &ub->state);
> return 0;
> }
> @@ -1199,9 +1256,14 @@ static void ublk_mark_io_ready(struct ublk_device *ub, struct ublk_queue *ubq)
> ubq->ubq_daemon = current;
> get_task_struct(ubq->ubq_daemon);
> ub->nr_queues_ready++;
> + pr_devel("%s: ub %d qid %d is ready.\n",
> + __func__, ub->dev_info.dev_id, ubq->q_id);
> }
> - if (ub->nr_queues_ready == ub->dev_info.nr_hw_queues)
> + if (ub->nr_queues_ready == ub->dev_info.nr_hw_queues) {
> + pr_devel("%s: ub %d all ubqs are ready.\n",
> + __func__, ub->dev_info.dev_id);
> complete_all(&ub->completion);
> + }

Too many logging.

> mutex_unlock(&ub->mutex);
> }
>
> @@ -1903,6 +1965,48 @@ static int ublk_ctrl_set_params(struct io_uring_cmd *cmd)
> return ret;
> }
>
> +static int ublk_ctrl_restart_dev(struct io_uring_cmd *cmd)
> +{
> + struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
> + int ublksrv_pid = (int)header->data[0];
> + struct ublk_device *ub;
> + int ret = -EINVAL;
> +
> + ub = ublk_get_device_from_id(header->dev_id);
> + if (!ub)
> + return ret;
> +
> + pr_devel("%s: Waiting for new ubq_daemons(nr: %d) are ready, dev id %d...\n",
> + __func__, ub->dev_info.nr_hw_queues, header->dev_id);
> + /* wait until new ubq_daemon sending all FETCH_REQ */
> + wait_for_completion_interruptible(&ub->completion);
> + pr_devel("%s: All new ubq_daemons(nr: %d) are ready, dev id %d\n",
> + __func__, ub->dev_info.nr_hw_queues, header->dev_id);
> +
> + mutex_lock(&ub->mutex);
> + if (!ublk_can_use_recovery(ub))
> + goto out_unlock;
> +
> + if (ub->dev_info.state != UBLK_S_DEV_QUIESCED) {
> + ret = -EBUSY;
> + goto out_unlock;
> + }
> + ub->dev_info.ublksrv_pid = ublksrv_pid;
> + pr_devel("%s: new ublksrv_pid %d, dev id %d\n",
> + __func__, ublksrv_pid, header->dev_id);
> + blk_mq_unquiesce_queue(ub->ub_disk->queue);
> + pr_devel("%s: queue unquiesced, dev id %d.\n",
> + __func__, header->dev_id);
> + blk_mq_kick_requeue_list(ub->ub_disk->queue);
> + ub->dev_info.state = UBLK_S_DEV_LIVE;
> + schedule_delayed_work(&ub->monitor_work, UBLK_DAEMON_MONITOR_PERIOD);
> + ret = 0;
> + out_unlock:
> + mutex_unlock(&ub->mutex);
> + ublk_put_device(ub);
> + return ret;
> +}
> +
> static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
> unsigned int issue_flags)
> {
> @@ -1944,6 +2048,9 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
> case UBLK_CMD_SET_PARAMS:
> ret = ublk_ctrl_set_params(cmd);
> break;
> + case UBLK_CMD_RESTART_DEV:
> + ret = ublk_ctrl_restart_dev(cmd);
> + break;
> default:
> break;
> }
> diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
> index 332370628757..a088f374c0f6 100644
> --- a/include/uapi/linux/ublk_cmd.h
> +++ b/include/uapi/linux/ublk_cmd.h
> @@ -17,6 +17,7 @@
> #define UBLK_CMD_STOP_DEV 0x07
> #define UBLK_CMD_SET_PARAMS 0x08
> #define UBLK_CMD_GET_PARAMS 0x09
> +#define UBLK_CMD_RESTART_DEV 0x10

Maybe RESET_DEV or RECOVERY_DEV is better given userspace does not
send STOP_DEV command.

Thanks,
Ming