[PATCH v2] ublk_drv: fix NULL pointer dereference in ublk_ctrl_start_recovery()

[linan666]

From: Li Nan <linan122@xxxxxxxxxx>

When two UBLK_CMD_START_USER_RECOVERY commands are submitted, the
first one sets 'ubq->ubq_daemon' to NULL, and the second one triggers
WARN in ublk_queue_reinit() and subsequently a NULL pointer dereference
issue.

Fix it by adding the check in ublk_ctrl_start_recovery() and return
immediately in case of zero 'ub->nr_queues_ready'.

  BUG: kernel NULL pointer dereference, address: 0000000000000028
  RIP: 0010:ublk_ctrl_start_recovery.constprop.0+0x82/0x180
  Call Trace:
   <TASK>
   ? __die+0x20/0x70
   ? page_fault_oops+0x75/0x170
   ? exc_page_fault+0x64/0x140
   ? asm_exc_page_fault+0x22/0x30
   ? ublk_ctrl_start_recovery.constprop.0+0x82/0x180
   ublk_ctrl_uring_cmd+0x4f7/0x6c0
   ? pick_next_task_idle+0x26/0x40
   io_uring_cmd+0x9a/0x1b0
   io_issue_sqe+0x193/0x3f0
   io_wq_submit_work+0x9b/0x390
   io_worker_handle_work+0x165/0x360
   io_wq_worker+0xcb/0x2f0
   ? finish_task_switch.isra.0+0x203/0x290
   ? finish_task_switch.isra.0+0x203/0x290
   ? __pfx_io_wq_worker+0x10/0x10
   ret_from_fork+0x2d/0x50
   ? __pfx_io_wq_worker+0x10/0x10
   ret_from_fork_asm+0x1a/0x30
   </TASK>

Fixes: c732a852b419 ("ublk_drv: add START_USER_RECOVERY and END_USER_RECOVERY support")
Reported-and-tested-by: Changhui Zhong <czhong@xxxxxxxxxx>
Closes: https://lore.kernel.org/all/CAGVVp+UvLiS+bhNXV-h2icwX1dyybbYHeQUuH7RYqUvMQf6N3w@xxxxxxxxxxxxxx
Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
v2: add the check to ublk_ctrl_start_recovery().

 drivers/block/ublk_drv.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 4e159948c912..ebd997095b65 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -2661,6 +2661,8 @@ static int ublk_ctrl_start_recovery(struct ublk_device *ub,
 	mutex_lock(&ub->mutex);
 	if (!ublk_can_use_recovery(ub))
 		goto out_unlock;
+	if (!ub->nr_queues_ready)
+		goto out_unlock;
 	/*
 	 * START_RECOVERY is only allowd after:
 	 *
-- 
2.39.2