[PATCH 6.18 250/396] ublk: reset kernel-owned dev_info fields in ublk_ctrl_add_dev()

6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ming Lei <[email protected]>

commit e65848e4ce352bac9e3465099354c8b8f845391f upstream.

ublk_ctrl_add_dev() memcpy()s the userspace ublksrv_ctrl_dev_info into
ub->dev_info and then fixes up the fields the driver owns, but misses
->state and ->ublksrv_pid.

A device added with ->state = UBLK_S_DEV_LIVE passes the
"->state != UBLK_S_DEV_DEAD" test that ublk_stop_dev_unlocked() uses as its
proxy for "a disk is attached", while ->ub_disk is still NULL, so DEL_DEV
right after ADD_DEV oopses in del_gendisk().  UBLK_S_DEV_QUIESCED plus
UBLK_F_USER_RECOVERY dies one step earlier, in ublk_force_abort_dev().  A
poisoned ->state also gets START_USER_RECOVERY and the char device
read/write path onto a device that was never started, and wedges START_DEV
at -EEXIST.  A poisoned ->ublksrv_pid just makes GET_DEV_INFO report an
unrelated task as the ublk server.

Reset both after the memcpy(), as ublk_detach_disk() does.  Userspace only
ever reads these back, so correcting them silently breaks nothing.

ADD_DEV has copied ->state in unsanitized since ublk was merged, but back
then it was harmless: the gendisk was allocated during ADD_DEV, and both
teardown and the START_DEV -EEXIST check keyed off disk_live() rather than
->state.  The oops became reachable once the disk allocation moved to
START_DEV and those checks switched to ->state.

Fixes: 6d9e6dfdf3b2 ("ublk: defer disk allocation")
Cc: [email protected]
Signed-off-by: Ming Lei <[email protected]>
Reviewed-by: Caleb Sander Mateos <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/block/ublk_drv.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -3288,6 +3288,15 @@ static int ublk_ctrl_add_dev(const struc
 	ub->dev_info.dev_id = ub->ub_number;
 
 	/*
+	 * ->state and ->ublksrv_pid are owned by the driver and only read back
+	 * by userspace, but they come from the copied-in dev_info, so reset
+	 * them. Otherwise a device added with ->state != DEAD looks live while
+	 * ->ub_disk is still NULL.
+	 */
+	ub->dev_info.state = UBLK_S_DEV_DEAD;
+	ub->dev_info.ublksrv_pid = -1;
+
+	/*
 	 * 64bit flags will be copied back to userspace as feature
 	 * negotiation result, so have to clear flags which driver
 	 * doesn't support yet, then userspace can get correct flags