nvme: do not reset controllers in NVME_CTRL_NEW state

During NVMe controller creation, the controller is exposed to sysfs via
nvme_add_ctrl() while it is still in the NVME_CTRL_NEW state.
This creates a narrow race window where a userspace process can write to
the reset_controller sysfs node before the initialization thread
transitions the state to NVME_CTRL_CONNECTING.

If a reset is triggered during this window, the state machine allows the
transition from NVME_CTRL_NEW to NVME_CTRL_RESETTING, and the reset work
is queued. However, the original creation thread continues its execution,
subsequently moving the state to NVME_CTRL_CONNECTING and finally to
NVME_CTRL_LIVE.

When the delayed reset work finally executes, it attempts to tear down
the controller and transition the state to NVME_CTRL_CONNECTING. Because
the state is now NVME_CTRL_LIVE, this transition fails, triggering a
WARN_ON in the reset work.

Fix this by removing NVME_CTRL_NEW from the allowed prior states for
the NVME_CTRL_RESETTING transition.

Fixes: 8bfc3b4c6f ("nvmet: switch loopback target state to connecting when resetting")
Reported-by: syzbot+4a1d521d19d6321f5aad@syzkaller.appspotmail.com
Reviewed-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/core.c

@@ -598,7 +598,6 @@ bool nvme_change_ctrl_state(struct nvme_ctrl *ctrl,
 		break;
 	case NVME_CTRL_RESETTING:
 		switch (old_state) {
-		case NVME_CTRL_NEW:
 		case NVME_CTRL_LIVE:
 			changed = true;
 			atomic_long_inc(&ctrl->nr_reset);