CVE-2024-42152: Missing Release of Memory after Effective Lifetime

In the Linux kernel, the following vulnerability has been resolved:

nvmet: fix a possible leak when destroy a ctrl during qp establishment

In nvmet_sq_destroy we capture sq->ctrl early and if it is non-NULL we know that a ctrl was allocated (in the admin connect request handler) and we need to release pending AERs, clear ctrl->sqs and sq->ctrl (for nvme-loop primarily), and drop the final reference on the ctrl.

However, a small window is possible where nvmet_sq_destroy starts (as a result of the client giving up and disconnecting) concurrently with the nvme admin connect cmd (which may be in an early stage). But *before* kill_and_confirm of sq->ref (i.e. the admin connect managed to get an sq live reference). In this case, sq->ctrl was allocated however after it was captured in a local variable in nvmet_sq_destroy. This prevented the final reference drop on the ctrl.

Solve this by re-capturing the sq->ctrl after all inflight request has completed, where for sure sq->ctrl reference is final, and move forward based on that.

This issue was observed in an environment with many hosts connecting multiple ctrls simoutanuosly, creating a delay in allocating a ctrl leading up to this race window.