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

Vulnerability Description

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.

References

• https://git.kernel.org/stable/c/2f3c22b1d3d7e86712253244797a651998c141fa
• https://git.kernel.org/stable/c/b4fed1443a6571d49c6ffe7d97af3bbe5ee6dff5
• https://git.kernel.org/stable/c/940a71f08ef153ef807f751310b0648d1fa5d0da
• https://git.kernel.org/stable/c/5502c1f1d0d7472706cc1f201aecf1c935d302d1
• https://git.kernel.org/stable/c/818004f2a380420c19872171be716174d4985e33
• https://git.kernel.org/stable/c/c758b77d4a0a0ed3a1292b3fd7a2aeccd1a169a4