[PATCH 3/3] hw/nvme: cancel inflight requests on controller reset

nvme_ctrl_reset() freed every SQ/CQ right after nvme_ns_drain(), which
only waits out requests on a per-namespace BlockBackend. That is safe
as long as the guest first tore down I/O queues gracefully (Delete
I/O SQ/CQ), since nvme_del_sq() already cancels and waits for
anything left on a queue before freeing it.

A reset that happens without that graceful sequence first (e.g. an
abrupt/asynchronous controller reset) can still have commands
inflight on blk_aio_*. Freeing sq/cq before those complete leaves
their completion callbacks (nvme_rw_cb() and friends) to run against
already-freed NvmeRequest/NvmeSQueue/NvmeCQueue memory via
nvme_enqueue_req_completion(), causing a use-after-free/segfault.

Run nvme_sq_cancel_inflight() over every queue in nvme_ctrl_reset()
before the free loops, so no in-flight blk_aio_* callback can fire
after sq/cq memory is freed.

Signed-off-by: Minwoo Im <[email protected]>
---
 hw/nvme/ctrl.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
index 86b86b2a0fbb..22b1b9636878 100644
--- a/hw/nvme/ctrl.c
+++ b/hw/nvme/ctrl.c
@@ -8035,6 +8035,18 @@ static void nvme_ctrl_reset(NvmeCtrl *n, NvmeResetType rst)
         nvme_ns_drain(ns);
     }
 
+    /*
+     * Cancel and wait out every inflight command on every queue first. A
+     * reset is not required to be preceded by the guest's graceful
+     * Delete I/O SQ/CQ sequence, so sq/cq must not be freed below while a
+     * blk_aio_* completion for them could still be in flight.
+     */
+    for (i = 0; i < n->num_queues; i++) {
+        if (n->sq[i] != NULL) {
+            nvme_sq_cancel_inflight(n->sq[i], NVME_CMD_ABORT_SQ_DEL);
+        }
+    }
+
     for (i = 0; i < n->num_queues; i++) {
         if (n->sq[i] != NULL) {
             nvme_free_sq(n->sq[i], n);
-- 
2.34.1