scsi: lpfc: nvme: avoid hang / use-after-free when destroying localport

We cannot wait on a completion object in the lpfc_nvme_lport structure in
the _destroy_localport() code path because the NVMe/fc transport will free
that structure immediately after the .localport_delete() callback.  This
results in a use-after-free, and a hang if slub_debug=FZPU is enabled.

Fix this by putting the completion on the stack.
Signed-off-by: NEwan D. Milne <emilne@redhat.com>
Acked-by: NJames Smart <james.smart@broadcom.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/lpfc/lpfc_nvme.c

@@ -297,7 +297,8 @@ lpfc_nvme_localport_delete(struct nvme_fc_local_port *localport)
 			 lport);
 
 	/* release any threads waiting for the unreg to complete */
-	complete(&lport->lport_unreg_done);
+	if (lport->vport->localport)
+		complete(lport->lport_unreg_cmp);
 }
 
 /* lpfc_nvme_remoteport_delete
@@ -2545,7 +2546,8 @@ lpfc_nvme_create_localport(struct lpfc_vport *vport)
  */
 void
 lpfc_nvme_lport_unreg_wait(struct lpfc_vport *vport,
-			   struct lpfc_nvme_lport *lport)
+			   struct lpfc_nvme_lport *lport,
+			   struct completion *lport_unreg_cmp)
 {
 #if (IS_ENABLED(CONFIG_NVME_FC))
 	u32 wait_tmo;
@@ -2557,8 +2559,7 @@ lpfc_nvme_lport_unreg_wait(struct lpfc_vport *vport,
 	 */
 	wait_tmo = msecs_to_jiffies(LPFC_NVME_WAIT_TMO * 1000);
 	while (true) {
-		ret = wait_for_completion_timeout(&lport->lport_unreg_done,
-						  wait_tmo);
+		ret = wait_for_completion_timeout(lport_unreg_cmp, wait_tmo);
 		if (unlikely(!ret)) {
 			lpfc_printf_vlog(vport, KERN_ERR, LOG_NVME_IOERR,
 					 "6176 Lport %p Localport %p wait "
@@ -2592,12 +2593,12 @@ lpfc_nvme_destroy_localport(struct lpfc_vport *vport)
 	struct lpfc_nvme_lport *lport;
 	struct lpfc_nvme_ctrl_stat *cstat;
 	int ret;
+	DECLARE_COMPLETION_ONSTACK(lport_unreg_cmp);
 
 	if (vport->nvmei_support == 0)
 		return;
 
 	localport = vport->localport;
-	vport->localport = NULL;
 	lport = (struct lpfc_nvme_lport *)localport->private;
 	cstat = lport->cstat;
 
@@ -2608,13 +2609,14 @@ lpfc_nvme_destroy_localport(struct lpfc_vport *vport)
 	/* lport's rport list is clear.  Unregister
 	 * lport and release resources.
 	 */
-	init_completion(&lport->lport_unreg_done);
+	lport->lport_unreg_cmp = &lport_unreg_cmp;
 	ret = nvme_fc_unregister_localport(localport);
 
 	/* Wait for completion.  This either blocks
 	 * indefinitely or succeeds
 	 */
-	lpfc_nvme_lport_unreg_wait(vport, lport);
+	lpfc_nvme_lport_unreg_wait(vport, lport, &lport_unreg_cmp);
+	vport->localport = NULL;
 	kfree(cstat);
 
 	/* Regardless of the unregister upcall response, clear

drivers/scsi/lpfc/lpfc_nvme.h

@@ -50,7 +50,7 @@ struct lpfc_nvme_ctrl_stat {
 /* Declare nvme-based local and remote port definitions. */
 struct lpfc_nvme_lport {
 	struct lpfc_vport *vport;
-	struct completion lport_unreg_done;
+	struct completion *lport_unreg_cmp;
 	/* Add stats counters here */
 	struct lpfc_nvme_ctrl_stat *cstat;
 	atomic_t fc4NvmeLsRequests;